JURASSIC CYNODONTS; Tritylodontidae, an internet directory
JURASSIC CYNODONTS; Tritylodontidae, an
internet directory: |
PLEASE NOTE: THIS PROJECT IS NOT SCIENTIFIC. IT IS A HOBBY.
"I was looking for information on an old animal and found this lot. What is this
project?"
It's got lots of information on old animals. For a short bit of background information, see
here.
A Breif Introduction: the longest surviving line of non-mammalian
cynodonts
In books on paleontology, (fossils, dinosaurs and so on), you might sometimes
come across creatures called cynodonts, or "mammal-like reptiles". Some of these
were extremely mammal-like. The ancestry of all mammals
is amongst them.
Basal mammals are known from the rocks of the Upper Triassic,
though reasonably complete material first turns up in the Lower Jurassic. Having given
rise to mammals, you might get the impression that those proto-mammals had served their
purpose and went extinct. However, seen from their point of view, the purpose of life, the
universe and everything wasn't to produce us lot. They had no intention of being replaced
by more derived upstarts, and doubtless had strong urges to
carry on procreating as before.
Several very mammal-like families didn't go extinct at the end of the Triassic, and these
form the subject matter of this directory on Jurassic cynodonts. Jurassic cynodonts is
actually a misnomer for several reasons, but I quite like the title. Some of the animals
featured predate the Jurassic, and a couple even postdate it. This directory concerns
animals called titylodontids. Some tritys survived until at least the Lower Cretaceous.
They're probably part of Probainognathia. |
Tritylodontidae
| Family: Tritylodontidae Cope, 1884 includes Bienotheriidae
Young, 1940
The snazzily named tritylodontids were plant-eating furry things, and very similar to
mammals. They made a living from terrorising the vegetation, and tried not to got trodden
on by careless prosauropod dinosaurs. Tritys were most fashionable during the Lower
Jurassic, when they enjoyed a worldwide distribution.
Origins
There are two main schools of thought. One sees them as close relatives, (and perhaps even
descendants), of animals called traversodontids.
The two families do have some features in common. This was the view I was originally
following. However, the similarities could also be due to convergence, seeing as the
lifestyles overlapped. I've had a change of heart and I'm now treating the tritys as
advanced, herbivorous members of Probainognathia,
the eucynodont line which includes mammals.
Were tritys protomammals?
"The hypothesis of a sister-group relationship between tritylodontids and mammals is
strongly supported by the similarities in the orbital wall between tritylodontids and early
mammals", (Luo 1994, p.102).
We have much in common, so we can't be all that distant. But:
"The hypothesis of a tritylodontid-mammal sister-taxon relationship is contradicted by
several dental apomorphies shared by tritylodontids,
diademodontids, and traversodontids", (Luo 1994, p. 109). Those factors mean tritys
are sometimes placed within a different lineage of overwhelming plant-eating eucynodonts;
Cynognathia.
How big were tritys?
It varied, but they probably ranged from about fifteen centimetres to a metre in length,
ignoring the tail. Oligokyphus is one of the most
completely known genera. Kemp, 2005 (p.71) reports a skull length of about nine
centimetres and a body length of near 28cm, (likewise disregarding the tail). A bit of
complex addition suggests Oligo was around 37cm, and that's more or less four times the
skull.
One of the miniest tritys would have been Bocatherium.
Its skull is 4.2cm. Tritylodon could manage up
to 25cm. Assuming the rest of the proportions are reasonably similar, that suggests a
range of about sixteen centimetres to a metre, (a small
black rat to a
small wolf).
During their Lower Jurassic heyday, tritys were the largest furry critters on the planet.
The great majority of Mesozoic mammals were smaller than Bocatherium. The largest
so far discovered is Repenomamus the
Magnificent from the Lower Cretaceous. R. giganticus is exceptionally enormous, but
only around 70cm (head and body). No mammals could compare with the dimensions of the
bigger tritys until about 63 million years ago.
How long did they survive for?
Until the last couple of years, it seemed the last tritys had finally kicked the bucket,
(died out), during the middle of the Upper Jurassic. Recent finds from Japan and Siberia
show this 'extinction' to have been an exaggeration. These extend the chronological range
into the Aptian, late Lower Cretaceous. That's something like 35 million years, (10
million generations? Pure, groundless guessing).
Why the strange name?
The family name refers to the highly unusual postcanine
teeth. They came equipped with rows of cusps to process food more effectively.
"The lower incisors of tritylodontids are enlarged and
fit between the uppers to yield a rodent-like appearance. The
postcranial skeleton of tritylodontids is mammal-like.
For example, the greater trochanter is separated from the femoral head by a notch and the
ilium is rod-like", (Rubidge & Sidor 2001, p.469).
These, and further similarities suggest one of three possibilities:
a. tritys, (or something closely related), included the ancestors of mammals; b. tritys and
mammals were closely related; c. a remarkable degree of parallel development.
Family characteristics
Kemp, 2005 (p.72) provides some discussion on the general trity anatomy. The skull is
strongly reminiscent of mammals. The postorbital bar (a bit of bone behind the eye) is
absent, and this means the large temporal fenestra and orbit
were no longer separated. The dentary virtually is the
whole lower jaw, and it's fitted with impressive features known as the coronoid and angular
processes. The postdentary bones have been shrunk into a small rod, which is stored tidily
in a groove at the back on the inside of the dentary. The major difference is the lack of
any dentary-squamosal contact. The only jaw
joint is fromed by a very small articular and the quadrate above. That's about as
'reptilian' as tritys got.
Teeth
The dentition is a bit rodenty, and this points to a liking for plants.
Canines must have fallen out of favour as there are none,
but the second incisors are enlarged and canine-like in
effect. In more basal representatives such as
Oligokyphus, the enlarged incisor is accompanied by two smaller colleagues. Advanced
forms (eg Kayentatherium) didn't bother with those. In both uppers and lowers,
a pronounced diastema comes between the incisors and
complicatedly crowned postcanines.
Complex crowns
Upper postcanines typically have three lines of cusps along thier lengths, while the
lowers have two. These operated like files against each other, so even relatively hard
material could be well worn down prior to consumption. |
| Genera:
Bienotherium (may partly = Lufengia),
Bienotheroides, Bocatherium,
Chalepotherium (=Oligokyphus), Chronoperates
(misassigned?), Dianzhongia, Dinnebitodon,
Kayentatherium, Likhoelia (=Tritylodon),
Lufengia (and partly = Oligokyphus), Mucrotherium
(=Oligokyphus), Nearctylodon,
Oligokyphus (and partly =Bienotherium), Polistodon,
Stereognathus,
Tritylodon, "Triglyphus"
(?=Tritylodon), Tritylodontoideus (=Tritylodon), Uniserium
(=Oligokyphus), Xenocretosuchus,
Yuanotherium, Yunnania
(=Yunnanodon), Yunnanodon,
ichno genera, other reports
Time-Line:
Lower Cretaceous: Xenocretosuchus, Japan
Upper Jurassic: Bienotheroides, Yuanotherium
Middle Jurassic: Bienotheroides, Polistodon,
Stereognathus, Isle of Skye, Siberia
Lower Jurassic: Bienotherium, Bocatherium (possibly Middle Jurassic),
Dianzhongia, Dinnebitodon, Kayentatherium, Lufengia,
Nearctylodon, Oligokyphus, Tritylodon, Yunnanodon, Antarctica
Upper Triassic: Argentina |
| Genus: Bienotherium Young CC, 1940
'Bien's beast'
Aka: Oligokyphus (partly)
Remarks: The postcanine teeth of this genus have two
completely divided roots. The equivalent gnashers in Bienotheroides have a single
root, (Luo 1994, p.108). Both taxa are named in honour of
paleontologist Edward Bien. |
| Species: | Bienotherium yunnanense Young CC, 1940 |
| Aka: | Bienotherium elegans Young, 1947; "Oligokyphus
sinensis" Young CC, 1974 |
| Place: | Dull Purplish Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | Hettangian?, Lower Jurassic |
| Remarks: |
With the exception of two referred limb bones, this species is restricted to the Dull
Purplish Beds. As it is, the referral of those bones to this
taxon is very questionable, as "no character of the
postcranial skeleton has been established to distinguish Bienotherium from other
tritylodontids", (Luo & Wu 1994, p.253). Abundant material has been collected.
"The cranial structure of Bienotherium yunnanense is primitive for tritylodontids
", (Luo & Wu 1994, p.257); eg, with regards to the front of the upper snout, the
premaxilla is relatively small, whilst the
maxilla is very large. This ratio is one feature that can
be used to distinguish the taxon from other Yunnan representatives, such as Lufengia
and probably Dianzhongia.
B. elegans is likely based on an immature B. yunnanense, (though not according
to a study by Sun & Cui, 1986), as is also possibly the case with Oligokyphus sinensis
, represented by a partial dentary, the lower
postcanines of which have a different number of cusps in
comparison to confirmed members of that genus. Luo & Wu, 1994 treat this as a junior
synonym, advice which I'm happy to follow.
According to Hurum, 1998, (p.84), Bienotherium has a skull length of about 14cm. No
mammals approaching this sort of size are known until the Lower Cretaceous, (eg.
Repenomamus). |
| References: | Young (1940), Preliminary notes on the Mesozoic mammals of
Lufeng, Yunnan, China. Bull. Geo. Soc. China vol.20, p.94-102. |
| Young (1974), [New material of therapsids from Lufeng, Yunnan.] Vertebrata
Palasiatica 12, p.111-114. [Chinese], (for O. sinensis). |
| Species: | Bienotherium magnum Chow M, 1962 |
| Place: | Dark Red Beds, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: |
Known from a single specimen and other undescribed material, this was a much
larger animal than any B. yunnanese specimen. "However, the range of size
variations for Bienotherium is still unknown", (Luo & Wu 1994, p.257).
These authors tentatively regard this as a valid species, whilst noting that it might simply
represent a large individual. It would also have to have been a surprisingly late one. |
| Reference: | Chow (1962), [A tritylodont specimen from Lufeng, Yunnan.] Vertebrata
Palasiatica, 6, p.365-367. [Chinese]. |
| Species: | ?Bienotherium minor Young, 1947 |
| Place: | Dull Purplish Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | Hettangian, Lower Jurassic |
| Remarks: |
This is perhaps synonymous with Lufengia. "However,
Cui and Sun (1987) regarded B. minor and L. delicata as two separate species.
Several major collecting expeditions by IVPP have shown that B. minor is restricted to
the Dull Purplish Beds (stratum 4), whereas Lufengia is found only in the Dark Red
Beds (stratum 6). On the basis of the stratigraphic separation of B. minor and
L. delicata and their differences in postcanine
structure (see later discussion of Lufengia), we retain B. minor and L.
delicata as separate taxa, pending further studies of
juvenile specimens of Bienotherium", (Luo & Wu 1994, p.257-258). |
| Reference: | Young (1947), Mammal-like reptiles from Lufeng, Yunnan, China.
Proceedings of the Zoological Soc. of London 117, p.537-597. |
| Link:
Polyglot Paleonotologist
http://www.uhmc.sunysb.edu/anatomicalsci/paleo/terms.html
This fabulous site hosts translations of many significant papers into English. I thank
Will Downs for drawing it to my attention.
Included is Sun A & Cui G (1989): The Discovery of a Tritylodont from the Xinjiang
Autonomous Region. Vertebrata PalAsiatica XXVII, No. 1, p.1-8, translated by Will
Downs. |
| Species: | Bienotheroides wansienensis Young CC, 1982 |
| Aka: | B. wanhsienensis; B. wanxshienensis; B. wanxienensis |
| Place: | Upper Shaximiao Formation, Sichuan & Mamenchisaurus beds,
Wucaiwan Formation |
| Country: | China |
| Age: | Middle Jurassic |
| Remarks: | This formation has previously been referred to as
Late Oxfordian/Kimmeridgian, Upper Jurassic, but that no longer seems viable.
The following is based upon my reading of Sun & Li, 1985 as translated by Will Downs in
1987. Thanks for its availability are due to the Polyglot Paleontologist. The page numbers
are in accordance with the translation. In the original, the pages were numbered 135-150.
The cited study centres upon postcranial remains from a number of individuals including the
holotype. It's not the original description. According to the authors, the presence of an
incipient suprasinatus fossa on the scapula may suggest a
closer relationship between tritys and mammals, than some
people had previously thought, (p.1). I won't attempt to provide elucidation on this
doubtlessly interesting feature. As far as I'm aware, it's not a characteristic which
receives much attention in recent considerations.
The descriptions of Lower Jurassic skeletons, (Oligokyphus
and Bienotherium), had already highlighted similarities
between tritys and mammals. Indeed, tritys were earlier placed within Mammalia. However,
Bienotheroides provided a look at a later version. At the time of publication, this
genus was about the most recent representative of the family. As far as postcranial
remains go, it still is. Lower Cretaceous tritys are now known, but they haven't yet
obliged us with so much as a single part of their legs to stand on. In this instance, the
fossils were provided by at least three individuals. Due to the requirements of further
preparation and study, only the holotype was diagnosed to the species level. Its two
companions belong to the genus.
Vertebrae
All individuals were generous with parts of their spines;
cervical vertebrae 1-4; five more from the neck and a front
thoracic specimen; and eleven vertebrae.
Collectively seen, that's a reasonable sample.
Neck
The neck bones feature a fused atlas and axis, (specimen V4734). This is very similar to
several derived non-mammalian
eucynodonts and mammals. However, the retention of a
well developed atlas centrum is not characteristic of Mammalia. The construction of the
odontoid process is reminiscent of Oligokyphus and
Morganucodon, (p.2), but it's more basal than in
existing mammals. In brutally truncated summary, the morphology of the neck has both
primitive and derived features.
Backbone
V7905 provides eleven vertebrae in three sequences, (p.3).
Each has the remains of ribs. They are clearly from the same animal. Some bits are missing,
but damage is relatively light. These are larger than the
cervical vertebrae, and a look at the neck and spine regions of an intimate acquaintance
would render the relative dimensions as unremarkable. (Should the intimacy go beyond the
neck and spine regions, those relative dimensions would probably slip into temporary
irrelevancy.)
Ribs
A number of the ribs are preserved, (p.4), and this includes cervical ribs. The
thoracic ribs are similar to those known from
Oligokyphus. Perhaps more attention grabbing are the neck ribs: "The presence
of cervical and axial ribs illustrates that this taxa still
preserves reptilian characters." [I'm not going to quibble over minor typos in
complex and generously provided translations.]
Shoulders
V 7905 allows a revealing glimpse of shoulder. Both clavicles,
the supporting interclavicle, both scapulae and all other
elements are present. They're also articulated in their natural positions. This goes well
beyond a revealing glimpse. It's brazen, proud, provocative posing. Excuse me for a
while. I urgently have to discuss something with my wife...
Eucynodont shoulders are wonderful. In the case of Bienotheroides, the assemblage
is roughly a 'T' shape about 6cm tall, with the cross at the top being about 10cm in
length. That crossbar is formed by the clavicles, and much of the central pillar is
contributed by the interclavicle. The base is made ornate by the bumpy presence of the
left and right presternum. (My description is very rough, and the plural of presternum
evades me.) Anyway, the clavicles look rather like a
yoke when seen from above, which is pretty much their function. Instead of buckets of
water, the shoulders carry the arms.
With some differences, the interclavicle isn't unlike the corresponding bone in
Morganucodon, while the squareness of the presternum is similar to
Oligokyphus, (p.5). There's a gap of about two
millimetres between the right and left presternum, which would have been bridged by
cartilage in life, and there are nodes for ribs.
"The tritylodontid shoulder girdle and sternum are extremely similar to those of
monotremes. The Echidna interclavicle differs in that
the terminal end has become inflated into a heart shape, and the presternum is thicker and
shorter", (p.6).
A complete scapula is a bit over 8cm long. The authors
think they can identify an incipient supraspinatus fossa, which is a
derived feature associated with mammals. The overall
shape of the whole bone is somewhat similar to the mammalian condition, (p.7).
Front legs
Skipping onto page 9 brings us to the front limbs of V7905. Available are the right
humerus, ulna,
radius and partial paw, and the left humerus, ulna and
radius.
Both ends of the humerus are greatly expanded, which is
typical for tritys and advanced non-mammalian eucynodonts. (In the genus
Bienotherium, this bone is longer and less robust, and
this actually characterises another of the specimens reviewed.) Attachment points for
various muscles are identifiable.
The radius and ulna are
preserved in their natural association along with remains of a foot, (p.10). The shaft of
the radius is relatively straight and even, which contrasts to Oligokyphus and
Morganucodon. It's a gracile bone with inflated ends.
The ulna is straighter (baton-shaped) and longer. It would serve well enough in a relay
race, at least in shape. There's little variation in width along its shaft. The
articulation condyle for the humerus is visible.
Front paw
The fossilisation of a front paw is unusual, especially for the carpal region. Most of
the wrist is available. One carpal, (which link with the
metacarpals, the base bones of the fingers), is missing, but all five metacarpals are
in attendance. Carpel I (ie. from the thumb) is relatively large, while carpal II is much
smaller. III and IV are linked to each other. V (ie. the little finger) is the absent
one, (p.11).
The metacarpals aren't only all present. They're
excellently correct too, (p.12). They're of modest length, rather than extended as in
Morganucodon. Each is similarly sized. Metacarpal V is the shortest with 14mm.
III wins with 18mm. I and II are somewhat slimmer. There's no indication that the thumb
(ie. I) splayed out from the paw, so all fingers may have pointed forwards when walking.
In advance mitigation, the bones of fingers and toes are delicate things, and a full set
of metacarpals is a fine haul. It could've been even better. When discovered, all the
phalanges (the outer finger bones) were present. However,
in the course of collection and preparation, they showed a tendency to disappear or suffer
damage. Consequently, only the middle toe is still available; both phalanges and the claw.
It would look at home on a mammalian paw.
Back legs
The femur is complete and well-preserved, should anybody
wish to ask about its health. It's very similar to those of Bienotherium and
Oligokyphus.
Discussion
Page 13 is a contribution for the present understanding of trity relationships to Mammalia,
a la 1985. It's twenty years old, and didn't have the benefit of many subsequent
discoveries, new methods and further studies. Unsurprisingly, it's been partly overtaken
by events. Nevertheless, it contains much of continuing relevance as well as being
historically instructive.
Tritys and mammals
The postcranial skeleton contains strong similarities with mammals, and these suggest
common descent. Features emphasized are: the shoulders; the structure of the
pelvis; the developed projection of the elbow; the
morphology of the atlas-axis on the vertebrae. This suite
of shared characteristics doesn't lose any validity simply because it was written a couple of
decades ago.
And nor do the contrasts in the skull. All mammals, (as
defined in this internet project), and some non-mammals have a dentary-squamosal joint
between the lower jaw and the skull. This hasn't been observed in tritys as far as I'm
aware, (although I have read assertions stating otherwise). Differences in the area of the
ear were also mentioned. However, the paper was a study of the postcranial skeleton and
not the skull.
And then there are also particular trity specialisations; their unique teeth, and a
different method of achieving a form of direct occlusion between uppers and lowers.
Holotype
The holotype is V4734. It was provided by the Hamachong Shiliang Production Brigade of
Gaoliang Commune in Sichuan.
Additional notes
The spilling of the specific name has been a subject of surprising variation.
According to Watabe et al, 2007 (p.264), contrary to the offerings provided by
various earlier authors, the correct form is the one I'm now using:
wansienensis. Hopefully, I've corrected every usage on this directory. |
| Reference: | Yang Zhongjian (aka Young CC) 1982, Bienotheroides. in Zhou
Mingzhen (ed.), Collected works of Yang Zhongjian. Academia Sinica, Beijing. |
| Species: | Bienotheroides zigongensis Sun A-L, 1986 |
| Place: | Lower Shaximiao Formation, Sichuan & Xinjiang |
| Country: | China |
| Age: | Bathonian/Callovian, Middle Jurassic |
| Remarks: | The following is based upon my reading of Sun &
Cui, 1989, as translated by Will Downs in 1990. Thanks for its availability are due to the
Polyglot Paleontologist. (There's a link above.) The page numbers refer to the
translation. I'm not sure whether they correspond exactly with the original.
The above study concerns subsequent finds of this species from northwestern China, rather
than the holotype from the Dashanpu fauna of Sichuan, (p.1). This conveniently extended
knowledge of the species, as some further characteristics were preserved.
These additional remains came from near Jiangjunmiao in the Junggar Basin, an area from
whence an increasing number of eucynodonts, (both
mammalian and non-mammalian), are being recovered. The
five specimens were collected in 1984 and, two decades later, paleontologists are still
kept busy in this part of Inner Mongolia. Among the fossils are three incomplete skulls,
mandibles and some postcranial material such as limb bones
and vertebrae. In very brief summary, this species is the
most basal member of the genus. As it's also the oldest,
that's not greatly surprising.
Mostly, the skull description is based upon V7909, which had a length of 11.2cm. At a rough
guess, I'd imagine the former owner would've have been something like 40 to 50cm long.
Although damaged in some areas, the general condition is very good. One feature that
strikes me as interesting is the lack of an identifiable
septomaxilla, (p.2). This bone is generally present in non-mammals and absent in
mammals. However, it's been reported in some mammals, (including
monotremes and
docodonts). That suggests the element was disposed of on several occasions.
Upper jaws
"The premaxilla is rather extended and is consistent
with other specimens of Bienotheroides in that it articulates directly with the
lacrimal, at which point, the maxilla is completely
concealed." The second incisor is particularly large,
and its root has caused a distinct swelling on the premaxilla, in which it's embedded.
Cheek bone
The zygomatic arch is well developed. This area is
discussed in more detail than I can presently digest.
Lower jaws
The left mandible is still articulated with the skull,
(p.3). Also available is the front 4cm of the right lower jaw. There's a slight extension
to the anterior of the dentary, but this isn't as marked as
in B. wansienensis. The mental foramen can be found between the first and second
postcanines; a feature situated further back in the other
species just mentioned.
Beautifully preserved are the post dentary bones. My ancestors were careless with mine, and
they got lost many, many, many generations ago. Behind the teeth is a triangular shaped
coronoid. While no living mammal has any such bone, a vestigial version may have been
maintained in some mammalian lines, (eg.
Henkelotherium). In such cases, there's a suspicious groove on the dentary in
an appropriate position. In Bienotheroides the bone is clear to see. As it happens,
as it's set further forward than in B. wansienensis, it also provides a further
distinction between the species. Other decidedly non-mammalian elements on the jaw include
bones called the splenial and quadrate, (p.4). The latter provides the lower part of the
of the jaw-cranium joint. There's no indication of a secondary jaw joint in any tritys, as
far as I'm aware. (Although I've read otherwise on occasions, such assertions do not seem
to be backed with evidence.). On a different specimen, V7913, the articulation surface on
the quadrate for the articular is better preserved, (p.5).
Teeth
It may have had its reasons, but the holotype's loss of its jaws was inconvenient. The
individual concerned left only six isolated cheek teeth to posterity. V7909 was more
generous in this regard, as it donated remains of the left
dentition in place. Many thanks.
Incisors
Note: In the interests of precision, the authors use the word incisiforms rather than
incisors. I'm allowing myself a more relaxed approach.
There are three upper incisors. The first has a root width of 3mm. Number two is far
larger, and blessed with a sharp point. The crown length is 12mm and the base is 7mm wide.
The third is a couple of millimetres distant on the jaw, and no wider than I1.
Two large lower incisors are present, and they're similar in size. These teeth are
directed diagonally forwards, and have a shovel-like shape caused by flattening on the
lingual side. The lowers are more closely packed than
their upper colleagues.
Postcanines
The authors prefer the term molariforms
The upper teeth are furnished with seven functional postcanines, and a further unerupted
one is at the end of the row. The first four are extensively worn, and this isn't a young
animal. Seen from the occlusal perspective, the crowns
are square with lightly rounded corners. They exhibit three rows of cusps:
labial 2; middle 3; lingual
three.
The lower jaw houses six postcanines, five of which are functional. These are rectangular
in outline, with lengths of 6-7mm. Two rows of cusps are present. Unlike the uppers, the
cusps are equivalent in size rather than variable.
Postcranial elements
Two femora are complete, while other bones are partially
preserved. However, as there were no significant differences to report from already
described material for the species, there was no need for further discussion.
Affinities
"With regard to genus, the tritylodontid material from Xinjiang manifests all the
diagnostic characters of Bienotheroides, including an extremely compressed rostral
region, a ventrally extended jugal, extremely expanded
zygomatic arches, and axis of the basicranium (pterygoid and anterior section of the
sphenoid) short, broad flattened and lacking corrugated or angled structures. The
maxilla is compressed. The
premaxilla, lacrimal, and palatine can be distinguished laterally and ventrally where
they come into direct contact", (p.6-7).
There's also a list of characteristics of relevance to the species assignment, one of which
is the cusp formaula of the upper postcanines. A couple
of further points have been mentioned above.
Holotype
The holotype is a partial skull which has lost its jaws, (presumably after its demise). |
| Reference: | Sun (1986), New material of Bienotheroides (tritylodont reptile)
from Shaximiao Formation of Sichuan, Vertebrata PalAsiatica, 24, p.165-170. |
| Species: | Bienotheroides ultimus Maisch MW, Matzke AT &
Sun G, 2004 |
| Place: | Shishugou Formation, Junggar Basin |
| Country: | China |
| Age: | Upper Jurassic |
| Remarks: |
On the face of it, having tritylodontid remains available from the Middle Jurassic and
Lower Cretaceous could be viewed as untidy, due to the chronological gap. Thankfully,
Chinese and German researchers attended to matters by recovering an Upper Jurassic one,
(p.649). The individual never reached maturity.
Distinguishing features
Among the characteristics which define this species are: the quadrate has a slender and
medially aligned stapedial process; the very small facet for contact between the quadrate
and petrosal; and only about 20° of torsion between both
ends of the humerus. Some of those strange words will
receive a bit of explanation below.
Teeth
Only three have been preserved, and two of those are fragmentary
incisors. They're roughly circular in cross-section. More informative is an upper
molar. This is probably from the front to middle of the row
of the right jaw. It's got the standard trity arrangement of three rows of cusps. The
numbers are (labial to lingual):
2,3,3. The presence of only two cusps on the external row is similar to B. zigongensis
but one less than for B. wansienensis. The tooth has a broadly rectangular outline.
Skull
Only a few elements have been found, but they're helpfully diagnostic ones, (p.650). These
are a large portion of the right cheek area (zygomatic arch), both quadrates (which form
the tops on non-mammalian jaw joints among other functions), and a poorly preserved section
of the skull roof.
As in other members of the genus, the zygomatic arch
is very deep. Of the quadrate bones, the right one is complete. The absence of a well
developed dorsal process and dorsal angle are derived features
when compared to Oligokyphus. The top of the head isn't
well preserved, but it does allow as estimation of the skull length. As other
Bienotheroides specimens are known to be short snouted, this probably didn't exceed
ten centimetres, (p.651). This is marginally less than for its immediate relatives. Given
that this individual's a subadult, then a mature body length of roughly 50cm or so wouldn't
appear unrealistic, (my guess).
Body
Seventeen vertebrae have been found, all of which come from
either the neck (five), or elsewhere above the hips. There are also numerous, fragmentary
ribs. Presently, they defy ordering into a sensible series. Parts of both shoulders are
present as well, which brings us to the...
Front legs
There's a near complete right humerus articulated with
parts of the lower arm bones (radius and
ulna). Judging by the sketch on page 654, the humerus has a length of something like
six centimetres. Fragments of its opposite colleague are also known. Excepting for the
aforementioned light torsion, the bone is typically trity. An effect of minimal torsion is
that, when set upon a flat surface, both ends of the bone are nearly at the same height,
and this isn't a product of distortion. This is reportedly different to the condition in
all cynodonts. (I wonder if that should be restricted to non-mammalian ones.)
Hips and rear legs
Little of the lower skeleton is known, (p.653), but parts of the pelvis are available; the
ilium, an end of a pubis and the
left ischium. The only identifiable bone of the leg is the
near complete right tibia, (p.654). This is very similar to
that known from Oligokyphus.
Family matters
Tritys appear to be a family of impeccable repute; all descendants of a unique, common
ancestor. Bienthoteroides is part of an advanced clade along with
Bocatherium and Stereognathus.
As the postcanine teeth of the latter genus resemble
those of Xenocretosuchus, the Lower Cretaceous critter
may also qualify for membership.
Holotype
The holotype is NIGPAS-SGP 1, and it lives at the Nanjing Institute for Geology and
Paleontology. Remains consist of a partial skeleton, parts of the skull, an upper molar and
two incisors. The specific name refers to it being the latest known Chinese trity. This
is an open invitation for someone to come up with a still more recent one, in order to make
nomenclatural nonsense of things. Should that occur, then I'm confident the authors would
be delighted.
(With thanks to Dr Michael Maisch, Tübingen and Dino Hunter for posting notice of the
publication. Further thanks are due to the kindly supplier.) |
| Reference: | Maisch, Matzke & Sun (2004), A new tritylodontid from the
Upper Jurassic Shishugou Formation of the Junggar Basin (Xinjiang, NW China), Journal of
Vertebrate Paleontology, 24(3), p.649-656. |
| Species: | Bienotheroides shartegensis Watabe M, Tsubamoto
T & Tsogtbaatar K, 2007 |
| Place: | Shar Teg locality, Ulaan Malgait Hills, Gobi-Altai Aimag |
| Country: | Mongolia |
| Age: | ?Upper Jurassic |
| Remarks: | The following is based upon my reading of
Watabe et al, 2007.
Mongolia is a treasure house of simply superb Mesozoic
eucynodont fossils, but these are provided by
mammals from the Upper Cretaceous. Another locality, Höövör, has delivered less
well-preserved specimens from their Lower Cretaceous antecedents. Until recently,
the land had shown less interested in yielding Jurassic remains. Perhaps, as preservation
doesn't match up to the high standards set by Ukhaa Tolgod -a cemetery packed to the
gills with skulls and even complete skeletons, this Central Asian land felt the
Jurassic eucynodont remains weren't worth bothering about.
Fortunately, members of a Japan-Mongolia Expedition Team persuaded it to provide a
partial skull during excavations at Shar Teg, southwestern Mongolia in 2002 (p.263).
It's somewhat bashed and battered, but can boast of having kept its lower jaws.
There's a further reason for greeting this acquiescence to primate curiosity about
our ancient relatives. Where one eucynodont fossil's been found, that's a promising
place to search for more.
The first Mongolian trity
Most people never get to see the word tritylodontid, let alone remember it. It
looks frightening, and that scares potential interest away. Given the nature of
tritys, this is a great pity. There are weird medical terms for breasts, but this
doesn't make the objects themselves repulsive. You can take my word on this point.
Tritys were plant-eating mammal-like things; members of a lineage that kept its
flag flying until the Lower Cretaceous. They appear to have shared a close common
ancestor with us mammals, rather than being our ancestral line.
The new skull represents a further species, but generic kith and kin were already
known from the Middle and Upper Jurassic of China. Bienotheroides shartegensis
is the fourth species named for the genus. Terming it a middling
derived trity would be fair enough. It's more
advanced than old-timers such as Oligokyphus and
Tritylodon, but primitive in comparison with a
lineage first encountered during the Middle Jurassic; eg.
Stereognathus.
Reasons for assigning it to Bienotheroides include: a relatively short snout,
its reduced maxilla and expanded
premaxilla (in contact with the palatine), and for
details of its postcanine teeth including the
numbers of cusps. However, some of those features display derivations of their own
debarring it from membership of previously established species. The first Mongolian
trity is the first of its kind.
A couple of examples of extremely mammal-like characteristics are provided: a great
reduction in size of the postdentary bones, and the complete less of bones termed
the prefrontal and postorbital. Further examples could be cited from all over the
trity body. However, in this case, only the skull is presently available.
News from the grave
The trity skull was recovered from red sandstone deposits in the Ulaan Malgait hills
(p.264). It lay ten metres above the border separating the underlying Shar Teg Beds
and its Ulaan Malgait Beds. Its associated fauna includes fish, turtles, dinos,
crocs, molluscs and ostracodes, and this lot was deposited courtesy of river action.
The fauna provides the basis of an Upper Jurassic date. Those lower beds are also
of interest as, among other things, mammal fossils have been collected from them.
About the size of things
The skull has a length of near ten centimetres, and that suggests a critter of
something like
bunny-dimensions, though not the build. Unlike most mammals of the time of
Earth, this animal could prove of interest to any hungry, time-travelling trappers
and, should any happen to arrive there earlier in the future, then please don't
dispose of the bones after the meal. I don't want to encourage predation on tritys,
but the skeleton would be much appreciated by their community of fans and friends.
Toothy terminology and my use of inverted commas for postcanines
Some may like to refer back to this short summary from time to time. It'd save
trying to remember everything at one go. Upper postcanines have three rows of cusps
designated B (buccal), M (middle) and L
(lingual). The cusp formula is stated as being
2:3:3 respectively. However, in addition, vestigial cusps just about occur at the
front of these rows, and they're numbered with a zero. The larger cusps receive
numbers in accordance with their row position. For example, the full lingual series
consists of L0, L1, L2 and L3.
Lower postcanines have two cusp rows: b (buccal) and l (lingual). Each row contains
three cusps; eg. l1, l2 and l3.
As won't necessarily be obvious to all, upper and lower case letters are of
significance in this scheme. Capitals refer to upper teeth and their features, and
lower case to lowers. A PC is an upper postcanine while a lower counterpart is a
pc. It's a good thing I'm writing this down and not reading it out, and the
abbreviation has nothing to do with so called 'political correctness', personal
computers or the Welsh Nationalist Party (Plaid Cymru). Indeed, in this
context, it's unconnected with any 'pc' pcs the PC may have. The numbers used for
postcanine positions in the paper appear to refer only to preserved teeth, and that
makes me a bit uneasy. For example, the left lower jaw has an
alveolus in front of what's termed pc1. I can only
conclude this postcanine must've been the second in the series when the owner was
alive. This prompts me to add inverted commas, although the authors do no such
thing. The numbers of incisors are clear.
Distinctions
The M1 cusp (yep, that's the first middle one on an upper postcanine) is small in
comparison to other species of the genus, and relative to B. zigongensis and
B. ultimus, the postcanines are shorter and broader. That applies both upstairs
and down. For the latter species, there's a projection from the middle of the front
of upper postcanine, but not in the case of the new species (p.265). Finally, in
contrast to B. wansienensis, there's no B0 cusp (check above), and no gap
(diastema) occurs between the first and second of
the upper incisors.
Head
Skull lengths are similar among all species of the genus. The snout is typically
short and broad when compared to basal tritys. This
specimen has suffered from breakage but, what is in place is rather like B.
wansienensis (p.267). A derived trity trait is the expansion of the
premaxilla at the expense of the
maxilla bone. Unusually for
cynodonts, including mammals, the maxilla no longer got to build any part of the
bony palate of the mouth (p.268).
Upper incisors
Three alveoli for incisors are found on the left premaxilla. Its right partner has
the front bit missing. I2 is next to I1, but I3 stands behind. The first and third
alveoli are 4.5 and 4.2mm across respectively. The second was wider, 7.7, so this
incisor was obviously the largest of the trio. Little space is found between the
incisors, but a 4.5mm diastema does occur between the I3 and the border of the
maxilla bone.
Upper postcanines
In contrast to lowers, upper postcanines are considerably wider than long. This
seems fair enough, given they've got the responsibility of carrying an additional
cusp row. All the crowns are of fairly similar sizes, and wear a thin suit of
enamel. Four are preserved per side, but this is presumably less than the full
complement. The shortest of them is 6.6mm (a "PC1" with a width of 9.9), whereas
the longest is 7.6 ("PC2", width 10.3).
From the occlusal perspective, the crown outline
is something like rectangular with rounded corners. As stated, there are three rows
of cusps running along the crown, with the buccal
and lingual rows set at about equal distances from
the central one. Valleys between the rows are deep. I may as well repeat the cusp
formula: 2:3:3 (buccal - lingual respectively). The margins of the crowns are
relatively straight, and there's no sign of any
cingulum. Some of the uppers and lowers on one side are still in occlusion.
The largest cusp on each tooth is B2. For the middle row, M1 has been drastically
reduced. While still present, it's got nothing much left to boast about. Other
than for the first cusps of each row, all have crescentric shapes. L1 and B1, in
contrast, have only a single ridge rather than two. The final cusps of the rows
align into a straight line running across the tooth.
Lower jaw
The great majority of the jaw is provided by the
dentary, with other elements contributing minor areas. This is broadly in line
with basal mammals, but not any recent ones, and such
a condition isn't found for any tetrapods outside of
Cynodontia. The lingual face of the dentary has a
Meckelian groove, and this channel also hosts remnants of the splenial bone.
Much of the rear jaw is missing, including the angular and articular processes and
the upper reaches of the coronoid process. The remaining ruins, however, show that
the latter element was strongly developed, and it held a coronoid bone on its
internal surface. Other 'accessory' bones would've been present as well, but they
haven't been preserved.
Lower incisors
There are a pair of incisors per side, but all these teeth happen to be broken
(p.209). The i1 is a procumbent tooth with a width of around 6mm. Its partner in
crime, the i2, was a considerably smaller tooth (p.210). They seem to be separated
by a diastema, but little space occurs between the
second incisor and the alveolus for the first lower postcanine.
Lower postcanines
Four per side are available but more were originally present. Lengths range from
9.2mm ("pc2" with a width of 7.1) to 9.7 ("pc3" and "4" with no widths determinable).
Statistical gymnasts may have noticed that, in contrast to the uppers, these teeth
are longer than wide. Again, the enamel's thin and there's no sign of any
cingulum.
There are two rows of cusps, and each has two members. All are crescents, and similar
in size and shape.
As stated, some postcanines are still in occlusion. These are from the right of
the set, and kindly provide information on how they operated. The style isn't direct
one-to-one. The front of "pc3" is set against the rear of "PC3", and its distal
portion meets the anterior part of "PC4". Equivalent circumstances prevail for
"pc2".
Tritynamics
To put things somewhat crudely, Bienotheroides is akin to a middling
advanced trity. This is shown by features such as the reduced snout, the expanded
premaxllia and the banishing of the maxilla from involvement in building the secondary
palate. Should an analogy with a Model T Ford be thought apt for Tritylodon,
then I suppose a Ford Cortina wouldn't be that far off for Bienotheroides.
(Or maybe I mean a Capri. I get muddled up with motorized chariots.) Whichever,
it's not exactly modern for current tastes, but it was the bee's knees when I had a
short-lived phase of noting down car registration numbers in 1971. The car parks of
Bournemouth offered many Morrises and Hillman Imps, along with a sprinkling of Minis
for the daring.
Various aspects of the dentition provide support
for admission of the skull into this Ford car. The upper cusp formula is
typical, excepting for an extra buccal cusp with B. wansienensis; cusp M1 is
pathetic; L3 is large; the three rearmost upper postcanine cusps form a straight line;
the upper crowns are rectangular in outline with rounded corners; there's a trio of
upper incisors per side, the middle one being the largest; the lower postcanine
cusp formula conforms; there are a pair of lower incisors per side; and finally, of
great significance, the authors say so. And, just as this collection of characters
admit the critter to this particular generic Ford model, it debars admission to
others, whether they be Model Ts, Cortinas, Capris,
Dinnebitodon, Stereognathus or
whatever.
The major reason blocking entry to an already established species is the pathetic
nature of the M1 cusp (p.271). There are further points as well, and some have been
mentioned above.
Holotype
MPC-Nd 10/301, the only known specimen, is enjoying the hospitality of the Mongolian
Paleontological Centre, Ulan Baatar. The specific name refers to the fossil
locality.
Additional notes
Abstracts submitted to The Society of Vertebrate Paleontology Annual Meeting 2004 include:
The first tritylodont from the Mesozoic in Mongolia, Watabe M & Tsogtbaatar K.
I'm relieved to hear it's not a specimen from the Precambrian. This concerned the
specimen you've just thoroughly enjoyed reading about. At the time the abstract
appeared, there was uncertainty about the age of the locality. It was held to be
either Upper Jurassic or Lower Cretaceous. The older date seems to have won.
Thanks to Marcel Opitz for alerting me to it. |
| Reference: | Watabe et al (2007), A new tritylodontid synapsid from
Mongolia, Acta Palaeontologica Polonica, 52(2), p.263-274. |
| Genus: Bocatherium Clark
JM & Hopson JA, 1985
'Boca beast'
Remarks: Does anybody need telling the generic name comes from the Boca
Formation? |
| Species: | Bocatherium mexicanum Clark JM & Hopson JA, 1985 |
| Place: | La Boca Formation, Tamaulipas |
| Country: | Mexico |
| Age: | Pliensbachian, Lower Jurassic |
| Remarks: | The following is based upon my reading of
Clark & Hopson, 1985. My thanks go to Eric and his photocopier.
When it came to Middle Jurassic, landlubbing
vertebrates, the entire continent of North America had been incapable of competing
with the richness of one small village in Oxfordshire. From the sun-kissed waters of
the Beaufort Sea to the permafrost of the Yucatan peninsula, there was not a scent
of a Middle Jurassic sausage of this particular recipe. The quarries of
Stonesfield had produced bits of dinosaurs, pterosaurs, crocs, mammals... The entire
North American landmass hadn't even registered a smear of land vertebrate dung. As
the presenter of the Eurovision Song Contest might be moved to sneer: "North America
no points, keine Punkte, sweet sod all."
Mexico's Bocatherium may have broken that dismal duck in 1985. May have.
The age remains less than clear, but Middle Jurassic is possible. In any case,
this small trity skull was then the oldest land vertebrate known from Mexico. Even
should part of this formation date from the Middle Jurassic, the continent
otherwise remains pathetic in this respect.
Small is beautiful
Rather like myself, Bocatherium is a fine specimen of a
eucynodont; an impressive giant in miniature
with a skull length of around five centimetres. It's possible the owner was less
than adult. My skull length is actually a bit more, but my wife attests to my
eternal juvenility. That means we're talking in terms of a fairly modest
rat-sized
creature. I'm referring to Bocatherium. It may have intended to do a bit
more growing but, even so, it would've remained one of the smaller tritys.
'Boca beast' was naturally given its due with a photo on the cover of Nature. It's
a good specimen of a skull with lower jaws, albeit lacking the rear left quarter of
its elegant head. Areas of the skull pointed to affinities with
Bienotheroides and
Stereognathus from the tritys available for comparison (p.398). This
fossil came from near Huizachal, Anacahuita and La Joya in Tamaulipas State,
northeastern Mexico.
Precisities
The skull measures 51.1 millimetres and lengths are provided for four upper and
three lower postcanines. Running from front to
back these are: (uppers): 4.2mm, 4.1, 4.0, 4.1; (lowers): 5.2, 5.2, 5.2. Upper
teeth are about a millimetre broader than long whereas the lowers are narrower
(3.8, 3.9, 4.0 respectively).
A unique character among then known tritys was a large boss on the outer side of the
dentary to the fore of the masseteric fossa. In
line with Bienotheroides and Stereo, the maxilla
had been reduced in size. It lacked a flange with which to contribute to the bony
palate roofing of the mouth.
Being a trity, each of the upper postcanines had three rows of cups and, in this case,
there were two members in each row. Most tritys were cuspier critters with three or
more in the middle row. This decrease in number is a
derived condition. In contrast to Bienotheroides, the
zygomatic arch of the cheek is gracile rather
than very deep. A contrast to Stereo, known only from jaw parts and teeth, is found
in the shape of the upper postcanines. The outline is oval for Mexico's Boca but
squarer for its British pal.
The dating game
I was always shy of asking girls out. The thought of them saying no was humiliating.
The possibility of their saying yes was down right terrifying. However, there were
certain things I had urges to express and undress. The Boca Formation has also been
subject to dating dilemmas, but I doubt it ever hoped that a romantic rendezvous in a
geology museum might lead to mutual disrobing and vigorous exercise, not necessarily
among the paleontological exhibits. The issue here is age uncertainty, a problem
that frequently arises with terrestrial localities. Marine deposits are found both
above and below, and their ages are clear; Permian and Upper Jurassic (Oxfordian).
The Boca meat in the middle of the sandwich is between those two slices. However,
rather as with some kebaby, not all remains parts of this meat are necessarily of
precisely the same age. Plant remains from 12km north of this beast's ancient bed
are from the Upper Triassic. According to paleomagnetic results (p.399), La Boca
Formation rocks divide into three units of differing ages. The trity came from the
Huizachal Canyon beds, and these belong to the most recent of those subdivisions.
As far as I'm aware, it remains unclear whether their age is Middle or Lower
Jurassic.
Comparative size and biological age
The smallest known trity is Lufengia from China.
'Boca beast' isn't much larger. The dentary is a relatively robust and deep one,
there are a low number of postcanines, and these are comparatively large. All
these points suggest the former owner was still attending school rather than being
an adult. This makes the size equality among the postcanines unusual. More
typically for trity kids, the teeth increase in size along the line. The most
distinctive feature of the lower jaw is the aforementioned large boss.
The reduction of the maxilla is an unusual feature for
cynodonts including mammals, but it's also
found with Bienotheroides and Stereognathus. This is a shared
specialisation. The premaxilla compensated by
being enlarged. There are also derived specialisations concerning the facial and
palatal bones.
Postcanine crowns
The low postcanine count seems of little significance given the young age. Sexual
pleasures lay in the never reached future along with the full
dentition. However, this limited number has no particular bearing on the
architecture of the individual crowns; three rows of two cusps -a low number. At
the front of the rows can be found small, accessory cuspules. As also the case
for Bienotheroides, the outline is oval when viewed from the
occlusal perspective. Stereognathus was a
bit of a square in this regard.
Holotype
The only then known specimen is called IGM 3492. It was clearly a bright student,
as it received a place on merit at the Universidad Nacional Autonoma de Mexico,
Mexico City. 'Boca beast' was provided with an apartment in the Instituto Geologia.
No information is provided as regards what it studied there.
Sadly, the authors refuse to reveal the significance of the specific name. It's
got me completely Vulpes-ed.
Additional notes
The Biosis Index solely credits Clark, which is incorrect. The skull
length is estimated as being 4.2cm, (Kemp 2005, p.71). That's about a centimetre
less than what the description says. Perhaps it shrank in the wash, but I have my
doubts. |
| Reference: | Clark & Hopson (1985), Distinctive mammal-like reptile from
Mexico and its bearing on the phylogeny of Tritylodontidae. Nature, 315(6018),
p.398-400. |
| Genus: Chronoperates
(misassigned?) Fox RC, Youzwyshyn GP & Krause DW, 1992
Remarks: Originally described as a tritylodontid, this genus was subsequently seen as a
symmetrodont-like mammal. Further details are at
Mesozoic Mammals: Basal Symmetrodonts: A.
Chronoperatidae.
However, this reassignment has apparently not been universally accepted. In Scott et al,
2002, the following appears on page 691: "... the non-mammalian cynodont
Chronoperates paradoxus...". The et al are Fox and Youzwyshyn, which suggests
they're sticking to their original interpretation. Details of this paper are in the
Bibliography at the foot of this page. |
| Genus: Dianzhongia Cui G, 1981
Aka: Diazhongia, Lufengia? (partly)
Remarks: I appear to have been using an incorrect spelling, by missing the first n.
The presently used form is reportedly that in the book from 1994, 'In the Shadow of the
Dinosaurs', and confirmed by Godefroit & Battail (1997). With thanks to Vince Ward.
|
| Species: | Dianzhongia longirostrata Cui G, 1981 |
| Aka: | ?Lufengia delicata, Chow & Hu 1959 |
| Place: | Dark Red Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: |
Dianzhongia is broadly similar to Lufengia, though there are
several differences. D. is distinguished by: "the large size of the skull, only
one upper incisor in each
premaxilla, the long and slightly constricted rostrum, and long postincisive
diastema. The total skull length of the holotype of
Dianzhongia longirostrata is 76 mm, whereas the lengths of several skulls of
Lufengia are around 40mm", (Luo & Wu 1994, p.260).
However, in other genera such as Kayentatherium and Oligokyphus, there's also
a wide variation in the size of the skulls. (Luo and Wu 1994 also notes a new skull of
Dianzhogia which is about 55mm long.) The loss of
incisors in presumably older individuals could account for the differing dental
formula and the diastema. This is apparently known from Bienotherium. Differences
in the constriction of the rostrum are also recorded from variously sized representatives
of Kayentatherium. These distinctions could be a matter of age.
Of course, they could also be the result of two differing genera. Luo and Wu leave this
matter open by tentatively recognizing two separate taxon, "pending further study.
" |
| Reference: | Cui (1981), A new genus of Tritylodontoidea. Vertebrata
PalAsiatica 19, p.5-10. |
| Genus: Dinnebitodon
Sues HD, 1986
'Dinnebito tooth'
Remarks: The generic name honours Dinnebito Wash, a place close to where the fossils
were recovered. |
| Species: | Dinnebitodon amarali Sues HD, 1986 |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Late Sinemurian-Early Pliensbachian, Lower Jurassic |
| Remarks: | The following is sort of based upon my
reading of Sues, 1986, but there's a catch. I found the first page lying around on
the internet, and that's the only part of the paper I've seen. The rest would cause
great joy to break out in my home village of
Dipwytch. All
Dipwytchians love a good gossip about tritys.
Update
Dipwytchians are gossiping with joy as a photocopy has indeed turned up in the village.
Thanks, Ian.
Dinnebitodon hails from the Kayenta Formation of northeastern Arizona, a
formation that's so far provided at least three -some would say four- trity genera.
Its local relatives arrested to date include the globetrotting
Oligokyphus,
Kayentatherium and (if distinct),
Nearctylodon.
A researcher named Lewis trapped the first Arizona tritys in 1953. That material,
from Comb Ridge, hasn't yet been fully described or named. A different locality
yielded part of a skul and two jaw pieces, and these were all presented to
Kayentatherium. That may also be the case for the fossils Lewis found.
The Navajo like variety
A further Kayenta site came to light on the land of the Navajo NDNs (Native Americans,
Indians or other terms may be inserted according to taste). This was harvested by
researchers from Harvard University and the Museum of Northern Arizona. These
Navajo novelties were more pleasingly diverse, and generously included remains from
the trio of Oli, Kay and newling Dinn.
An early end
Sadly, page 758 is running out. The distinctions cited in comparison to
Kay are found in the upper teeth. This genus has three
incisors per side rather than merely one, and the
lingual row of the upper postcanines contain two cusps instead of three. As
always with tritys, upper postcanines possess three cusp rows. In this case, the
formula is (buccal to lingual): 2:3:2.
And another thing
Fascinatingly... Oh, the page finished.
Holotype
The type fossil, MNA V32222, is a crushed snout with teeth in the custody of the
Museum of Northern Arizona in Flagstaff. Also included was its lower left jaw and
bits of the body. The specific name refers to its discoverer, William W Amaral, a
collector and preparator of vertebrate fossils. |
| Reference: | Sues (1986), Dinnebitodon amarali, a new tritylodontid
(Synapsida) from the Lower Jurassic of western North America. Journal of Paleontology 60,
p.758-762. |
Genus: Kayentatherium Kermack DM, 1982
'Kayenta beast' |
| Species: | Kayentatherium wellesi Kermack DM, 1982 |
| Aka: | Kayentotherium |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Late Sinemurian-Early Pliensbachian, Lower Jurassic |
| Remarks: | "Kayentatherium shows a very broad
range in the size and proportions of the skull (Sues, 1986a)", (from Luo and Wu 1994,
p.257). Kemp, 2005 offers a skull length of up to 25cm; the upper range of tritys.
A fossil is at the Smithsonian Institution Museum of Natural History, Washington DC, USA,
and a possible, (hard to be precise because the head's missing), at the Schuler Museum,
Dallas, Texas, USA. Sources suggest that Nearctylodon may be a synonym, though
doubts have been expressed. |
| Reference: | Kermack (1982), A new tritylodontid from the Kayenta Formation of Arizona. Zool.
J. Linn. Soc. 76, p.1-17. |
| Genus: Lufengia Chow M &
Hu CC, 1959
'from Lufeng'
| Reassigned species: L. delicata (partly) see
Oligokyphus lufengensis | |
| Species: | Lufengia delicata Chow M & Hu CC, 1959 |
| Aka: | ?Bienotherium minor Young, 1947 |
| Place: | Dark Red Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: |
A single specimen of this genus was reported from the lower Dull Purplish
Beds, but this seems to have been a juvenile Bienotherium yunnanense, (Luo & Wu
1994, p.258). This is the smallest known trity of the Yunnan community, with a complete
skull length of about 4cm. It's more 'advanced' than Bienotherium, in that its
premaxilla is considerably larger, whilst the
maxilla is correspondingly smaller. |
| Reference: | Chow & Hu (1959), [A new tritylodontid from Lufeng, Yunnan.]
Vertebrata Palasiatica 3, p.9-12. [Chinese]. |
| Species: | ?Lufengia minor (Young CC, 1947) |
| Aka: | ?Bienotherium minor Young, 1947 |
| Place: | |
| Country: | |
| Age: | |
| Remarks: |
I originally had Lufengia delicata listed as a synonym of
this taxon, which doesn't seem to be correct. L. delicata is clearly valid, whilst
L. minor is an alternative interpretation of B. minor, which is where further
information may be found. |
| Reference: | |
| Species: | Nearctylodon broomi Lewis GE, 1986 |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Late Sinemurian-Early Pliensbachian, Lower Jurassic |
| Remarks: | Some sources suggest this may be a synonym of
Kayentatherium. However, it's listed as a separate genus in the review by Godefroit
and Battail, 1997. Clarification would be welcome. |
| Reference: | |
| Genus: Oligokyphus Hennig E,
1922
'small curved animal'
aka: Chalepotherium plieningeri Ameghino, 1903; Mucrotherium von Huene, 1933;
Uniserium von Huene, 1933
Remarks: The lower postcanines of oligo have two lines
of three principal cusps. All other reported tritys have two cusps in each row, (Luo
& Sun 1993). Smaller cusps are also sometimes present.
From the same source: "The broad distribution of Oligokyphus indicates that there
were no major barriers separating the terrestrial
vertebrate faunas of Europe, North America, and China." This conclusion is
supported by finds of other small vertebrates from Yunnan, including mammals and proper
reptiles.
Savage, 1971 (p.80) reports for the upper postcanines: "In Oligokyphus the
length exceeds the width; in all other genera width exceeds length." Whether this
applies to all genera which weren't then published is something I don't know.
On the same page he writes: "The genus Chaleopotherium is based solely on a
broken postcanine from Wurtemberg. There is disagreement about the cusp interpretation;
probably it had two on the outer and three on the middle row, with the inner row missing.
However it is so inconclusive that it contributes nothing to our knowledge of the
group."
| Reassigned species: O. biserialis Hennig, 1922 see O. triserialis;
O. minor Kühne, 1956 see O. major; O. sinensis Young, 1974 see
Bienotherium yunnanense | |
| Species: | Oligokyphus triserialis Hennig E, 1922 |
| Aka: | aka: O. biserialis Hennig, 1922; Mucrotherium
cingulatum von Huene, 1933; Uniserium enigmaticum von Huene, 1933 |
| Place: | Rhaetian-Liassic Bonebed, Tübingen |
| Country: | Germany |
| Age: | Rhaetian, Upper Triassic |
| Remarks: | A number of molars have been found, and they at
least mostly come from a site called Olgahain. The uppers have three lines of cusps while
the lowers make do with two. This helps to explain the two species names.
The type fossil of O. triserials is water-worn, (with thanks to an abstract by
Corfe I, Martin T & Reif W-E, 2004). The material they described consisted of eleven
further partial and complete teeth collected in 1948.
Holotypes
And from Ian Corfe himself (pers. comm. 2008) comes further information. The
type fossil of O. triserialis should be part of the paleontological collection at
Tübingen University, and indeed was. However, recent efforts to find it were
unsuccessful. The same applies for the holotype of O. biserialis. The latter was
a lower postcanine while the former was an upper, and
both appear to represent the same species. A full paper dealing with the material
mentioned in the abstract above is under preparation. Many thanks. |
| Reference: | Hennig (1922), Die Säugerzähne des württembergischen Rhät-Lias-
Bonebeds. Neues Jahrbuch f. Mineralogie, Geologie und Paläontologie, Beilage-Band 46,
p.181-267. |
| Species: | Oligokyphus major Kühne WG, 1956 |
| Aka: | O. minor Kühne, 1956 |
| Place: | Windsor quarry, Somerset |
| Country: | England |
| Age: | Sinemurian, Lower Jurassic |
| Remarks: | O. minor and O. major were found in
close association. O. major is bigger. Probably male & female (say Hopson
& Kitching). Another possible find was made at St Bride's Island, Glamorgan, Wales.
Kemp, 2005 (p.71) includes a skull length of nine centimetres and a body length of 28cm,
(ignoring the tail).
On page 72 he provides a few words on the nearly completely known skeleton. For fans of
shoulder girdles, the 'non-mammalian' coracoid has been reduced, and the acromion is
reflected sidewards. He reports a very slender humerus,
and mammalian-like details of the hips. The femur is also
mammalian.
Some Oligokyphus sp. remains are housed at Bristol City Museum, UK. |
| Reference: | Kühne (1956), The Liassic Therapsid Oligokyphus. London:
Trustees of the British Museum (Natural History). |
| Oli of Windsor Quarry, Somerset
The following is largely based upon my reading of Benton et al, 2005, and thanks go
top the generous supplier.
The fauna of Windsor Quarry near Shepton Mallet is both generous and very restricted
for eucynodonts (p.32). There are lots of
fossils but only one guilty taxon. The German paleontologist, Walter Kühne, and his
wife collected more than 2,000 specimens there over a decade but, as this effort
began in 1938 -just in time for World War Two, the British government slowed things
down with enforced internment on the Isle of Man. This was despite the couple's
impeccable anti-Nazi credentials and the urgent need of more cynodont fossils for the
war effort. The fact that all cynodont material was donated by Oligokyphus is
both a pity and good. This has made Oli the best known trity in the world. No
complete individual came out of the fissure concerned but, but one critter or
another, much of a complete corpse could be reconstructed.
While lots of Olis found their way into the fissure, other local residents indicate
it was a grave beneath the waves. As well as suggesting a Sinemurian age, remains
of fish and ammonites state this wasn't a suitable home for landlubbing tritys. Oli
doubtlessly enjoyed some water, but this was salty and too much to be tolerable for
a terrestrial animal with a skull length of around 7.5cm. Judging by the sketch
(p.33), the body amounted to around 20cm and the tail about matched the length of
the head and body combined.
A food grinder
Oli's lower jaw is comparatively deep, and it enjoyed the benefits of powerful muscles.
It didn't have the range of jaw movements available to more derived eucynodonts, such
as myself. We mammals can drive our jaws forwards and, to some degree, sidewards.
Oli could only manage the fore and aft parts of the repertoire, with the emphasis
being on a backwards drag of the lower jaw. Given the build of trity trity
teeth, a lateral element would've been rather pointless. The
dentition featured long incisors, nothing
remotely answering to the name of a canine (ie. there
wasn't one), and then between four to six large, crushing
postcanines per side. Of those, the lowers had two rows of cusps, and this
acted as grooves for three upper rows. Thus, a backward drag provided two processing
channels per side.
Such us your body, Oli!
Superficially, there's an element of weaselness to the general build, but its tastes
certainly differed. This critter attacked plants rather than the local equivalents
of hamsters or bunnies, should there have been anything vaguely alike available.
The legs were short and left the feet firmly planted flat on the ground. Other than
for its comparatively large size, this body most closely resembles contemporary
mammals. Oli is essentially mammalian excepting for the less mammal-like head.
Originally, two species were proposed on the basis of differing size. O.
minor is around a third smaller than O. major, and presumably achieved
but half the weight. However, and as stated by Kühne, this could've been a
difference of sex. It's also worth bearing in mind that the genus wasn't originally
based on fossils from Windsor Quarry. I'm not sure where the generic type is, but
that came from Baden-Württemberg in Germany. Presumably, it's an isolated
tooth.
That watery grave
As for what those Olis were looking for in a fissure beneath the sea, the most
probable answer involves them no longer having been capable of searching for anything;
complete blindness caused by being dead and dismembered. Kühne envisaged the animal
as perhaps the sole plant-eating vertebrate on a small island and, as there were lots
of botanical goodies to be tidied up, it was numerous (p.34). There seems to be a
bias towards the preservation of larger body bits, and this would be consistent with
the first dumping stages for water driven garbage disposal. A plentiful supply of
terrestrial rubbish must've first accumulated elsewhere prior to its delivery into
the sea. And rich supplies of bones take some killing. What's required is a
plausible explanation for mass slaughter. For example, perhaps a disastrous
drought was initially broken by a cloud burst induced flash flood. Suddenly, water
roared through the recently dried out water course, and the bones of drought victims
were swept along to be dumped. That's my quickly sketched possibility.
Kühne offered more spectacular violence with blood and ooze. It was the dry
season. There was a spring near the coast offering a precious supply of water, and
this attracted thirsting Olis. The essential assembly provided a meals-on-paws
service for some gang of unknown thugs and, in gratitude, they left a heap of
left-overs lying around. And then came the flash flood.
While some kind of bias ensures the remains in the fissure can't possibly reflect
the make up of the relatively local terrestrial vertebrate fauna, trying to account
for its composition can be fun.
Shepton Mallet!
It's a place near by rather than a hammer, and its renowned (in fairly obscure ways)
for a couple of reasons. Firstly, it has a bizarre name. Secondly, the military
prison was unpopular with certain soldiers. Thirdly, it's closer to the site of the
Glastonbury Rock Festival than Glastonbury is. Unless the view has changed over the
past couple of decades, that location is adorned by a whacking big silver pyramid
in the middle of a field. In terms of planning legislation, this unusual and impressive
structure was built as a cow shed for cattle with surprising architectural tastes.
Planning legislation happened to be disinterested in cow sheds on farms, even if
they were thirty foot high with large peace symbols on top. The law on stages for
rock concerts was far more involved, and this helps explain why the farmer... The
cows have a holiday shed further up the hill for when Rock and Roll megastars turn
up in their field. The animals insisted on this. They complained about the pongy
stink, and said it put them off their milk.
Rock festivals have a history in this area stretching back decades. They've been
happening since at least the 1970s, and include some of the biggest in Britain.
Very few of the tens of thousands of people would know anything about the much,
much older animals of Windsor Quarry.
Further Mesozoic site summaries can be found at Localities.
|
| Species: | Oligokyphus lufengensis Luo Z & Sun A, 1993
|
| Aka: | partly Lufengia delicata |
| Place: | Dull Purplish Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | Hettangian?-Sinemurian?, Lower Jurassic |
| Remarks: | The following is based upon my reading of Luo &
Sun, 1993.
The lower postcanines possess two rows of three main
cusps running along their lengths, as is typical for Oligokyphus (p.477). Other
tritys favour rows with two main cusps. A distinguishment of this particular species from
the rest of the genus is the lack of a cingulum at the
front of these teeth.
Oligo of Lufeng
A species called 'O. sinensis' was established by CC Young in 1974, but this appears
to have been an error. The cusp pattern of the lower postcanines concerned differs
strongly from the genus, and the fossil possibly represents a juvenile
Bienotherium. However, this is the most geologically
widespread trity in the world, and its stamping grounds do now mirror those of the mammalian
Morganucodon. A species was subsequently
found in the Lufeng to go alongside its sisters from Europe and North America.
The individual was kind enough to donate part of its right
dentary to posterity. It's been a bit damaged by weathering, but petty complaints
would show ingratitude. The fossil was originally referred to
Lufengia. Further preparation revealed the tell-tale cusp
arrangement on the postcanines. Congratulations, it's an Oligo.
Jaw
Preserved is a three centimetre long partial dentary with four postcanine teeth and two
alveoli for incisors. It
was found in association with several skull fragments. The rear of the jaw including the
coronoid process isn't included. The external side features a mental foramen below the
front of the first postcanine. A poorly preserved
Meckelian groove graces the internal side. With regards to the teeth, a seven
millimetre diastema separates the second incisor from the
postcanines, (p.478).
Postcanines
The main cusps are crescents with a convex face at the front and a concave one behind;
typically trity. There are two rows of them. On the buccal
side, the rearmost cusp is smaller than its two proceeding colleagues. That also applies
for the lingual row, but there's a smaller accessory cusp
behind as well. This characteristic is shared with some postcanines for O. major,
(but not all). As other trity postcanines are limited to two main cusps per row, Oligo
teeth are proportionately longer, (p.479).
Holotype
The type fossil, IVPP 4008, is a partial dentary in the collection of the Institute of
Vertebrate Paleontology and Paleoanthropology, Beijing. The specific name honours the
Formation for contributing yet another Lufeng trity. Thanks are due to the Dull Purplish
Beds.
The JVP link states the age is Lower Triassic. That's not what's in the paper. |
| Reference: | Luo & Sun (1983), Oligokyphus (Cynodontia:
Tritylodontidae) from the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China. J. of
Vertebrate Paleontology 13 (4), p.47-482. |
| Species: | Oligokyphus sp. Sues H-D, 1985 |
| Place: | Kayenta Formation, Arizona |
| Country: | USA |
| Age: | Late Sinemurian-Early Pliensbachian, Lower Jurassic |
| Remarks: | |
| Reference: | Sues (1985), First record of tritylodontid Oligokyphus
(Synapsida) from the Lower Jurassic of Western North America. Journal of Vertebrate
Paleontology 5, p.328-335. |
| Genus: Polistodon
He XL & Cai KJ, 1984
Remarks: It's January 2007 and I've only just heard of this genus! Kindly Kees
sent in a Chinese paper from 1999, and this is mentioned in the 'suggested
cladogram' on page 121 of Setoguchi et al. That study is on still unpublished
remains from Japan. As I've seen a request posted elsewhere for a translation of
He & Cai, 1984 into English, I'd imagine the original description of this genus is
in Chinese. |
| Species: | Polistodon chuannanensis He XL & Cai KJ,
1984 |
| Place: | Dashanpu, Sichuan Province |
| Country: | China |
| Age: | Middle Jurassic |
| Remarks: | Setoguchi & Co concluded this critter was
most closely related to Stereognathus and fossils
they've obtained from the Lower Cretaceous of Ishikawa, Japan. I haven't yet given
great attention to their paper, but they talk in terms of this trio having a reduced
number of cusps on the upper postcanine teeth. In particular, the cusps known as
M1 and L1 are absent. Those are the ones (in these cases) not found at the front
of the middle and lingual rows.
What a lot of choppers!
Hu et al, 2009 also make mention of this genus (p.389). They report the cusp formula
of upper postcanines (not all of them, I assume) is the same as for Stereognathus,
but a small cuspule occurs at the front of each row for Poli. These teeth are wider and
shorter than trity norms. Unusual is the number of postcanines. This genus boasts of
thirteen, and that quantity makes a comparative lack of length unsurprising. That's a
lot to fit in on one jaw! |
| Reference: | He & Cai (1984), The tritylodont remains from Dashanpu,
Zigong, Journal of the Chengdu College of Geology, Supp. 2, p.33-45. |
| Genus: Stereognathus
Charlesworth E, 1854
'twin jaw'
Remarks: Savage, 1971 (p.81) reports on a then unique feature of the upper
postcanines of this genus. As in other tritys there are
three rows of cusps but, in this case, there are only two cusps per row (P4). For other
taxa then described the most usual condition was 2-3-3,
(outer to inner rows). Oligokyphus went in for 3-4-3.
1854 is the year indicated by Maisch et al, 2004, (p.649), and that's where the reference
has been taken from. It's not impossible that the paper was actually published the following
year.
Britannien, Das Heimat des Stereognathus!
Readers may be wondering why I just wrote a headline about Britain in German. The reason's
very simple. I felt like it. All known specimens of this genus come from Middle Jurassic
localities in Britain, and the number stands at eight. Ian Corfe has supplied a full
list: Oxfordshire -Stonesfield and Kirtlington; Dorset -Watton Cliff and Swyre; Gloucestershire -
Hornsleasow and Tarlton; Wiltshire -Liegh Delamere; the Isle of Skye.
Between you and me, on an informal basis, the postcanine teeth so far described fall
into two size groups. Material from some of the localities hasn't been described, and
that includes further teeth from the Isle of Skye. My ill informed suspicion is that
two species are justifiable on that basis. In almost all cases known to me, the
different class sizes don't occur in the same localities as each other. A possible
exception to that is encountered in Dorset.
On public view in its full nude glory
Voyeurs in the area of Dorchester will enjoy practising their peeping-Tommery.
The Dorset specimen of Stereognathus was seen flaunting its sexy features
behind a tantalisingly transparent glass plane in the Geology Department of the
Dorset County Museum. Nothing is left to the imagination. Every voluptuous curve
is revealed! I spent about half-an-hour of an August Sunday in 2006 panting
appreciatively in front of this arousing performer, before being dragged away by
the authorities for urgent de-excitification. (Apparently, the glass was beginning
to melt in response to my lustfully warmed breath.) If a sight such as this
doesn't bring you near to the limits of even orgasmic pleasures, then questions
should be raised concerning your sanity. This beauty is hot, evocative,
provocative, stripped joyously naked; totally exposed to rouse the full experiences
of eucynodont sexual gratification. Hardly a detail is left denied!
Of course, one or two things are slightly absent. For example, the left
rear leg, parts of the rib cage, the rest of the rib cage, the spine, shoulders and
other legs, possibly significant parts of the skull and the rest of that as well,
the neck, hips, shoulders...
Nevertheless, the lower right molar alone is worth
the journey (and it is alone). While a magnifying glass might've been a good idea,
it's large enough to show the general outline without such assistance. I'd guess
at a length of around 0.5cm, not that I measured it. The two rows of cusps are
distinct enough.
Another resident of the same glass case was announced as being the holotype of
Echinodon, should anybody wish to pay it regards. This huge maniraptor
worked as a dinosaur during the Lower
Cretaceous, and it donated part of a jaw. This suggests a ferocious monster of
something less than a metre in length. However, as these two missed each other
by 25 million years or so, they appeared relaxed companions in this museum.
Catching up with earlier news from Dorset
The following is based upon my reading of Ensom, 1994 and thanks are due to the
supplier.
This study concerns the isolated postcanine I was
salivating about above. The Dorset County Museum was also the location of its
rediscovery in 1979 (p.139). Quite how it got there is uncertain, but it probably
wandered in as part of the collection made by GM Mansel in the late nineteenth century,
and indications suggest it has to be from the Forest Marble Limestone.
It was found lurking in a small ammunition box along with a few shark teeth and a bit of
bone. Associated matrix and sediments are consistent with outcrops of Forest Marble
stretching from Bath down to the Dorset coast, and the relevant species and state of
preservation match remains Paul Ensom had collected at West Bay. This included a fragment
of a tooth previously identified as Stereognathus. Various parts of the
collection absconded to the Natural History Museum in London during the 1950s, but the
documentation doesn't include the Mansel material. Presumably, at least some of it
sensibly refused to leave what is a far more attractive and pleasant town.
Brushing up on the tooth
When I met this tooth, using no artificial aids at all, I pleased myself by concluding
it had to be a lower postcanine and around half-a-centimetre long. There was a sheet of
glass between the two of us, and I now know I was near enough right. The length's a
touch more at 5.3mm and the width 3.2. That's closer in size to specimens of S.
hebridicus rather than S. ooliticus of Oxfordshire, which are smaller.
Working out it was a lower postcanine wasn't difficult to do. It has two rows of
crescentric cusps whereas uppers have three. The lingual
row is the narrower of the two, and its members have more height. All these cusps are
strongly convex on one face, and that's a useful clue for showing it's the front one.
All cusps have somewhat concave lingual surfaces and slightly convex
buccal ones.
A root is partially present (p.141), and there's no indication there ever was more than
one. It has a depth of 5.7mm at the front but only 2.2 behind. However, there has been
breakage.
The earlier Dorset find had been a worn fragment and, if I'm decoding things correctly,
it's suggested as pertaining to a separate species. Presumably, this would be on grounds
of size. The length of the rediscovered one compares best with S. hebridicus
(range 5.3 - 5.8mm) and not S. ooliticus. Size alone can be somewhat misleading,
and especially so with small samples. After all, there are factors such as age, individual
variation and perhaps sex. However, as the size range known from Skye specimens is
significantly larger than size range in Oxfordshire, then it seems reasonable to conclude
these represent distinct species. Presumably, southern England housed at least two
species. |
| Species: | Stereognathus ooliticus Charlesworth E, 1854 |
| Place: | Stonesfield Slate of
Oxfordshire, (& a S. sp., Forest Marble of Dorset and Hornsleasow Quarry,
Gloucestershire) |
| Country: | England |
| Age: | Bajocian, Middle Jurassic |
| Remarks: | Simpson, 1935 (p.161) provides some information.
At that time, the genus was represented by two fragmentary specimens. They appeared to be
remains of Trtiylodon-like upper jaws. The
postcanines are roughly square in the occlusal view,
and have three rows of cusps, with two cusps in each row. Subsequently, more material has
been identified from other locations. |
| Reference: | Charlesworth E (1854), Notice on new vertebrate fossils,
Report of the British Association for the Advancement of Science for 1854, p.80. |
| Link:
Living Gloucester, Hornsleasow Quarry
http://www.livinggloucester.co.uk/histories/museums/cmag/dinosaurs/hornsleasow/
"In 1987 Kevin Gardner and his six year old daughter Lisa found some fossils in
Hornsleasow quarry near Cheltenham. They thought there might be a dinosaur nearby, but
actually there were dozens and more."
And there was also Stereognathus, and fossils of close relatives called
mammals. That, rather than the dinosaurs, is what made
this site important. I'm informed that about fifty teeth and fragments of
Stereognathus reside in the collection of The City Museum, Gloucester.
Kevin Gardner kept sieving and accumulated further fossils. The results of ten years of
(amateur) hard labour were donated to the Bristol City Museum and Art Gallery. This
collection contains similar specimens to those in Gloucester. (With thanks to
Roger Vaughan of the City Museum, Bristol for the information.) He also recommended a paper
on this locality:
S.Metcalfe & R.F.Vaughan et al. A New Bathonian (Middle Jurassic) Microvertebrate Site,
within the Chipping Norton Limestone Formation at Hornsleasow Quarry, Gloucestershire.
Proceedings of the Geologists Association Vol 103, part 4 1992, pp.321-342. |
| Species: | Stereognathus hebridicus Waldman M & Savage RJG,
1972 |
| Place: | Kilmaluag Formation, Isle of Skye |
| Country: | Scotland |
| Age: | Bathonian, Middle Jurassic |
| Remarks: | The following is based upon my reading of
Waldman & Savage, 1972, and thanks are due to the supplier.
Jurassic vertebrate hunting in the Hebrides off the
western coast of Scotland goes back to at least the activities of Hugh Miller, during the
middle of the 1800s (p.119). He reported finding such fossils on the Isle of Eigg in
1858. However, until August 1971, finds had been limited to reptiles and fish. As the
sediments had built up in lagoons and estuaries, then fish and bits of occasional
plesiosaurs provide a better reflection of the immediate inhabitants. These fossil beds
didn't form in the kind of environment then occupied by mammals and the like, but bits
of dead ones did end up in non-marine deposits on the Isle of Skye.
The locality provides fossils from near the top of the Great Estuarine Series, and that
in turn contains strata ranging from the Bajocian to the Bathonian of the Middle
Jurassic. Being from near the top, the eucynodonts
qualify as Bathonian; probably a bit old than England's
Forest Marble Formation. Traditionally, the Scottish have always been keen on
getting in before the English, with the notable exception of graves. Factors helpful
for the preservation included the waters being not prone to violent habits of the open
seas, land not being very far away, plenty of silty mud and a constant supply of remains
being dumped by rivers (p.120). On the minus side, such conditions aren't very
favourable when it comes to maintaining articulation. Skeletons tended to get broken
up and scattered.
A trity of the Hebrides
The reason the authors established a new trity species was essentially a matter of size.
The remains consist of isolated postcanine teeth,
and they happen to be around 60% larger than similar fossils from Oxfordshire. Both
uppers and lowers were collected. Lowers have two cusp rows with a pair of crescentric
members in both (p.121). All cusps are said to be "selenodont". I think that translates
as crescentric, but I'm not sure.
Upper postcanines evidently enjoyed being multi-rooted. There are two per side and another
to the middle of the front. These teeth have three cusp rows, with the central cusp
described as "selenodont". Other cusps have but one ridge.
As the fossils hadn't been fully cleaned up, the description provided is an exercise in
minimalism (p.122). A more detailed one was intended, but none has since appeared as
far as I know. Four teeth were referred and, some seven years later, a similar fossil
turned up in the County Museum of Dorchester, southern England. However, that wasn't
allocated to any particular species of the genus.
The matter of size
Postcanines of this species are either squarish (uppers) or more rectangularly formed
(lowers), and a handy table of sizes is available. There's little variation in the sizes
of postcanines in a tooth row. At least, that's the situation on the jaws known for
S. ooliticus.
Uppers:
S. ooliticus holotype (3 postcanines): lengths 3.1-3.3mm; width (1) 3.6mm.
S. hebridicus (2 specimens): lengths both 5,3; widths both 5.4.
Lowers:
S. hebridicus (2 specimens); lengths 5.2-5.8mm; widths (2) 3.1-3.7.
A passing mathematician informs me that means upper teeth are proportionately wider
than lowers. They need to be for the chewing system to work, as uppers have an
additional cusp row to house.
Holotype
The type fossil, UBGM 20572, entertains visitors to a collection which was seemingly too
shy to be named. If the abbreviation's decoded in the study, then I somehow missed it.
I expect Bristol University would be a good place to search. I refuse to divulge what
the specific name of hebridicus says about this critter from the Hebrides. You'll
just have to guess.
Additional notes
Not all researchers seem to regard this species as a valid one. Presently, not that my
opinion on this need concern anybody beyond the confines of my own skin, I think it
probably is a separate taxon, and a specific distinction seems justifiable. The case
might be weaker if larger and smaller fossils occurred in the same fauna, but that
doesn't yet apply. Besides, a 60% variation in
postcanine size within one species seems odd.
Thanks are due to Nigel Trewin for informing me of the original citation. In case
anybody is puzzled by its reference to a Jurassic mammal, that concerns a
docodont named
Boreolestes, another taxon established in the paper.
Maisch et al, 2004 confirms the presence of the genus in Scotland, (p.649). |
| Reference: | Waldman M & Savage RJG (1972), The first Jurassic mammal
from Scotland, Journal of the Geological Society of London, 128, p.119-125. |
| Genus: "Triglyphus"
Fraas O, 1866
'three carvings'
Remarks: This genus is not valid, but it's of geographical interest. It's based on a
single tooth which was later lost. Illustrations show clear similarities to
Tritylodon, and it is therefore treated as a junior synonym. The name also happens
to be preoccupied by a syriphid fly, T. primus Loew, 1840, just to add to the
confusion.
The Greek glyphus is translated as Fraas to the German Kerbe, a name which
can have several meanings in English; eg. `groove´. However, it doesn't refer to that in
this case. (There are only two grooves.) Rather, it refers to the crown having an
appearance as if it's been carved into three sectors; the three cusp rows.
References: Fraas (1866), Vor der Sündfluth
Loew (1840), Bemerkung uber die in Posener Gegend einheimischen Arten mehrerer Zweiflugler
Gattungen" in Zu der offentlichen Prufung der Schuler des Koniglichen Friedrich-
Wilhelms-Gymnasiums zu Posen, (page 30). |
| Species: | "Triglyphus fraasi" Lydekker, 1889?/90? |
| Place: | Rhaetian-Liassic Bonebed, Tübingen |
| Country: | Germany |
| Age: | Rhaetian-Liassic, Upper Trias-Lower Jurassic |
| Remarks: |
Fraas never published a full description. The species name was
added by Lydekker. Thanks for the above information are due to Dr Michael Maisch, Tübingen
and Nigel Wyatt of the Natural History Museum, London.
Guess what I found yesterday (ie. 2nd July, 2009)?
One of my activities is being a secondhand book dealer, and this involves buying stock in
and bringing it home for sorting. I took a quick glance at a box of books yesterday
afternoon, and Fraas's 1866 work happened to be waving to me from the top. I've got it
here on my lap, and it's gorgeous. This is a book I won't be offering for sale.
The brief description of Triglyphus (no specific name is given) appears on pages
215-216 along with drawings of the upper postcanine tooth itself. The maximum width was
close to half a centimetre.
The use of the word 'was' is significant. Fraas was unable to describe the well-preserved
tooth more fully as it was no longer available for interview. It had been discovered in
1860 but, by 1866, had performed a vanishing act. He gives the locality as having been
Schlößlesmühle auf den Fildern.
Based on what he terms analogs with living creation, he concluded that the tooth
presumably belonged to some marsupial or other, and thought the original owner couldn't
have been larger than a ratty to hedgehoggy sort of size. A point he lays much stress
upon is that this find confirmed the presence of "mammals", although it's now clear tritys
weren't mammals as such, in the rock of ages as distant back as the Upper Triassic. |
| Reference: | Fraas, O (1866), Vor der Sündfluth, Stuttgart, Carl Hoffmann
Verlag, p.215-216, |
| Genus: Tritylodon Owen R, 1884
'three cusped tooth'
aka: Likhoelia, ?"Triglyphus" Fraas O, 1866,
Tritylodontoideus 'Tritylodon form' Fourie, 1962
This generic name has also been applied to indeterminate and isolated teeth from the European
Rhaetian, eg Tritylodon fraasi Lydekker, 1887. I've also seen mention of material
from the Lower Jurassic of southwestern USA, from where tritylodontids have since been
described, (eg. Olsen PE & Galton PM, 1977, p.983, places Tritylodon sp. in the
Glen Canyon Group). Now its usage is restricted to forms from southern Africa.
Likhoelia
My original information (ultimate source unknown) was that Ginsberg established a taxon
called Likhoelia ellenbergeri in 1961. While there may well be some connection,
Knoll, 2005 (p.85) suggests that can't be entirely correct. He ascribes the generic
name to Ellenberger P, 1970 and, at that time, no specific name was suggested. Presumably,
somebody added one later. In any event, it must be regarded as a nomen nudum
(aka a name that's frankly a waste of ink).
The basis is a poorly preserved skull with lower jaw from the upper reaches of the
Elliot Formation, and Ellenberg apparently termed it a "mammalien". It was neither
described nor pictured. As its identity is presently unknown, I've no particular
confidence in it being synonymous with Tritylodon. However, I'm leaving it here
for want of anywhere of more compelling suitability.
The fossil, which was collected by Ginsberg, presently resides in the Museum National
d'Histoire Naturelle in Paris, and the poor thing hasn't as yet even been granted the
diginity of a catalogue number. Nevertheless, at least kindly Knoll has published a
photo (p.86). My rough guess from that is the skull has a length of something like
four centimetres. It may be some form of basal mammal
rather than a trity.
Likhoele, as you doubtlessly already know, is in the Mafeteng District of Lesotho.
Therefore, I won't bother mentioning that here. |
| Species: | Tritylodon longaevus Owen, 1884 |
| Place: | Red Beds and Cave Sandstone, especially Upper Middle
Elliot Formation (Tritylodon-acme zone), Orange Free State |
| Country: | South Africa and Lesotho |
| Age: | Hettangian/Sinemurian, Lower Jurassic |
| Remarks: | As suggested by the reference, this group were
often regarded as mammals until the 1920s and later. Simpson, 1935 includes it as possibly
representing an early suborder within
Multituberculata. He reports a probable skull length of over 15cm. "The sagittal
crest is high and stout, the zygomatic arches arise
opposite the anterior cheek teeth, and the snout is blunt, somewhat depressed, and expanded
at the end. Septomaxillary bones, seldom recognizable
in recent mammals, are present between the nasals,
maxillaries, and
premaxillaries, but in spite of occasional statements to the contrary no exclusively
reptilian osteological characters are shown by the skull as preserved."
Kemp, 2005 (p.70) offers a skull length of up to 25cm, making this one of the largest
tritys.
Dentition
The teeth include three incisors; the second is greatly
enlarged whilst the others are small. There are seven
postcanines. Generally, they're square in outline and have three rows of cusps. He
regarded the relationship of Tritylodon and multis as either rather distant or
doubtful, (Simpson 1935, p.-156-158).
Paw prints?
The Elliot Formation is overlain by the also Lower Jurassic Clemens Formation. This
includes a varied collection of footprints made by dinosaurs and crocodylomorphs. There
are people who specialize in studying such traces, (ichnofossils), which give information
about ancient animals in live action. In this case, an ichnogenus named
Ameghinichnus may represent the wanderings of a tritylodontid, (Lucas & Hancox
2000, p.7).
Likhoelia
The data from Savage, 1971 (p.82) suggests Likhoelia was somewhat smaller than
T. longaevus but otherwise, (at least as far the upper
postcanine measurements go), rather similar.
Tunnellers?
Fossils studied by Ray et al, 2004 included a number of Tritylodon bones. Four of
these were humeri, and the lengths ranged from about 5.3
to 8.2cm, (p.635). These had relatively thick walls, (RBT range of 25-44%, p.640). I'll
add that ratios of 30% and higher are often associated with amphibious, aquatic or
tunnelling lifestyles, (according to Botha & Chinsamy, 2004, p.626). Some further
comments on that theme are contained in the entry for
Trirachodon.
Bone grwoth
Returning to Ray et al, 2004 (p.642): "The bone histology of Tritylodon reveals
fibrolamellar bone tissue... suggesting rapid growth similar to the cynodont,
Cynognathus...". (Reference numbers have
been omitted.) Continuing on the theme, (p.644): "The bone microstructure and growth
strategy of Tritylodon, an Early Jurassic form and most closely related to the early
mammals, suggests a fast, sustained growth that probably slowed down after attaining adult
size. The bone histology of Tritylodon is similar to that of other tritylodontids
such as Bienotherium and Oligokyphus... and suggests that this family had
undergone a progression towards overall rapid growth." They also report a skull length
of about 8cm, (p.645). I don't know how many individuals that figure's based upon.
Holotype
The holotype is in the collection of The Natural History Museum, London. |
| Reference: | Owen (1884), On the skull and dentition of a Triassic Mammal
(Tritylodon longaevus) from South Africa. Quart. Jour. geol. Soc. London XL, p.146
-152. |
| Link:
Proceedings of the Royal Society of London, Vol LV, 1894
http://gallica.bnf.fr/Fonds_Tables/005/M0056148.htm
This is the view of HG Seeley, 1894, (see p.227).
"The skull described as Tritylodon longaevus is examined, and the close resemblance
to the skulls of new Theriodonts is pointed out. The author believes that it shows
evidence of possessing both pre-frontal and post-frontal bones, which were situate as in
Theriodonts, and circumscribed the orbits in the same way;
so that, although the post-frontal bones appear to have met in the median line to form a
crest, at the back of the frontal, there is no other
character in the skull by which it can be distinguished from the skull of a Theriodont. It
therefore appears to be reptilian, and thus would make known divided roots to the
molar teeth in Reptilia, and a more complicated type of crown
than in any Theriodont yet known." |
| Species: | Tritylodon maximus (Fourie, 1962) |
| Aka: | Tritylodontoideus maximus, Fourie, 1962 |
| Place: | Clarens Formation, Stromberg Series, Orange Free State |
| Country: | South Africa |
| Age: | Sinemurian / Pliensbachian, Lower Jurassic |
| Remarks: | Possibly a large T. longaevus in the view of
Hopson JA & Kitching JW, 1972. Savage, 1971 records this genus as being significantly
larger and equipped with nine upper postcanines rather
than seven. However, such differences in other non-mammalian
eucynodonts appear to be connected with biological age,
rather than different taxonomic affinities. |
| Reference: | Owen (1884), On the skull and dentition of a Triassic Mammal
(Tritylodon longaevus) from South Africa. Quart. Jour. geol. Soc. London XL, p.146
-152. |
| Link:
M.A. Cluver, South African Museum
http://www.museums.org.za/sam/resource/palaeo/cluver/later.htm
A fine introduction to the cynodonts and early mammals of a world-class fossil site.
This ascribes the Red Beds of Karoo to the Upper Triassic, rather than Lower Jurassic,
though recent stratigraphic works suggests a younger age, (eg. Lucas & Hancox, 2000.) |
| Genus: Xenocretosuchus
Tatarinov LP & Matchenko EN, 1999
'foreign Cretaceous crocodile' |
| Species: | Xenocretosuchus sibiricus Tatarinov LP &
Matchenko EN, 1999 |
| Place: | Shestakovo, Kemerovo Region of Siberia |
| Country: | Russia |
| Age: | Upper Aptian?, Lower Cretaceous |
| Remarks: |
Based on five isolated teeth, with similarities to Stereognathus and, less clearly,
Yunnanodon (Dr Maisch, pers.comm.). The holotype, a right upper
postcanine, is resident at the Paleontological Institute
of the Russian Academy of Sciences.
Slight update, 2008
More teeth have since been found from several loclities in western Siberia. I seem to recall
at least three sites are now contributing fossils. |
| Reference: | Tatarinov & Matchenko (1999), A find of an aberrant
tritylodont (Reptilia, Cynodontia) in the Lower Cretaceous of the Kemerovo region.
Paleontological Journal, 33, p.422-428. |
| Species: | Xenocretosuchus kolossovi Lopatin AV & Agadjanian
AK, 2008 |
| Place: | Vilyui River, Teete Creek (left tributary of the Botomoyu River),
Republic of Sakha (Yakutia) |
| Country: | Russia |
| Age: | Upper Jurassic or Lower Cretaceous |
| Remarks: | The following is based upon my reading of the
English version of Lopatin & Agadjanian, 2008, which isn't quite the same as the original
Russian language citation. As well as the language, the page numbering also varies.
Thanks are due to the supplier.
A brief geographical meander
The fossils under interrogation came from a locality many would regard as somewhat remote,
but that's not the case for some citizens of the Russian Republic of Sakha (aka Yakutia).
However, most Yakutians probably think it's remote as well. Yakutia is a small Republic
comparable in size with something like Luxembourg and much of the rest of Europe as well.
I haven't checked the land areas involved but, in any case, Yakutia utilizes three different
time zones. About 40% of the Republic is Arctic tundra. Another vast feature in this
vastness is a river system feeding the River Lena. An apparent oddity might be thought
posed by the lack of a single bridge crossing that river but, for most the year, bridges
would be pointless. Yakutians prefer to simplify things by just driving across the ice.
Ferries run in the short summer.
To get an approximate fix on the locality in question, look up the city of Yakutsk in a
suitable atlas, head northwest towards the Lena River and keep going some more. You're
looking for the Vilyui River, a left tributary of the Botomoyu (p.107). Even if, like me,
you actually fail to find it on your map, then at least you'll have gained some rough
idea. After all, this is a huge tract of land with a wealth of rivers, and most of them
proudly bear challenging names to the uninitiated.
So, the relevant locality, known as Teete Creek, is well northwest of the city of Yakutsk somewhere
in the midst of the back of beyond. It's also a locality that's previously yielded dino
fossils and is of uncertain age, either Upper Jurassic or Lower Cretaceous. It qualifies
as one of the planet's most northerly dino digging places.
Late tritys
For most of the Earth, the tap of fossil tritylodontids sadly stopped running during the
Middle Jurassic. Late tritys from the middle of Siberia, while most welcome, aren't
actually all that surprising. Upper Jurassic representatives have emerged from China,
while Cretaceous stragglers have been found padding around in both Western Siberia and
Japan. Or, at least, their teeth have. The teeth in the instance of Yakutia, both of
them, happy to be broadly similar to specimens from Shestakovo, Siberia, and that led to
them being referred to the already established genus of Xenocretosuchus. Nevertheless,
divergent details indicate a distinct species.
Upper postcanine
The upper postcanine is in fairly good condition but incomplete. Available for inspection
are most of the buccal and central portions, with the
lingual flank broken off near the front. Enough remains to
show there were the trity trademark three cusp rows on an upper postcanine. The grooves
between the rows become narrower from back to front, and they close at the end of the
tooth. There are two middle row cusps in positions M2 and 3, and these are crescent-shaped.
The pair of buccal cusps, in contrast, are accused of being "elongated teardrop-shaped".
They're diagonally inclined so as to run towards the buccal arm of the relevant middle
v-shaped colleague, and are named B1 and B2. B2 actually meets and with M3, and this
causes a midway blockage of the intervening valley between the rows.
The front and rear of the crown preserve details concerning interlocking habits with
neighbouring postcanines. For the middle row, in front of the first cusp (M2), there's a
triangular shaped forwards projection. Judging from the architecture of the rear of the
tooth, seeing as it must perform a reasonably close approximation of the neighbouring
teeth that once inhabited the same mouth, this interlocked into a into a gap on a projection
behind the final cusp (M3) of the tooth in front. Similarly, a ridge-like projection in
front of cusp B1 fitted into a hollow behind the preceding B2.
Lower postcanine
This is a narrower tooth with two rows of two cusps each (p.108). All cusps are similarly
sized, and both rows are separated by a deep groove. The cusps are crescentric (v-shaped
looks like a reasonable approximation), with the opening to the rear. And, unsurprisingly,
the lower specimen also retains evidence of an interlocking system (p.109)
Sizes
Lower: length 4.6mm, width 2.75mm
Upper: length 5.4mm, width ca. 6.0mm.
Differences between the new X. kolossovi and X. sibiricus lie in details of
grooves and ridges. Crests for his newer species run deeply into the central groove between
the cusp rows of lowers, and into the buccal groove of uppers, and those grooves become
partitioned. Such blockages aren't apparent for X. sibiricus. Another difference
is the presence of: "longitudinal ridges on the areas for interlocking the lower cheek
teeth..." Those don't feature for the previously established species. The sizes are
similar.
Interlock
Interlocking structures on trity postcanines don't seem to have been discussed before.
It would be odd if they only occur for one species, although it's possible they're
unusually strongly pronounced in this case. Only comparisons can tell. In any event, I
think I can hear the sound of drawers being slid open around the world, as researchers
prepare to take another look at their trity friends with this perspective in mind.
Holotype
The type fossil, PIN 4874/11, a right lower postcanine, spends its days at the
Paleontological Institute of the Russian Academy of Sciences in Moscow. At least, I guess
it does judging by the catalogue number. The specific name honours PN Kolosov. He
collected the specimens in 2004.
The listed reference is in Russian. The English translation is Doklady Biological
Sciences, 2008, Vol.419, p.107–110. That's the version I've got. |
| Reference: | Lopatin & Agadjanian (2008), (A Tritylodont
(Tritylodontidae, Synapsida) from the Mesozoic of Yakutia), Doklady Biological Sciences,
Doklady Akademii Nauk, 2008, Vol.419(2), p.279–282. |
| Genus: Yuanotherium Hu Y,
Meng J & Ckark JM, 2009
'Yuan's beast'
Remarks: The generic name honours Yuan Fuli, a Chinese paleontologist and geologist active
in Xinjiang during the early twentieth century. |
| Species: | Yuanotherium minor Hu, Meng & Clark, 2009 |
| Place: | Shishugou Formation, Junggar Basin |
| Country: | China |
| Age: | Oxfordian, Upper Jurassic |
| Remarks: | The following is based upon my reading of Hu, Meng
& Clark, 2009.
I confess to being a tritylodontidphile. Their bodies turn me on. They are exotic,
erotic... Tritys are sexy. Kind of sadly, this new one from Inner Mongolia failed to
immediately raise my dander as much as most. It's hum drum and lacks outrageous novelty.
However, that's kind of happily as well. Other Chinese Mesozoic
eucynodonts of astonishing beauty and completeness -a stampede of them over the past
fifteen years- have managed to dull my taste for a further trity known presently from much
more modest remains. I'm yearning for a trity corpse packing the punches that
Eomaia,
Sinodelphys, Repenomamus,
Castorocauda and
Volaticotherium pummelled me with. All I want for Christmas is a thoroughly
dead and gob-smackingly complete trity, and I don't mind what time of the year it arrives
at! Yuanotherium has so far managed nothing more than a fragment of upper jaw,
and the wild excess of other riches has impoverished my appreciation for such small
blessings. Nevertheless, this scrap of jaw was once part of the mouth of a small, yet
gorgeous trity. It's not that animal's fault that Dame Nature treated the rest of its
body so callously over the 160 million years since its death.
Yuan Fuli's friend
Upon reading the abstract, I immediately allowed my mind to leap to a careless mistake
(p.385) by muddling up the name. Instead of a Chinese researcher named Yuan, my memory
conjured up Yunnan, a province in southern China that bequeaths the world Lower Jurassic
tritys. This one, in reality, hails from Xinjiang in northern China, and is around 20
million years younger; Oxfordian, Upper Jurassic.
The fragment of jaw contains one partial and two complete
postcanine teeth with, as always for trity uppers, three longitudinal rows of cusps.
These number (buccal to lingual)
2, 3-4 and 4. The middle row of the foremost tooth has a trio of cusps while four applies
for the following teeth. The observable features of the jaw indicate these are the first
three postcanines of the series.
The jaw fragment preserves parts of different bones with the postcanines housed on a thin,
reduced maxilla. Such a reduction is a derivation shared
with trity colleagues including Bienotheroides.
Postcanines
The outline of the teeth is squarish but with the internal and external sides being
curved in an unsquarish manner. Complete teeth, namely the first two, have lengths of
2.6mm (PC1) and 2.8 (PC2). Widths are about 0.1mm and 0.2 greater; also not a literally
squarish characteristic. The rear end is missing from the fairly complete PC3, but its
width indicates it was a somewhat larger tooth than PC2, and its cusp rows are fully
represented.
The detailed description concentrates most attention on the first postcanine, seeing as
much is very similar for all three. The most obvious differences are matters of size and
the differing complement of middle row cusps; three rather than four.
Seen in occlusal view, the front of the tooth has a rounded profile while the rear edge is
straight. The three cusp rows are reasonably similar in length, but the middle one wins
clearly enough at the photo finish by thrusting its front cusp ahead of those of the other
two contenders. All those leading cusps are comparatively small, but both those on the
flanks are biasedly crescentric. The leading buccal cusp, for example, has an internal
ridge termed sharp and an external one here accused of bluntness. The lingual cusp has
a similar but reversed attitude; externally sharp. The middling leader has no such
pretensions towards crescentricity, a word I've just needlessly invented. Still at the
front of the crown, and ahead of the cusp rows, are four small cuspules.
The two cusps of the buccal row are similarly asymmetrical in form, with the rear one
being the taller. For the middle row, the final pair of cusps are similar to the final
buccal cusp, although they're not quite as long (p.387).
The second postcanine beats both the length and the width of the first one by around 10%.
Apart from that, the most obvious distinction from PC1 is a fourth cusp in the middle row,
with the final pair of cusps there positioned close to one another. Those of a romantic
disposition may be heartened to hear this closeness allows them to share a common base.
Other distinctions are minor. Apart from being incomplete and slightly larger, PC3 is
much like PC2.
How old are you, you young whipper-snapper?
The wear apparent on the front edge of crests is too strong for the teeth of a kid (p.388).
Rather, it's consistent with a young adult age. And that, in turn, suggests the closely
packed rear two middle cusps of PC2 and 3, those with a common base, don't represent a
juvenile condition. It's an adult character not presently known from other trity
genera.
A position in Tritydom
The maxilla component of the jaw, as said, is comparatively
reduced, and the premaxilla gets to meet a bone called
the palatine. This is a derived trity trait known, from
among others, Bienotheroides and
Stereognathus. That's not surprising for an Upper Jurassic trity. The animal
itself is kind of "reduced", in that it's at the lower size range of the family; smaller
than all excepting for Lufengia and
Yunnanodon. As that comparison is made upon the basis of the lengths of
(mostly, with exceptions cited) second upper postcanines, it's not likely to be
significantly biased by biological age of individuals, in my opinion.
Trity postcanine eruption and matters of possible taste
Another mistake I made during my first reading of this paper was to somehow miss
interesting discussion of postcanine replacement in tritys. Apparently (p.390), there's
no evidence showing tritys replaced any of their postcanines at the same dental position.
Rather, freshlings were added at the rear of the row while, when strongly worn, older ones
were dispensed with at the front.
In the case of 'Yuan's beast', the degree of wear and the morphology of the foremost
postcanine make it probable that this is the first such tooth this individual ever grew.
The comparatively slender cusps and weakly developed ridges aren't particularly suitable
for processing hard, tough food. Consequently, this trity presumably favoured softer
nibbles than most of its colleagues. The authors point to the possibility that tastes
may have been those of an omnivore rather than a strict herbivore.
Holotype
The type fossil, IVPP V15335, is employed as an entertainer at the Institute of Vertebrate
Paleontology and Paleoanthropology, Beijing. Remarkably or otherwise, the specific name
alludes to the critter's minor (as in small) size. |
| Reference: | Hu, Meng & Clark (2009), A new tritylodontid from the Upper
Jurassic of Xinjiang, China, Acta Palaeontologica Polonica, 54(3), p.385-391. |
| Genus: Yunnanodon (Cui G,
1976) Cui, 1986
'Yunnan tooth'
Aka: Yunnania Cui, 1976 |
| Species: | Yunnanodon brevirostre (Cui,1976) Cui, 1986 |
| Aka: | Yunnania brevirostre Cui, 1976 |
| Place: | Dark Red Beds, Lower Lufeng
Formation, Yunnan |
| Country: | China |
| Age: | probably Sinemurian, Lower Jurassic |
| Remarks: |
This is the smallest tritylodontid known from this formation. The length of
the skull ranges from about 3,5 to 4,5 cm, (Luo, 2001, p.83). Dental features are relatively
derived, as is the case with Dinnebitodon. Some
specimens reside in the collection of the Institute of Vertebrate Paleontology and
Paleoanthropology, Beijing.
It has been suggested that this genus is synonymous with Lufengia. However:
"These two forms differ in the pattern of the upper
postcanine cusps. Lufengia has three cusps in the
lingual row, with the posterior cusp reduced in size; Yunnanodon has only two
lingual cusps. The transverse dentine sheet connecting the upper postcanine roots in the
same row is much better developed in Lufengia than in Yunnanodon (Cui and
Sun, 1987). In Lufengia, the anterolingual root of the upper postcanine is large
and ellipsoid in cross-section. By contrast, this root is small and rounded in transverse
section in Yunnanodon (Cui and Sun, 1987)", (Luo & Wu 1994, p.259-260).
Plainly put, the teeth are somewhat different. |
| References: | Cui (1976), Yunnania, a new tritylodont genus from
Lufeng, Yunnan. Vertebrata PalAsiatica 25, p.1-7. |
| Cui (1986), Yunnanodon, a replacement name for
Yunnania Cui, 1976. Gu Jizhui Dongwu yu Gu Renlei (Vertebr. PalAsiatica 24), p.9.
|
Usual kind of warning. The following is my own ill-qualified
speculation.
It's largely based upon 'The inner ear and its bony housing in tritylodontids and
implications for evolution in the mammalian ear', by Dr Zhexi Luo, 2001, (further details
in the Bibliography).
Earnotes
"The inner ear structures underwent fundamental changes during the evolution from
non-mammalian cynodonts ("mammallike reptiles") to early mammals. The
petrosal bone in mammals has an enlarged pars cochlearis
containing an elongate cochlea," (p.81).
The above cited paper concerns the internal structure of the ear of Yunnanodon, and
provides some comparisons with non-mammalian and mammalian critters. Some very unusual
words can be found within its pages. I'll concentrate my attentions on a couple of the
less exotic terms.
In us lot and marsupials, the cochlear canal is
coiled, which makes the route sound vibrations must travel longer. This allows the ear to
do more with them: "Mammals are most specialized among living
vertebrates in their hearing adaptation, much of which
is attributable to their derived inner and middle ear structures. The pars cochlearis
containing a cochlea is one of the most complex character systems of the mammalian skull,
and is crucial for more sensitive hearing, especially for high frequency sound,"
(p.93).
In us lot and marsupials, all these and more wonderful hearing aids are housed within one
bone called the petrosal. In general, non-mammalian
cynodonts had several bones for this purpose: "the prootic and the opisthotic, known
collectively as the periotic bones, as well as by the exoccipital and the basioccipital",
(p.81). They had both the more complex packaging and the simpler contents.
Yunnanodon, as an extremely mammal-like cynodont, is somewhere in between these two
typicalities. "The petrosal forms the bony housing for the entire inner ear of
Yunnanodon", (p.83).
As for this sound processor, the cochlea, the usual non-mammalian therapsid characteristic
is a relatively simple cavity. In derived types, such as Yunnanodon, this had
lengthened into a canal, with a bit of a bulge in the middle. Basal mammals, eg.
Morganucodon, enjoyed the advantages of an even greater elongation. As stated, our
cochlear canal is longer still, as it's coiled, making it yet more effective. Interestingly,
monotremes, (eg duck-billed platapussies), have an equivalent though different trick:
"The living monotremes have a coiled cochlear duct (membranous labyrinth) but without
the corresponding coil of the bony cochlear canal (bony labyrinth)", (p.94).
The mammalian exploitation of sound and scent, (more sophisticated than their sense of
sight), encourages the consideration of an early predilection for a nocturnal tendency.
With thanks to Dr Luo for kindly supplying the paper. |
| Ichno Genera
Ichno-fossils refers to traces left by the behaviour of former earthly inhabitants, and
tritys artists that have produced such works; eg. paw prints. Further examples have been
blamed on tritys, perhaps incorrectly. The following cast list need not be complete.
|
| Species: | Ameghinichus patagonicus Casamiquela RM, 1964 |
| Place: | La Matilde Formation |
| Country: | Argentina |
| Age: | Middle Jurassic |
| Remarks: | Rainforth & Lockley 1996 (p.265) informs me
these tracks are pentadactyl. Whether they were produced by tritys or mammals of some
kind isn't known to me. R & L say mammals at first, but then add the possibility of
"mammal-like reptiles" (p.266). The paws apparently measure a full centimetre in
length (p.267). One of its hoppy movements could shift the critter 9cm forwards. |
| Reference: | Casamiquela RM (1964), Estudios Ichaologicos, Buenes Aires,
Colegio Industrial Pix. IX, 229pp. |
| Species: | Ameghinichus sp. |
| Place: | Elliot Formation, Karoo |
| Country: | South Africa / Lesotho |
| Age: | Lower Jurassic |
| Remarks: | A number of tracks may pertain to these former
feet (Knoll 2005, p.85). Off hand, I can't remember if I've got information on
specific names. |
| Reference: | |
| Species: | Brasilichnium duijrara Leonardi G, 1980 |
| Place: | Botucatu Formation |
| Country: | Brazil |
| Age: | Lower Jurassic |
| Remarks: | Rainforth & Lockley 1996 contains some
information (p.266). The former owner had paws of a length of about 2cm. As it was
capable of merrily bounding along at 15 to 20cm per spring, it qualifies for the word
hopper. |
| Reference: | |
| Species: | Brasilichnium elusivum Leonardi G, 1981 |
| Place: | |
| Country: | Brazil |
| Age: | Lower Cretaceous |
| Remarks: | If this is indeed Cretaceous, then a mammal is far more likely
to blame than an extremely late trity. My only sources for this entry are what could be
scratched together on the internet. |
| Reference: | |
| Species: | Masitistherium primordialis Ellenberger P, 1970 |
| Place: | Elliot Formation, Karoo |
| Country: | South Africa / Lesotho |
| Age: | Lower Jurassic |
| Remarks: | This track was accused of being a trity production
and was figured in a 1972 study by the original author (F Knoll 2005, p.85). However, in
that same work it was also charged with being a small mammal. Later still, the original
author opted for a new course and plumped for avian affinities (p.84).
Kitching and Raath termed it all a load of nomen nudum. Presently, I'm regarding
it as a sumint (Dorset dialect for a something or other).
Thanks go to FK for forwarding a copy of FK, 2005.
And there's more...
On page 82, Knoll kindly provides a table containing the names of other tentatively assigned
cynodont ichnogenera from the "Upper Stormberg Group" mentioned, or established, by
Ellenberger in 1970, 1972 and 1975. There are hardly more than a couple of dozen!
Acropentapodiscus, Ameghinichus, Aristopentapodiscus,
Calibarichnus, Cavotetrapodiscus, Dinopentapodiscus,
Dromicotetrapodiscus, Embrithopeniapodiscus, Entodipodiscus,
Eodipodiscus, Eopentapodiscus, Eotetrapodiscus, Euacropentapodiscus,
Euameghinichus, Francipentapodicus, Grypopentapodiscus,
Lehahichnus, Megadipodiscus, Mesodipodiscus, Microtetrapodiscus,
Molapopentradiscus, Myopentapodiscus, Nanopodiscus,
Paradipodiscus, Paraeopentapodiscus, Pseudameghinichus and
Vandijkopentapus.
If all are justified, then Waterloo train station at rush hour must be considered quiet
in comparison, as well as exhibiting far less cynodont diversity.
Olsen & Galton 1984 (p.94) opine...
"Of the 46 genera founded on upper Elliot and Clarens material (Zone B of Ellenberger,
1970), 26 appear to be based on indeterminate material, 19 are congeneric with Newark
forms, and one (Episcopopus) is distinct but possibly indeterminate."
The figure of 46 genera refers to cynodont and other terrestrial vertebrate
ichnotaxa. |
| Reference: | Ellenberger P (1970), Les niveaux paleontologiques de
premiere apparition des manmiferes primordiaux en Afrique de sud et leur ichnology, p.
343-370, in Haughton SH (ed.), Proceedings and Papers 2 nd Gondwana Symposium, South
Africa. |
| Other reports:
William R. Hammer, Antarctic Dinosaurs
http://darwin.apnet.com/dinosaur/hammer.htm
Reports on various finds in Antarctica, (interesting place), including tritylodontid
remains ascribed to the Pliensbachian. Suggests, in passing, that Bienotheroides is
Lower Jurassic, without making an issue of it.
June 2007 update: I'm reliably informed that a Lower Jurassic trity will be
appearing from the tropical Antarctican continent at some time. My understanding is
that this has no direct connection with material collected by Hammer & Co.
The Isle of Skye, Scotland
http://www.bambi.demon.co.uk/skyedata/nature_conservation.html
Mid to late Bathonian Tritylodont material. Relevant is 19. Elgol Coast. This may well be
connected with Stereognathus hebridicus, but I'm not yet sure.
Argentina
http://www.ischigualasto.com/es/ischigualasto.htm
Tritylodont finds included in Annexo VII, 6. Formacion Los Colorados. This formation is
Upper Triassic (late). The extensive report is in Spanish.
Ishikawa, Honshu, Japan
http://www.netlaputa.ne.jp/~pantheon/bienoyokou.html
This page is in Japanese. M Alan Kazlev obtained a translation. It seems to involve one
or several teeth of the Lower Cretaceous and is presumably, therefore, somewhat dubious.
It begins, "Are discovered from chalkstone type lower part * hand taking formation the
nursing similar type reptilia which..." A translation of the translation would be
appreciated.
Remarks: News has arrived, courtesy of David Marjanovic.
Makoto Manabe, Paul M. Barrett & Shinji Isaji: A refugium for relicts?, Nature 404, 953
(27 April 2000)
"The Kuwajima Formation has yielded more than one hundred isolated teeth of a new
genus of tritylodontid synapsid^4. Before these discoveries, tritylodontids were thought to
have become extinct sometime in the Middle or early Late Jurassic, as the youngest-known
tritylodontid (Bienotheroides) was recovered from late Middle Jurassic deposits."
David adds:
The formation is Hauterivian in age. I've never seen ref. 4 = T. Setoguchi, H. Matsuoka
& M. Matsuda in Proc. 7th Annu. Meet. Chinese Soc. Vert. Paleontol. (eds Y. Wang &
T. Deng) 117 -- 124 (China Ocean, 1999).
I add, there seems to be a good variety of differentiated teeth,
postcanines and incisors,
(some complete). A dentary fragment has also been found.
This is probably a new genus but as yet, it's not been published, (14.1.2002). A copy of
Manabe et al, 2000 has just turned up. The formation is thought to be either Valangian or
Hauterivian by comparison to the nearby Okurodani Formation.
Hirayama et al, 2003 offers a brief summary of the Kuwajima Formation vertebrate fauna:
fish of various groups, three taxa of semiaquatic turtles,
seven or more types of lizard, various dinosaurs, pterosaurs, a indeterminate bit of bird,
trtylodontids (plural), and a multituberculate and
triconodont mammal. This is one of the most concise
publications in history. It has nine authors and runs to three paragraphs.
Thailand, Mickey Mortimer
http://www.cmnh.org/fun/dinosaur-archive/2000Sep/msg00116.html
A possible tritylodontid snout.
Shestakovo, Kemerovo Region of Siberia
As well as Xenocretosuchus, a second, not yet named genus has been identified. This
seems to be from a different, but similar location. More details when I have some.
Holwell Quarry, England
A trity maxilla was recovered from near Shepton Mallet,
which is a few miles away from where Oligokyphus remains were found by Kühne. It was
originally assigned to that genus, but was revised to incertae sedis, (Savage, 1971).
That short paper contains some information on tritys in general.
In adults, the number of upper postcanines was usually
six or seven per side. Exceptions were Lufenia (five) and Tritylodontoideus
(nine). I think I'll rudely interrupt Dr Savage by mentioning the first genus is relatively
small and the second large. That may or may not be of some significance.
Berezovsk Quarry, Western Siberia
Averianov et al, 2005 includes mention of a fragmentary, upper
molariform tooth in this Middle Jurassic fauna (Bathonian). It's regarded as an
indeterminate trity. |
A. Tritylodontidae B. Tritheledontidae
Eviction Notice
This directory used to have two sections. Following four years of squabbling, the trithes
have now been relocated as of April, 2005. Follow them to:
Mesozoic Cynodonts: Tritheledonta |
| B. TRITHELEDONTIDAE (and associates) |
Eviction Notice
This directory used to have two sections. Following four years of squabbling, the trithes
have now been relocated as of April, 2005. Follow them to:
Mesozoic Cynodonts: Tritheledonta |
| Help:
Should anybody have any further information, I'd be pleased to hear of it.
Regarding references and Bibliography:
I haven't and can't verify all the references, so beware. Traditional papers used in
constructing this page are in the bibliography. If you feel these are too few, then send
some more.
Return to top of page
Trevor Dykes, April 2001. Last update: 9.12.2009
ktdykes@arcor.de |
With further thanks for assistance due to:
Mrs Karin Dykes, for her computer skills
Mr Paul Ensom, The Natural History Museum, London, for the Dorset Stereognathus
sp..
Professor Pascal Godefroit, for the papers on Upper Triassic European
microvertebrates.
Mr M. Alan Kazlev, for his clarifications and further advice.
Mr T. Mike Keesey, for his confirmation of the ages of the Shaximioa Formation,
Sichuan.
Dr Zhexi Luo, for further papers, kind words and encouragement.
Shirley Sparks, for kindly supplying the paper by Dr Savage.
Ian Corfe, for supplying information from his trity studies.
HitBox Central, and
Animation Library for the animations.
The Society of Vertebrate Paleontology's Bibliography of Fossil Vertebrates (John Damuth)
http://www.bfvol.org/
Biosis Index to Organism Names
http://www.biosis.org.uk/triton/indexfm.htm |
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Morphometric Considerations. Palaeontology, Vol. 45, Part 6, p.1151-1170.
Averianov AO, Lopatin AV, Skutschas PP, Martynovich NV, Leshchinskiy SV, Rezvyi AS,
Krasnolutskii SA & Fayngertz AV, (2005), Discovery of Middle Jurassic mammals from
Siberia, Acta Palaeontologica Polonica, 50(4), p.789-797.
Benton MJ, Cook E & Hooker JJ (2005), British Mesozoic fossil mammal GCR
sites, Chapter 2 of Benton, Cook & Hooker, Mesozoic and Tertiary fossil mammals and
birds of Great Britain, Geological Conservation Review Series, No. 32, Joint Nature
Conservation Committee, Peterborough, p.27-66.
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