TRIASSIC CYNODONTS; Cynognathia, 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.
Cynognathia was a group of non-mammalian
therapsids, though its membership became increasingly
more mammal-like as time went by. The most basal known
representative is Cynognathus. Unlike most cynognathians, it was a carnivore. As
the group isn't composed of one ancestor and all of its descendants, it's
paraphyletic.
For those of a technical disposition, (Rubidge & Sidor 2001, p.468):
"Cynognathians can be diagnosed by several synapomorphies
including a very deep zygomatic arch that extends
above the middle of the orbit..., a suborbital process on the
jugal... for the origination of the masseter jaw closing muscle, and a very deep groove on the
lateral surface of the squamosal that connected the middle ear with the outside world..."
(The bits of the sentence I've neglected to include are references.)
Of gomphodonts...
As well as the animals featured in this directory, Cynognathia contains the further derived
gomphodonts, ('peg teeth'). "Gomphodont cynodonts
more derived than Diademodon and Trirachodon typically lack
sectorial teeth and have traditionally been termed
tids", (Rubidge & Sidor 2001, p.468, and 'sectorial' means 'blade-like').
Traversodontidae is dealt with on a separate
directory.
...and tritys
Even more mammal-like, and generally later occurring, is a family called
Tritylodontidae. Some authors have interpreted the
tritys as being possible descendants of traversodontids and, therefore,
derived cynognathians. They can be admired at
Jurassic Cynodonts, Tritylodontidae. Admittedly, it also
involves the Triassic and Cretaceous animals but I like the title. Many see a closer
relationship with the meat-nibbling tritheledontans
and mammals. |
| Genus:
Platycraniellus (van Hoepen, 1916)
Aka: Pltycranion van Hoepen, 1916; Platycranium van Hoepen, 1917
Remarks: This genus is mentioned in Kemp, 2005 (p.64). It's possibly an aberrant, early
and basal eucynodont. Thanks for the authorship and
synonyms are due to Toby White of Palaeos.
Update
The 2007 redescription has now winged its way in from South Africa. This genus is
accused of being a member of the sister lineage of Eucynodontia, rather than a
eucynodont as such. I suppose it should be relocated to the compound for
non-eucynodontian cynodonts along with Galesaurus,
Thrinaxodon and Co. However, its
closely enough related for my liberal tastes, and I can't be bothered to move
it. |
| Species: | Platycraniellus elegans (van Hoepen, 1916) |
| Aka: | Platycranion elegans van Hoepen, 1916; Platycranium
elegans van Hoepen, 1917 |
| Place: | Lystrosaurus Assemblage Zone, Karoo |
| Country: | South Africa |
| Age: | Lower Triassic |
| Remarks: | The following is based upon my reading of
Abdala, 2007, and thanks are due to the supplier.
Platycraniellus is a cynodont from the Lower Triassic of South Africa and,
for some reason or other, I find it horribly difficult to spell. Apparently, either
the original author or his type-setter had similar problems (p.591). Originlly, it
was named Platycranion. However, van Hoepen decided Platycranium
(presumably the intended version) was somehow or other: "preoccupied twice in the
form of Platycranius..." I can't make head nor tail of that, so don't expect
more enlightenment. Regardless of whether necessary or what the original name was
supposed to be in the first place, it was revised to its present form by van Hoepen
in 1917. The thing nobody ever quite got around to doing was actually describing
the fossil in much detail. Paleontological wheels can roll rather more sedately
than might be desired, so Abdala thought it time to give them a shove some nine
decades later. Gentle pushes have previously been applied but others, but the
vigour involved didn't go as far as a detailed description.
There were complicating encouragements for apparent neglect. For one thing, the
original attempts at preparation left future researchers with something to desire;
for example, the front of the jaws and some of the teeth. In freeing the fossil
from its surrounding matrix, enthusiasticly conducted grinding inflicted fairly
extensive damage. However, more careful additional work brought further details to
light, and a helpful second specimen added to the supply of information. More
means meant it was time for a redescription.
Additionally, 32 therapsids were interviewed
about 96 characteristics of their skulls and teeth. Most of these were cynodonts.
According to this survey, Platycraniellus is the nearest known relative of
eucynodonts which fails to quite qualify for
membership. It's closer, however than Thrinaxodon, it's contempoarary
friend.
Happy Harrismith
Harrismith Commonage is a charmingly named fossil locality in Free State Province.
It's a generous place with Lystrosaurus Assemblage Zone
vertebrates from the Lower Triassic. The fauna is relatively diverse and stars
of the cast are three cynodonts; big(gish), bad, beautiful
Thrinaxodon -who, I hope, looked after Lystrosaurus kids- and smaller
killers named Galesaurus and Platy C.
The latter is the rarest with only two specimens known. I should mention that
Thrinax wasn't all that much bigger. Larger specimens came in a fairly moderate
pussy cat sort of size. However, it was large enough for Lystrosaurus
babies; indeed, too large for their tastes.
Platy C has received some coverage from several authors, and one view regarded it as
a galesaurid. The same accolade applied
for Thrinaxodon in the 1970s. Thrinax, however, typically possessed something
galesaurids aren't supposed to have; a fully ossified palate at the roof of the
mouth. As a bony structure, this was not quite complete for galesaurids. A gap
persisted in the middle, and that would presumably have been canvased over with
some cartilage. The extra refinement helped get Thrinax thrown out of that
family (p.592).
Revision of Platy C
Further preparation of the holotype revealed details not previously clear for
Platycraniellus, and a second undescribed specimen added more to the picture.
Another fossil, previously assigned to the species, was also interrogated. That one
probably is a galesaurid.
What a beautiful broad!
To speak in extremely obscure Anatomese, Platy C had one heck of a wide head for a
cynodont of the time (p.593). The maximum width is close to 90% of the length of
the skull. In case you might think this could indicate a generously sized brain box,
it doesn't. The effect is more a matter of wider cheek regions, but the skull is
generally broad all over. The snout is proportionately short. As with most
specimens of Thrinaxodon, the secondary palate is completely boned, and reaches
to the level of the last but one postcanine. It's
somewhat shorter for the second specimen.
While preservation of the type fossil was rather good, earlier methods of preparation
involved works of destruction that natural forces managed to avoid. Grinding led to
collateral casualties; the front of the mandible
and most remains of the lower teeth. A few roots survived the carnage on the right.
Friendly fire also accounted for the left side of the upstairs dental department.
Obscurity is further enhanced by odd scraps of the body which presently feel much
attachment for the skull. As one of these elements is a humorous
humerus, this position appears to be well beyond
the wildest ambitions of even deranged yoga adicts. Traditionally, land critters
stored that bone in the upper arm.
The second specimen shows several details kept to itself by its friend. At some
stage during its fossil career the lower jaw may also have been present. Certainly,
partial lower postcanine teeth have been left hanging onto the palate (p.594).
The length of the holotype suggests a cynodont of something like
hamster
proportions, although this has no relevance for the build; 8.4cm. Its proportional
width (88% of length) is the greatest known for any non-mammalian cynodont. The
snout earns the term short as it only contributes 39% of the skull, and the region
with the eyes is miserly as well (17%). That leaves the rest of the skull with no
option apart from being comparatively long. The less complete second skull was
donated by a smaller individual; about 6.5cm. I wonder if that has something to
do with the comparatively shorter bony palate; age difference?
Lovers of fine art will be horrified to learn that the resident site artist, TD
Dykes, has expressed the desire to inflict a quick sketch upon this unfortunate
cynodont. Sadly, despite the precaution of hiding his official black sketching pen,
he's found a blue one. The rear of the skull is supposed to be largely taken up
by two big holes, the fenestrae, and the narrow brain case lies between them. (This
refers to the situation for Platy C and, equally, the resident site artist.) Hopefully,
our own answer to Picasso has managed to depict the outlines of those holes in ink.
Various squiggly pencil lines supposedly represent stuff going on below.
Platycraniellus
Oh dear. He did a side view as well.
At least the poorly sighted bird's eye view manages to convey the idea of a wide
head and short snout. The cheek bones of the
zygomatic arch are fairly sturdy, and the hight of them remains similar all along
their length (p.596). The arrangement became more gracile in the lineage leading
to mammals. What these sketches can't attempt to depict, given the perspectives
abused, is the bony palate forming the roofing of the mouth. In most
basal cynodonts, for example the galesaurids, this
character wasn't completely developed. As mentioned, it's all bone for Platy C.
Teeth
Thanks to the editing provided by the earlier, well-intentioned efforts at
preparation, less of the dental story is now available for perusal. The upper count
on one side was: 4 incisors, 1
canine, 6 or 7 postcanines (p.598). A short
gap (diastema) separates the incisors from the
canine, but the rest of the series runs without such interruptions. Generally, the
earlier efforts smashed the crowns to smithereens leaving just the roots. A few
uppers and lowers survived, and three upper postcanines came delivered with the
second specimen.
One remaining lowerling is the right canine. This tooth is smooth with some weak
scratches, and large incomparison to the postcanines. Additionally, a sixth lower
postcanine also survived the devestation.
The upper team fared somewhat better. Crown parts of five postcanines remain on
the right jaw. The foremost possesses a tall main cusp at the front and a small
accessory one behind. The closest match for the front two teeth was provided by a
Nanictosaurus (aka Cynosaurus).
The final survivor was somewhat more comlex in build (p.599), as it also possessed
an accessory cusp at the front. There's no evidence showing any cusps on a
lingual cingulum.
A non-Platy C
Earlier, a skull from the same locality had been referred to this species, and this
had much to do with its relative proportions. For example, it's also somewhat
broad. However, it had suffered from distortions. In many aspects, including the
greater number of postcanines (nine uppers), Abdala found it was more likely a large
specimen of Galesaurus. Poor preservation, however, leaves some room for
doubt (p.600).
Affinities of Platycraniellus
According to the results of this analysis, Platy C belonged to a lineage placed
between that of Thrinaxodon and
Eucynodontia. Of all known non-eucynodont cynodonts, this is the eucynodontiest;
the closest known relative of a taxon including
Cynognathus and my wife. The findings indicate two main groups within
Eucynodontia; Cynognathia and
Probainognathia. That conclusion in itself
is far from new, but the membership -if correctly identified- includes a couple of
surprises along with much confirmation of previous studies.
Cynognathia
With one exception, this branch ran as I would've guessed. Cynognathus is
close to the root. Successively more derived are
members of Diademodontidae,
Trirachodontidae and Traversodontidae.
Eventually, after the demise of the travies at the end of the Triassic, any encores
were made trickier by extinction.
The surprise here is that somebody claimed to be more
basal than Cynognathus; South America's
Ecteninion. There are a couple of reasons why that seems odd and,
personally, I'll await for confirmation or otherwise from further studies. Firstly,
it lived considerably later than Cynognathus during the earlier rounds of the
Upper Triassic. That doesn't mean it can't be more basal; the survivor of a lineage
that arose earlier. A platypus is more basal than a mammoth, but it could manage
to derive far more satisfaction from having sex. For that matter, a platypus appears
more basal than a dryolestid that dropped
dead during the Upper Jurassic. More importantly, until this study, Ecteninion
had generally been interpreted as belonging to the more derived branch of the
cynodont club; Probainognathia. These results suggest that's incorrect.
(As it
happens, it's another genus that seems almost impossible to spell.)
Probainognathia
Other than for the attempted desertion of Ecteninion, the affinities of which
have rarely seemed all that clear, the probainognathians behaved much as would've
been anticipated. Its non-mammalian members formed a reasonably orderly queue
stretching ever closer towards Mammalia, and the
most mammalianest of all was indeed a brasilodontid.
Pachygenelus, tritylodontids,
Brasilitherium and mammals all
claimed to be closely related descendants of a unique common ancestor.
However, there was a bit of argy-bargy in the queue. While Brasilitherium
came out with a tropy for being in the sister lineage of Mammaliformes (in the
terminology of the paper), Brasilodon
wasn't found guilty of being in a monophyletic
clade including Pachygenelus and my wife. It was more remote. If correct,
then Brasilodontidae would be a disfunctional family. This would be a pity given
its attractiveness and recent establishment. However, as a further possible
brailodontid is due to be described from the Middle Triassic of Brazil, further
analysis on this issue will presumably become available at same point. (Note: A
new study on Chaliminia has the
brasilodontids paired together, but I haven't written up any notes for that at
present - 5.9.2007).
Cynodonts
Sixteen shared derived characteristics (
synapomorphies) indicate that all cynodonts are descended from a unique common
ancestor, with Procynosuchus and
Dvinia being closest to that base (p.602).
Cynosaurus had an uncertain position
somewhere more derived than that pair, but it failed to laid on the runways reserved
for galesaurids or thrinaxodontids. Platy C also failed, but that was on account of
being too derived; in the sister lineage of we eucynodonts.
Holotype
TM 25 is a near complete skull employed by the Transvaal Museum, Pretoria. This is
accompanied by its partial lower jaw and some bits and pieces of skeleton.
Additional notes
Kemp reports the taxon
has a very short snout and wide temporal fenestrae. "The secondary palate is complete
and extends posteriorly as far as the end of the tooth rows, a feature characteristic of
later, more advanced forms. Unfortunately, few details of the dentition of the structure
of the lower jaw are clear in the one reliably identified specimen."
This is referred to the now published manuscript by Fernando Abdala (2007). The
original authors explicitely termed it a
galesaurid, and that would be outside of Eucynodontia. It's briefly mentioned
in Abdala et al, 2005, (p.192), but no comment is made on its affinities beyond it
being a cynodont. |
| References: | Hoepen ECN van (1916), Preliminary notice of new
reptiles of the Karroo Formation, Annals of the Transvaal Museum, 5 (Supplement 2),
p.1-2. |
| Hoepen ECN van (1917), Note on Myriodon and
Platycranium, Annals of the Transvall Museum, 5, p.217. |
A. Cynognathidae B.
Diademodontidae C. Trirachodontidae
| Taxon: Cynognathidae Watson, 1917
Includes Karoomysidae Haughton, 1924a
This family is presently contains a single genus which, over the years, has been adorned
with a dictionary of different names. "Hopson and Kitching recognize only a single
species, pending a thorough revision of the family," (see Links: Kazlev,MA). This
would've been a remarkably long-lived and widespread single species. I await a revision
with interest.
Cynognathus is the most basal known cynognathian, and
the sole clear carnivore in the taxon.
| Reassigned species: C. beeryi Seeley, 1895 and C. minor Bonaparte,
1967 and C. platyceps Seeley, 1895 see C. crateronotus | |
| Species: | Cynognathus crateronotus Seeley HG, 1895? |
| Aka: | Cistecynodon parvus Brink & Kitching, 1953;
Cynidiognathus broomi Haughton, 1922; Cynidiognathus longiceps Haughton, 1922;
Cynidiognathus merenskyi Broli & Schröder, 1935b; Cynognathus beeryi
Seeley, 1895b; Cynognathus merenskyi; Cynognathus minor Bonaparte, 1960;
Cynognathus platyceps Seeley, 1895b; Cynogomphius berryi Broom, 1932;
?Karoomys browni Broom, 1903; Lycaenognathus kannemeyerz Broom, 1931;
Lycaenognathus platyceps Broom, 1925; Lycochampsa ferox Broom, 1915b;
Lycognathus ferox Broom, 1913a; Nythosaurus browni Broom, 1912a . (Main
source: Kazlev MA). |
| Nomenclature!: | Whilst having 15 names for one species
might be regarded as excessive, it's by no means a record. The dinosaur, Plateosaurus
engelhardti, has been named well over 20 times.
Karoomys, Cistecynodon and Nythosaurus are based on tiny juveniles,
whilst Lycognathus cucullatus seems to be a snake from the Mediterranean Balearic
Islands, although confirmation is elusive. |
| Place: | Burgersdorp Formation, Karoo &
Omingode Formation (Nam.) &
Puesto Viejo Formation &
upper Fremouw Formation & |
| Country: | South Africa/Lesotho & Namibia & Argentina & Antarctica & China |
| Age: | Spathian, Lower Triassic - ?Anisian, ?Middle Triassic |
| Remarks: | Kemp, 2005 (p.67) reports the skull is both large
(30cm in length) and robust, and the teeth are those of a killer.
Canines are big and the postcanines like blades, with
the main cusp curving inwards. There are accessory cusps in line with that, and they become
more significant as the tooth row progresses to the rear. Signs of wear show there was no
direct occlusion between the uppers and lowers.
Biosis offers 1915 as the year for the species. This seems strange, seeing as
Harry Govier Seeley
died in 1909, but it's not completely impossible.
Hundreds of websites feature this
small-wolf-sized
creature, which must have been uncommonly common. It's also been depicted on postage
stamps from North Korea and Poland.
Antarctica
The fossil from the Fremouw Formation has been referred to the genus rather than a
species. It's a fragment of lower jaw and lacks any noticeable distinguishing features.
Hammer et al, 1990 (p.164) mentions a second specimen, which may belong to a further
derived eucynodont. A total of four cynognathid fragments
are mentioned by Abdald et al, 2005 (p.197).
Extra names
The type and only fossil of Cistecynodon is a skull recovered from the Burgersdorp
Formation. It's now known to its admirers as BPI 2520 and lives at the Bernard Institute
for Palaeontology, University of the Witwatersrand, Johannesburg. This has been variously
referred to the families Chiniquodontidae and
Cistecynodontidae Abdala, 1996. These interpretations are both rejected by Abdala &
Giannini, 2002 (p.1157).
Karoomys browni Broom, 1903 was referred to a taxon
called Ictidosauria in 1929, and that rendered it as an applicant for
Tritheledontidae. However, it was thrown out for
misbehaviour, and recognised as Cynognathus in disguise. The title of the description
indicates it had earlier pretended to be a mammal.
This information has come from Sidor & Hancox, 2006 (p.333).
Holtypes
The following are contained in Abdala, 2007 (p.612):
AM 460, type of Cynognathus platyceps, Albany Museum, Grahamstown
BMNH R2571, C. crateronotus, Natural History Museum, London
BSP 1934VIII6, Cynidiognathus merenskyi, Bayerische Staatssammlung für
Paläontologie und historische Geologie, Munich
PVL 3859, Cynognathus minor, Colleccion Palaeontologica de Vertebrados Lillo,
Universidad Nacional de Tucuman
SAM-PK-1056, Cynidiognathus broomi, Iziko, South African Museum, Cape Town
SAM-PK- 6224, Cynidiognathus longiceps, Iziko, South African Museum, Cape
Town
I'd happily upload a complete listing of holotypes and original descriptions, so
additional information would be welcome. |
| References: | Seeley (1895), Researches on the structure, organization and
classification of the fossil Reptilia. Part IX, section 1. On the Therosuchia. Phil.
Transactions of the Roy. Soc. of London, series B 185 (21), p.987-1018. |
| Broom R (1903), On the lower jaw of a small mammal from the Karroo
beds of Aliwal North, South Africa, Geological Magazine, 10, p.345. |
| Brink & Kitching (1953), On some new Cynognathus Zone
specimens. Palaeontologica Africana, 1, p.29-48. |
| Bonaparte JF (1969), Cynognathus minor n. sp. (Therapsida -
Cynodontia), Nueva evidencia de vinculacion faunistica afro-sudamericana a principios del
Triasico, In: Gondwana Stratigraphy, IUGS Symposium, Mar del Plata 1967, p.273-281. |
| Links:
Enchanted Learning, Cynognathus
http://www.enchantedlearning.com/subjects/therapsids/Cynognathus.shtml
A straightforward description with a picture to colour in, if you so desire.
Yale Peabody Museum, Collection Search (VP)
Nythosaurus larvatus is there
The Peabody collection includes a cast of the holotype of a fossil named Nythosaurus
larvatus Owen, 1876. This was collected in the Orange Free State, South Africa. It's
listed as a member of Galesauridae. This would
seem to rule out a direct connection with Cynognathus, unless it's been rediagnosed.
Galesaurids are close relatives of eucynodonts, so
that's not impossible. The Peabody also have some cast specimens of Cynognathus.
Reference: Owen (1876), Descriptive and illustrated catalogue of the fossil Reptilia of
South Africa in the collection of the British Museum. London: 88p.
AMNH, New York; Reptile Bird and Dinosaur List
http://paleo.amnh.org/fossil/FRC.spec_list?A=Therapsida&X=ORDER_X
Amongst the specimens in the American Museum of Natural History collection are fragments of
bone, a lower jaw and various models and casts of South African fossils, one of which is
surprisingly listed as Permian. Several of the alternative names also appear. Catalog No.
24422 refers to a fossil from Antarctica.
M Alan Kazlev, Cynognathidae
http://www.kheper.auz.com/gaia/biosphere/vertebrates/therapsida/Cynognathidae.html
A page of high quality. Attributes the remarkable confusion of names in part to
"characters which vary with age."
Sehome High School, Bellingham, Washington, USA
http://wwwshsl.bham.wednet.edu/curric/science/geophys/james/pan4.HTM
Part of a school project on tectonics, this is a look at the fossil evidence for
continental drift, including the distribution of Cynognathus. As an introduction to
the subject, this is good. I'm filled with admiration, tinged with some jealousy. My
school didn't do geology!
Samantekt um Cynognathus
http://www.simnet.is/xpert/cynognathus.htm
This is the best page on the Mesozoic I've ever come across in Icelandic. "Til
baka" takes you to the title page.
Valdosta State University's Virtual Museum of Fossils
http://gatito.valdosta.edu/fossil_pages/fossils_tri/t56.html
Images of the skull and lower jaw from this fairly new resource. These photos are of cast
specimens made from fossils found in South America.
The Dinosaur Collector Museum, Triassic
http://members.aol.com/_ht_a/rsknol/Triassic.html?mtbrand=AOL_US
Simply astonishing fun, but organized according to sound scientific knowledge. Randy Knol
enjoys collecting plastic models of Mesozoic animals. I've got a few as well. But what he
then does with them is… Just see for yourself. More admiration and jealousy.
The Journal of Vertebrate Paleontology, 1995, 15(1): 105-112
http://www.vertpaleo.org/jvp/15-105-112.html
WR Hammer's abstract on Triassic goings on near the Beardmore Glacier, Antarctica.
Paläontologisches Museum, Munich
http://www.palaeo.de/pmm/virt_m/index.html
Scroll down to the end of 'Galerie 4'. There's a photo of a C. platyceps skull,
which is resident in the collection.
Quick report
I was there early in November 2004. While in fine health, the skull is presently in
storage. As luck would have it, the person who knew precisely where Cyno could be found,
happened to be absent. I have to tearfully report I didn't get a chance to talk to the
animal. I'm sure if I'd asked with a couple of days notice, things would've worked better.
Nevertheless, it's an impressive collection in an attractive, old building. Sign-posting
isn't a priority, so it's a good idea to pay close attention to the street number,
Richard-Wagner-Strasse 10. Go up the steps.
Some of the cast
An Archaeopteryx, Compsognathus and various interesting fossils can be
admired. I'd never previously seen a placodont. (They were fans of shellfish from the
Middle-Upper Triassic, and this specimen was roughly seal-sized). Also admirable is the
traditional, free entry policy. (Please leave a donation.) An added extra is the
neighbouring geology collection. If the thirst for knowledge is still unsated, a beer
garden is available in the nearby Old Botanical Gardens.
Pech gehabt!
I seem to have some influence with German museums. The Senckenberg in Frankfurt has an
excellent collection of Eocene fossils from
Messel, and this includes beautifully preserved dog-sized, leaf-eating, fifty million
year old horses. My anticipation sharpened, we paid a visit a couple of years ago.
Knowing this was an occasion worthy of special measures, they chose that time to shut the
department for renovation. Not a morsel from Messel could be viewed. |
Testing the limbits
The following is based upon my reading of Botha & Chinsamy, 2000.
When it comes to postcranial remains, Cynognathus
and Diademodon are not only broadly similar, but they're also bedmates. They're
found in the same rock beds, at least in South Africa (p.705), where they range from the
Lower to the Middle Triassic. The diagnostic differences are in the head and teeth. If
you've just happened across an isolated limb, this paper might be what you need. It
concerns growth patterns as figured out from fossilized bone.
The authors refer to Diademodon (next section) as an omnivore, (which seems a good
bet given its mixture of sectorial and
gomphodont teeth), and Cynognathus as a
carnivore. There are postcranial differences but they're slight; eg. details of the
vertebrae. At least, these differences are slight if you
confine yourself to studying shape. Take structure into account and a different perspective
opens up.
The way bones grow can show up well in long elements. Therefore, the authors got their
hands on some arms and legs. The was limited to fossils that had been found in
direct association with diagnostic material, which added a useful control. It consisted
of 13 specimens recovered from the Beaufort Group of South Africa. These were photographed,
measured and then thin cross-sections were prepared for microscopic examination.
The lengths they'll grow to
Page 706 contains Table 1, which gives the estimated lengths of the bones examined, which
were calculated, where possible, in accordance with diameter or condylar width.
(Cross-sectioning excellently preserved fossils can perhaps lead to complaints.) As
different limb bones from a restricted sample of mainly juvenile and subabdult individuals
are listed, I'm not sure this provides the basis for a reasonable representation as to the
size of these genera, (but that wasn't an objective of this study). Nevertheless, a fully
adult femur of Cynognathus was calculated as having
been about 28cm long. (That's about 14cm less than the one in my wife's leg, but it
approximates to my lower arm with the hand cut off). An equivalent for Diademodon
seems to work out at about 16cm (my calculation: ca. 12 x 4/3). Based solely on that,
wolf-sized sounds fair enough for the former genus, whilst mainly vegetarian fox-sized
might be better for the second, (though larger specimens are also known).
Rings and things
With Diademodon growth rings are often evident. However, there's a tendency for
these to be resorbed, (p.707), especially in older representatives. Page 709 contains:
"Experiments conducted on modern reptiles have shown that the growth rings present in
their bones are annual, i.e., a zone is formed during the favourable growing season and an
annulus is formed during the unfavourable season". The authors assume it was much the
same in this instance, which doesn't seem unreasonable.
(I can't help noticing two less juvenile femora, (in terms of
the aforementioned Table 1), are, (in terms of estimated growth rings, Table 2, p.708),
apparently younger than the more juvenile humeri.
Nevertheless, there are growth rings, (small sample?, different bones?).
Remains of the paleo-environment suggest a floodplain in a semi-arid climate with seasonal
rainfall. When favourable, Diademodon got plenty to eat and grew. However: "The
presence of peripheral rest lines in the tibia and
fibula of Diademodon indicate that these bones are
from mature individuals whose overall growth had slowed down", (p.710). The authors
conclude this genus utilized a strategy of determinate growth. They achieved an adult size
and more-or-less stayed with it.
A rodent asks
"So what?" our adult guinea pig just said. "I gave up growing months ago."
Whilst true, that's not what most non-mammals do.
Apparently, it's also not what Cynognathus did. In the three specimens of that
taxon, (all femora), the authors
found no growth rings: "The Cynognathus femora are all large (68.40%, 72.38%,
and 100% of the adult length). The bone tissue consists of a thick cortext surrounding a
medullary cavity that contains a large amount of cancellous bone", (p.707-708). This
indicates that these carnivores didn't lay on bone in seasonal spurts. This difference in
broadly similar animals can't be put down to environmental factors, seeing as they lived
alongside, (and in one case), presumably from eating each other. Maybe that's part the
explanation. "It is however, also possible that these differences in their growth
strategies of Diademodon and Cynognathus reflect inherent physiological
differences", (p.709).
More please
It's certainly an interesting line of enquiry. I'd like to know something about the
situation in mature remains, and from other taxa. The
non-eucynodont, Thrinaxodon, could be an
intriguing candidate. Then again, I'd be reluctant if someone suggested making
cross-sections from my limbs. |
A. Cynognathidae B.
Diademodontidae C. Trirachodontidae
| Taxon: Diademodontidae Haughton, 1924
This family's known from Africa and perhaps Asia, (though I haven't yet found confirmation
for the second case). |
| Links:
Mikko K Haaramo, Tritylodontoidea (Gomphodontia)
Mikko Haaramo's Trtylodontoidea (Gomphodontia)
If you want a fuller cladogramme you'll have to write your own.
Early Triassic World, edited by Caroline Northwood, University College London
http://evolution.anat.ucl.ac.uk/people/northwood.index.html
This is an ambitious and continuing project, which seeks to combine research into all
aspects of Lower Triassic paleontology.
Paleomaps, Early Triassic
http://www.geo-as.de/Geologie/Paleomaps/pages/09Trias.htm
Ancient geography. An impression of the globe from the days of Diademodon. Look
down towards the bottom, and you'll notice the proximity of South Africa and Antarctica. A
number of non-mammalian therapsid genera have been found
in both continents. With thanks to Scotese.
Genera:
Cragievarus (= Diademodon), Cyclogomphodon (= Diademodon),
Cynochampsa (= South Africa, Diademodon,
Gomphognathus (= Diademodon), Hazhenia (?),
Microgomphodon (= Diademodon), Octagomphus (= Diademodon),
Ordosia (= Ordosiodon), Ordosiodon
(?), Protacmon (= Diademodon), Sysphinctostoma (= Diademodon),
Titanogomphodon, Trirachodon
(partly = Diademodon; other reports
Time-Line:
Middle Triassic: Titanogomphodon
Lower Triassic: Diademodon, Hazhenia, Ordosiodon, Antarctica?
|
| Genus: Diademodon Seeley HG, 1894
'crown tooth'
Aka: Cragievarus Brink, 1965; Cyclogomphodon Broom, 1919;
Cynochampsa laniaria Owen, 1859; Gomphognathus Seeley, 1895;
Microgomphodon, Octagomphus, Protacmon Watson, 1920;
Sysphinctostoma Broili & Schroeder, 1936; Trirachodon (partly)
Remarks: Over the years, sufficient material has been identified to generate a reasonable
degree of generic confusion. Exactly who named what and when is often difficult to trace.
Previously, I had missed out the m in Cynochampsa. Thanks to Vince Ward for
noticing.
Corect spilling avoids confusun.
Kemp 2005 (p.67) states the animal is known from the Lower to the Middle Triassic. The
incisors were simple and the
canines large. The postcanines are unusual, and
can be divided into three subtypes. The first three or four have crowns which are
straightforward cones.
The gomphodont postcanines
Then come up to nine wide, multicusped teeth. (The number is largely dependant upon
biological age.) The centre of the buccal side of the
upper variety carries a main cusp, and this has crenulated crests running to the front and
rear. The rest of the tooth is surround by very small cusps. The lowers are broadly
similar but not as wide. However, the crowns eroded quickly.
Behind came between two and five sectorial postcanines,
and these compare closely with the teeth of Cynognathus.
Replacement
As there are a good number of skulls available, much is known about the pattern of dental
replacement. Postcanine teeth were discarded from the front of the row, and replaced with
new ones at the rear. The system is strange, as the three different postcanine types were
all maintained by what sounds like a form of juggling. A gomphodont tooth would be
replaced by a simple one, while a sectorial slicer gave way to a gomphodont successor.
Further sectorial teeth were added as well, and the overall numbers of each kind remained
reasonably similar.
"In der äußeren Form ähnelt der Schädel zwar dem von Cynognathus, aber ein Blick
auf die Zähne des Oberkiefers zeigt erhebliche Unterschiede. Die Backenzähne bei
Diademodon sind kurz und breit und haben eine kompliziert ausgebildete Krone, die
sich bei erwachsenen Tieren weitgehend abgeschliffen hat, aber bei Jungtieren noch gut zu
erkennen ist", (Benton M 1993, p.86)
[My translation: The outer form of the skull closely resembles that of
Cynognathus, but a look at the teeth in the upper jaw shows significant differences.
The cheekteeth of Diademodon are short and wide and the crown has a complex
construction, which is heavily worn down in adult animals, but is easily recognized from
young animals.]
When seen in the occlusal view, the upper
postcanine teeth of this genus are roughly oval
in outline, whilst the corresponding lowers are more rounded, (Abdala & Ribeiro 2003,
p.538).
Amongst other places, specimens feature in the collections of The Natural History Museum,
London and The South Africa Museum, Cape Town.
Some names I haven't yet pinned down
There are a number of holotypes kicking about which have presumbly been transferred
to some species or other of Diademodon, but I'm unsure as to which.
AM 458 is the type of Gomphognathus kannemeyeri, and delights visitors to
Albany Museum in Grahamstown. In fact, it performs as part of a double act along
with AM 3753, Octagomphus woodi.
London's Natural History Museum is partly illuminated by the charisma of BMNH
R3304, the type fossil of Diademodon browni. It enjoys romping around at
night along with BMNH R3305, Microgomphodon oligocynus, and BMNH R3581,
Microgomphodon eumerus. I'd imagine D. browni was known as
Trirachodon browni in 1915, but I'm less than certain.
Meanwhile, in Munich, the Bayerische Staatsammlung für Paläontologie und historische
Geologie plays home to BSP 1934VIII 18, the type fossil of a species called
Gomphognathus broomi. It may be in conversation with BSP 1934VIII 19, the
type of Gomphognathus houghtoni. On the other hand, they might get interruptions
from BSP 1936II 8, an individual who enjoys telling visitors it's
Sysphinctostoma smithi.
Of course, should you be in the University Museum of Zoology, Cambridge, you
could call in on UMZC T.436 and share a cup of tea with Diademodon
laticeps. |
| Species: | Diademodon entomophonus |
| Place: | |
| Country: | South Africa |
| Age: | Scythian, Lower Triassic |
| Remarks: | Specimen at the Peabody Museum, Yale,
USA. YPM 7725.
Holotype
BMNH R3765 is the type of this species. It's possible part of its head is known as
BMNH R4092 but, if so, then Abdala, 2007 involves a holotype typo on page 612. There
can be read D. entomophoneus. |
| Reference: | |
| Species: | Diademodon grossarthi (Broli & Schroeder,
1935) |
| Place: | |
| Country: | |
| Age: | |
| Remarks: | Further information welcome.
Holotype
BSP 1934VIII 17 received political assylum in the Bayerische Stastsammlung für
Paläontologie und historische Geologie in Munich. Next time I happen to be in
that city, I really must contact the institution in advance and get to meet some
of their dead eucynodonts. |
| Reference: | |
| Species: | Diademodon mastacus Seeley HG, 1895 |
| Place: | Burgersdorp Formation, Karoo |
| Country: | South Africa |
| Age: | Induan, Lower Triassic |
| Remarks: | Big. A body length of about 1.5m.
Holtype
BMNH R3303 lurks in the shadows of the Natural History Museum in London. |
| Reference: | |
| Species: | Diademodon platyrhinus |
| Aka: | Cyclogomphodon platyrhinus Broom, 1919 |
| Place: | Burgersdorp Formation, Karoo |
| Country: | South Africa |
| Age: | Scythian, Lower Triassic |
| Remarks: | |
| Reference: | |
| Link:
The American Museum of Natural History On-line Catalogue of Fossils
http://paleo.amnj.org/fossil/FRC.dist_family
The AMNH houses several diademodontid specimens. Some of the D. platyrhinus material
was collected by Broom in the early twentieth century. |
| Species: | Diademodon polyphagus |
| Aka: | Gomphognathus polyphagus |
| Place: | |
| Country: | |
| Age: | |
| Remarks: | The type fossil with this specific name
can be visited at the Natural History Museum, London. Simply ask in the gift shop
for BMNH R2576-7, and let me know what the confused cashier replies. |
| Reference: | |
| Species: | Diademodon rhodesiensis Brink, 1963 |
| Place: | Ntawere Formation |
| Country: | Zimbabwe |
| Age: | Triassic |
| Remarks: | A skull is pictured in Kemp, 2005 (p.68). This
has a length of approximately 23 centimetres. This is also the source of the
citation.
Holotype
BP/1/ 3639 is employed at the Bernard Price Institute in Johannesburg. |
| Reference: | Brink (1963), Two cynodonts from the Ntawere Formation in the
Luangwa Valley of Northern Rhodesia, Palaeontol. Afr., 8, p.77-96. |
| Species: | Diademodon tetragonus Seeley, 1894 |
| Aka: | Cragievarus kitchingi Brink, 1965;
Cynochampsa laniaria Owen R, 1859; Diademodon browni, Trirachodon
browni Broom R, 1915 |
| Place: | Burgersdorp Formation, Karoo, Ntawere
Formation (Zam.), Manda beds (Tanz.), Omingonde Formation
(Nam.), (I'm not sure of the locality in Argentina, but it may be the Puesto Viejo
Formation) |
| Country: | South Africa, Zambia, Tanzania, Namibia, Argentina |
| Age: | Scythian, Lower Triassic |
| Remarks: | Nomenclature: Cy. predated D.
However, because D. had been in broad usage for many years, the ICZN awarded
priority to the junior synonym. Diademodon is therefore valid.
Several specimens held by the New York AMNH.
Abdala & Giannini, 2000 (p.504) reports that a number of studies have subsumed 24
different species into this one taxon, which would probably
account for most (and perhaps all) of the species listed above.
Holotype Corner
Somewhere, I think I read that T. browni is BMNH R3721, from the Natural
History Museum, London. Confusingly, I've definitely just read that D. browni
lives there with the number BMNH R3304 (Abdala, 2007, p.612). As the first number
is repeated on page 614 of that publication, these must be different specimens and
somebody named Brown may have been immensely popular.
The situation with C. kitchingi is hopefully clearer; BP/1/3776, Bernard
Price Institute, Johannesburg.
Additional news -South America
Abdale & Smith, 2009 reports on a report of the presence of this species in the Middle
Triassic of Argentina. They blame this upon: Martinelli AG, Fuente MS de la & Abdale F
(2008), First occurrence of Diademodon tetragonus Seeley (Therapsida, Cynodontia)
in the Triassic of South America and its biostratigraphic implications, Acta de Resúmenes
III Congreso Latinoamericano de Paleontologia de Vertebrados, Neuqén, 152. This is an
abstract I haven't personally seen.
The same authors also point to the presence of the genus in Namibia. |
| References: | Seeley (1894), Researches on the structure, organization and
classification of the Fossil Reptilia. Part IX, Section 3. On Diademodon.
Philosophical Transactions of the Royal Society of London, 185, p.1029-1041. |
| Broom R (1915), On some new carnivorous therapsids in the
collection of the British Museum, Proceedings of the Zoological Society of London b,
1915, p.163-173. |
| Melville RV (1985), Opinion 1324. Diademodon Seeley,
1894 and Diademodon tetragonus Seeley, 1894 conserved by the suppression of
Cynochampsa Owen, 1859 and Cynochampsa laniaria Owen, 1859 (Reptilia,
Therapsida). Bull. Zool. Nomencl. 42, p.185-187. |
| Grine FE (1981), Cragievarus kitchingi Brink, 1965: a
subjective junior synonym of Diademodon tetragonus Seeley, 1894 (Reptilia, Therapsida).
Annals of the South African Museum Vol. 84, p.151-168. |
| The following is based upon my reading of
Abdala et al, 2005.
Eucynodonts of the Karoo Basin, Lower - Middle Triassic
The Karoo Basin is in southern Africa, and it's justifiably famous for its fossil
vertebrates. These come from strata deposited between the Upper Permian and Lower
Jurassic. Remains are of various terrestrial faunas spread over about 90 million years.
Eucynodonts have been found from all the main
divisions of the Triassic and the Lower Jurassic. This article is centred on animals from
the Cynognathus Assemblage Zone dating back to around 243 - 234 million years
ago.
A somewhat broader picture in time
The first Karoo cynodont fossils, (a wider grouping than
eucynodonts), have come from the Balfour Formation, and are uppermost Permian. The top
part contains a fauna dominated by a dicynodont
herbivore called Dicynodon, and this is referred to as the Dicynodon
Assemblage Zone, (p.192). It was a very varied vertebrate
community, but the Permian-Triassic transition happened amidst the most catastrophic mass
extinction event(s) in the history of the planet. Most Upper Permian species had a common
characteristic; no future. This episode was far more profound than the famous K-T
extinction(s), when the non-birdy dinosaurs were deaded.
At the level of animal and plant families, the casualty rate was about 50%. The
destruction of species has been put as high as 95%. In the terminology employed by
statisticians, this was a bleeding terrible catastrophe. Typical vertebrates were dead
vertebrates.
The morning after
The start of the Triassic in Karoo is represented by the Katberg Formation. Fossils are
scarcer and less diverse than previously. Easily the most common genus is a further
dicynodont; Lystrosaurus. The fauna is termed the Lystrosaurus Assemblage
Zone.
"The dicynodont Lystrosaurus, distantly related to the Late Permian dicynodonts,
was the most common reptile on the Earth - to the extent that if formed over 90% of every
animal community from South Africa and Antarctica to China, India and the eastern Russia",
(Benton MJ 1990 (1998 reprint), p.64). As that book is a bit old, there's a chance the
situation may have changed somewhat in the light of subsequent finds. Even allowing for
that, this domination by a single taxon is astonishing.
However, as up to 95% of animals had gone extinct, biodiversity was entitled to feel
off-colour.
Abdala and colleagues report the presence of at least four cynodonts in this zone, with
Thrinaxodon being the most famous. Although close, it doesn't quite qualify for
Eucynodontia.
Putting the eu before cynodont - 'true dog teeth'
After approximately three million years of further deposit, the Katberg Formation is
succeeded by the Burgersdorp. This represents roughly 243 - 234 million years and contains
faunas in which eucynodonts are prevalent. It's referred to as the
Cynognathus Assemblage Zone, and that genus is present during the whole
sequence. It presently enjoys the company of four other eucynodonts, (Diademodon,
Trirachodon, Cricodon and
Lumkuia - with the last being rare). There's
also a rare cynodont, (Bolotridon).
Dividing the subdivision
The Cynognathus zone, (I'm still talking about the AZ but prefer less formality),
isn't a single fauna. Nine million years was enough time for comings and goings, and most
fossils from the top don't occur at the bottom. These factors have allowed the recognition
of three subzones. The oldest is A, the youngest C and the other one is in the middle.
This scheme is mainly defined by convenient amphibians called temnospondyls
reinforced by the rest of the faunas. Previous studies concentrated on the lower two
subzones.
Fieldwork in the Bamboeshoek Valley of Eastern Cape Province has produced an array of
fossils from the top 150 metres of the Formation; subzone C. This includes amphibians and
dicynodonts, but euycynodonts predominate. (It's now 235 million years later, and our
domination of the area has increased. Eucynodonts include you.)
Geological Ages and other measures
Geologists and paleontologists use all kinds of funny terms when referring to approximately
the same things. Different words reflect various approaches. The concepts are effectively
similar but not strictly synonymous. The starting phase of the Triassic is geologically
the Lower Triassic. This is because the rocks were deposited below the level of subsequent
ones. As they are lower, they must've been laid down earlier, but that's not particularly
relevant. In terms of time, (rather than stratigraphy), the rocks were deposited during
the Early Triassic. Lower and Early coincide. They're not synonyms because they refer to
different concepts; stratigraphy and time. My personal preference is for stratigraphic
terminology.
Paleontologists tend to favour chronological terms, but they may also add biostratigraphic
concepts. I've already mentioned some; eg. the Dicynodon- , Lystrosaurus- and
Cynognathus-zones (AZs). These are defined in terms of the first appearances of
index taxa. (The paper discusses LVFs - Land Vertebrate Faunachrons - but I think I'll do
no more than mention that.)
The geological age of the Cynognathus-zone has been subject to various
interpretations over the past century. Suggestions have ranged from Upper Permian to Upper
Triassic, (p.193). Present research suggests it spans the Lower - Middle Triassic
transition. Subzone A is Olenekian, B is lowermost and C uppermost Anisian
(Middle Triassic).
Bringing in the harvest
The material collected came from two farms within twenty kilometres to the west of
Sterkstroom. These are the most southerly exposures of the Burgersdorp Formation.
Cynognathus provided the front of a lower jaw. Diademodon donated a similar
body part as well as a more complete specimen. Trirachodontids
were more generous. Five fossils were collected, and all have been assigned to
Cricodon, which was previously known from Tanzania.
Faunal content and comparisons
Subzone C contains three eucynodonts, a dicynodont called Angonisaurus, a
shansiodont (which is also a dicynodont) and a mastodonsaurid
temnospondyl amphibian (Paracyclotosaurus, p.195). As Diademodon,
Cricodon and Angonisaurus all occur in the Tanzanian Manda Formation, the
ages are presumably similar. However, there are doubts about the temporal integrity of the
Manda, (p.196). It's usually assigned to the upper Anisian but may include a somewhat
younger fauna.
Paracyclotosaurus occurs in the Indian Denwa Formation and the Ashfield Shale of
the Wianamatta Group, Australia. The former is normally considered lower Anisian, but the
presence of this genus allows the suggestion that it might be a bit more recent. The
Ashfield Shale is probably from the upper Anisian. That's the likely age for subzone C.
The Omingonde Formation, Namibia shares elements with both subzones B and C. It presently
boasts four eucynodonts. Of these, Trirachodon is common in the upper Omingonde.
Interestingly, these attain larger sizes than individuals from subzones A and B, and that
reflects the pattern for tirachodontids in South Africa.
There's at least one more eucynodont in the Namibian fauna, and it's an intriguing one.
It has been reported as possibly Massetognathus,
(p.197), which is otherwise known from the Ladinian of South America. In any case, Abdala
et al refer to it as a traversodontid.
(Traversodonts also feature in the Manda Formation, Tanzania.)
Antarctica also has an Anisian fauna in the upper Fremouw Formation. The fossils are
relatively scarce and fragmentary. They include bits of cynognathid jaws, and part of a
skull with teeth of a diademodontid from the Gordon Valley locality. This is usually
thought to be about the same age as subzone B, but it could be a bit younger. Palynological
studies (pollen) also indicate and Anisian dating.
Further Mesozoic site summaries can be found at Localities.
Meet the eucynodonts of Karoo (Lower - Middle Triassic)
(6 genera, 7 species)
Cynognathia (4 genera, at least 5 species)
Cynognathidae (1 genus, 1 species)
Cynognathus crateronotus (zones A, B and C)
Diademodontidae (1 genera, at least 1 species). Notes:
I'm uncertain as to which species of Diademodon might be considered useful. The
genus is present in zones B and C. A further genus, Ordosiodon,
is mentioned in the collection of the AMNH, New York, but I'm presently regarding that as
invalid for Karoo.
Diademodon
Trirachodotidae (3 genera, 4 species).
Cricodon metabolus; Langbergia
modisei; Trirachodon berryi, T. sp.
(subzone A)
Probainognathia (1 genus, 1 species)
Lumkuia fuzzi
Additionally, a eucynodont genus may be present in the underlying Lystrosaurus zone.
The affinities of Platycraniellus are presently unclear.
Fans of Karoo might like to visit:
# The Permian-Triassic Transition: Think global, die
local,
# The Triassic - Jurassic transition in the Karoo Basin.
|
| Genus: Hazhenia Sun A & Hou L,
1981
'from Hazhen'
Remarks: This genus has also been assigned to the family Ordosiidae Hou, 1979.
Ordosiodon is possibly a diademodontid, thus the tentative appearance of Hazhenia
here. |
| Species: | Hazhenia concava Sun A & Hou L, 1981 |
| Place: | Heshanggou Formation, Hazhen, Fugu, Shaanxi Province |
| Country: | China |
| Age: | Lower Triassic |
| Remarks: | H. concava is based on a complete skull
and several other bones. |
| Reference: | |
| Genus: Ordosiodon
Aka: Ordosia Hou, 1979
Remarks: This genus has also been assigned to the family Ordosiidae Hou, 1979.
Ordosiodon is perhaps a diademodontid. Its inclusion here is thus tentative. |
| Species: | Ordosiodon lincheyuensis Young, 1961 |
| Place: | Lower Ermaying Formation, Linzheyu, Baode, Shaanxi Province |
| Country: | China |
| Age: | Scythian, Lower Triassic |
| Remarks: | The holotype is a fragmentary left lower jaw. |
| Reference: | |
| Species: | Ordosiodon youngi Sigogneau-Russell & Sun,
1981 |
| Aka: | Ordosia youngi Hou, 1979 |
| Place: | Lower Ermaying Formation, Jungar Qi, Inner Mongolia |
| Country: | China |
| Age: | Scythian, Lower Triassic |
| Remarks: | Based on an incomplete skeleton. |
| Reference: | |
| Species: | Ordosiodon sp. |
| Place: | Burgersdorp Formation, Karoo |
| Country: | South Africa |
| Age: | Lower Triassic |
| Remarks: | Remains were collected by Kitching JW &
Colbert EH in 1962. Two specimens are at the AMNH, New York. The genus isn't mentioned
as being present in the Cynognathus zone by Abdala et al, 2005. I assume it's no
longer seen as valid. |
| Reference: | |
| Genus: Titanogomphodon
Keyser AW, 1973
'giant Gomphodon' |
| Species: | Titanogomphodon crassus Keyser AW, 1973 |
| Place: | Omingonde Formation |
| Country: | Namibia |
| Age: | Anisian, Middle Triassic |
| Remarks: | As the name suggests, it's big. |
| Reference: | Keyser (1973), A new vertebrate fauna from South West Africa,
Palaeontologia Africana, 16, p.1-15. |
| Other reports:
Frenmouw Formation, Antarctica
Remains of an indeterminate diademodontid specimen. The Formation is possibly Scythian,
Lower Triassic. Aspects of the uppermost fauna, however, suggest Anisian, Middle Triassic.
That second possibility now seems to be winning.
Link:
The Journal of Vertebrate Paleontology 15(1), p.105-112.
http://www.vertpaleo.org/jvp/15-105-112.html
The JVP abstract by WR Hammer. This dates from 1995.
Vellberg, South-western Germany
Some perhaps gomphodont teeth have been reported from
the Middle Triassic of Baden-Württemberg. I'm informed there's a strong possibility that
they're chiniquodontid choppers. Therefore, for further information, see
Chiniquodontidae: other reports. There's also part
of a front leg. (With thanks to Marcel Opitz and Dr Michael Maisch.) |
A. Cynognathidae B.
Diademodontidae C. Trirachodontidae
| Taxon: Trirachodontidae Romer, 1967
Abdala et al, (2005), include the following within the family (p.194-195): Trirachodon
berryi (including T. kannnemeyeri), T. sp. (Cynognathus zone A),
Cricodon metabolus, Sinognathus gracilis and Neotrirachodon expectatus.
Additionally, isolated teeth have been found in India and a series of skulls are known from
Namibia. A less secure record has been reported from the USA.
This family seems to fit anatomically somewhere between Diademodontidae and
Traversodontidae. For a cladogramme, see
Mikko Haaramo's Tritylodontoidea (Gomphodontia), as for Diademodontidae. Certainly in
the cases of Trirachodon and Cricodon, the
postcanine teeth are characterized as ellipsoid in outline, when seen from above,
(Abdala & Ribeiro 2003, p.538).
A taxonomic tale of trirachodontids
The following is based upon my reading of Abdala et Al, 2006.
Trirachodon began enthusiastically by sneaking into an 1894 paper by HF
Seeley in a comparison with Diademodon (p.385).
This was a bit naughty as the genus wasn't established until the following year
with two species. A partial skull was the basis of T. berryi and three
further fossils won assignment to T. kannemeyeri. The differences cited
concerned the size of the snout, and the width and number of postcanine teeth.
These distinctions have since been found too indistinct, and only the first
species tends to be recognised.
The next significant friend of trirachodontids was Robert Broom, the fossil
hunting Scottish doctor in South Africa. His work remains highly respected, but
he does seem to have been overly keen on handing out names to fossils. A misshapen
and weathered snout was christened T. minor in 1905 and a further small snout
became T. browni (1915). There wasn't any particular diagnosis for the
first, and the second was justified on the grounds of the length of the row of the
'seven largest molars'. This measurement happened to be less for this smaller
skull, which isn't exactly surprising. What he also proposed, in 1932, was
transferring T. berryi to the separate genus of Trirachodontoides,
although he didn't offer a new diagnosis.
So things hered and thered for a while, with the number of specimens gradually
accumulating from South Africa. Tanzania decided to join in (1946) when Parrington
assigned a narrow skull to T. angustifrons. This actually turned out to
be a traversodont (Scalenodon), but
Crompton came up with a trirachodontid from the same place in 1955,
Cricodon. Meanwhile, back in South Africa, a further
generic name had appeared in 1953 for a smalling, Inusitatodon smithi.
However, all the South African species were synonymized in 1972 with the exception
of T. browni. That was transferred to Diademodon tetragonus.
T. kannemeyeri has since sometimes be seen as valid.
Sinognathus from China was added to the family
in 1972 after originally serving time as a
galesaurid. More recently a jaw from Russia agreed to serve as the basis for
Neotrirachodon in 2002. As mentioned above,
isolated teeth have been found in both India and the USA (p.386), and the next
excitement is due to erupt in Namibia. Abdala et Al, 2006 express doubts about the
relevance of some of the fossils mentioned above for this family. They also state
a study of cynodonts from Namibia is underway, and trirachodontids are
promised.
Genera:
Antecosuchus (partly = Neotrirachodon),
Beishanodon, Cricodon, Inusitatodon
(= Trirachodon), Langbergia,
Neotrirachodon, Sinognathus,
Trirachodon, Trirachodontoides (= Trirachodon), other reports
Time-Line:
Middle Triassic: Cricodon, Neotrirachodon, Trirachodon
Lower Triassic: Beishanodon, Langbergia, Sinognathus,
Trirachodon, China, Antarctica |
| Genus: Beishanodon Gao K-Q,
Fox RC, Zhou C-F & Li D-Q, 2010
'Beishan tooth'
Subfamily: Sinognathinae Gao et al, 2010
Remarks: This genus is presently known from much of a single skull lacking its lower jaws.
The name honours the Beishan Hills from whence the fossil came. |
| Species: | Beishanodon youngi Gao et al, 2010 |
| Place: | Beishan locality, Quarry 3, Gansu Province |
| Country: | China |
| Age: | Lower Triassic |
| Remarks: | This is rather a big critter. The only available
skull manages a length of 27cm and a maximum width of 19. Get hold of a sheet of A4 paper,
and there'd just about be room enough to place this fossil on it. The authors took the
opportunity to establish a subfamily for the accomodation of both this genus and its
compatriot Sinognathus. Shared characteristics include
an unusually short snout for trirachodontids. |
| Reference: | Gao et al (2010), A new nonmammalian eucynodont (Synapsida:
Therapsida) from the Triassic of northern Gansu Province, China, and its biostratigraphic
and biogeographic implications, American Museum Novitates, 3685, p.1-25. |
| Genus: Cricodon Crompton Aw,
1955
'ring tooth'
Remarks: The generic name refers to the rings of cuspules found on the crowns of the
gomphodont teeth. |
| Species: | Cricodon metabolus Crompton AW, 1955 |
| Place: | Manda Formation & Burgersdorp Formation,
Karoo |
| Country: | Tanzania & South Africa |
| Age: | Lower?-Middle Triassic |
| Remarks: | The following is based on my reading of Abdala
et al, 2005, supplemented by information on the material from Tazania. (Thanks are due to
Dave Godfrey for providing many notes on the holotype and confirming the citation.)
New from Karoo
Five specimens of Cricodon were harvested from two farms in the Sterkstroom District
of Eastern Cape Province, (p.193). They're from the upper part of the Cynognathus
zone, and include a complete, poorly preserved skull, partial snouts and lower jaws. Three
of these individuals were significantly larger than trirachodontids obtained from lower
levels. The skull has a length of 16 centimetres. A partial snout suggests a 20
centimetre skull. The earlier fossils are assigned to
Trirachodon and the biggest is a bit over eleven centimetres. However, a larger
animal wouldn't necessarily point to a different genus.
Teeth
The incisors are high-crowned and the back edges are
serrated. The canine has serrations on the front and rear
edges. The upper canine is hypertrophied, (ie. very big). There's a notable
diastema between the last upper incisor and canine. The
incisors are higher than the postcanine crowns. The
tallest is the fourth incisor, and it's more than twice the height of the most lofty
postcanine.
An upper snout (BP/1/6102) preserves nine upper postcanines, with the rear pair being
sectorial. A larger individual has an incomplete set
with nine gomphodont postcanines, (p.194). Generally,
the postcanine crowns are ovoid in shape, and have three cusps joined by a ridge running
laterally across the middle of the tooth. The best developed cusp is the external one
(labial). The other two are close together. In one case,
two accessory cingular cusps are present on the labial
edge. These might have been on further teeth as well, but the effects of wear and poor
preservation make that unclear.
Assignment
The ovoid shape of the upper gomphodont teeth is a characteristic of Cricodon,
(p.195). Further details fit with that genus, as does the larger size. The closeness of
the central and lingual cusps on the postcanines is a
pattern familiar from traversodonts. In the forms
which have three cusps, that's the arrangement found.
From Tanzania
The original material was collected by Parrington from Stockley's 1931 Bone Locality B11,
which is near Njalila. It consisted of a partial skull and upper jaws, much of the lower
jaws and some skeleton, (ribs, vertebrae, a
femur, bits of the pelvic and
pectoral girdles and some front paw). The jaws were found in articulation, but Crompton
separated them.
Teeth - uppers
No information was originally available on the incisors or
canine, but the subsequent material exhibits 4 and 1
respectively. The number of postcanines in this case
is 10 (+ 1?), with the last being ovoid but long. It's wider at the front than behind.
Numbers six to nine are transverse, and there's a decrease in complexity going forwards
along the line. This seems to have been the result of differing amounts of wear. The rear
teeth were younger. The maximum diameter of an upper postcanine is 13 millimetres.
Lowers and dentary
The formula (pre side) is given as: 3 incisors, one canine and eleven postcanines. There
was a fair amount of damage and neither the dentary nor its
complement of teeth were complete. A six millimetre diastema
separated the canine from the teeth behind. The root of the canine was 34mm long, and the
large pulp cavity suggests it was relatively freshly hatched. In this instance, the maximum
diameter of a postcanine was nine millimetres. At the rear, an eleventh was in the process
of erupting. This one was relatively long.
Towards the back of a jaw is long groove on the internal side. This contains the
postdentary bones, and it's mirrored by a convex ridge on the opposing surface.
Holotype
The holotype is UMCZ T 905, and it resides in the University Museum of Zoology,
Cambridge, UK.
It's a fragmentary skull from Tanzania, and has an approximate length of 15 to 16
centimetres. The specific name honours the replacement of one mode of postcanine tooth
with a different style. At the ninth postcanine position on the left
maxilla, the type specimen has a transverse tooth erupting
in exchange for a sectorial predecessor. When described,
this was the first known evidence of postcanine replacement in a gomphodont. |
| Reference: | Crompton (1955), On some Triassic cynodonts from Tanganyika,
Proceedings of the Zoological Society of London, 125, p.617-669. |
| Species: | Langbergia modisei Abdala F, Neveling J &
Wellman J, 2006 |
| Aka: | Trirachodon kannemeyeri (partly) |
| Place: | Burgersdorp Formation, Karoo |
| Country: | South Africa |
| Age: | Lower Triassic |
| Remarks: | The following is based upon my reading
of Abdala et al, 2006
As doubtlessly for many other people, the
eucynodont family of Trirachodontidae always brings that old song to mind
-Ta-ra-ra-Boom-de-ay. They don't write them like that any more, thankfully; they
don't breed them like this any more, sadly; and it's always interesting to hear a
new variation on a long known melody. At least, it sometimes always is.
Langbergia is a reprise of the trirachodontid theme, but some of the notes
have been tweaked and twiddled. Whereas the gomphodont upper
postcanines of
Trirachodon are widened ellipses, and those of
Cricodon are more voluptuously oval, the ones in the mouth of the new
genus are nearer to round in outline (p.383). A further novelty is a characteristic
of a platform built by the maxilla of the upper
jaw which normally runs parallel to the tooth row. The characteristic in this case is its
complete absence. That's right, there isn't one. It's present in other
trirachodontids (and typically in the later gomphodonts of
Traversodontidae but, and in common with
Diademodon, this maxilla ain't got such a
platform.
Let's have a quicky
Langbergia was a small omnivore mammal-like thing with a skull length of
about ten centimetres; something like up to
rabbit-sized. It lived in burrows (three skulls came from a fossilised
burrow) but was nothing like hare-brained. The head didn't have anywhere near enough
room for a mind of that size. (There would've been no point in calling
Langbergia stupid as it was too dumb to understand about such things. Brain
expansion got going later.) Nevertheless, as a fair few specimens have been
recovered, it was obviously talented when it came to sex. And many
derived eucynodonts (aka people) prefer having
sex to thinking about it, although they tend to spend much more time doing the
latter.
Home, home on the Cynognathus Assemblage Zone
The Beaufort Group of rocks dates from the Upper Permian until the Middle Triassic,
and a succession of fossil bearing strata were deposited on this floodplain. These
are named after particular vertebrates, who
have volunteered their services as convenient index
taxa. The uppermost of these divisions is the Cynognathus Assemblage
Zone. The name reflects the fact that Cynognathus
fossils first occur in this level, and that's the sort of logic which even
Langbergia might have been able to grasp. Further vertebrates, mostly
temnospondyl amphibians in this instance,
allow for finer subdivisions; A to C with the C being the uppermost subdivision.
Langbergia resided in the lowest, subzone A. Both
dicynodonts and
cynodonts have offered opinions in support of
temnospondyl conclusions.
Subzone A isn't all that fossil rich, and many of the specimens are fragments,
poorly preserved or both. Despite being part of the Cynognathus AZ, the
most common remains are from at least three families of those temnospondyls.
Another resident was some kind of archosaur,
the group which later invented crocs and dinos (p.384).
Gomphodonts
Gomphodonts were originally understood as an informal group of cynodonts with
sort of similar postcanine teeth. They're wide and have 'tuberculate crowns'.
HF Seeley midwifed Gomphdontia in 1895. A century of research and study has since
gone by, many more fossils have been found, and the original concept seems robust.
It's turned out to be a monophyletic taxon
including Diademodontidae, Trirachodontidae and
Traversodontidae.
Tritylodontidae has also sometimes been
included, but that seems less secure. Some authors (including Abdala and friends)
have mercilessly evicted the tritys and, for what it's worth, I'm presently
drawn to that opinion.
The oldest known specimens are provided by this subzone A in Karoo, although a
couple of traversodonts from South America may be of a similar age (eg.
Pascualgnathus). If so, then this
level of diversity suggests a still earlier origin. Some remains from subzone A
were previously assigned to Trirachodon kannemeyeri (and this included
burrow complexes). However, distinguishing features show them to represent a
different genus; Langbergia.
Specimens
Fourteen specimens from nine localities have been referred to the new species
(p.386). A number of these are skulls with lower jaws, and some bits of associated
body are also known. An unusual one happens to be part of a fossilised burrow
containing three skulls, and they leave no doubts concerning the identity of the
construction workers and architects.
A deeper delve
The skull length of this species is typically between eight to ten centimetres,
and that's similar to Trirachodon. Unusually, adults favour less upper
postcanines than the kids with numbers dropping
down to seven or eight. Nine is popular among the younger generation. The
postcanines are gomphodont in style to wards the front, but they then give way to
sectorial slicers at the rear; essentially
meat-choppers. In occlusal outline the gomphodont
teeth are more circular than the equivalents of its relatives. The width in this
case is little more than the length. There's a high cusp set centrally on the
crown, and a ridge runs across the halfway line allowing it to commune with smaller
cusps on either side (both labial and
lingual.
The lower counterparts are even more restrained in terms of width and, rather than
standing across the jaw bone in a 90° kind of way, they choose to jut more
jauntily at around 45°. The basic morphology matches that of the uppers, but that
slanted alignment may well have been responsible for some sympathetic tampering
of cusp position. The labial cusp has snuck forwards of the halfway line (which
wouldn't be allowed at kick off in football),and its lingual team mate has retreated
with the blessings of, and in accordance with, the rules proscribed by FIFA.
(Apologies, but the 2006 World Cup ended a week ago, and withdrawal symptoms are
inevitable.) Further cuspules are located on a
cingulum.
The lack of a platform on the maxilla paralleling the dental row has been
mentioned previously. I don't intend to repeat reporting this absence is unusual
for gomphodonts in general (except for Diademodon), but it appears that I
just did so anyway. More apologies, but the point is of diagnostic utility.
What a charming head
Ten skulls were available and the lengths range from 6.6 to 11.3cm (p.387). Six
of them cluster between 8 and 10. While the largest exceeds the size of any
known skull of Trirachodon berryi, it doesn't do so by much and most
compare closely in dimensions. As regards Cricodon, that was a significantly
larger critter; 16-20cm. One trirachodontid trait is the possession of a relatively
short snout. In the type fossil of the new genus it contributes only 4.3cm to the
full skull length of 9.9.
Another characteristic held in common with Trirachodon
is that the zygomatic arch runs straight in
line with the skull, and this results in the opening behind the eye (the temporal
fenestra) being near rectangular is shape. The largeness of that hole didn't leave
anywhere near enough space in the head for a mammal-like brain capacity, and that's
generally applicable to all known non-mammalian
eucynodonts, although the later brasilodontids do show signs of more potential
cognitive dexterity (eg. Brasilodon.
Despite producing some nifty architecture in terms of communal burrows,
trirachodontids must've been dunces; incapable of such philosophical masterpieces
as being thoroughly bored, or spending fifteen hours playing a simulated World
Cup on a Game Boy.
I'm sure many must now be on tenterhooks concern the lack of that platform on the
maxilla. What happens with both Trirachodon
and Cricodon is that this bone curves strongly
inwards. This is not due to curiosity concerning what the teeth are getting up
to, but it does provide a platform by the postcanines (p.389). The curvature is
much less enthusiastic with the new genus. Another feature of the maxilla is a
healthy peppering of little holes (foramina) at the level of the
canine (p.391). A further foramen occurs to the
back of the bone in front of the eye. This is stronger on the left side of the
type fossil than on the right, but the equivalent is even larger for
Trirachodon (and it divides into two holes in many individuals).
At this juncture the official Mesozoic Eucynodonts site artist wishes to
inflict a couple of sketches upon us.
Langbergia from on
high.
Langbergia
in profile.
Teeth
Tooth numbers varied in these critters (p.392) as they were subject to serial
replacement. The identified ranges are as follows (per side): (uppers): 4
incisors, 1 canine, between 6-10 postcanines;
(lowers): 3, 1 and possibly 6-8 respectively. (There were less sets of lower
available for interview, and that could account for a narrower range.)
Incisors
These were simple pegs and the numbers (four uppers and three lowers) are commonly
found in early eucynodonts. The uppers point vertically down while their lower
colleagues slant diagonally forward. You may call me ill-mannered, but these are
frankly rather boring teeth with round cross-sections. At least the tips attempt
to add some style by being 'slightly recurved'. (They point in a bit to
the rear.) Lovers of serrations may be disappointed to hear that there weren't
any; neither front nor back.
Canines
These are somewhat more exciting and provide information on replacement. New
canines have been caught coming through in front of their predecessors on upper
jaws. This is reversed with the lowers, as a new one is erupting behind its
senior. Usually (but not always) there's no
diastema between the upper canine and the postcanines, but there is in some
specimens. A diastema is always favoured by lower
dentitions.
Postcanines, but first a brief résumé
Earlier, should anybody still be awake, I asserted Langbergia was something
like up to rabbit-sized, although
hamster-sized is probably more typical. I also claimed it enjoyed having
sex and was an omniovre. Oh, I also called it stupid. Are these charges
justifiable?
# Size: You've now seen the skull length, and that's enough to provide a reasonable
basis for estimating the length of the whole animal.
# Stupidity: I've already covered that point well enough so, should it have passed
you by, then get a more literate friend to explain what the words meant.
# Sex: Thirteen specimens are available, and none resulted from immaculate
conceptions. They were bonked into the world.
# Omnivore: That information comes from the postcanine teeth, as teeth strongly
reflect diet. They point to an unwritten shopping list. Teeth often look as if
they're designed for the very poison the animal prefers, but this is because
they've been adapted towards it.
Upper postcanines
The most popular complement is seven or eight postcanines per maxilla, and the
first number applies for the holotype. The series is begun with a simplistic
thing and it's followed (on the type specimen) by three
gomphodont teeth. A trio of
sectorial teeth are at the rear. The first of
those was being replaced by a gomphodont postcanine. This mixed dentition was
maintained through life, and that's what points to mixed tastes in food.
The postcanines become bigger from front to back until position four or five, and
then they diminish. Number one is much the smallest. Its immediate followers are
round to oval in outline, with the width being not much more than the length. The
centremost of the trio of cusps dominates when compared to those on either flank,
and a ridge links all three. Further ridges of accessory cuspules occur both to
the front and back of the tooth.
The rear postcanines have similarities with those of
Thrinaxodon and many other meat-eating non-mammalian cynodonts. There
are two to three per side. The crown also has an oval outline but these teeth are
longer than wide. There's a recurved main cusp, a fairly large cusp in front of
it and two accessory cusps behind, and all these are arranged in a straight line.
The final cusp is very small. A cingulum with
four or five cuspules is positioned on the lingual
side.
Lower postcanines
These are a bit smaller than their upper colleagues, and they're set obliquely across
the jaw rather than straight. The first is again unimpressive and it's followed
by gomphodont, and then sectorial teeth. A distinction of the gomphodonts lowers
has been mentioned; the labial cusp is a bit in
front of the halfway line and its lingual friend stands behind.
Lower sectorials are much like the uppers, but the lingual cingulum is less
developed (p.396).
Affinities
An analysis of 43 characteristics and 18 taxa was
performed (p.398), with the objective being to identify Langbergia's
nearest and dearest. It inevitably tested other relationships as well. Cynognathia
(as constituted in this study) was found to be a
monophyletic clade represented by Cynognathus
(basal) and all gomphodonts (not including
tritylodontids -p.399). Langbergia
itself was accused of being a trirachodontid most closely related to
Cricodon and, given the chronological sequence involved (p.401), that's
somewhat contrary. It suggests that Trirachodon is more basal despite
occurring (at least mainly) in the strata between Langbergia (lower and
earlier) and Cricodon (higher and later). However, the overwhelming
majority of terrestrial vertebrates drop dead
leaving no fossils at all, and basal lineages do persist alongside of (and even
beyond) more derived relatives. What is called into question is the tidier
pattern of morphological change and stratigraphy cited by Rubidge & Sidor in
a 2001 study, but so it goes.
Now, if you'll excuse me, two hours of highlights of the 1995-95 German Bundesliga
are about to begin on telly, and then the day's action from Le Tour de France
requires my attention.
Holotype
NMQR 3255 is a skull in the collection of the National Museum, Bloemfontein. The
specific name honours the work of the deceased preparator, Gert Modise, who
provided dedicated service at the Bernard Price Institute. His efforts included
part of the preparation conducted on fossils of Langbergia.
Cheers for the help
Thanks are due to Alan H for the prompt notice of publication and a copy of the
paper. Further thanks are due to Fernando A for similar reasons. |
| Reference: | Abdala, Neveling & Wellman (2006), A new trirachodontid
cynodont from the lower levels of the Burgersdorp Formation (Lower Triassic) of the Beaufort
Group, South Africa and the cladistic relationships of Gondwanan gomphodonts, Zoological
Journal of the Linnean Society, 147(3), p.383-413. |
| Species: | Neotrirachodon expectatus Tatarinov LP, 2002 |
| Aka: | Antecosuchus ochevi |
| Place: | Donguz Formation, Orenburg Region |
| Country: | Russia |
| Age: | Middle Triassic |
| Remarks: | Abdale & Smith, 2009 briefly mention this
genus (p.10). They accuse the postcanine teeth of being more like those of a bauriid
therocephalian. If so, then it can't be a cynodont let alone a trirachodontid or any
form of gomphodont cynodont.
Additional notes
Abdala et al, 2006 also provides information
on this animal (p.398). The fossil is question is a left
dentary with postcanines. It was first
referred to Antecosuchus, which was held to be a
traversodont. The animal didn't mind that
too much, but it was then told it was perhaps a
therocephalian therapsid. However, that didn't make it happy. Advisors
suggested it apply for membership of Trirachodontidae on the grounds of the
approximate skull length of twelve centimetres and trirachodontid-like
postcanines. Similarites include the crest running across the crown and the
presence of cingular cusps.
However, that transverse crest is set further forwards, there's no cusp on the
lingual side of the crown and the cingular cusps
are more prolific in number. Those first two conditions are traversodontid
characteristics. This genus appears to be somewhere between the tiras and travies
and has difficulties qualifying for either family. Abdala and friends (2006)
suggest waiting for further fossils before stating anything other than it's a
gomphodont. They do call it intriguing.
This genus is based on a reassigned lower jaw, and was described as the first
trirachodontid from Russia. |
| Reference: | Tatarinov (2002), Gomphodont Cynodonts (Reptilia, Theriodontia)
from the Middle Triassic of the Orenburg Region, Palaeontological Journal, 36 (2), p.58-61.
|
| Genus: Sinognathus Young
CC, 1959
'Chinese jaw'
Subfamily: Sinognathinae Gao et al, 2010
Remarks: "Sinognathus" Fan Q & Li L, 1995, enjoyed a brief career as a
garlic-loving mite. It annoyed Chinese farmers and still does, though now known as
Paraneognathus. (Shamelessly, I originally called it a spider. The original
description of the doubtlessly charming pest may be enjoyed in Acta-Zootaxonomica-Sinica.
1995, 20: 3, p.323-327. With thanks to Joy Tyson for the citation and correction.) |
| Link:
ACTA ENTOMOLOGICA SINICA 2000 Vol.43¡¡No.4¡¡P.421-428
ACTA ENTOMOLOGICA
A phylogenetic analysis of the family Caligonellidae. |
| Species: | Sinognathus gracilis Young CC, 1959 |
| Place: | Upper Ermaying Formation |
| Country: | China |
| Age: | Lower Triassic |
| Remarks: | Abdala et al, 2006 contains some
information (p.398). The genus is based on a skull and lower jaw. Originally,
Young thought it was closely allied with
Thrinaxodon, but that was before the fossil had been fully prepared.
The upper postcanines aren't well preserved yet
they appear to be trirachodontid-like. Apart from lacking accessory cusps at the
front and rear, they are reminiscent of Trirachodon
beeryi. The skull though is eccentric; short snouted and with an "extraordinarily
expanded temporal opening".
The skull length is about 12 centimetres. |
| Reference: | Young CC (1959), Note on the first cynodont from the
Sinokannemeyeria fauna in Shansi, China, Vertebrata PalAsiatica, 3, p.124-132. |
| Genus: Trirachodon
Seeley HG, 1895
Aka: Inusitatodon Brink & Kitching, 1953; Trirachodontoides
Broom R, 1932 'Trirachodon form'
'three spine tooth' (With thanks to C.V. Vick)
Remarks: According to Kemp, 2005 (p.67), a contrast between this genus and
Diademodon is that the
postcanines can be subdivided into two rather than three subtypes. There are no
relatively simple ones at the front of the series. As with
Cricodon, the crown of the gomphodont postcanines has a line of three cusps
arranged transversely across the middle. In this genus, however, it's the central cusp
which is largest rather than the external one. The front and rear edges of the tooth are
graced with rows of small cuspules.
An interesting feature of this genus is the way in which the teeth change through
its stratigraphic range: "The earliest-occurring form, known only from recently collected
material, maintains sectorial teeth along much of its
tooth row (Neveling 1998). The succeeding morphospecies, Trirachodon kannemeyeri,
has transversely widened (gomphodont) teeth anteriorly
in its tooth row but retains sectorial teeth more posteriorly. The final species,
Trirachodon berryi, by contrast, has a full complement of gomphodont teeth",
(Rubidge & Sidor 2001, p.468).
For clarity: sectorial teeth are blade-like ones, which are fine for slicing meat. In
contrast, these gomphodont choppers are widened and best suited for chomping salad. The
earliest known member of this genus had many slicers, (like Cynognathus). A later
species had plant-eating teeth at the front, but meat-eating ones at the back. The latest
representative had only the chompers.
Abdala et al, 2005 makes things slightly murkier by failing to recognise T. kannemeyeri
as a separate species. Three genera and five species were assigned to T. berryi by
Hopson & Kitching in 1972, (p.194). Subsequently, T. kannemeyeri was revived.
Abdala and colleagues recognize only a single species in subzone B of the Cynognathus
zone, and that's T. berryi. They do accept a distinct, unnamed species in subzone
A. There will be a future study on trirachodontids. Fossils are also known from Namibia.
Institutions with specimens include the Bernard Price Institute, Johannesburg and The South
African Museum, Cape Town.
More limbits
The following is based upon my reading of Botha & Chinsamy, 2004.
Having previously conducted a study on growth rates as shown by bones of
Cynognathus and Diademodon,
(which is featured above on this directory), the authors have also turned their attentions
upon this genus. They report the cranium is broadly similar to Diademodon, (p.619).
There's a short, narrow snout and a broad orbital region.
Differences include: the much smaller size (a maximum bodylength of 50cm as opposed to two
metres), and fewer gomphodont postcanine teeth. These
are also wider in Trirachodon.
I'd imagine the technical details involved can only be of interest to specialists, so I'll
content myself with easy-to-grasp information and the conclusions. The scope of the study
was provided by eleven bits of bone, (p.620). These were mostly from limbs, though ribs
and scapulae were also microscopically examined. The
longest bone in the collection was a tibia of over 6cm in
length. It's presumably adult, (p.621). Unsurprisingly, juvenile bones tend to show signs
associated with quicker recent growth. Should that nevertheless require emphasis:
"Thus, the decrease in vascularization indicates their overall growth slowed with
age", (p.624).
As with Diademodon, the growth rate appears to have varied in line with the season.
However, these cycles are better defined in the larger genus, (p.625). Trirachodon
was presumably less affected by fluctuations in food supply. A similar pattern has also been
reported for the Middle Triassic
Gomphodontosuchus from Brazil. That was also at least predominantly a plant-muncher.
This contrasts to what's known from Cynognathus and Belesodon, (both
carnivores, although I have the latter as Chiniquodon),
Clearly though, type of diet isn't the decisive factor. The Middle Triassic
Traversodon shows no particular signs of
seasonal growth, and it was a herbivore.
The relative thickness of wall to diameter of the bone is known as RBT. A figure of over
30% is often associated with amphibious, aquatic or tunnelling animals. As it's obvious
Trirachodon lived in burrows, an average RTB if 30% for
femurs isn't a surprise. Thick walled bones are useful for digging, (p.626).
Link:
Acta Paleontologica Polonica
http://app.pan.pl/acta49/app49-619.pdf
The full paper is freely accessible on-line. (It may require time to open.)
| Reassigned species: T. angustifrons Parrington, 1946 see
Scalenodon angustifrons;
T. browni Broom R, 1915 see Diademodon
tetragonus; T. kannemeyeri Seeley, 1895 see T. berryi &
Langbergia modisei; T. minor Broom,
1905 see T. berryi | |
| Species: | Trirachodon berryi Seeley HG, 1895 |
| Aka: | Inusitatodon smithi Brink & Kitching, 1953;
T. kannemeyeri Seeley, 1895 (partly); T. minor Broom R, 1905;
Trirachodontoides berryi (Seeley, 1895) Broom R, 1932 |
| Place: | Burgersdorp Formation, Karoo |
| Country: | South Africa |
| Age: | Anisian, Middle Triassic |
| Remarks: | Abadala et al, 2005 report the species is known
from at least five sites. Some have yielded hundreds of individuals, (p.195). Typical
skull lengths are ten centimetres or less, although one individual managed 11cm,
(BP/1/5362).
Of size and toothiness
Abdala et al, 2006 contains further information. They interviewed 14 skulls of
this species during their enquiries into a relative called
Langbergia (p.392). 13 of them agreed to provide either completely
measured or estimated skull lengths, and these ranged from 52 to 100mm. More
alert readers might realise the first mentioned specimen is the smallest. The
next two steps up in the line managed 75 and 77mm; three were in the upper eighties;
two reached 90mm; one the upper nineties; and two hit the jackpot with 100mm.
In contrast to Langbergia (and more typically for gomphodonts), there was
a tendency for more upper postcanines to be
sported on the longer jaws. For example, the shortest had six and the largest
eleven. The toothiest of the pack was a 90mm jaw with twelve. A tendency isn't
an absolute rule.
Add teeth or get rid of them, that is the question.
Although this species shares plenty of similarities of skull with Langbergia,
they had some radically different approaches to postcanine teeth (p.397). Both
may (or may not) have a diastema separating the
upper canine from the postcanines,and there's no
obvious reason for this variation. It seems to be random. The range of postcanine
numbers is greater in Trirachodon, but that might conceivably be due to a
biased fossil record. Trirachodon has six to twelve upper postcanines per
side as opposed to six to ten.
Of more significance is the tendency of longer jaws in this genus to have more
postcanines than those of their shorter friends. Langbergia preferred
losing teeth with growth. Furthermore, the maximum number of
sectorial upper postcanines in this later genus
has been reduced to two (as opposed to three for L.), and the three
toothiest incividual had reduced those further to none whatsover. All their
postcanines are of the gomphodont style. This
indicates the dental battery altered with advancing age, and this would make sense
in terms of changing tastes; an increasing preference for plants. Lanbergia,
on the other paw, retained a mixed diet.
I'm also (hopefully) following information from that paper with regards to
synonyms.
Holotypes
T. berryi: BMNH R3579, Natural History Museum, London. This is the valid
type fossil of the species. Treat the rest as potentially interesting imposters.
T. kannemeyeri: AM 434 461, Albany Museum, Grahamstown, South Africa.
T. minor: SAM-PK-5873, South African Museum, Cape Town.
Inusitatodon smithi: BP/1/1194, Bernard Price Institute for Palaeontological
Research, Johannesburg.
The AMNH, New York has a specimen of T. kannemeyeri, which was collected by Broom in
the early 1900s.
|
| References: | Seeley HG (1895), Researches on the structure,
organization and classification of the Fossil Reptilia, Part IX, Section 4, On the
Gomphodontia, Philosophical Transactions of the Royal Society of London, 186,
p.1-57. |
| Broom R (1905), Preliminary notice of some new fossil reptiles
collected by Mr. Alfred Brown at Aliwal North, S. Africa, Records of the Albany
Museum, 1, p.269-275. |
| Broom R (1932), The mammal-like reptiles of South Africa
and the origin of mammals, London, H. F. & G. Witherby. |
| Brink AS & Kitching JW (1953), On some new Cynognathus
Zone specimens, Palaeontologica Africana, 1, p.29-48. |
| Link:
Science News Online 9.6.2001, Beyond Bones by Sid Perkins
http://www.sciencenews.org/articles/20010609/bob9.asp
Lower Triassic Housing Projects
This is an accessibly written article on trace fossils; burrows, footprints and so on. It
includes a couple of burrow complexes made by members of this genus. The inhabitants were
apparently
hamster-sized warren dwellers.
"Each of the burrows had an entrance tunnel about 15 centimetres wide and 6 cm high
that gently sloped downward toward the interior, says MacEachern. The center of the tunnel
floor had a slightly raised, flat-topped ridge marked by scratches and flanked by two
smooth grooves, each a few centimetres wide. At deeper levels in each burrow, the tunnel
became more curved and progressively smaller in diameter. In some places, it branched at
right angles. Many of these small tunnels ended in smooth-floored chambers.
The animals trapped in the second tunnel system were of several different ages. Two adults
and one juvenile died together in one chamber, which suggests that some portions of the
burrows were places for rearing young. A few chambers contained fecal pellets, indicating
that these dead ends were latrines. Other larger chambers could have been for food storage,
MacEachern notes."
MacEachern JA is one of the authors who described this complex in 2001.
Another, but a home alone this time
In the description of this find, the presence of various other burrows in the Karoo Basin
is reported, but these don't show evidence of communal dwelling. Amongst the
non-eucynodont diggers around were Diictodon
and Lystrosaurus, (Groenewald et al, 2001).
On a similar theme, Damiani et al, 2003 contains a description of a bachelor pad for the
fox-sized Trirachodon. This was a meat-eating
cynodont with reasonably close affinities to
eucynodonts, (but not quite close enough). The identity is clear as the critter is still
at home about 250 million years later. Its curled up and snoozing soundly.
As also for Trirachodon: "In both cases, the shaft has a cross-section in which
the floor has a central ridge that divides it into laterally sloping halves", (p.1748).
This characteristic is explained by the way the critters walked, and is only known from the
burrows of non-mammalian cynodonts. Their legs sprawled less to the sides than was the case
for other therapsids, but more than mammals. The tunnels of more basal therapsids are
relatively wider, as their inhabitants had less elegant legs. It was the more mammal-like
locomotion which produced parallel depressions in cynodont burrows. The Thrinaxodon
house is presently the oldest known cynodont home. It was built about five million years
before the community above.
Also mentioned (p.1747) is the presence of Trirachodon burrows with skeletal remains
from the Middle Triassic of Namibia. The species isn't indicated. |
| Other reports:
New Mexico
The Peabody Catalogue includes indeterminate trirachodontid material from the Redonda
Formation, Quay County. It was collected in 1958.
China, Gansu Province
The Society of Vertebrate Paleontology abstracts for 2004 include: Gao KQ, Fox R, Li D &
Zhang J, A new vertebrate fauna from the Early Triassic of northern Gansu Province, China.
The Beishan area of the Black Gobi was probably explored by Sino-Swedish Expeditions in
1927 - 1935, but it has been more recently visited by workers from Peking University and
the Geological Survey of Gansu Province. The finds suggest they've been rather successful.
They've evidently come up with a freshwater shark, a coelacanth, other fish, a couple of
amphibians, a lizard-like diapsid, and a eucynodont. It's said to be
Sinognathus-like, and is equipped with a short snout, flaring zygomatic arches,
(known as the cheek bones in polite society), and a well-developed sagittal crest.
Most specimens are fully articulated, and there are few signs of disturbance or
scavenging, (apart from that done by the paleontologists. They scavenged anything they
could lay their hands on). That suggests the place used to be a quiet, watery area.
Update
This was described in 2010 and received the generic name of
Beishanodon.
Upper Fremouw Formation,
Antarctica
A gomphodont cynodont has been reported from a fauna, and they seem to have similarities
with Cricodon and some traversodontids. Another view is
that the remains are of a diademodontid. The fossil
mentioned in the Other reports for that family is presumably the same specimen as in this
entry.
Reference: Hammer et al (1990).
Yerrapali Formation, India
Abdala et al, 2005 mention isolated teeth, (p.195).
Redonda Formation, USA
Abdala et al, 2005 mention a 'taxonomically dubious record', (p.195). Conveniently,
Renesto & Lucas, 2009 report that doubts have been expressed about the trira credntials of
a find from New Mexico (by Abdala et al, 2006), so I conclude these different
authors are discussing the same thing. That's where the Redonda Formation happens to
be.
The original citation has to be Lucas SL, Estep JW, Heckert AB & Hunt AP, (1999), Cynodont
teeth from the Upper Triassic of New Mexico, USA, Neues Jahrbuch für Geologie und
Paläontologie Monatshefte 1999, p.331-344.
Anybody wanting a pdf copy would have to send me one first, seeing as I've not seen this
paper. Yet.
Omingonde Formation, Namibia
Abdala et al, 2006 state work is underway on cynodonts from this Middle Triassic
rock, and trirachodontids are represented (p.398). However, that doesn't include
specimens previously attributed to Trirachodon.
Those turned out to be the traversodont
Luangwa and Aleodon, a
probainognathian. |
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| 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.
With thanks to all the featured sources.
Trevor Dykes, October 2001 Latest update: 4.9.2010
Ktdykes@arcor.de |
Bibliography:
Abdala F (2007), Redescription of Platycraniellus elegans (Therapsida,
Cynodonita) from the Lower Triassic of South Africa, and the cladistic relationships
of eutheriodonts, Palaeontology, 50(3), p.591-618.
Abdala F & Giannini NP (2000), Gomphodont cynodonts of the Chanares Formation:
the analysis of an ontogenetic sequence. Journal of Vertebrate Paleontology, 20 (3),
p.501-506.
Abdala F & Giannini NP AM (2002), Chiniquodontid Cynodonts: Systematic and
Morphometric Considerations. Palaeontology, Vol. 45, Part 6, p.1151-1170.
Abdala F, Hancox PJ & Neveling J (2005), Cynodonts from the uppermost
Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and
correlation of the Triassic Cynognathus Assemblage Zone, Journal of Vertebrate
Paleontology, 25(1), p.192-199.
Abdala F, Neveling J & Welman J (2006), A new trirachodontid cynodont
from the lower levels of the Burgersdorp Formation (Lower Triassic) of the Beaufort
Group, South Africa and the cladistic relationships of Gondwanan gomphodonts,
Zoological Journal of the Linnean Society, 147, p.383-413.
Abdala F & Ribeiro AM (2003), A new traversodontid cynodont
from the Santa Maria Formation (Ladinian-Carnian) of southern Brazil, with a
phylogenetic analysis of Gondwanan traversodontids. Zoological Journal, 139 (4),
p.529-545.
Abdala F & Smith RMH (2009 -'Proof only'-copy), A Middle Triassic cynodont
fauna from Namibia and its implications for the biogeography of Gondwana, In press,
Journal of Vertebrate Paleontology.
Benton MJ (1990), The Reign of the Reptiles. Eagle Editions, (printed 1998), ISBN
1-902328-17-5.
Benton MJ (1993), Das große farbige Dinosaurier-Lexicon. ars edition GmbH, Munich,
(Sonderausgabe für Gondrom Verlag GmbH & Co KG).
Botha J & Chinsamy A (2000), Growth patterns deduced from the bone histology of
the cynodonts Diademodon and Cynognathus, Journal of Vertebrate Paleontology
20 (4), p.705-711.
Botha J & Chinsamy A (2004), Growth and life habits of the Triassic cynodont
Trirachodon, inferred from bone histology, Acta Palaeontologica Polonica, 49(4),
p.619-627.
Damiani R, Modesto S, Yates A & Neveling J (2003), Earliest evidence of cynodont
burrowing, Proceeding of the Royal Society of London B, 270, p.1747-1751.
Gao K-Q, Fox RC, Zhou C-F & Li D-Q (2010), A new nonmammalian eucynodont (Synapsida:
Therapsida) from the Triassic of northern Gansu Province, China, and its biostratigraphic
and biogeographic implications, American Museum Novitates, 3685, p.1-25.
Groenewald GH, Welman J & MacEachern JA (2001), Vertebrate burrow complexes from
the early Triassic Cynognathus zone (Driekoppen Formation, Beaufort Group) of the
Karoo Basin, South Africa. Palaios, 16(2), p.148-160.
Hammer WR, Collinson JW & Ryan WJ (1990), A new Triassic vertebrate fauna from
Antarctica and the depositional setting, Antarctic Science, 2(2), p.163-167.
Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press,
pp.331.
Renesto S & Lucas SG (2009), Cynodont teeth from the Carnian (Late Triassic) of
northern Italy, Acta Palaeontologica Polonica, 54(2), p.357-360.
Rubidge BS & Sidor CA (2001), Evolutionary patterns among Permo-Triassic
therapsids. Annual Reviews of Ecology and Systematics 32, p.449-480.
Sidor CA & Hancox PJ, Elliotherium kersteni, a new tritheledontid from the
lower Elliot Formation (Upper Triassic) of South Africa, Journal of Paleontology, 80(2),
p.333-342. |
