MESOZOIC CYNODONTS; Tritheledonta, an internet directory
MESOZOIC CYNODONTS; Tritheledonta, 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.
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You could visit the
Book Centre and look around.
Tritheledontans were generally 10 - 20 cm long insect-eating
furry things, which evolved from
chiniquodontoideans. These creatures were virtually, but not quite
mammals. My use of the taxon
is inspired by Kemp, 2005. On page 66 can be found: "Tritheledonta: a possibly
paraphyletic series of very small, highly advanced
carnivorous forms including Tritheledontidae and Therioherpetontidae." A further
family exists for dromatheriids. However, as
they're presently extremely poorly known, (and the various members aren't necessarily even
closely related with each other), I'll leave them stored elsewhere for now.
But isn't Tritheledontidae more generally used for some of these animals?
Yes, but there's disagreement over what constitutes a tritheledontid. Bonaparte JF,
Ferigolo J & Ribeiro AM (2001) expressed the opinion that only
Tritheledon actually qualifies. They prefer a family called Pachygenelidae for
other genera. I thought I'd get out of that tangle and use a looser term. I'm also going
to use a straightforward A-Z listing.
Use of language, the possible meanings of Tritheledontidae
Broom, 1912
As the family name is commonly used, it would be as well to note which taxa are often
included as strict(ish) tritheledontids: Tritheledon, Diarthroganthus,
Pachygenelus, Pattsia. Additionally, some add Chaliminia (to the
chagrin of the authors of that genus). I'd never seen the other genera on this directory
referred to the family. (Several have now been included!)
The following (and perhaps more) names have (and often are) in use for various
tritheledontans:
Families: Tritheledontidae Broom, 1912b, (Hopson & Kitching), includes Ictidosauridae
Young, 1947; Diarthrognathidae Crompton, 1958; Pachygenelidae Bonaparte, 1980; Riograndidae
Bonaparte, Ferigoglo & Ribeiro, 2001; Therioherpetontidae Bonaparte & Barberena,
1975.
By the way, a spelling of Trithelodontidae also sometimes occurs. As far as I can make out
this is technically incorrect, but it's a long established habit.
The following is based upon my reading of Martinelli et al, 2005 (p.2).
A concise family history
Broom set up the family of Tritheledontidae in 1912, and this was in order to accommodate
the sparse remains of Tritheledon. That trithe remains
rare and illusive. Watson found a partial lower jaw of a friend from the same area of
South Africa, and named this Pachygenelus in
1913. Subsequent finds make this second critter better known, and show it was more
widespread. At least very similar fossils have been discovered loitering in eastern Canada.
At the time, these animals were known as ictidosaurs, and Broom introduced two further
specimens in 1929. Ictidosaurian A was a near complete skull and Icti. B a partial skull
with much of the skeleton. The second became Diarthrognathus
in 1958, and this was then the only specimen of that genus.
Shocking accusations arose in 1972, when Diarthro was charged with being a juvenile of
Pachygenelus. It whimpered protestations but was told to shut up. Such tantrums
were typical of juveniles. However, more material demonstrated it had a good point, and
Diarthrognathus was vindicated as indeed belong to a distinct genus.
The taxonomic rank of Ictidosauria has been abandoned, but 'ictidosaur' remained in
informal usage when similar creatures began emerging from Brazil; first
Chaliminia, then Riograndia and,
in 2005, Irajatherium. Prompted perhaps by jealousy,
South Africa retaliated in 2006 with
Elliotherium
The relationships between these 'ictidosaurs' (or tritheledontids in current terminology)
are somewhat unclear. Presently, I prefer using the vaguer concept of Tritheledonta for a
collection of reasonably similar, small insectivores and carnivores. As used by Martinelli
et al, 2005, the family was defined as the most recent common ancestor of
Riograndia and Pachygenelus, and all of its descendants.
Introducing trithes
Like the tritylodontids, members of this group
(particularly ones sometimes placed in Tritheledontidae) have been accused of being the
sister-line of mammals: "This hypothesis gains the strongest support from the
characters of the temporomandibular joint, and from the occlusal movement of the lower jaw
inferred from the dental wear and symphasis in the tritheledontids", (Luo 1994,
p.109). On page 111, Luo goes on to observe, "...the main weakness of the
tritheledontid-mammal hypothesis is that too many tritheledontid characters are primitive
(e.g., the orbit and the braincase)."
On the trity or trithe roots of mammaldom, his research favours this second option because
it "has consistently fewer transformational steps than the tritylodontid-mammal
hypothesis, regardless of the out-groups. Nevertheless, the difference between the two
hypotheses is quite small", (p.111). From which group mammals emerged isn't
necessarily an either-or question though. The third option is 'from a different group'.
In any case, both tritys and trithes appear to be closely related to mammals.
Mammalosities
Kemp, 2005 obligingly provides some general discusion starting on page 72.
Not much is presently known beyond jaws and skulls, but what there is can be very
mammalian. As with the tritylodontids, the postorbital bar
of bone had gone, so the eye hole and temporal fenestra combined into one space. A
contrast to the tritys is that the temporal fenestra is longer. This, and several other
details, may simply be due to the comparatively small body sizes of trithes.
A characteristic independent of size can be found on the jaws of
Pachygenelus. The articular-quadrate
jaw joint is standard issue for non-mammalian tetrapods. The only exceptions on Earth are
we mammals. We hold our jaws and skulls together with a
dentary-squamosal one. Pacygenelus had
both. (This had also been reported as present in
Diarthrognathus, but this is not absolutely clear.)
Pachygenelus also had fairly strong tooth enamel on its relatively well-aligned
postcanines. As with basal
mammals, the uppers and lowers were in occlusion and, due to the way the jaws worked, only
one side of the teeth could be used with each bite. However, wear facets aren't all that
well developed, so the alignment wasn't quite up to the standards of say
Morganucodon. (Oddly enough, 'Morgan's
tooth' had weaker enamel.) Regardless of precisely which animals were the closest
relatives of basal mammals, Pachygenelus was closer than most.
Trithe teeth
"Tritheledontidae can be distinguished from other nonmammalian cynodonts by the
following dental features; (i) presence of only two upper and two lower
incisors..; (ii) transversely expanded upper
postcanines...; (iii) longitudinally ovate postcanines
with large anterior cusp followed by one or two posterior accessory cusps and a
lingual cingulum; (iv)
upper postcanines with a buccal cingulum; (v) postcanine
teeth with incipiently divided, massive roots", (Shubin et al 1991, p.1064. I've
omitted the reference numbers from the quotation).
Bonaparte et al, 2001 presents a different interpretation of the relationships between
these genera. In their view, Tritheledontidae only seems to be a valid family for
Tritheledon. The upper postcanines of Pachygenelus, Chaliminia and a
then undescribed representative from Greenland (Mitredon) present a different
morphology. They conclude a family name based on Pachygenelus would therefore be
more appropriate, and might also include Diarthrognathus.
Riograndia has postcanines which present a further state of characteristics. They
see these as suitable precursors of the more derived
condition in Pachygenelus and Co. This would have required an increase in size for
the central cuspule, and the loss of some accessory cuspules, (p.632). |
| Genera:
Brasilitherium, Brasilodon,
Chaliminia, Charruodon,
Diarthrognathus, Elliotherium,
Irajatherium, Karoomys (=
Cynoganthus),Lycorhinus (= a falsely identified
dinosaur), Meurthodon,
Minicynodon, Mitredon,
Pachygenelus,
Pattsia, Protheriodon,
Prozostrodon,
Riograndia, Therioherpeton,
Thrinaxodon (partly = Prozostrodon), Tritheledon,
Other reports
Time-Line:
Lower Jurassic: Diarthrognathus, Pachygenelus, Pattsia,
Tritheledon
Upper Triassic: Brasilitherium, Brasilodon, Chaliminia,
Charruodon, Elliotherium, Irajatherium, Meurthodon,
Minicynodon, Mitredon, Prozostrodon, Riograndia,
Therioherpeton,
Brazil
Middle Triassic: Protheriodon |
| Genus: Brasilitherium
Bonaparte JF, Martinelli AG, Schultz CL & Rubert R, 2003
'Brazilian beast'
Family: Brasilodontidae Bonaparte JF, Matinelli AG & Schultz CL, 2005
Remarks: Kemp, 2005 (p.73) includes an estimated skull length of 2.4cm. The family was
established thnaks to further finds of both this genus and Brasilodon. Articulated
skulls and lower jaws provided further information, and confirmation for the close
relationship of brasiliodontids with mammals. The new abstract contains: "The new
phylogenetic analysis presented here corroborates the position of both genera as
sister-group of mammals as previously proposed." I haven't yet seen either the 2003
or 2005 papers.
Reference for the family: Bonaparte et al (2005), New information on Brasilodon
and Brasilitherium (Cynodontia, Probainognathia) from the Late Triassic of
southern Brazil, Revista Brasileira de Paleontologia, 8(1), p.25-46. |
| Species: | Brasilitherium riograndensis Bonaparte JF,
Martinelli AG, Schultz CL & Rubert R, 2003 |
| Place: | Caturrita Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Carnian or Norian (early), Upper Triassic |
| Remarks: | The abstract states this was a very small critter
with presumably a fondness for eating insects. The upper
postcanines are quadrangular as in Brasilodon (below). Their lower colleagues,
however, have an asymmetrical shape, and some are similar to the teeth of
Megazostrodon, which is a
basal mammal.
The abstract also contains: "Several derived characters
of the skull in Brasilodon and Brasilitherium, and a
morganucodontidlike lower
dentition in Brasilitherium, suggest closer
relationships to the morganucodontid mammals than for either
tritheledontids or
tritylodontids." This suggest the direct ancestors of mammals can't be traced to
either of those families.
Some further information is provided by Kemp, 2005. A skull length of 2.4cm is given on
page 73. Brief discussion comes on page 75. The upper postcanines are similar to
Brasilodon, but the lowers differ. The main cusp is set further forward. There's
a small cusp in front and up to three behind. A further cingulum cusp is also at the
front.
As this is a very recently described pair of genera, I'm looking forward to any further
studies and specimens. |
| Reference: | Bonaparte et al (2003), The sister group of mammals: small
cynodonts from the Late Triassic of southern Brazil, Revista Brasileira de Paleontologia,
5, p.5-27. |
| Genus: Brasilodon Bonaparte
JF, Martinelli AG, Schultz CL & Rubert R, 2003
'Brazil tooth'
Family: Brasilodontidae Bonaparte JF, Matinelli AG & Schultz CL, 2005
Remarks: The length of the skull is offered as 2.2cm, (Kemp 2005, p.73). |
| Species: | Brasilodon quadrangularis Bonaparte JF, Martinelli
AG, Schultz CL & Rubert R, 2003 |
| Place: | Caturrita Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Carnian or Norian (early), Upper Triassic |
| Remarks: | Both upper and lower
postcanines are quadrangular in this genus, which provides a clue as to the meaning of
the species name. There's little morphological variation along the series.
Proportions in the preorbital and orbiotemporal regions of the skull, (in anatomy,
orbits are the holes for the eyes), show this fossil
represents a distinct species from Brasilitherium.
Kemp, 2005 helps here as well. The skull length is 2.2cm (p.73). The teeth of both these
Brazilian beasts are structually much as would be expected from a very close mammalian
ancestor. For Brasilodon: "the crowns of the postcanineds are symmetrical
about the main cusp, with equally well-developed anterior and posterior accessory cusps in
line, and an anterior and posterior cingulum cusp on the
inner face." |
| Reference: | Bonaparte et al (2003), The sister group of mammals: small
cynodonts from the Late Triassic of southern Brazil, Revista Brasileira de Paleontologia,
5, p.5-27. |
| Link:
Paleontologia em Destaque no 44 (Big document)
http://www.ufrgs.br/sbp/boletim44.pdf
This file contains a series of abstracts in Portuguese. Page 46 features Bonaparte JF,
Soares MB & Schultz CL, 2003. The event was called Paleo 2003. I'm going to quote the
abstract in its entirety, (ca. 300 words), because I speak Portuguese like a native..., of
Portsmouth (Bournemouth actually, but you get the general idea). I think it includes the
following points, but don't take my word for it. Your Portuguese is at least as good as
mine and the numbers and letter are referring to the text below.
(i) Brasilitherium and Brasilodon are less
derived than the basal mammal
Morganucodon in aspects of cranial anatomy
and the jaw.
(iii) Brasilitherium has lower postcanines of a
morganucodontid grade, but the uppers are more like Brasilodon.
(ii) Brasilodon has upper postcanines which are more derived than Morganucodon,
and closer to those known from Kuehneotherium.
(v) Morganucodon and Kuehneotherium are in a
monophyletic clade, which these two non-mammals are at least close to.
(F) That clade doesn't include the members of Harimiyidae (see
Haramiyida for a rough explanation). Haramiyids have origins which are independent from
those of Morganucodontidae and Kuehneotheriidae.
If those points have been anything like accurately understood by myself, this is fascinating
stuff. Feel free to forward the published description and / or improve my attempted
translation.
- Paleontologia em Destaque nº 44 -
- Página 46 -
JOSÉ F. BONAPARTE*, MARINA B. SOARES & CESAR L. SCHULTZ
Depto. Paleontologia e Estratigrafia, IG/UFRGS, RS,
Los pequeños cinodontes Brasilodon y Brasilitherium de la Formación
Caturrita, Triásico Superior de RS, Brasil, presentan caracteres anatómicos de interes para
ampliar los conocimientos actuales en relación al tan discutido origen filético de los
mamíferos. Si bien su anatomia ósea cráneo-mandibular es del tipo presente en cinodontes
que han sido considerados como el grupo hermano de los mamíferos (tritheledóntidos), la
estructura de sus postcaninos ofrecen interesantes perspectivas de análisis e implicancias
de estos cinodontes en relación al origen de los mamíferos [sensu Simpson, J.G. 1960.
Evolution, 14:388-392]. Estas denticiones nos indican que: (i) si tomamos como referencia
al arquetipo de los mamíferos primitivos, Morganucodon, el grado de derivación de
los postcaninos de Brasilodon y Brasilitherium es mayor que lo observado em
Morganucodon, pero en términos de anatomía craneana, los géneros brasileros
presentan una condición más primitiva; (ii) Brasilodon posee postcaninos superiores
e inferiores más derivados que en Morganucodon, y con un plán básico próximo al
presente en Kuehneotherium; (iii) Brasilitherium posee postcaninos inferiores
del tipo presente en Morganucodontidae, pero postcaninos superiores más derivados, del tipo
presente en Brasilodon; (iv) en consecuencia, las características dentarias básicas
de los mamíferos Morganucodon y Kuehneotherium, que están presentes en los
citados géneros de cinodontes, se habrían desarollado, básicamente, en un nivel
premamaliano; (v) Morganucodontidae y Kuehneotheriidae serían monofiléticos en el sentido
que, eventualmente, descienden de una misma familia de cinodontes [Crompton, A.W. &
Jenkins, F.A. 1979. In: Lillegraven, J.A. et al. (eds.), Mesozoic mammals: the first
two-thirds of mammalian history. Univ. of California Press, p. 59-73], y polifiléticos en
el sentido que tendrían ancestros distintos dentro de Mammalia [Szalay, F.S & Delson,
E. 1979. Evolutionary history of primates, Academic Press, 580 p.]; (F) Brasilodon y
Brasilitherium no muestran afinidades ni relaciones dentarias con Haramyidae
Multituberculata, por lo que estos mamíferos se habrían diferenciado independientemente de
Morganucocontidae y Kueheneotheriidae. [*CAPES] |
| Species: | Chaliminia musteloides, Bonarparte JF, 1980 |
| Place: | Los Colorados Formation (upper) |
| Country: | Argentina |
| Age: | Norian (late), Upper Triassic |
| Remarks: | The following is based largely upon my
reading of Martinelli & Rougier, 2007, and thanks are due to the supplier.
Presently, Tritheledontidae isn't a family I'm very fond of. I don't object to the
animals involved. No, they're charmers. And nor are my "oh no, not agains" directed
to the researchers. The 'family' just happens to be unstable and the fossil record
is to blame. Almost every new study seems to lead to a spot of tinkering around the
edges; loosening, tightening and then loosening again. The definition is constantly
being changed, and that's the sort of thing an amateur paleo-bookkeeper finds
inconvenient. I want a robust unit! Truth be told, that's what this tinkering is
meant to bring about.
According to one view, proper trithes consist of the most recent common ancestor of
Riograndia and
Pachygenelus, and all of its descendants. Martinelli and Rougier accept
that as a unit, but raise it to a higher status; Ictidosauria. They restrict the
membership of the family to the most recent common ancestor of
Irajatherium, Pachyg and etc. And to hell with amateur
paleo-bookkeeping! Tain't fair, and I'm still not going to adopt the latest
structure!
However, even if they do necessitate some further systematic tinkering, new specimens
are welcome; far better than a charade of stability built upon persistent ignorance
of wider diversity. If systematics can't hold its shape during a bout of severe
kicking, then it deserves being disrupted.
A new pal for Chal
A new specimen of Chaliminia came to light from the upper reaches of
Argentina's Los Colorados Formation, a source with a diverse array of
vertebrates but not all too many
cynodonts (p.442). The only such company this
genus can enjoy is part of a front leg provided (perhaps) by a
tritylodontid. Both the Chal fossils are
more generous with information than that as they happen to be skulls. The newling
was found near La Esquina in 1994, and kindly provides some information not previously
available. That was used for a series of comparisons with twenty or so other
cynodont taxa, including
Sinoconodon and Morganucodon,
in order to identify its place in the scheme of things. That analysis chummed it up
most closely with a South African, Elliotherium,
and the authors erected a subfamily for that pair; Chalimininae. A further newly
proposed subfamily, Pachygenelinae, was opened for three further
derived trithes; Pachygenelus,
Diarthrognathus and
Tritheledon.
A quick glance
This is a relatively small probainognathian
cynodont with a skull length of around 3.5cm (p.445). The type fossil is around
25% larger. Unusual for a trithe is the high number of
postcanine teeth; 13 on one maxilla. Elliotherium
is also toothy but most were less enthusiastic in this regard. In contrast to more
advanced models, eg. Pachygenelus, postcanines are also more simply built, as
they lack buccal cingula.
The canines are smaller than those sported by Elliot, and the
zygomatic arch of the cheek differs by remaining slender along its whole course.
An eccentricity not shared with other trithes (ictidosaurs in the language of the
paper) is a fourth upper incisor near the
canine, and it could be housed on the maxilla.
Through the press
Geological forces have conspired to squash and distort the new skull, and much of the
roof and right side declined to turn up for interview. What remains is half a snout
with parts of some other skull bones. Despite a break below the fourth postcanine,
much of the lower jaw remains available. Nature has shoved a large chunk inwards,
and that includes at least the base of the coronoid process. The various
postdentary bones are still in place on the lingual
side, albeit not in very good condition. Many of the lower postcanines hurried off
for appointments elsewhere, but some are retained on the right jaw. Otherwise, the
teeth survived their time journey reasonably well. In that regard, it's better
than the type specimen. Sutures between bones are often hidden from view by plenty
of small cracks.
Head
The joint between maxilla and premaxilla is
visible for the lower two thirds but not higher up. It's positioned between the
final two incisors, as far as can be seen. Presumably, there was also a septomaxilla
bone involved despite no sutures being displayed. It would be odd if there weren't.
Going back to the cheek, as is typical for trithes excepting Elliotherium, the
zygomatic arch remains gracile whereas, for the eccentric South African, it deepens
towards the rear (p.446). Teeth from the right maxilla are contained in the
sediment, although the bone itself has vanished.
Lower jaw
Various aspects of the lower jaw are addressed, but my attention was particularly
grabbed by the situation at the rear. That's where mammals have a dentary condyle;
the lower part of the dentary-squamosal
jaw-skull joint. No living jawed non-mammals have anything of the kind. They possess
either an articular-quadrate joint or are
in urgent need of seeing a vet. That's not quite true. It'd generally be a bit
late for that. Anyway: "A distinct dentary condyle is not visible in this specimen
nor in the holotype, but the morphology of the condylar process suggests some
participation of the dentary in the cranio-mandibular joint" (p.447).
Upper teeth
Four incisors per side is one more than usual for
trithes, and diastemata separate them from one
another. There's a small tooth free zone at the very front of the jaw. They're
simple teeth and, excepting for the second, have similar sizes. I2 is large. All
incisors point straight downwards. The fourth is probably in the maxilla bone, but
the lack of a clear suture at that point makes it less than certain. As one of these
'extra' incisors is found on each half of the upper jaws, the possibility of them
being replacements for canines is remote. According to norms, such teeth are
allowed to erupt to the front, but they ought not do so simultaneously. First one
side and then the other is the proper etiquette. The
canine itself is no higher than the tallest incisor, but it is thicker. Its
internal side's flat whereas the outer one is convex.
On the left jaw stand 13 postcanines of similar
height. The crowns become somewhat more complex from front to rear, and all are
held in position by single roots. Evidence of alternate tooth replacement is found
at the front of this row; fully erupted are PCs 1, 3 and 5 whereas 2 and 4 are still
experiences the latter stages of the process. At least, they would've done so had
not death altered the owner's appointment plans around 220 million years ago. The
remaining postcanines are all full eruptees. Seen
lingually, there's a short but wide main cusp with a nearly straight surface
(convex on the buccal side). A small and sharp
ridge is forwards of that, and a small cusp occurs behind.
Lower teeth
3 incisors hang out together per side along with 1 canine and at least 10 postcanines
(p.448). The first incisor is the largest of that type and diagonally procumbent.
A vertical stance is favoured by i3 and, befitting of its middling position, i2's
attitude is inclined between the angles of its partners; somewhat diagonally
procumbent. Actually, it isn't strictly middling as its base is close to that of the
first incisor. A diastema separates it from the
third. Further incisor-length diastemata are present to the front and rear of the
not very impressive (and rather boring) canine. It's a bit taller than the i3 and
significantly robuster than all the incisors. Perhaps wallpapering or a splash of
paint could improve the interest there, but I doubt it.
Lower postcanines are broadly similar to those of
Pachygenelus. They have narrow crowns with three cusps, and these
decrease in size from front to back. The teeth are single-rooted within even a
hint of bifurcation; no, not even a trace of a groove beginning to adorn the middle.
Whether, as is the case for Pachy, a cingulum
offered some balcony space on the lingual side is
unknown. No specimens can be viewed like that. Again, as with the uppers, there
are signs of alternate replacement. The partial right
dentary has pcs 1 and 3 in the process of eruption while 2, 4 and 5 show root
exposed above the bone.
Affinities
22 cynodonts were questioned concerning 93 morphological characters, and they did
their best to be obliging. As Irajatherium was
unable to answer as many questions as the others, perhaps due to relative stupidity
as well as being less well preserved, its position is less clear. It thought it was
probably more derived than
Riograndia and less so than those referred to (in this study) as
tritheledontids. However, it wasn't all that sure. Chaliminia, meanwhile,
happily paired up with Elliotherium. Indeed, so content was this union, that
they were invited to found a subfamily together. With romantic music and faded
lighting providing a suitable atmosphere, the researchers quietly moved onto other
matters, while the two critters cuddled and snuggled with one another.
Holotype
The type fossil, PVL 3857, is a partial skull in the collection of the Instituto
Miguel Lillo, Universidad Nacional de Tucumán. As to the meaning of the specific
name, that's a matter covered by the Official Secrets Act or, to put it somewhat
differently, something I don't presently know.
Additional notes
The affinities of this genus subject to debate. It was represented by one, poorly
preserved specimen, (Shubin et al 1991, p.1064).
Bonaparte et al, 2001 clearly group it with Pachygenelus, (eg. p.631). They also
point out the Shubin et al (1991) were incorrect in suggesting Bonaparte had referred this
genus and Therioherpeton to Tritheledontidae in 1980. They were referred to
Pachygenelidae and Therioherpetidae respectively, (p.633).
Then came Martinelli et al, 2005, and the et al included Bonaparte. These authors
widened the definition of the family, and incorporated Chaliminia into its
ranks. |
| Reference: | Bonaparte (1980) El primer ictidosaurio (Reptilia-Therapsida)
de América del Sur, Chaliminia musteloides, del Triásico Superior de La Rioja,
Argentina. Actas, II Congreso Argentino de Paleontologia y Bioestratigrafia y I Congreso
Ltinoamericano de Paleontologia, 1 (Asociación Paleontológica Argentina, Buenes Aries),
p.123-133. |
| Link:
'La importancia turistica de Ischigualasto' preparado por Dr William Sill
http://www.ischigualasto.com/es/ischigualasto.htm
A description and inventory of fossil sites and environments in Argentina. A useful site for
people who, unlike myself, can understand Spanish. Relevant is Annexo VII, 6. Formacion Los
Colorados. |
| Genus: Charruodon Abdala
F & Ribeiro AM, 2000
'Charruas tooth'
Family: "Therioherpetidae"? Bonaparte & Barberena, 1975
Remarks: The generic name honours the Charruas, a tribe which lived in southern Brazil. |
| Species: | Charruodon tetracuspidatus Abdala & Ribeiro, 2000 |
| Place: | Santa Maria Formation, Rio Grande
do Sul |
| Country: | Brazil |
| Age: | Carnian, Upper Triassic |
| Remarks: | The following is based
upon my reading of Abdala & Ribeiro, 2000.
This genus has sectorial,
postcanine teeth, and they designate a diet of animal protein. As they're close to the
morphology known from Therioherpeton, a tentative
referral to the same family was made, (p.589).
The fossil came from the Santa Maria Formation which straddles from the Middle to Upper
Triassic, (Ladinian-Carnian), and provides a diverse array of
eucynodonts. The most common are plant-eating
traversodonts, and they probably attracted the attentions of middling to largish
chiniquodont predators, (p.590). Smaller prey fuelled more
diminutive hunters such as this one, (and an increasing range of colleagues). The holotype
was unearthed in what might seem an unusual location; lurking in the collection of a museum.
Actually, many museum specimens hang around patiently awaiting examination.
This is a fragment of lower left jaw, and it contains alveoli
for three incisors, the roots of a
canine and three postcanines. Also identified was
the well preserved crown of a further postcanine, which was caught in the process of
eruption. It was removed for study, (p.591).
Postcanine teeth
The postcanine has a line of four cusps; from front to back these are b-a-c-d. a is the
largest, although it's not that much bigger than c. The three rearmost cusps slant
jauntily backwards towards the throat, perhaps in order to helpfully guide pieces of victims
towards their destination. The root shows no intentions of dividing. The jaw fragment has
a length of about 2.4cm, (p.592), so the complete jaw would've been longer. This animal
was 'large', (in comparison to a mouse). The crown of the tooth manages nearly 5mm in
length.
The authors compared the material with chiniquodontids,
dromatheriids and therioherpetids. In the first instance, the lack of root division
is a similarity. Front chiniq postcanines are simpler constructions though, and the
main cusp is more dominant, (p.593).
Dromatheriids have various styles of postcanine, which reflects the lack of familial
integrity. However, where known, the ramus of the
dentary is lower, and the tooth crowns are narrower. It does share similarities with
Meurthodon gallicus, but that critter had developed
divided roots on its teeth.
"Thus, it is noteworthy that the crown morphology of Charruodon tetracuspidatus
is similar to that of T.[herioherpeton] cargnini in both the number and the relative
development of the cusps. Nevertheless, the latter species differs from the former in
that the cusps do not seem to be recurved, and each root exhibits a longitudinal furrow, a
feature that has been interpreted as an "incipient bifurcation of the root"",
(p.594). (In terms of size, Charruodon was probably a bit smaller than the
previously mentioned Meurthodon, but both were considerably larger than therioherp.)
Anyway, the authors placed it in this family until any further evidence shows up.
Holotype
The holotype, MCP-3934 PV, has resided for years in the collection of the Pontifica
Universidade Católica de Rio Grande do Sul. The specific name refers to the presence of
four cusps on the postcanine.
| Reference: | Abdala & Ribeiro (2000), A new therioherpetid cynodont
from the Santa Maria Formation (Middle Triassic), southern Brazil. Geoversitas: Vol. 22,
(4), p.589-596. | |
| Genus: Diarthrognathus
Crompton, 1958
'two joint jaw'
Family: Pachygelidae Bonaparte, 1980 or perhaps
Tritheledontidae
Remarks: The generic name highlights the fact that this critter was reported as having
both the 'reptilian' (articular-quadrate) and
mammalian (dentary-squamosal) jaw joints. This
conclusion hasn't been accepted by all concerned, (Kemp 2005, p.72). However, the closely
related Pachygenelus certainly has both joints. |
| Species: | Diarthrognathus broomi, Crompton, 1958 |
| Place: | Clarens Formation, Orange Free State |
| Country: | South Africa |
| Age: | Sinemurian / early Pliensbachian, Lower Jurassic |
| Remarks: | The following is based upon my reading of
Gow, 1980.
The first description of Diarthrognathus predates the establishment of the
genus by decades, as it was the work of Broom in 1929. He gave the now type fossil
the alluring name of Ictidosaurian B (p.462). This is part of a skull and much of
an articulated skeleton from Ladybrand, and it now resides in the National Museum,
Bloemfontein.
Crompton then set up the genus nigh on thirty years later. He identified the
typical mammalian jaw joint (the
dentary-squamosal) as being present (p.462), although doubts have been expressed
about the correctness of that; for example, by Gow, 1980 on page 462. No detailed
description was made of the teeth back in the fifties, although one was envisaged on
the basis of a second specimen originally called Ictidosaurian A. Although those
teeth were mentioned in a subsequent study by Crompton (1963), they somehow managed
to remain undescribed until Gow bit the bullet in 1980.
First catch your Diarthrognathus
Gow was interviewing a friend of the type fossil, but it did first require rescue
from imprisonment in a broken block of stone. As that meant losing some areas
preserved as impressions in the matrix, resin copies were made (p.463). Eventually,
it was possible to describe the remains.
Upper postcanines
These teeth number seven (p.474), as is also usually the case for
Pachygenelus, and they appear to be derived
versions of much that sort of dentition. All
positions were represented. However, PC1 was mostly gone. The main cusps are cones
with flat lingual sides. The curve at the rear of the
cusp is narrower than the one at the front, and this gives the impression of a
slight forwards tilt.
A contrast to Pachygenelus concerns the first accessory cusp found with
that genus. It's not present for Diarthrognathus. There's a
cingulum instead, and it's best developed on the
sixth tooth. These postcanines also lack wear facets. While crowns have been
damaged, none of the suffering was inflicted by wear. Evidence of replacement isn't
readily available but, according to the varying heights of the teeth, 1, 3, 5 and 7
are freshly erupted, and this suggests a pattern of alternate replacement as for
Pachygenelus (p.476). Should that require closer explanation, then look at
the entry for that genus.
Lower postcanines
The survivors are limited to the final four of the set. These are larger than their
upper co-workers, and the main cusp is found at the front. A groove separates it
from accessory cusps that follow on the buccal side,
and these diminish in size from front to back. They number up to three. Seen from
above, these teeth are wider than long, and set diagonally in the jaw. Quite how
the uppers and lowers occluded is hard to work out, especially given the lack of
wear facets.
A problem with toothless skeletons
While it's obviously informative to have much of a skeleton available, its comparative
relevance is necessarily limited to other forms that have provided the same body
parts. And, as the most common fossils are teeth and fragments of jaw, it can be a
drastic limitation. Teeth are of great significance when it come to attempting to
unravel internal eucynodont interrelationships,
and that helps explain why some impatience may arise from the delayed appearance of
a description of the dentition.
Additional notes
Two possibly juvenile specimens, which may represent something akin to
Pachygenelus. A fair few webpages give this genus a mention, though
most do little more.
A dentary pictured in Kemp, 2005 has the length
given as five centimetres, (p.73). |
| Reference: | Crompton (1958), The cranial morphology of a new genus and
species of ictidosaurian. Proceedings of the Zoological Society of London 130,
p.183-216. |
| Genus: Elliotherium Sidor
CA & Hancox PJ, 2006
'Elliot beast'
Remarks: The generic name honours the lower Elliot Formation of South Africa, which kindly
come up with this beast. |
| Species: | Elliotherium kersteni Sidor & Hancox, 2006 |
| Place: | lower Elliot Formation, Karoo |
| Country: | South Africa |
| Age: | Norian, Upper Triassic |
| Remarks: | The following is based upon my reading of Sidor and
Hancox, 2006. My thanks go to the kindly sender.
Elliotherium is a tritheledontid in the sense used by Martinelli et, 2005, in which
the family was rooted on the most recent common ancestor of
Riograndia and Pachygenelus. Elliot is among
the more basal wave, being more closely related with
Chaliminia from Brazil than with subsequent South Africans;
Pachygenelus and Diarthrognathus.
There are a number of ancient touches with this 'Elliot beast'. The
postcanines are very numerous and relatively simple
teeth, in that all the uppers have no cingula on the
labial base (p.333). The secondary bony palate at the roof
of the mouth is proportionately short. There are also more obscure points; a smaller
interpterygoid vacuity and a retained vomerine ridge behind the palate. It also happens to
be a relatively large trithe, with a skull length approaching six centimetres.
No place like home
The skull came from the lower reaches of the Elliot Formation in the northern Karoo Basin,
roughly two hundred kilometres northeast of Bloemfontein (p.334). The lower Elliot
corresponds to the Euskelosaurus Range Zone and appears to date from the Norian,
Upper Triassic. Deposition was largely the result of fairly constant river action, whereas
subsequent rocks were formed by more sporadic means in a climate of greater aridity. The
northern Elliot Formation is between 80 to 100 metres thick. It can reach 450 metres in
the south.
Upper jaw
The more complete maxilla is on the right side. This has
the root of a large canine and remains of thirteen
subsequent teeth. As the rear is missing, that's the minimum number of postcanines. In
technical language, that's a hell of a lot. I'm a somewhat abnormal
eucynodont and make do with four postcanines. The joints
of the maxilla with other skull bones are difficult to determine, as the events of the last
215 million years or so haven't treated the fossil all too kindly. Contact with the
lacrimal bone appears to have been near the front of the orbit
(p.335), and the sutre with the jugal was below this opening for the eye.
Teeth
We've established Elliotherium was an enthusiast for
postcanines. As well the thirteen on the right, ten are preserved on the left maxilla.
In comparison to Pachygenelus the teeth are slender which, given
the quantity, they would have to be. None have cingula on
their labial bases. Most are tri-cusped and, in a couple of instances, the central cusp is
very dominant with the others being poorly developed (p.336). Wear facets occur on the
internal face of most the visible teeth, and that indicates good levels of occlusion
between uppers and lowers. Judging on the basis of size, the replacement pattern was
presumably alternate. No information could be determined for the roots.
Skull
The nasals are large bones and form the front of the brain
case. Lacrimals are also large in comparison to earlier
cynodonts. They're triangular in shape and form the anterior part of the orbit. The
jugal of the cheek bone is only partly preserved on the left side, and the
zygomatic arch appears to deepen towards the back. In
later trithes and basal mammals, this arch remained thin
along its course. Elliotherium could be termed transitional in this regard, as the
deepening effect isn't as strong in comparison with more basal cynodonts.
The frontal is relatively small in this head case, and
located between the nasal in front, and the parietal
behind (p.337). The exposure of the frontal is narrower than in other trithes.
Age
This skull is the first trithe recovered from the lower Elliot Formation. All the other
specimens from South Africa and Lesotho date as Lower Jurassic (p.339). While there is
some room for uncertainty, Elliotherium is probably Norian in age. Radiometric
dating of volcanic basalt flows stratigraphically above the Formation has yielded an age
of 183 million years. Consequently, all the Elliot fossils (whether upper or lower) are
older than that.
Holotype
BP1/6106 is a partial skull in the collection of the Bernhard Price Institute for
Paleontological Research, Johannesburg. The specific name honours Mrs Olga Kersten, who
found the fossil on the land of Beatrix Farm, Free State Province. |
| Reference: | Sidor CA & Hancox PJ (2006), Elliotherium kersteni,
a new tritheledontid from the Lower Elliot Formation (Upper Triassic) of South Africa,
Journal of Paleontology, 80(2), p.333-342. |
| Genus: Irajatherium Martinelli
AG, Bonaparte JF, Schultz CL & Rubert R, 2005
'Iraja's beast'
Remarks: The generic name honours the Brazilian invertebrate paleontologist, Professor
Irajá Damiani Pintos. |
| Species: | Irajatherium hernandezi Martinelli AG, Bonaparte JF,
Schultz CL & Rubert R, 2005 |
| Place: | Caturrita Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Carnian or Norian (early), Upper Triassic |
| Remarks: | The following is based upon my reading of Martinelli
et al, 2005. The page numbers below don't (repeat don't) correspond to the publication.
They refer to my differently formatted print, and I'm including them for my own purposes.
This is because I've got a memory like one of those metal utensils with holes in. You know,
thingies.
Irajatherium is referred to the family of Tritheledontidae, but the authors are using
a new definition: "The clade including the more recent common ancestor of
Riograndia and Pachygenelus,
and all its descendants" (p.5 and 'more' should presumably read 'most').
A single specimen was collected during fieldwork at a road cutting eight kilometres west of
Candelaria. Remains included the left maxilla with a
canine, five postcanines
and a further alveolus, two bits of lower jaw, a couple of
limb bones and other indeterminable scraps. Analysis suggests its relatives include
Riograndia, Chaliminia,
Pachygenelus and
Diarthrognathus (p.1). As a bonus, the fossil provides some insight into tooth
replacement.
Iraja's beast
Irajatherium is described as a small trithe (p.2). The partial lower jaw is about
2.5cm long, and that's suggestive of roughly
rat-sized dimensions. Most its postcanine teeth were narrowly built and relatively simple.
The front uppers had a tall cusp A with a small cusp C behind (p.5). The rear ones were wider
possessed two cusps on the lingual side; ie. there was a B
as well as C. There were no cingula.
Several lower teeth are preserved, and these are middle postcanines. An unusual
aspect is a wear facet on the buccal face, as this indicates
the uppers and lowers must've been well aligned.
Upper jaw
The left maxilla is reasonably complete but other skull
areas aren't known (p.6). It houses a canine and five postcanines, with an alveolus
attesting to the original presence of a sixth. The start of the
zygomatic arch is all that remains of the cheek area,
and there's no sign remaining of bone joints. Two foramina for nerves are visible on the
outer side of the jaw, and the scheme is similar to that known from Pachygenelus,
Diarthrognathus and Morganucodon, a
mammal (p.7). More basal carnivorous eucynodonts had
smaller foramina.
A groove by the canine is an accommodation area for the lower canine. This is unusual for
trithes, as they generally had small lowers. It must've been rather large in this case.
Lower jaw
The left of the dentary is partly represented by a natural
cast (p.8). There's a high coronoid process. A medial ridge shows the presence of a
postdentary trough on the internal side, and this has a wide, deep groove below it, which
was the storage space for postdentary bones. A further fragment of bone with two teeth
contains part of the Meckelian groove. It runs
parallel with the lower border of the bone.
The trough and ridge are typical of non-mammalian eucynodonts and Morganucodon, and
the position of the Meckelian groove is in line with most non-mammalian cynodonts and
Sinoconodon. This lowly position is a
basal eucynodont characteristic. The situation was more varied
among early mammals. It reached the lower margin of the
jaw in some (eg. Gobiconodon), but was
set at a higher level in others (eg. morganucodontids
and docodonts).
Upper teeth
The canine and final postcanine
weren't fully erupted (p.9). The canine is a conical shape, and its alveolus indicates a
large tooth. A lengthy diastema divides it from the rear
choppers.
The postcanines are narrow and bereft of any cingula.
They increase in size from front to back, with PC1 being small and single-cusped. It was
probably not fully erupted. The second postcanine is similar but larger. As its root has
been pushed high up, it was probably experiencing the earlier stages of replacement. PC3
has two cusps, with the largest at the front. This curves slightly inwards. The following
tooth is poorly preserved but broadly similar, and PC5 must've had pressing business
elsewhere, as its alveolus is vacant. PC6 was newly
emerged. Cusp A is high and towards the buccal side of the
crown. Two smaller cusps occupy the lingual portion. In
contrast to the other postcanines, this tooth is triangular from the
occlusal perspective. Rather than being narrow, the
maximum width is similar to the length. This is effectively a different type of tooth.
Most of the postcanines are reasonably reminiscent of the earlier
Chiniquodon, but the final one is a relatively simple version of a
tritheledontid tooth. The simplicity concerns the lack of a buccal cingulum.
Lower teeth
Three postcanines are preserved and the original number is unknown (p.10). The foremost is
on the natural cast. This tooth is small and two-cusped, with the front one being much the
highest of the pair. A couple of teeth adorn a fragment of bone. These are narrow and
contain evidence of clear wear facets on the buccal face.
The first of these has a line of four cusps which become smaller from front to rear. Traces
of four cusps are also on the remains of the last crown, but breakage has removed details.
Two small additional cusps are found on the lingual base.
The roots of both these more posterior teeth have incipiently bifurcated roots.
The lower postcanines are similar to those known from
Pachygenelus, but the lack of a lingual cingulum is a clear difference.
Limbs
An arm thoughtfully provided a humerus and a leg chipped in
with a femur. Details of the humerus suggest the owner may
have enjoyed digging. For example, it's a fairly broad bone and has space and supporting
furnishings for some well-developed muscles. How committed a digger the owner might have
been isn't known, but burrowing abilities wouldn't be surprising. The upper arm could
perhaps be more instructive, but it declined to be interviewed.
Trithes
The authors' particular usage of Tritheledontidae has Riograndia
as the most basal known member followed by
Chaliminia. (In 2006, other researchers established
Elliotherium from South Africa and, following the same definition
of the family, placed it as a close relative of Chaliminia.) The other animals
included were Irajatherium, Pachygenelus and Diarthrognathus. No
opinion was offered concerning the placement of Tritheledon.
Their analysis rated Iraja's beast as being more primitive than both P. and D..
Also not included were Brasilitherium and
Brasilodon. Both are viewed as being more closely related
with mammals.
Tooth replacement
As is often the case for non-mammalian cynodonts, the
replacement pattern of teeth seems to have been alternate (p.20). The first upper postcanine
postdates the eruption of PC2. As two types of postcanine are present, it could be that
newer teeth differ in morphology from simpler predecessors. However, the similarity among
the front postcanines indicates nothing of the sort and, generally, replacements tend to be
either similar or simpler. For example, adult postcanines of
Thrinaxodon from the Lower Triassic are less complex than juvenile ones. This is
also common in mammalian mouths.
Holotype
UFRGS-PV 0599T consists of part of a maxilla with teeth,
bits of dentary, a couple of limb bones (a
humerus and femur) and other
bits and pieces. It's in the collection of the Universidade Federal do Rio Grande do Sul,
and the specific name honours Daniel Henández, the discoverer. |
| Reference: | Martinelli et al (2005), A new tritheledontid (Therapsida,
Eucynodontia) from the Late Triassic of Rio Grande do Sul (Brazil) and its phylogenetic
relationships amon carnivorous non-mammalian cynodonts, Ameghiniana, 42(1), p.191-208. |
| Genus: Lycorhinus, Haughton S, 1924
Remarks: Sidor & Hancox, 2006 (p.333) report this genus was described as a trithe (an
ictidosaur) from South Africa. However, the lower jaw dropped in surprise. Had any more
of the head been available, it would have been shaken in disbelief. The animal correctly
considered itself to be an ornithischian dinosaur,
and this explained its obvious aversion to fresh meat. It was a case of mistaken
identity. |
| Species: | Lycorhinus augstidens, Haughton S, 1924 |
| Place: | Karoo Basin |
| Country: | South Africa |
| Age: | |
| Remarks: | |
| Reference: | Haughton S (1924) The fauna and stratigraphy of the Stromberg
Series, Annals of the South African Museum, 12, p.323-497. |
| Genus:
Meurthodon Sigogneau-Russell D & Hahn G, 1994
'Meuthe tooth'
Family: "Therioherpetidae"? Bonaparte & Barberena, 1975
Remarks: The Meuthe is a river located near to the fossil locality. |
| Species: | Meurthodon gallicus Sigogneau-Russell & Hahn G, 1994 |
| Place: | Saint-Nicolas-de-Point |
| Country: | France |
| Age: | Norian (late) - Rhaetian, Upper Triassic |
| Remarks: |
Further M. teeth from this site was reported by Godefroit P & Battail B in 1997. Similarities were noted with remains from both Therioherpeton and the basal mammal, Sinoconodon. However, at least some of M.'s teeth were double-rooted.
These choppers look quite exciting. They're longish and narrow in shape with four cusps.
The front point's generally the smallest and is usually aligned more-or-less vertically,
though it sometimes tilts back a bit. The second's always the largest, the third the next
biggest, with the fourth usually outgrowing the first, (though not always). The latter
three curve backwards. In outline, it can look vaguely like three jauntily hatted dwarfs
behind a hedge, lining up to confront their astonished smaller colleague.
The largest cusp is, as said, the second; cusp b. That's an unusual feature shared
with the more recently described Deccanodon
from Carnian aged deposits in India. However, that needn't indicate particular
affinities. They differ in other ways, and notably in the degree of incipient root
division. It's more strongly pronounced for this later European critter.
Affinities unclear
As is usual for dromatheriids, (which maybe a better
home for this taxon), there's not much difference in shape
between upper and lower dentition, though this is also
true for the further advanced Sinoconodon
(Mammaliaformes), which is described by Godefroit & Battail 1979 (p.584) thus:
Sinocondon rigneyi "is now clearly recognized as a true
mammal, forming the sister-group of a monophyletic taxon
that includes all the other mammals..."
Whether it's a 'true mammal' naturally depends upon the definition used. I confess,
it doesn't seem clear to me! I think I could compromise with 'a very nearly a true
mammal...'
Overall: "the postcanine teeth of Meurthdon
present a mosaic of plesiomorphic (low development of
cingular elements) and apomorphic (better separated roots,
wear facets, ? contacts between adjacent postcanines) characters. As the taxon is
currently only known by its postcanine teeth, it is not possible to decide whether
Meurthodon is a very advanced cynodont or a true early mammal. Waiting for further
evidence, this genus is provisionally and questionably classified with the Dromatheriidae,
as suggested by Hahn et al. (1994). This seems the most conservative course, in the
present state of knowledge", (Godefroit & Battail 1997, p.586)
In the light of that, perhaps I should relocate it slightly. Then again, all members of
"Therioherpetidae" are sometimes referred to
Dromatheriidae.
Update, February 2011
I must've been a very well-behaved fellow last year as Father Christmas sent a copy of
'In the Shadow of the Dinosaurs' down my chimney, and the on page 207, whereas the
formal description is in an appendix on pages 212 and 213.
The authors describe the crown as bearing four cusps in an asymmetrical arrangement, with
the second of them being the largest. Their are two roots which are clearly divided
from just below the crown. That suite of characters is closely matched by
Therioherpeton from South America although, for that
genus, the root division is somewhat less distinct thanks to a connection provided by a
thin sheet of dentine.
Holotype
The type fossil, SNP-1-W, presently works at the Muséum National d'Histoire Naturelle in
Paris, and the specific name celebrates the Roman Province of Gallia which, today, some
modernists insist on calling France. Why these people can't leave the names of places
alone is beyond my understanding. Bah! It's political correctness rearing its empty and
ugly head again. The Franks were immigrants, for goodness sakes! |
| Reference: | Sigogneau-Russell & Hahn (1994), Upper Triassic
microvertebrates from Central Europe, p.197-213 in Fraser & Sues (eds.) In the Shadow
of the Dinosaurs: Early Mesozoic Tetrapods, Cambridge University Press, Cambridge. |
| Genus: Minicynodon
Bonaparte JF, Schultz CL, Soares MB & Martinelli AG, 2010
'Mini cynodont'
Family: Brasilodontidae Bonaparte JF, Matinelli AG & Schultz CL, 2005
Remarks: "El cranéo mide sólo 23mm de largo total, representando el cranéo más pequeno do
cinodonte no mamaliano conocido hasta el momento" (p. 242). I don't happen to read
Spanish, but I think that refers to a skull with a length of 2.3cm from what is presently
the closest known cynodont relative of Mammalia. In any event, it'll be interesting to
see how this one pans out in future cladistic studies. The authors, who were describing
various finds from a locality, don't present such an analysis.
A helpful soul in Lisbon informs me this Brazilian paper is written in Spanish rather than
Portuguese. |
| Species: | Minicynodon maieri Bonaparte JF, Schultz CL,
Soares MB & Martinelli AG, 2010 |
| Place: | Caturrita Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Upper Triassic |
| Remarks: | From what I can follow of the paper, the authors
conclude this a small individual, but not a juvenile member of an already established
genus. Therefore, they felt obliged to establish a new one.
One of its charming features is reported as a secondary jaw-skull joint. As well as the
usual "non-mammalian" articular-quadrate joint
there's a second articulation between part of the dentary and the quadrate (cuadrado).
This feature hasn't been observed on other brasiliodontids. It also contrasts to what's
known from the earlier cynodont Probainognathus
and later basal mammals. Probaino has a secondary joint
involving the surangular and the squamosal whereas, for mammals, it's the primary
dentary-squamosal.
cynodont
Holotype
UFRGS-PV-1030-1 housed at the Universidade Federal do Rio Grande do Sol, Porto Alegro.
The specific name honours a Tübingen based researcher, Wolfgang Maier. |
| Reference: | Bonaparte JF, Schultz CL, Soares MB & Martinelli AG (2010),
La Fauna Local de Faxinal do Soturno, Triasico Tardio de Rio Grande do Sul, Brasil, Rev.
bras. Paleontol., 13(3), p.233-246. |
| Genus: Mitredon Shapiro MD &
Jenkins FA, 2001 |
| Species: | Mitredon cromptoni Shapiro MD & Jenkins FA,
2001 |
| Place: | Fleming Fjord Formation |
| Country: | Greenland |
| Age: | Upper Triassic |
| Remarks: | The abstract reportedly states:
"A new genus and species of cynodont from the Upper Triassic Fleming Fjord Formation
of East Greenland possesses double-rooted postcanine
teeth and a nonalternate pattern of tooth replacement. The specimen represents an addition
to the known diversity of Early Mesozoic taxa with
multirooted dentitions (
tritylodontids, Sinocondon sp.,
haramiyids,
morganucodontids, Meurthodon gallicus), and
casts doubt on traditional interpretations of the interdependency of reduced tooth
replacement patterns and teeth with multiple roots."
(With thanks to Ben Creisler for posting notification on the DML.) Further info would be
welcome.
Before the description was published Bonaparte et al, 2001 (p.631) mentioned "a
very derived pachygenelid" from the Upper Triassic. Their list of references
contians: Shapiro & Jenkins (in press), A new cynodont from the Greenlandic Triassic:
dental succession and multiple roots. In: A symposium in honor of Fuzz Crompton. Harvard
University Press, Cambridge. I'm daring to assume this refers to the same fossil. |
| Reference: | Shapiro & Jenkins (2001), A cynodont from the Upper
Triassic of East Greenland: Tooth replacement and double-rootedness. Bulletin of the Museum
of Comparative Zoology, 156(1), p.49-58. |
| Genus: Pachygenelus
Watson, 1913
Aka: Pachygenelius
Family: Pachygenelidae Bonaparte, 1980 or perhaps
Tritheledontidae
The teeth of this genus feature enamel arranged into prisms, which helps strengthen them.
The precise arrangement is termed plesiomorphic
prismatic enamel. Apart from Pachygenelus, prismatic enamel in any form has only
been identified amongst mammals, (Wood et al 1999, p.178).
Kemp, 2005 (p.72) mentions further mammalian or very-near-mammalian aspects of the teeth.
Wear facets on the lingual sides of the upper and external
faces of the lower postcanines, show these teeth were
well-alinged. Uppers and lowers occluded. However, as the facets are not all that well
matched, the occlusion wasn't as close as in mammals.
Not much is yet known of the skeleton, but some bones have been described, (p.74). From
the limbs, the humerus and
femur are very similar to their equivalents from mammalian
Morganucodon. Further material is apparently
available but not yet described. |
| Species: | Pachygenelus monus Watson DMS, 1913 |
| Place: | Red Beds and Cave Sandstone (Middle and Upper
Elliot Formation), Orange Free State |
| Country: | South Africa and Lesotho |
| Age: | Hettangian to Sinemurian, Lower Jurassic |
| Remarks: | The first block of the following is based
upon my reading of Gow, 1980. Then come notes based on other sources, and
there will undoubtedly be some overlap involved.
A number of specimens have turned up over the years (p.401), and they came from
individuals of various sizes and ages. Skull lengths begin at two centimetres and
range up to a fairly impressive ten (p.464). The latter applies only for the type
fossil, which happens to be considerably larger than the others. (It's much bigger
than I expected.) This relatively generous collection allows soundly based
conclusions to be drawn concerning maturation; aka growing up. Gow described the
dentitions from five volunteers for the species
donated by both adults and kids. Rather than taking advantage of each description,
I'll limit my prose to one and his more generalized observations. The latter
obviously refer to information from all the specimens under interrogation.
SAM K1329
This particular SAM is an inmate of the South African Museum in Cape Town, and it's
from the middle of the size range. Its owner was an adult. The animal took fine
care of its teeth. Although a couple of postcanines had fallen out, it kept them
securely in the matrix of rock around the fossil, and left no possible doubt about
where they fitted.
Incisors and
canines
The number of incisors had been reduced down to two per side, and this number's low
when compared to basal mammals. These lower teeth are
procumbent, and wear is concentrated on their tips and
lingual sides. The upper counterparts, presumably also a pair, pointed downwards
and were somewhat curved.
The canines take a different approach. The upper is angled a bit forward while the
lower is vertical. When in action, the lower worked in front of the upper, and
somewhat labial from it. This is a mammalian
habit (p.465). Also of interest is an absentee. Generally, non-mammalian
cynodonts have pits in the palate bone of the
upper mouth, and they're in front and lingual of the upper canine. These were sheaths
for storing the lower. When asked about this, one skull looked mystified and shook
its head. The owner convincingly denied having any such pits about its personage.
It sneered at chiniquodontids for
possessing such features, and made disparaging comments regarding oldies being so
uncool.
Postcanines
This specimen has a formula of seven postcanine teeth per jaw half for both up and
down, but this number was somewhat variable. In contrast to
mammals, tooth replacement was an on-going process through the lifetime. Another
specimen, for example, has eight postcanines on a jaw of a larger length. Replacement
occurred in alternating waves: tooth 1, 3, 5, 7, 2, 4, 6 and so on. The lowers are
bigger than the uppers, and the build of the two teams is different. Furthermore,
replacement teeth aren't carbon copies of the previous generation. The crowns can
differ, with more complex ones eventually congregating to the rear, nearest the
point of maximum bite power. All teeth appear to be single-rooted.
There's a further feature which is audacious for non-mammalian cynodonts. Despite
the serial replacement habit, uppers and lowers were directly aligned, and that allowed
for the formation of clear wear facets.
Upper postcanines
Postcanine number one is one of the simpler teeth; a main cusp with small additional
ones fore and aft (p.466). There's an attempt at a
cingulum on the buccal side, but it's half-hearted
and gives up completely halfway along. The tip and
lingual face of the tooth are extensively worn. Tooth number two is much the
same except for being larger and more worn. Wear also occurs on the rear accessory
cusp. This postcanine is older and its replacement was underway. The tip of a
younger tooth was pushing up from directly below, and its intentions are revealed by
convenient damage to the bone. The third postcanine conforms to most themes; broadly
similar and still bigger. The rear accessory cusp is more pronounced. While there's
wear on the crown, this is interrupted by a fresh patch of enamel, and this meant
that PC3 is a younger tooth than PC2.
Should anybody feel like predicting that PC4 was an older tooth, then please accept
my congratulations on being interestingly wrong. It'd just been replaced; young,
unworn and recently delivered by the manufacturers. The buccal cingulum is stronger
with this tooth, and ran nearly to the rear. The front accessory cusp is also
stronger and, for the first time along the postcanine series, a cutting edge is clear
to the rear of the main cusp. PC5 is a simpler tooth with its features more in line
with the first three. The cingulum gives up halfway, and wear is extensive. Much of
the main cusp is absent. The sixth in the team reverts to the characters of number
four, and is also a fresh arrival. Finally, the seventh upper has some crenulations
(little riffles and ruffles) on its continual cingulum, and is elongated in
comparison to the sixth.
Lower Postcanines
These are narrow teeth with a lingual
cingulum, and this increases in strength along the
row. They also differ from the uppers by having the main cusp at or very near the
front of the crown, whereas their colleagues keep their main cusps nearer the
centre. Furthermore, the lower gang is more uniform.
The five foremost have a main cusp which curves a bit inwards, and one smaller cusp
behind with, in the case of the fifth, a bump at the rear. That has cuspy ambitions
but of a fairly hopeless nature. The cingulum hugs along for around two-thirds of
the internal length, with this feature attaining the whole length for pc5 (p.467).
On the final two postcanines, the equivalent of that aforementioned bump at the back
builds a more respectable accessory cusp than on pc5, the cingulum sharpens at front
into a cusp-like structure and, as it wraps around the rear of the crown, it adds a
further one there as well. Seen from the buccal
perspective, the profile of pc7 is vaguely like the hand of a five-fingered alien,
albeit one with weirdly sized and strangely stubby fingers. Despite this additional
complexity, those teeth are still only single-rooted and, in contrast to early
mammals, there's no obvious demarcation between the root and the crown. No bulge
attests to whence one finishes and the other begins.
The crowns of pc2, 4 and 6 are worn; strongest on 4 and lightest on 6. Numbers 3
and 5 are unworn, and pc7 isn't yet fully erupted and, sadly, nor will it ever be.
This pattern is in accordance with the alternate replacement policy popular with
such critters.
The other specimens
Gow is then kind enough to offer his readers a guided tour of four further specimens,
which were generously supplied by animals of various ages. One is the larger and
older individual with eight postcanines. Of the ones sufficiently well preserved,
upper PCs 5, 6 and 7 have the buccal cingulum continuing for the whole length in each
case, and that indicates it strengthened with advancing age (p.468). A lower jaw
has the remnants of seven postcanine teeth, but there's room for an eighth between
the last and the coronoid bone (p.469). These teeth are more tightly packed than
on another specimen.
A summary of generalities
The most usual number of postcanines is seven per side but, due to dental comings
and goings, more can sometimes be present. Upper postcanines (p.474) are dominated
by a fat, centrally placed cusp. The lingual face is flat. There was an alternate
replacement system as well modelled by a number of specimens. Replacements emerge in
the jaw directly above the oldies and, after eruption, they shift into a more lingual
position.
Lowers are larger and narrower teeth with the main cusp to the front, and the buccal
surface is even. The cingulum is lingual rather than buccal. Replacements erupt
furiously directly below the older teeth, and rudely evict them.
Holotype
Gow didn't specify the catalogue number of the type fossil (his descriptions were of
further specimens), but it's the front half of a lower right mandible. This preserved
the roots for two incisors, a canine and remains of five postcanines.
Abdala, 2007 does give the type fossil (p.613). It's BMNH R4091, and may be fed at
the Natural History Museum in London.
Additional notes
The teeth of what many authors call tritheledontids,
(pachygenlids to a minority), are most fully known from Pachygenelus. Kemp, 2005
(p.74) gives a brief outline. Both lower and upper jaws have two
incisors per side. The
canines are coordinated as in mammals, (and in contrast to non-mammals). The
lower functions against the outer-front part of the upper, rather than its inner side.
Postcanines
There are generally seven postcanines on each jaw, and the roots
are incipiently divided. The upper specimens are round from the
occlusal perspective, and there's a single main cusp. Smaller cusps are found both to
the front and the rear. The lower colleagues are larger and narrower teeth. The biggest
cusp is at the front, and it's followed by a line of up to three smaller ones. The enamel
is thin where the teeth occlude, and quickly eroded down to leave useful, sharp enamelized
edges for cutting.
The length of a lower jas is around three centimetres, (p.73).
Several studies have reported significant wear on the incisors
and canines of Pachygenelus, including Shubin et al,
1991. From Luo 1994, (p.111): "Because the teeth must have functioned long enough for
the wear to have developed, these well-developed wear facets of Pachygenelus suggest
that the functional life of the individual teeth must have been quite long relative to the
life span of the animal. This suggests that the tooth replacement rates would have been
slow by comparison with other cynodonts (excluding
tritylodontids), which lack any evidence for slow replacement.".
Specialised
Sidor and Hancox, 2006 point to a snag with this genus. Despite descriptions not yet
having been completed, it's nevertheless the most fully known trithe (p.339). In some
regards, it happens to be a rather atypical representative. For example, the skull boasts
of an enlarged and rounded interpteryoid vacuity (a hole with a complex name); the first
upper incisor was disposed of by its ancestors, leaving
part of the premaxilla toothless (p.340); the first
lower incisor is enlarged and procumbently orientated; labial
cingula are well developed on upper
postcanines; and lower postcanines possess large cusps
at the front with progressively smaller ones behind. |
| Reference: | Watson (1913), On a new cynodont from the Stromberg.
Geological Magazine, 10, p.145-148. |
| Species: | ? Pachygenelus milleri Chatterjee S, 1983 |
| Place: | Dockum Formation, Texas |
| Country: | USA |
| Age: | Upper Triassic |
| Remarks: | Shubin et al (1991) regarded this as doubtful.
They found that it lacked several diagnostic cynodont characters. The opinion of the author
obviously differed. He found it so similar to P. monus, that he erected a new
species for it in the same genus.
Fishy
Sidor & Hancox, 2006 (p.334) report that Hopson has drastic doubts, and views the
fossil as probably part of some kind of fish. |
| Reference: | Chatterjee (1983), An ictidosaur fossil from North America.
Science 220, p.1151-1153. |
| Species: | Pachygenelus cf. monus Shubin N., Crompton AW, Sues HD
& Olsen P, 1991 |
| Place: | McCoy Brook Formation, Fundy Bay, Nova Scotia |
| Country: | Canada |
| Age: | Hettangian, Lower Jurassic |
| Remarks: |
Mr Ken Adams, of the Fundy Geological Museum, informs me that
Pachygenelus is, as yet, "the only Tritheledontid listed as part of the McCoy
Brook (Jurassic) fauna," (April, 2001). The species may be monus, but the
available material does not allow a precise diagnosis.
The following is based upon my reading of Shubin et al, 1991.
Pachygenelus usually associated with the Karoo Basin
of Southern Africa, but further fossils have turned up in Nova Scotia, (p.1063). It's one
of several Lower Jurassic eucynodonts known to have
been globetrotters, with others including
Oligokyphus and Morganucodon. As
much of the global supply of land was still united in the megacontinent of Pangaea,
apparently surprising wide geographical ranges are mainly illusions caused by subsequent
tectonic developments. They're not surprises in the paleogeographic circumstances.
Trithe
The authors follow the usual interpretation by regarding Pachygenelus as a member
of Tritheledontidae. An alternative view favours
Pachygenelidae, and involves strong doubts about Tritheledon
being closely related. All sides agree this particular genus comprises small insectivores
which were very mammal-like indeed. Among other features in common with
mammals are: tooth enamel arranged in prisms (albeit in a
basal form); a buccal
cingulum on upper
postcanine teeth; no postorbital bar in the skull, so that the
orbit and temporal fenestra ran into each other; the loss of the postfrontal bone of
the skull; the extension of the bony palate to the level of the final postcanines; and the
presence of the mammalian jaw joint (
dentary-squamosal).
Location and remains
The fossils came from two strata of the McCoy Brook Formation, which is the youngest of the
five units making up the Fundy Group. The entire Group reaches a thickness of about 1,000
metres, and was deposited from the Middle Triassic until the Lower Jurassic. A
Hettangian age for the McCoy Brook fauna is supported by radiometric information and studies
of pollen and footprints. Further evidence is provided by the presence of
vertebrates known otherwise only from similarly aged
remains; eg. Pachygenelus.
Finds are fragmentary but well preserved. At the time of publication, the genus was
represented in the locality by parts of two premaxillae,
ten maxillae and six dentaries.
As they couldn't be distinguished from P. monus of Southern Africa, they appear to
be at least very close relatives.
Tooth implantation, replacements and roots
The jaw parts contain information on tooth replacement and structure. Overall, these
characteristics reflect non-mammalian traditionalists such as Thrinaxodon. The jaw
has small pits ready for replacement teeth. The dentition
isn't diphyodont. Old teeth are attached to the
alveoli with a small ring of bone until newly erupting ones
force them out.
The postcanines of basal mammals generally have two distinct roots; one fore and the other
aft. With Pachygenelus, the single root is incipiently divided.
Mammalian traits
The tooth enamel is similarly organised as in
morganucodontids, (Morganucodon and -if so regarded-
Megazostrodon), which is a contrast to other
non-mammalian eucynodonts. (As the description was published in 1991, I'm not sure whether
the following is still strictly valid: "This pattern is not seen in any other
non-mammalian cynodont.")
Also evident are several characters concerning occlusion of upper and lower teeth, although
Pachygenelus hadn't achieved the more effective alignment of postcanine cusps known
from its contemporary mammals. Uppers and lowers did occlude unilaterally, but wear is
spread along the whole tooth face; lingual for uppers and
buccal for lowers (p.1064). It isn't organized into
distinctive facets. To a minor degree, this may be because tooth replacement seems to have
continued throughout life. Therefore, each individual tooth did less work. However, it's
largely a consequence of the comparative unsophistication.
The authors note that this pattern of lingual or buccal wear isn't known from
tritylodontids, and that suggests unilateral
occlusion didn't occur in those animals.
Some of the neighbours
Other McCoy vertebrates also turn up in fossil faunas which are now far apart. A
lizard-like sphenodontid, Clevosaurus, is found in both Nova Scotia and Lower
Jurassic or possibly Upper Triassic fissure fillings in England. Close relatives were
around in the Lower Jurassic Forest Sandstone of Zimbabwe and
the Lufeng Formation, China. Protosuchus is a protosuchid crocodyliform
shared with Southwestern USA and the upper Stromberg Group of
Karoo. Dino remains included bits of an anchisaurid prosauropod and ornithischian
teeth. The latter are very similar to Lesothosaurus. This cosmopolitan character
is also reflected in the fossil fauna. |
| Reference: | Shubin et al (1991), New fossil evidence on the sister-group of
mammals and Early Mesozoic faunal distributions. Science 251, p.1063-1065. |
| Genus: Pattsia Lees PM &
Mills R, 1983
Family: Pachygenelidae Bonaparte, 1980 or perhaps
Tritheledontidae
Remarks: The material this genus is based upon is sparse and not overly informative.
It may well belong with some other known (or unknown) trithe genus. In any event, the
generic name honurs Bryan Patterson who, in turn, honours his nickname of Pat. |
| Species: | Pattsia likhoelensis Lees & Mills, 1983 |
| Place: | Upper Elliot Formation |
| Country: | Lesotho |
| Age: | Hettangian - Sinemurian, Lower Jurassic |
| Remarks: | The following is based largely upon my reading
of Lees & Mills, 1983. My copy happens to be incomplete. It runs out on page 177.
Back in 1968, a team of researchers from London's University College could think of
nothing in particular to do, so they went fossil hunting in Lesotho (p.171). Among the
souvenirs they returned with were photos, postcards, leaflets and some bucketsful of
matrix that may have contained fossils. Oh, and they also had some more obviously
recognisable specimens in their luggage. Eventually, Patricia Lees had the fortune or
misfortune to search through some of that matrix. Whilst so occupied, she happened upon
a roughly centimetre long fragment of fossilized bone. That's the only known remains of
Pattsia, and it's not outrageously generous with information.
Naturally, the limited nature of the remains can only permit a very limited diagnosis,
and calling it one of questionable utility would be stretching the use of language into,
at the least, the realms of extremely diplomatic diplomacy. The sort of language in which
a declaration of all out war might be made by wishing the other party a pleasant morning.
To summarize, terming this genus as somewhat dubious would be overly polite.
Still, there was once a small animal attached to the jaw fragment, and it was presumably
a non-mammalian cynodont. It had an upper
canine, something like seven
postcanines, and doubtlessly the rest of a head and a delightful body. Somebody must've
loved it.
Teeth, remains thereof
Available for discussion is a partial maxilla with remains
of a canine and perhaps seven postcanine teeth or erstwhile tooth positions. Or, as
stated in the paragraph after the diagnosis, possibly eight postcanines! Tooth lengths
that could be measured are (according to the possible positions as given in the table).
Only uppers: Canine 1.56mm; PC4 0.96; PC5 1.52; PC6 1.38.
The authors readily state they're not overly confident that the positional numbers they
used are necessarily correct.
The rear four or five postcanines have a main cusp with additional cuspules positioned
both before and after it. At least, those that are well preserved do.
Canine
Remains of the first available tooth, interpreted as a canine, consist only of the root.
It's been displaced since death and very possibly turned 90°.
Postcanines
The postcanine count given in the paper is inconsistent. Tbe uncertainty as to the
actual number presumably reflects the state of preservation, but it's also conceivable
to me that ontogenic factors may play some role; ie. aspects of an animal's body changing
with advancing biological age. Behind the canine is an apparently toothless area of
jaw. However, flattened surfaces of perhaps two roots seem to be present. The former
crowns have been sliced off at or a bit below the alveolar level, and those could be
front postcanine positions that were routinely dispensed with as part of the owner's
normal mode of growing up. As recognition is less than clear cut, the first tooth now
on dental parade tentatively gets the appellation of PC3 or, at least, what's left of it
does. That amounts to a circular root and the rear of the crown.
The next postcanine is more cooperative. It features a main cusp and two much smaller
cuspules, one to the front and a smaller one at the rear. These cuspules are at either
end of a crenulated cingulum enriching the geography of
the buccal side of the crown. No sign of a cingulum occurs
lingually. There's but a single root with no visible
propensity whatsoever to division. The length of this tooth is only moderately greater
than its width.
The following tooth is damaged. In the sketch, accompanying the description, it's
obviously heavily cracked, and that leaves me wondering as to the whether the given
length (nearly twice its width) may not be exaggerated, something the authors don't
mention. Be that as it may, the better preserved PC6 has a length:width ratio of 150%.
The best preserved postcanine was PC7 (p.175), with the word "was" being unfortunately
apt. It was tri-cusped, undamaged, unworn and rootless. Apparently, it hadn't gotten
around to eruption or, indeed, full development. Sadly, efforts to extract it from the
matrix for closer examination resulted in the loss of the postcanine. It was smaller
than the preceding tooth, and that could indicated it was the last member of the line.
Holotype
The type fossil, UC C146, is a fragment of upper jaw studying at the University College,
London. The specific name refers to the locality of Likhoele.
Additional notes
Knoll 2005 (p.85) briefly mentions this genus. It's based on a damaged
maxilla. One interpretation teamed it up with early
mammals as a member of Eozostrodontidae (aka
Morganucodontidae). However, more probably it's a trithe; perhaps synonymous with
either Pachygenelus or (less likely)
Tritheledon. |
| Reference: | Lees & Mills (1983), A quasi-mammal from Lesotho, Acta
Palaeontologica Polonica 28, p.171-180. |
| Genus: Protheriodon
Bonaparte JF, Soares MB & Schultz CL 2006
'before beast tooth' |
| Species: | Protheriodon estudianti Bonaparte JF,
Soares MB & Schultz CL 2006 |
| Place: | Southern Brazil |
| Country: | Brazil |
| Age: | Middle Triassic |
| Remarks: | My information is presently limited to the
name, authors and citation. It may be of no direct relevance at all, but there
was reported to be a Middle Jurassic brasilodontid awaiting publication, and there's
no obvious inconsistency between that possibility and the title of the study. Of
course, that could be an uncanny coincidence. Information would be welcome. |
| Reference: | Bonaparte et al (2006), A new non-mammalian cynodont
from the Middle Triassic of southern Brazil and its implications for the ancestry of
mammals, in Harris HD, Lucas SG, Spielmann JA, Lockley MG, Milner ARC &
Kirkland JL (eds.), The Triassic-Jurassic terrestrial transition, New Mexico Museum
of Natural History & Science, Bulletin, 37, p.599-607. |
| Genus: Prozostrodon
Bonaparte JF & Barberena MC 2001
Aka: Prozoostrodon; Thrinaxodon (partly).
'before girdle tooth' |
| Species: | Prozostrodon brasiliensis (Barberena et al. 1987)
Bonaparte JF & Barberena MC 2001 |
| Aka: | Thrinaxodon brasiliensis Barberena MC, Bonaparte JF
& Teixeira AMS, 1987 |
| Place: | Santa Maria Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Carnian, Upper Triassic |
| Remarks: | This material was first described as a species of
Thrinaxodon, which is an earlier form of proto-
eucynodont from South Africa. It received a mention and a small illustration in
Schultz, Scherer & Barberena, 2000 (p.497): "This specimen is being re-studied by
Bonaparte and Barberena (in prep.), which interpret it now as an ictidosaur
(Prozoostrodon)." For some reason, the in press publication they included in
the references of the 2000 paper, didn't turn out as expected, and the planned generic name
was given an extraneous 'o'.
(With thanks to Max Cardoso Langer.)
Teeth
Up to five upper and four lower incisors are present for
each side, (Abdala & Giannini 2002, p.1157). This is a bit odd, as the ancestral
condition, (thrinaxodontidae plus eucynodont level), seems to be four uppers and three in
the dentary. However, a couple of these teeth are
extremely small, which suggests older gnashers were being replaced by newer ones, (p.1159).
The postcanine dentition shows up to seven uppers and ten
lowers, though this varies on each side, and also involves newly erupted teeth, (p.1060).
Judging by the photos, it was a reasonably sized critter with a lower jaw of six cm or so
in length. The canine looks impressive; a stabber with
about one cm exposed. I wouldn't want to be bitten by it.
Relationships
The authors briefly discuss similarities to Thrinaxodon from South Africa and
conclude (p.1160): "On the one hand, its postcanines
are similar to those of T. liorhinus and thus to
morganucodontids (Crompton and Jenkins 1968), and
on the other hand, it shares synapomorphies, such as
the extended osseous palate (Text-fig. 8B), with late eucynodonts."
Holotype
The type fossil (UFRGS PV 248T) is a resident in the collection of the Universidade Federal
de Rio Grande do Sul, Porto Alegre, Brazil, (Abdala & Giannini 2002, p.1153). It's
known from a fragmentary skull, the lower jaws and some
postcranial material, (p.1157), and was once referred to
Chiniquodontidae.
Additionally
A bit more information comes from Kemp, 2005 (p.74). This animal is larger than most in
this directory, and also more primitive. A big rat-sized seven centimetre skull compares
with the upper range for Probainognathus.
The absence of a postorbital bar in the skull is nevertheless a derived touch, as is the
strong articular process of the dentary. Whether this formed a contact with the squamosal
of the skull is unknown. A few bits of skeleton are also known.
It's toothier than critters such as Pachygenelus
although, (as mentioned by Abdala & Giannini but not in Kemp), some may be in the
process of replacement. The Upper postcanines are adorned with a line of up to four cusps.
For the lowers, the ones at the back are the most complicated, in that they have a small
cusp at the fron, a main cusp and two more behind.
On adding this info, I found my writing was previously far from clear. Hopefully the
revised version is an improvement. |
| References: | Barberena et al (1997), Thrinaxodon brasiliensis sp.
nov., a primeira ocorrencia de cinodontes galessauros para o Triássico do Rio Grande do
Sul. Anais do X Congresso Brasileiro de Paleontologia, 1, p.67-74. |
| Bonaparte & Barberena (2001), On two advanced carnivorous
cynodonts from the Late Triassic of southern Brazil. Bull. Mus. Comp. Zool., 156, p.59-80. |
| Riograndia Bonaparte JF,
Ferigolo J, & Ribeiro AM, 2001
'from Rio Grande'
Proposed Family: Riograndidae Bonaparte et al, 2001 |
| Species: | Riograndia guaibaensis Bonaparte et al, 2001 |
| Place: | Caturrita Formation, Rio Grande do Sul |
| Country: | Brazil |
| Age: | Carnian or Norian (early), Upper Triassic |
| Remarks: | The following is based upon my reading of Bonaparte
et al, 2001.
Riograndia guabiensis is described on the basis of three specimens recovered 8km west
of Candelária City, (p.623). Nine additional specimens have also been collected. The authors
term it: "a primitive 'ictidosaur' from lower Norian beds..." Fieldwork led to
the discovery of this fossil rich locality yielding both 'ictidosaurs' and other mini
cynodonts. The latter are also new and a paper is in preparation. Fossils from other
outcrops suggest the age, though this needs better chronological information for certainty.
Skull
The holotype preserves the snout to the front part of the
parietals, (p.624). Please don't try this at home, but imagine the skull of a
mousey-sized dog which has been sliced just before the back of the
orbit, and that's vaguely the situation. What's left of the
jugal indicates a weak zygomatic arch. At the front
of the upper jaw are the premaxillae with a
maxilla on either side. Slightly further up the snout can
be found the nasals. At least, that's how my face works, but
I'm a mammal. As is typical for non-mammalian
eucynodonts, Riograndia packed a further bone
in between the premaxilla and nasal. This is the
septomaxilla. We manage without that; it's old baggage of our ancestry.
Another typically non-mammalian eucynodont feature is the secondary bony palate which, in
this case, extends back until a bit past the final postcanine.
This useful device permits simultaneous breathing and swallowing; essential for animals with
relatively high metabolic rates. The evolutionary history of this bone extends back into
pre-eucynodont times, and it's still going strong. It's part of our inheritance we're still
using.
A further feature the authors report may be of interest, in the light of their subsequent
discussion, though it's not a point they go onto mention themselves: "The
postcanine tooth row is well set in from a lateral border of the maxilla, which shows a
pronounced maxillary bulge, a feature commonly seen in
gomphodont cynodonts", (p.625)
Lower jaw
One specimen is a near-complete, left mandible. It's robust
and broadly similar to Pachygenelus, (p.625). For gourmets and masochists, the
symphasis is large and leans forward. The horizontal ramus is high and thick, and the medial
angular process is distinct. There's a high coronoid process, and most of the back of the
jaw is formed by a well defined articular process. It exhibits and impressive postdental
groove at the rear of the inner side of the jaw. This thins and feeds into the narrow slit
of Meckel's groove. This extends along near the lower
edge of the bone until roughly below the first postcanine,
(judging by the diagram on page 627).
Upper dentition
The upper teeth on each side consist of three incisors, a
canine, and seven postcanines. Whilst being far from
horizontally directed, the incisors are somewhat forwardly inclined. The first is small
and I2 is the largest. It's oval in cross-section and there's a long wear facet on the
lingual side. Only the
buccal surface has enamel. I3 is similar but smaller. There's a distinct
diastema followed by an unimpressively sized canine,
(p.625-626). This is smaller than both I2 and I3. It's followed by a short diastema, and
then the closely packed postcanines. These teeth are all
blade-like constructions, equipped with 6-9 cuspules in a line. One cuspule is a bit larger
than the others, and this is generally the middle one. "Probably an adjusted shearing
occlusion was preset because the anteolingual border of postcanines 5-7 shows strong
lingual wear, suggesting alternating occlusion",
(p.628).
Lower dentition
The previously mentioned lower jaw is fitted with reasonably well preserved teeth. The first
incisor is impressively long and thick, (p.628).
"Lingual wear is probably not from occlusion with
upper incisors but only from food wear", (p.629). Enamel is only found on its
buccal surface, which is probably the original condition.
The i2 is rather pathetic. The i3 is smaller than i1 and not as forwardly slanted, (p.630).
For both these teeth, the enamel is distributed as on the first incisor. The small, vertical
canine has strong wear, which was perhaps the result of
occlusion with its upper counterpart.
As with the uppers, the postcanines are packed tightly
together, similarly sized and there's a diastema between
them and the canine. These teeth have 5-9 cuspules of a similar size. Usually, the crown
is bigger than the root. The final postcanines have incompletely subdivided roots; perhaps
incipient bifurcation.
So how big was one of these things?
I'm pleased you asked. The twelve specimens known suggest that the holotype and left jaw
are both sub-adult, (p.630). The adult skull length was probably about 3.5cm. As a rough
guide, that's about the same as for a big rat or a hamster. Evidence indicates a low rate
of replacement teeth, (p.631)
The postcanine teeth are unusual. "Their transversely
compressed, multicusped postcanines are different from the morphotype present in galesaurids,
cynognathids, chiniquodontids, and probainognathids", (p.632). All those examples have
three or four buccal cusps and sometimes a buccal
cingulum (uppers), and a lingual
one (lowers). These characteristics may mean that the possibility of any of these groups
being ancestral for Riograndia is remote.
However, at least with regards to the last postcanines, the authors do see similarities in
the juvenile teeth of Andescynodon, which is a relatively early
traversodontid. If juvenile Andescynodon-like
teeth had a wider distribution among gomphodonts, and
were contained as the adult condition in a presently unknown group, then that might be more
appropriate as a possible ancestral line.
Derived and basal
features
A list of derived characters which support the diagnosis of Riograndia as an
'ictidosaur' (Tritheledon not included) are offered on page 632: "(1)
dorsoventrally deep lacrimal; (2) reduced upper incisor
1 (convergence with Tritylodontidae); (3) hypertrophied lower incisor 1 (convergence with
Tritylodontidae); (4) imbricating implantation of the last
postcanines in the maxilla and
dentary; (5) one large infraorbital foramen and two medium-sized foramina on the maxilla;
(6) grooved roots on the last three postcanines (also present in Therioherpeton); (7)
jaw articulation with the skull higher than the line of alveoli
(also present in Pachygenelus)."
On the same and the subsequent page, they offer a list of primitive characteristics:
"(1) postcanines with poorly differentiated main
cuspule and several secondary ones that are more numerous posterior to the main cuspule
than anterior to it; (2) upper and lower postcanine crowns transversely narrow; (3) absence
of cingula in postcanines; (4) articular process of
dentary without articular concyle."
Although tentatively favouring unknown gomphodont
ancestry for this genus, the authors also accept that something more like a
chiniquodontid might be to blame.
Holotype
The holotype is MCN-PV 2264 and it lives in the collection of the Museu de Ciencias Naturais,
Porto Allegre, Brazil. It was collected by Eduardo Borsato. The specific name refers to the
Guaiba Basin, which is where it was found. |
| Reference: | Bonaparte JF, Ferigolo J, & Ribeiro AM (2001), A primitive
Late Triassic 'Ictidosaur' from Rio Grande do Sul, Brazil: Palaeontology, v. 44, part 4,
p.623-638. |
| Link:
NAPC 2001
http://www.ucmp.berkeley.edu/napc/abs2.html
A new fauna of very mammal-like Cynodonts from the Late Triassic of Brazil. An abstract of a
paper presented at the North American Paleontological Convention, June 2001. |
| Genus:
Therioherpeton Bonaparte & Barberena, 1975
Aka: Theioherpeton
Family: "Therioherpetidae"? Bonaparte & Barberena, 1975
Remarks: Further information on this genus is lurking in my extensive 'things to do'
warehouse, and this entry will be renovated at some stage.
"Therioherpetidae" Bonaparte & Barberena, 1975
The members of the proposed family, "Therioherpetidae", are often assigned to the
family Dromatheriidae.
The family name proposed in 1975 was actually written Therioherpetontidae. The spelling
employed on this page was emended by Battail in 1991, (Abdala & Ribeiro 2000 p.593).
These authors go on to report: "The validity of the family has been alternately denied
and supported by various authors. Hahn et al. (1984, 1994) and Godefroit &
Battail (1997) assigned Therioherpeton cargnini Bonaparte & Barberena, 1975 to
the Dromatheriidae, whereas Sigogneau-Russell & Hahn (1994) recognized a
Therioherpetidae that included Therioherpeton and Meurthodon gallicus." |
| Species: | Therioherpeton cargnini Bonaparte & Barberena, 1975 |
| Place: | Santa Maria Formation, Rio
Grande do Sul |
| Country: | Brazil |
| Age: | Carnian, Upper Triassic |
| Remarks: | Much of the following is based upon my
reading of Oliveira, 2006.
This study was a re-evaluation of material originally described 31 years earlier, and
rather a lot of developments had occurred during the intervening time. These included
a healthy supply of new relatives. An analysis found some reason for placing this
genus into the family of Therioherpetidae along with
Riograndia but support for this, in the words of the author, "is weak"
(p.447). This taxon was found to be a sister group
of Tritheledontidae (in the terminology of the paper). However, as another current
definition of that family has Riograndia as its most
basal known member, Therioherpeton could presumably be admitted.
Nevertheless, there are several points distinguishing the two members of this
proposed narrower family from all other
probainognathian cynodonts. The rear upper
postcanines exhibit (what is termed) an increasing "imbrication angle". This is
doubtlessly true but beyond my present levels of appreciation. Rather than puzzling
further to recognize the point from the picture in the paper, I'll move on for now.
Lower postcanines for the family are noticeably narrow. (I understand that
point!)
Instead of reacting to this conclusion by erecting a special enclosure for the
family proposed -especially as support "is weak"- I'm going to continue with the
presently vaguer structure of this directory for 'tritheledontans'.
Nearly mammals
Regardless of the small print of zoological classification, in terms of the traditional
language of crude classes, the main point is this: Therioherpeton was much
more like a mammal than a so called 'reptile'*. The indications point to a joint
ancestor of both this critter and full-blown mammals having had sex in the then
none-too-distant past. This sharing of carnal knowledge was presumably
pre-Carnian (the time of Earth for Therio), but not all that much pre.
(* As was often known at the time, referring to non-mammalian
cynodonts as 'mammal-like reptiles' was
nonsense. They were synapsids and not
reptiles.)
The lower level affinities of Therioherpeton are less well resolved. It's
more mammal-like than the
chiniquodontids (p.448), but doesn't seem as close as the brasilodontids such
as Brasilodon. Oliveira also authors fairly
extensive thoughts on the stratigraphy of vertebrate sites of the Santa Maria and
Caturitta Formations involving a number of controversial issues. Radiometric dating
would help bring more clarity, but none has so far been undertaken (p.450). Some
geological matters are mentioned in the article below.
The nature of the beast
The preserved skull has most of the right side and less of the left. What's
available has a length of 3.3 millimetres, and it can't have been that much longer
when freshly dead; perhaps a millimetre more could have been at the front. It was
a small animal presenting a vast menace to even littler ones.
The frontal bones of the skull were wedge-shaped to the rear and, at the front, a
lateral flange of bone fingers forward to tenderly caress the lacrimal (p.452).
This affection isn't merely romantic. Along with other features of the limbs and
vertebrae, it's atypical for probainognathians of this age and earlier. Its
postcanine teeth are more modest than those of
Charruodon, both in terms of development and size,
and less cuspy than those worn by Riograndia. In the opinion of Oliveira,
those two are the closest known relatives.
Incompleteness isn't the end of difficulties with the skull, as it's also out of
shape. Nevertheless, the available outline has something of the flavour of
both Sinoconodon and
Brasilodon. For example, a bone called the
squamosal is well developed, and meets up with the
parietal towards the middle of the head. This is Sinoconodon-like, but
not in line with more basal chiniquodontids or
Probainognathus. Further elements are discussed in the paper.
Upper postcanines
It had previously been stated that there were eight of these teeth (p.453), but
there actually only seem to be seven. For several reasons, particularly life-long
habits of tooth replacement, numbers can even vary somewhat on different halves of
the same mouth and, in contrast to mammals,
postcanine formulae are more rules of thumb than strict laws of construction. With
Therio, lengths generally increase along the row with one exception. PC5 is the
second largest in the band, and thus bigger than PC6. The range runs from 0.7mm
(PC1) to 2.1 (PC7).
This brings us to the point the author terms: "one of the most remarkable characters,
but I'm unsure quite what "a crescent imbrication angle posteriorly" is. I can see
the postcanines are set diagonally in the jaw, rather than straight towards the front,
and perhaps that's at least part of the story. I can't detect anything I'd
recognize as a "crescent". Then again, I'm not sure where I should be looking. Be
that as it may, I'm informed the range of imbrication varies from 5° (front
postcanine) to 30° (final one) in the case of
Riograndia, and that the situation is similar for Therioherpeton.
A further point regarding more basal probainognathians, specifically those snazzily
named chiniquodontids, is that the postcanines have no obvious demarcation between
the root and the crown (p.454). Where the one begins and the other ends isn't obvious
from the tooth itself. It is clear for Therio. In one instance, the crown contributes
a third of the total height. The root has a characteristic of wrinkled enamel on
both the labial and lingual
sides. Another 'advance' in the direction of mammalosity occurs just below the gum
line, as the root shows an incipient tendency of division. As well as not applying
for the chiniqs, these two point are also absent with
Pachygenelus (personal addition).
Of crowns and canines
One tooth is referred to as "PC4". The quotation marks are there for a purpose, but
I'm not sure what it is! This has a line of four cusps running along its centre, with
the main one, A, being longer than the others, and set above the point of incipient
root division. Wear is concentrated on the heights of the tooth and the lingual
side, with none apparent on the labial face. There's no sign of any
cingulum.
The width of the last four upper postcanines is about half the length, with the
difference being less extreme for the front trio. Lovers of
canines may be pleased to hear this tooth is as long as the PC6 (1.8mm) and has
a width of 1.6mm.
Upper postcanine distinctions
On account of this upper "PC4", Therioherpeton has been denied admission to
the Dromatheriidae, and it only has
itself to blame for any disappointment on the matter. Whimpering complaints will
garner no sympathy. Although cusp A is the highest on the crown, it's not all that
much taller than the others. The cusps also fail to be as narrow, and the root is
too short in comparison to the crown.
It also differs to the relevant teeth of Pachygenelus and
Diarthrognathus. Their upper postcanines are
more bulbous in build, the main cusp is more dominant and they have a cingulum on
the buccal side.
How old was this Therio?
The type fossil has, at one time or another, been accused of being a juvenile and
an adult. Oliveira agrees with the latter option (p.456). The postcranium bones
seem mature in terms of ossification, and the degree of wear on "PC4" also points
in that direction. Furthermore, that amount of wear is consistent with a more
restricted system of tooth replacement than for more basal probainognathians.
Holotype
For some reason, the catalogue number hadn't been published prior to 2006. Better late
than never. MVP 05.22.04 is a partial skull with an associated fragment of lower
jaw and other skeletal parts. These include 29 articulated, partial
vertebrae, limb bones, shoulder parts and hips.
It all resides in the Museu Vincente Pallotti in Santa Maria, Brazil. The specific
name honours a local fossil-hunting priest, Daniel Cargnin, who has provided much
useful information on local sites.
Additional notes
Based on an incomplete skull, this was a smallish
critter "which has fully sectorial
postcanines", (Abdala & Ribeiro 2000, p.590).
"Therioherpeton, from the mid-Triassic of South America, could belong either to
this group (Hahn et al. 1994)..." [a reference to
Dromatheriidae] "... to Tritheledontidae
(Kemp 1982; Sues 2001), or to a stem mammal group, (Bonaparte & Barberena 1975).
Until its fossils are better described, affinities of Therioherpeton to mammals, and
to other nonmammalian cynodonts, will remain uncertain", (Luo, Kielan-Jaworowska &
Cifelli 2002, p.5).
Eucynodont thinknology
As well as the outside of the skull, its contents are known to some extent. An endocast
preserves some information about the brain. The olfactory bulbs are well developed, which
are features associated with the sense of smell. The abstract of Quiroga JC (1984) is
linked below and contains: "The morphology of the endocast and relative brain
size of Therioherpeton cargnini are in general agreement with other features
of the species that locates it as one of the more advanced cynodont toward mammalian
patterns..."
Kemp, 2005 (p.74-75) mentions similarities of the skeletal material with
Morganucodon and
Oligokyphus
The skull has no postorbital bar, so the temporal fenestra and
orbit aren't separated. The zygomatic arch is
slender. Upper postcanines are incipiently double-rooted, but the lowers are presently
unknown. |
| Reference: | Bonaparte & Barberena (1975), A possible Mammalian
ancestor from Middle Triassic of Brazil, Journal of Paleontology, 49 (5),
p.931-936. |
| Rio Grande do Sul, Triassic Vertebrates
from Brazil
The following is largely based upon my reading of Lucas, 2001.
The Rosário do Sul Group refers to rock in southern Brazil rather than a jazz combo. It
contains three formations with remains of Triassic land animals, (p.13), and their
stratigraphic affinities have been the subject of differing interpretations. The
landscape's thick with vegetation, and exposures revealing more than a few metres of the
sequence are rare. However, there are three distinctly differing faunas.
The Sanga do Cabral Formation contains Lootbergian tetrapods; the Dinodontosaurs
Assemblage Zone can be found in the middle of the Alemoa Member, Santa Maria Formation;
the upper part of the Alemoa and the Caturrita Formation contain the Hyperodapedon
Assemblage Zone. The Dinodontosaurus Zone is similar in age to the
Charnian Assemblage of Argentina. The
Hyperodapedon Zones equates to the Ischigualastian.
Pardon?
If anyone's now none the wiser as to what that might mean, I offer my sympathies. It's not
always easy to follow this sort of terminology. I'll attempt a rough translation. There are
these three layers of fossil bearing rock in the same area of southern Brazil, and they
were all deposited at somewhat different times. That's why they contain differing fossils.
One layer must be the oldest, another's the youngest, and there's a middling one as well.
If the whole sequence were conveniently exposed at one site, then telling bottom from top
would be a doddle. Unfortunately, it's not. Meanwhile, as, in two instances, similar fossils
are known from restricted rock layers in Argentina, the relevant strata in both countries
date from pretty much the same time.
Time for a snack
If it's still a bit hard to take in, then make a sandwich with two kinds of bread and a
slice of ham. Cut it into bits. Eat some of each layer at random. Put the remnants onto
small plates and place them here and there around the room. You can tilt some pieces at
angles, should you wish, and flip the odd bit upsidedown. Ask a friend, (who'll possibly
conclude you're mad), to reassemble the sandwich as neatly as possible.
That's pretty much the basis of the science of stratigraphy, though it's not generally as
straightforward. For one thing, there are more layers involved. For another, the information
doesn't come served up on a plate, (other than for a tectonic one).
A trio of formations
All three of the formations are composed of mainly fluvial deposits. The Sanga do Cabral,
(which also involves sandstones produced by the action of winds), has a maximum thickness
of about thirty metres. Above are found the various elements of the much thicker Santa
Maria Formation. This consists largely of floodplain deposits. The Caturrita is thinner,
(up to sixty metres), and is mainly the product of river channel actions.
Sanga do Cabral
The oldest of the tetrapods, (p.14), come from the Sanga do Cabral. Among them are
rhytidosteid amphibians, (Procolophon), and bits of a protosaurid and a
pareiasaur, which generally turn up in the Upper Permian. However, the fauna best
correlates to the Lystrosaurus "zone" of Karroo in South Africa, (p.15).
This suggests a Lower Triassic age (Lootsberian). If correct, this is only the second
instance of a post-Permian pareiasaur. The other is Sclerosaurus from the border
area of Germany and Switzerland. Additionally, Kellner & Campos, 1999 (p.238) mentions
remains of dicynodonts and fragments of amphibian have also been found in the Formation.
(They have the Rio do Rasto Formation as the source of the pareisaurid. According to their
survey, this would be Upper Permian. Both formations are in the Paraná Basin.)
Santa Maria
The fauna from the Santa Maria Formation is considerably more diverse, (p.16). Among the
residents were rhynchosaurs, rauisuchids, aetosaurs, dinosaurs, dicynodonts, cynodonts and
others. There are at least two assemblages present, (Middle to Upper Triassic), and they
correlate with the Chanarian and Ischigualastian faunas of Argentina respectively. It's
possible that some fossils are actually earlier. The presence of
Luangwa is suggestive of an Anisian age.
Dinodontosaurus Assemblage Zone
The first assemblage is dominated by a dicynodont, Dinodontosaurus. It had the
companionship of a colleague called Stahleckeria. Cynodontia is represented by
Traversodon, Belesodon
(Chiniquodon to others) and
Massetognathus. The age is probably
Ladinian and in this study it's termed the Dinodontosaurus Assemblage Zone.
Hyperodapedon Assemblage Zone
The Upper Triassic fauna is best known from near the city of Santa Maria. This zone has had
several names, but Lucas designates it the Hyperodapedon Assemblage, as that
genus is the most common of the plant-eating rhynchosaurs. The cynodonts include
Charruodon, Therioherpeton,
Gomphodontosuchus and an increasing
number of subsequently described genera, some of which are exceedingly mammal-like,
(eg. Riograndia, Prozostrodon,
Brasilitherium and
Brasilodon). Also present are dinosaurs: Staurikosaurus, Teyuwasu
and Saturnalia. Comparisons with assemblages in India, Britain, Argentina, the USA
and mainland Europe suggest this is Carnian in age, and near coeval with the
Ischigualastian fauna.
Caturrita Formation
The Caturrita Formation is stratigraphically higher, (p.17), which means it must be
younger still. However, it shares biostratigrafically significant
taxa with Ischigualasto, (Ischigualastia,
Exaeretodon and Hyperodapedon), and so
is probably about the same sort of age. There's not yet sufficient evidence to verify it as
significantly more recent, although that has been proposed in the past.
Update: Ictidosaur Assemblage Zone
Rubert & Schultz, 2004 proposed a new biozone for the upper unit of the Currita
Formation, which they named after the association of small eucynodonts (ictidosaurs). This
zone is thought to be predominantly lower Norian, with some upper Carnian at its base. As
well as small and delightfully mammal-like brasilodontids, the fauna includes further
cynodonts, a procolophonid (Soturnia caliodon), a dinosaur (Guaibasaurus
candelariensis), a somewhat late dicynodont (Jachaleria candelariensis), and
bits and pieces of crocodile-like phytosaurs and lizard-like sphenodontids.
Further Mesozoic site summaries can be found at Localities.
The Eucynodonts of Rio Grande do Sul (15
genera, 16 species)
Further generic names are sometimes in use.
Santa Maria Formation
?Anisian
Traversodontidae (one genus, one species):
Luangwa sudamericana
Ladinian: Dinodontosaurus Assemblage Zone
Traversodontidae (four genera, four species): Massetognathus ochagaviae;
Protuberum cabralensis;
Santacruzodon hopsoni;
Traversodon stahleckeri
Probainognathia (one genus, one species):
Chiniquodon theotonicus
Carnian: Hyperodapedon Assemblage Zone / Caturrita Formation
Traversodontidae (two genera, three species):
Exaeretodon frenguelli; E. riograndensis;
Gomphodontosuchus brasiliensis
Probainognathia (eight genera, eight species): Brasilitherium riograndensis;
Brasilodon quadrangularis;
Charruodon tetracuspidatus;
Irajatherium hernandezi;
Prozostrodon brasiliensis;
Minicynodon maieri;
Riograndia guaibaensis;
Therioherpeton cargnini
The presence of Luangwa raises the possibility of the base of the Santa Maria
Formation being Anisian in age, but this requires confirmation (or otherwise). | |
| Species: | Tritheledon riconoi Broom R, 1912 |
| Place: | Red Beds, Upper Elliot Formation,
Orange Free State |
| Country: | South Africa |
| Age: | Hettangian / Sinemurian, Lower Jurassic |
| Remarks: | The following is based upon my reading of
Gow, 1980, a study of trithe dentitions.
A toothy trithe
Tritheledon is a somewhat eccentric South African trithe, as it displays
an abnormal fondness for postcanines.
Pachygenelus and
Diarthrognathus got along with a usual number of seven per side.
Tritheledon appears to have gone in for double figures, but incompleteness
adds some obscurity. Remains of eight occur on the one available left jaw (p.476),
and more were presumably in front of them. Its partnering right jaw preserves
remains of seven front postcanines with alveoli for
followers behind; perhaps as many as four. None of the teeth have been treated very
kindly by the passage of a couple of hundred millennia. Uppers are short postcanines
of which the crowns of two erupting replacements are putting in appearances. The
rest are, at best, smashed down (or rather up) to gum level. New arrivals on the right
side have provided one near complete representative, and two more damaged ones. What
there is available is consistent with an alternate pattern of replacement as for
Pachygenelus.
Upper postcanines
These differ strongly from their counterparts in Pachygenelus and
Diarthrognathus, and that makes an actual family relationship less than
convincing for some. Rather perversely, they compare most closely with the lowers
of the second mentioned genus (p.478). There's a main cusp with a series of
accessory ones to the lingual side.
Lower postcanines
Certainty here is ever so slightly lacking, as are specimens. Gow was tempted to a
prediction, and reckons they're likely to resemble the uppers. Obviously, this could
only be tested if part of a set turned up, and lots of digging over many decades
hasn't yet revealed any traces of a friend for the still lonely type fossil.
Holotype
The type specimen consists of a pair of upper jaws in the collection of the South
African Museum, Cape Town. I suppose one might have been granted some kind of
seniority but, although physically separated, they both issued forth from the same
snout. The left is known as SAM 1885 and it calls its partner SAM 2782. |
| Reference: | Broom (1912), On a new type of cynodont from the Stromberg.
Annals of the South African Museum, 7, p.334-336. |
| Other reports:
Brazil
A new tritheledontid was announced in October. Further details welcome.
Reference, Matinelli AG, Bonaparte JF & Schultz CL (2002), Un nuevo tritheledontidae
(Therapsida, Eucynodontia) del Triásico Tardio de Brazil, y la posicion filogénetica de este
taxón entre los cimodontes carnivoros no-mamalinos. VIII Congresso Argentino
de Paleontologia y Bioestratigrafia, Corrientes, Argentina -(October 2002).
At a guess, this may refer to either Brailitherium or Brasilodon, although
the subsequent descriptions didn't refer them to Tritheledontidae.
http://exa.unne.edu.ar/eventos/congresos/paleontologia/public_html/programa1.htm
|
| Help:
Should anybody have any further information, I'd be pleased to hear of it.
Regarding references and Bibliography:
I haven't and can't verify all the references, so beware. Traditional papers used in
constructing this page are in the bibliography. If you feel these are too few, then send
some more.
Return to top of page
Trevor Dykes, April 2001. Separate directory since: 20.4.2005, last updated 25.2.2011.
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 AM (2002), Chiniquodontid Cynodonts: Systematic and
Morphometric Considerations. Palaeontology, Vol. 45, Part 6, p.1151-1170.
Abdala F & Ribeiro AM (2000), A new therioherpetid cynodont from the Santa Maria
Formation (Middle Triassic), southern Brazil. Geodiversitas. Vol. 22, (4), p.589-596.
Bonaparte JF, Schultz CL, Soares MB & Martinelli AG (2010), La Fauna Local de
Faxinal do Soturno, Triasico Tardio de Rio Grande do Sul, Brasil, Rev. bras. Paleontol.,
13(3), p.233-246.
Bonaparte JF, Ferigolo J & Ribeiro AM (2001), A primitive Late Triassic
'ictidosaur' from Rio Grande Do Sul, Brazil. Palaeontology, 44(4), p.623-635.
Godefroit P & Battail B (1997), Late Triassic cynodonts from Saint-Nicolas-de-
Port (north-eastern France). Geodiversitas 19(3), p.567-631.
Gow, CE (1980), The dentitions of the Tritheledontidae (Therapsida: Cynodontia),
Proceedings of the Royal Society of London, B208, p.461-481.
Kemp TS (2005), The Origin and Evolution of Mammals, Oxford University Press,
pp.331.
Knoll F (2005), The tetrapod fauna of the Upper Elliot and Clarens formations in
the main Karoo Basin (South Africa and Lesotho), Bulletin Soc. Géol. Francais, 176(1),
p.81-91.
Lees PM & Mills R (1983), A quasi-mammal from Lesotho, Acta Palaeontologica
Polonica 28, p.171-180. (Note: My copy runs out on page 177.)
Luo Z (1994), Sister-group relationships of mammals and transformations of diagnostic
mammalian characters, p.98-128 (Chapter 6 of) In the Shadow of the Dinosaurs - Early
Mesozoic Tetrapods, (eds Fraser NC and Sues H-D), Cambridge University Press.
Luo Z (1994), Sister-group relationships of mammals and transformations of diagnostic
mammalian characters, p.98-128 (Chapter 6 of) In the Shadow of the Dinosaurs - Early
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