Kammerer 2019 nests a new dicynodont

Figure 1. Cladogram of the anomodontia and dicynodontia from Kammerer 2019. Blue taxa are proximal outgroups.

Figure 1. Partial cladogram of the Anomodontia (including Dromasauria) and Dicynodontia from Kammerer 2019. Blue taxa are proximal outgroups in this cladogram.

In a description of a new dicynodont, Thliptosaurus,
Kammerer 2019 presented a comprehensive cladogram of the dicynodonts, the dromasaurs and several outgroup taxa (Fig. 1), including the dinocephalians, Biseridens (Fig. 2), Archaeosyodon and Titanophoneus.

Figure 1. Biseridens and Phthinosuchus, two related therapsids that have been giving paleontologists fits.

Figure 2. Biseridens and Phthinosuchus, two related therapsids. According to Kammerer 2019, Biseridens is the proximal outgroup to the Anomodontia, who’s

Unfortunately 
Kammerer 2019 excluded several outgroup and ingroup taxa pertinent to the origin of dicynondonts and anomodonts. In the Therapsid Skull Tree (TST,  67 taxa, Fig. 4), the Anomodontia (dicynodonts, dromasaurus and kin) arise from basalmost therapsids, like Cutleria, Stenocybus (Fig. 3) and Hipposaurus. These appear prior to Biarmosuchus. Elsewhere on the cladogram, Biseridens and Titanophoneus arise from more derived tapinocephalids unrelated to basal Anomodontia, more distant descendants of Biarmosuchus.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Kammerer 2019 was attempting to produce a cladogram
of the clade Anomodontia. I cannot comment on the tree topology of dicynodonts, because the TST includes so few of them. However, Kammerer followed tradition by including Biseridens and Titanophoneus as outgroup taxa, omitting those recovered by the LRT and TST.

So… taxon exclusion
put a small damper on an otherwise comprehensive report. This happens way too often in paleontology.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.


Biseridens (Fig. 2) was too distinct

to be the ancestor to the tiny dromasaurs, Suminia and Galepus (Fig. 3) and the rest of the Anomodontia. The taxa shown above (Fig. 3) demonstrate a more gradual accumulation of traits, better modeling deep time events.

Yesterday we looked at the uncontroversial key role
two small dromasaurs, Patranomodon and Galeops (Fig. 3), played in the origin of the Dicynodontia. Kammerer’s tree and the TST are in agreement on that point. Likewise the two trees agree that Eodicynodon is the basalmost dicynodont and that Suminia is closely related to Otsheria + Ulemica, close relatives of Venjukovia.


References
Kammerer CF 2019. A new dicynodont (Anomodontia: Emydopoidea) from the terminal Permian of KwaZulu-Natal, South Africa. Palaeontologia africana 53: 179–191. ISSN 2410-4418.

Maybe Anomocephalus had canine fangs, too!

Two dicynodont-mimics,
Tiarajudens (UFRGS PV393P, Cisneros et al. 2011) and Anomocephalus (Modesto et al. 1999) were discovered in the last few two decades. Tiarajudens had sharp teeth and a fang/canine/tusk. Anomocephalus had flat teeth and apparently no tusk (Fig. 1).

Working from the published tracing
I put the scattered teeth of Anomocephalus back into the jaws and discovered that maybe there is a tusk/fang in there, too (Fig. 1). If valid, the fang was broken in half during typhonomy, so it became the same length as the other teeth, all of which had narrow roots, unlike the fang.

Figure 1. Anomocephalus in situ and reconstructed. Apparently a fang/canine/tusk was hiding among the broken teeth.

Figure 1. Anomocephalus in situ and reconstructed. In situ image from Modesto et al. 199. Apparently a fang/canine/tusk was hiding among the broken teeth.

Tiarajudens and Anomocephalus
are considered middle Permian primitive herbivorous anomodonts by the author(s) of Wikipedia, who also suggest they were ancestral to dicynodonts. By contrast, the large reptile tree (Fig. 2)  nests Tiarajudens and Anomocephalus in a clade close to, but separate from dicynodonts (Fig. 2).

Figure 3. Basal therapsid tree.

Figure 3. Basal therapsid tree. Note the nesting of the Anomodontia and the dicynodonts here, both derived from smaller dromasaurs.

According to the LRT, the ancestors of dicynodont mimics were 
Venjukovia and Otsheria. The ancestors of dicynodonts include Suminia, a late-survivor of an early radiation. Both were derived from smaller dromasaurs (Fig. 3).

Figure 3. Venjukoviamorphs include the dicynodont mimics, Tiarajudens and Anomcephalus. now with long canines.

Figure 3. Venjukoviamorphs include the dicynodont mimics, Tiarajudens and Anomcephalus, the latter now with mid-length canines. The Anomocephalus drawing is modified from Modesto et al. 1999 and appears to have certain problems.

References
Cisneros, JC, Abdala F, Rubidge BS, Dentzien-Dias D and Bueno AO 2011. Dental Occlusion in a 260-Million-Year-Old Therapsid with Saber Canines from the Permian of Brazi”. Science 331: 1603–1605.
Modesto S, Rubidge B and Welman J 1999. The most basal anomodont therapsid and the primacy of Gondwana in the evolution of the anomodonts. Proceedings of the Royal Society of London B 266: 331–337. PMC 1689688.

Anomodont tree problems

We still need to add more taxa to our matrices.

Figure 1. Cisneros et al. 2015 cladogram nesting Tiarajudens and Anomolocephalus as basal anomodonts. This is odd because both are quite derived.

Figure 1. Cisneros et al. 2015 cladogram nesting Tiarajudens and Anomolocephalus as basal anomodonts. This is odd because both are quite derived.

 

Figure 2. Cladogram of taxa listed by Cisneros et al. but using the Peters 2015 matrix.

Figure 2. Cladogram of taxa listed by Cisneros et al. but using the Peters 2015 matrix.

Case in point:
Cisneros et al. 2015, is a recent paper on Tiarajudens (Fig. 4) behavior. Their cladogram (Fig. 1) does not match a larger study (Fig. 2) with regard to the way they ordered basal therapsids.

Two problems right at the start:
Everyone knows Dimetrodon is not basal to therapsids. It is far too derived. No basal therapsid has dorsal spines.

There’s a body of work that demonstrates that Tetraceratops is not a basal therapsid. Again, it is too derived, too bizarre, too different — and it does not nest with synapsids!  In the large reptile tree it nests with Tseajaia. Actual basal therapsids include Cutleria and Biarmosuchus, which Cisneros et al. did use. Even so, they missed several taxa listed here (Fig. 3). Every taxon counts and adds value to the tree.

Adding taxa is a chore.
So, is that why paleontologists don’t like to add any more than they have to? It seems they often ask a grad student to do the work, and they’re new at it! They’re not experts until after they’ve done their studies. Workers can always reference the large reptile tree (Fig. 3). It works in whole or in part.

Figure 3. Where Tiarajudens and Anomocephalus nest as a subset of the large reptile tree.

Figure 3. Where Tiarajudens and Anomocephalus nest as a subset of the large reptile tree. Here they nest as derived taxa, not basal taxa. They did not produce descendants.

Anomocephalus and Tiarajudens
are giant, terrestrial dromasaurs, a clade of otherwise small, long-tailed, arboreal anomodonts. Giant dromasaurs converge with dicynodonts in several regards (short toes, tusks, size). Perhaps that leads to confusion generally.

Figure 4. Dromasaurs to scale. Tiarajudens and Anomocephalus are giant terrestrial dromasaurs.

Figure 4. Dromasaurs to scale. Tiarajudens and Anomocephalus are giant terrestrial dromasaurs. The pmx/ms suture IMHO probably includes four teeth, like Suminia.

BTW
Biseridens
has nothing to do with basal anomondonts. It’s a derived dinocephalian (Fig. 3) when more taxa are added. Let’s get that straight, too.

References
Cisneros JC, Abdala F, Jashashvili T, de Oliveira Bueno A and Dentzien-Dias P 2015. Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana.

Kenyasaurus not a tangasaur… not a diapsid… It’s a very basal dromasaur!

Earlier we looked at marine younginiformes. Perhaps conspicuous by its absence was Kenyasaurus, which was originally considered related to tangasaurid younginiformes. Last night I found data, plugged it into the large reptile tree and was surprised at where Kenyasaurus nested.

Kenyasaurus mariakaniensis
(Harris and Carroll 1977; Early Triassic; KNM-MA1, National Museum of Kenya) is represented by a headless skeleton with only a partial forelimb and pectoral girdle (Fig. 1).

Figure 1. Kenyasaurus in situ. Click to enlarge. This rather plain specimen nests not with tangasaurids, but with dromasaurids according to the large reptile tree. Boxed area: the primitive dromasaur, Galechirus and its foot to scale for comparison. Haptodus foot for comparison, not to scale. Pink and green tarsals are absent in Kenyasaurus and dromasaurs.

Figure 1. Kenyasaurus in situ. Click to enlarge. This rather plain specimen nests not with tangasaurids, but with dromasaurids according to the large reptile tree. Boxed area: the primitive dromasaur, Galechirus and its foot to scale for comparison. Haptodus foot for comparison, not to scale. Pink and green tarsals are absent in Kenyasaurus and dromasaurs. Note the similarity of the pes of Kenyasaurus and Haptodus, sharing the same number and proportion of pedal elements, less the two tarsals.

Originally considered
a relative of Tangasaurus and Hovasaurus, the large reptile tree nested Kenyasaurus with the arboreal herbivorous dromasaurid synapsids. If so, the purported ‘well-developed sternum’ (Fig. 1, lavender) must instead be the posterior coracoid because synapsids do not have a sternum*. Harris and Carroll (1977) noted the long tail was unlike those of the Tangasaurus and Hovasaurus and that the tarsus lacked a fifth distal tarsal, as in dromasaurs. The caudal transverse processes gradually diminished over 30 vertebrae creating a cylindrical, muscular tail similar to those found in dromasaurs, only longer.

Figure 2. Two other dromasaurs, Suminia and Galechirus.

Figure 2. Two other dromasaurs, Suminia and Galechirus. Note the similar ilium shapes.

Currie 1982
also examined Kenyasaurus. At that time Currie did not have a computer or software to test traditional nestings. And he had just been studying Tangasaurus and Hovasaurus. So he considered Kenyasaurus a tangasaurid.

Currie (1982) diagnosed Kenyasaurus on the basis of five autapomorphies:

  1. low but anteroposteriorly elongate neural spines in the dorsal region
  2. 56 caudal vertebrae and
  3. 28 pairs of caudal ribs and transverse processes.
  4. Astragalus almost triangular rather than primitive L-shape
  5. Pronounced process on fifth metatarsal for insertion of peroneus brevis

How do these compare to dromasaurs?

  1. Neural spines in known dromasaurs and outgroups are taller than long
  2. About 45 caudal vertebrae are present in Galechirus, but they get very tiny at the tip, 52 are present in Suminia
  3. 22 pairs of caudal ribs and transverse processes are present in Suminia
  4. Astragalus triangular present in Suminia, square present in Galechirus
  5. No pronounced process on fifth metatarsal

So, no wonder Kenyasaurus was not considered a dromasaur.

Bickelmann, Müller and Reisz 2009
did have a computer and software to test traditional nestings. They found support for two distinct families within “Younginiformes”: the aquatic Tangasauridae, and the terrestrial Younginidae. However, they found no support for the inclusion of Kenyasaurus within any of those families. Unfortunately that study also included the unrelated Lanthanolania, Palaegama, Saurosternon and Coelurosauravus (all basal lepidosaurifomes related to Triassic rib gliders) within the same clade that also included Claudiosaurus and the Younginiformes. Very odd.

Shift Kenyasaurus closer to Tangasaurus
and you’ll add 10 steps to the most parsimonious tree. Whether a sternum was present or not makes little difference.

Delete the two dromasaurs
from the large reptile tree and Kenyasaurus creates a large polytomy (loss of resolution) among basal synapsids.

Post-pectoral characters shared by Kenyasaurus and dromasaurs
to the exclusion of basal synapsids include:

  1. Gastralia present and rodlike (otherwise last seen in Ophiacodon)
  2. Ventral pelvis: separate plates, small medial opening
  3. Pubis orientation: medial
  4. Overall size: < 30 cm tall, 60 cm long

So, not a lot to work with.

Other dromasaurids
are known from the Late Permian, so Kenyasaurus would have been a late-survivor in the Early Triassic, despite its more basal nesting. That’s another black mark against Kenyasaurus being a dromasaur. Nevertheless, among the 542 taxa in the inclusion set, Kenyasaurus is most attracted to the dromasaurs with the present data set and scores.

Some final thoughts
Kenyasaurus displays no reduction of the middle phalanges of digits 3 and 4 of the manus and pes, so it resembles more primitive pelycosaur-grade synapsids in this regard. Based on this fact, the reduction of the three middle pedal phalanges may have occurred by convergence  within Therapsida, once in anomodonts and again in the main line beginning with biarmosuchids.

Basal anomodonts likely split from basal therapsids, like Stenocybus and Cutleria in the Early Permian. So Kenyasaurus was a very late (Early Triassic) remnant of that earlier radiation. So the autapomorphies that Currie listed (above) could have evolved during those tens of millions of years. And yes, I am making excuses for this taxon because it does not exactly match the ideal we might imagine. But those excuses could be true.

References
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.
Currie P 1982. 
The osteology and relationships of Tangasaurus mennelli Haughton. Annals of The South African Museum 86:247-265. http://biostor.org/reference/111508
Harris JM and Carroll RL 1977. Kenyasaurus, a New Eosuchian Reptile from the Early Triassic of Kenya. Journal of Paleontology 51:139–149.

* We’ll look at the mammals sternum/manubrium issue later….

Ever wonder about Galepus?

As opposed to the wildly popular bird-like dromaesaurs, the squirrel-like dromasaurs (lacking the “e” in the middle), like Galepus (Fig. 1, Broom 1910) are rarely studied. Brinkman (1981) made an important contribution. These less popular anomodonts are cousins to the hippo-like dicynodonts (Fig. 2). Both were herbivores of the Late Permian, nesting within the Therapsida and Synapsida.

I’ve seen a century-old reconstruction of the skull of Galepus, but I’ve never seen the whole body reconstructed (Fig. 10. That seems a shame as it is represented by a nicely curled nearly complete skeleton at the American Museum of Natural History (hirez color images kindly provided by their staff). And it’s been known for some time now. Much of the skull and skeleton is represented by impressions of missing bone in coarse sandstone.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, reconstructed from the complete skeleton at the AMNH.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, synapsid reconstructed from the complete skeleton #5541 at the AMNH. Wrist and ankle are reconstructed according to patterns seen in Galechirus and Suminia (Fig. 2, wrist and ankle inserts copied above). Note the oversized clavicle here. I’m wondering if I made a misidentification here, or is this taxon just odd that way? The hands are indeed robust with great symmetry, like a mammalian burrower, the mole, also known for its strong forelimbs.

The skull is only a cast of the internal surface of the roofing bones. Well marked, but odd.

Galepus has been nested (ref) with Galechirus close to Galeops at the transition to Eodicynodon (Fig. 3) between dromasaurs + kin and dicynodonts + kin.

Figure 2. Two other dromasaurs, Suminia and Galechirus.

Figure 2. Two other dromasaurs, Suminia and Galechirus. Galepus was close in size. Note the small clavicles here. Those go along with smaller forelimbs and a more asymmetric manus.

However,
The large reptile tree found a different relationship, with dromasaurs + dicynodonts splitting from the other therapsids at the base of that clade. Earlier we looked at differences and similarities between Galeops and Eodicynodon (Fig. 3). While they share many traits, phylogenetic analysis finds more parsimonious relationships when more taxa are introduced. Earlier we also looked at the base of the Anomodontia and the new taxa now nesting there.

Figure 1. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Not likely according to the large reptile tree which nests Stenocybus as their last common ancestor.

Figure 3. Click to enlarge. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Despite several convergent traits, not likely according to the large reptile tree which nests Stenocybus as their last common ancestor and recovers other taxa closer to both.

Earlier we looked at Stenocybus nesting at the base of the Anomodontia. Here’s the new synapsid tree (Fig. 4).

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids.

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids. And dromasaurs are distinct from dicynodonts. Stenocybus is their common ancestor. Here sister taxa are more parsimoniously nested. IOW they look more like each other and share more traits.

References
Brinkman D 1981. The Structure and Relationships of the Dromasaurs (Reptilia: Therapsida). Brevioria, 465: 1-34.
Broom R 1910. A comparison of the Permian reptiles of North America with those of South Africa. Bulletin of the American Museum of Natural History 28: 197-234.

Galeops – a toothless(?) dromasaur NOT at the base of the Dicynodontia

Earlier we looked at the Ruta et al. (2013) family tree of the Anomodontia and noted their placement of Galeops (Fig. 1, AMNH 5536) as the transitional taxon linking more basal dromasaurs to more derived dicynodonts. Liu et al (2009) had the same results.

Indeed, the short high face and toothless grin of Galeops does remind one of dicynodonts. But was that by convergence?

Figure 1. Galeops, a dromasaur found without teeth, but the jaws have tooth sockets. Apparently not related to dicynodonts, contra Ruta et al. 2013.

Figure 1. Galeops, a dromasaur found without teeth, but the jaws have tooth sockets. Apparently not related to dicynodonts, contra Ruta et al. 2013. Above and below, in situ from Brinkman 1981. Middle, reconstructed.

Figure 2. Basal therapsid family tree. Galeops nests with other dromasaurs, not at the base of the dicynodonts.

Figure 2. Basal therapsid family tree. Galeops nests with other dromasaurs, not at the base of the dicynodonts.

Dromasaurs and Dicynodonts.
According to the results of the large reptile tree (Fig. 2), the Anomodontia (dicynodonts + dromasaurs) have ancestors going back to a primitive short-faced therapsid, Stenocybus, a taxon ignored by Ruta et al. (2013).

According to the results of the large reptile tree (Fig. 2) Galeops finds its closest sister in Galechirus, another small dromasaur with tiny teeth, a long tail and was a likely tree-dweller. Their purported sisters, according to Ruta et al. (2013), were dicynodonts like Eodicynodon. Arguing against this, dicynodonts were not tree-dwellers, but had short toes, a short tail and a large body. According to the large reptile tree, dromasaurs were closer to the smaller less tubby ancestors of dicynodonts, not the derived forms, like Eodicynodon.

Yesterday we looked at Microurania, a rarely studied ancestor of dicynodonts and their phylogenetic predecessors. That’s the taxon missing from the Ruta et al. (2013) tree that would probably upset their topology, as it does here (Fig. 2).

No teeth?
No teeth were found with Galeops (Fig. 1), but small root impressions remain in the both jaws, all the same size.

Galeops had a shorter, taller face than other dromasaurs. The jaw “joint” permitted the jaws to slide back and forth relative to each other, a trait dromasaurs shared with dicynodonts.

The clavicles were larger in Galeops than in other dromasaurs studied.

Different than other therapsids?
The current basal therapsid family tree (Fig. 2) indicates the Anomodontia had a different origin than the rest of the Therapsida, including mammals. Add in a few taxa like Stenocybus and Microurania and the traditional topology changes to the heretical one.

So is the Therapsida diphyletic? Perhaps so… another heretical result produced by expanding the taxon list.

Addendum: Giving credit where credit is due, Olson 1962 remarked that therapsids might have had a dual origin, with anomodonts arising from the edaphosaur pelycosaurs. 

Is Galeops the sister to the dicynodonts? Apparently no, for the same reason.

References
Brinkman D 1981. The Structure and Relationships of the Dromasaurs (Reptilia: Therapsida) Breviora 465:34 pp. online here.
Broom, R. 1912. On some New Fossil Reptiles from the Permian and Triassic Beds of South Africa, Proc. zool. Soc. London 1912:859—876. online here.
Liu J, Rubidge B and Li J 2009. A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont. Proceedings of the Royal Society B 277 (1679): 285–292.
Olson EC 1962. Late Permian terrestrial vertebrates, USA and USSR. Transactions of the American Philatelci Society N.S> 25: 1-225.
Ruta M, Angielczyk KD, Fröbisch J and Benton MJ 2013. Decoupling of morphological disparity and taxic diversity during the adaptive radiation of anomodont therapsids. Proceedings of the Royal Society B (Biological Sciences) online here. Supp material here.]