Teraterpeton: more post-crania

Pritchard and Sues 2019
bring us additional post-cranial data on Teraterpeton (Fig. 1, Sues 2003), the long-snouted sister to Trilophosaurus with an atypical antorbital fenestra and displaced naris.

Figure 1. Teraterpeton with new elements added. Toes are largely unknown, but added here based on proximal phalanges.

Figure 1. Teraterpeton with new elements added. Toes are largely unknown, but added here based on proximal phalanges. None of these elements come as a surprise, based on phylogenetic bracketing in the LRT. Note the lepidosaur-like hind limbs, because this IS a lepidosaur.

Teraterpeton hrynewichorum (Sues 2003, Pritchard and Sues 2019) Late Triassic, ~215 mya, was described as euryapsid (lacking a lateral temporal fenestra) and possibly related to the rhynchocephalian, Trilophosaurus on that basis. Here Teraterpeton is a sister to Trllophosaurus, but with a stretched out rostrum, an antorbital fenestra and fewer teeth, still characteristically narrower at the root line. Teraterpeton also nests between Sapheosaurus and Mesosuchus. at the junction between the primitive sphenodontids and the advanced rhynchosaurs (see the LRT), all within the Lepidosauria. The manual unguals are robust with disparate sizes. The large acetabulum was open posteriorly and taller than the rest of the ilium. The metatarsals overlapped considerably. The asymmetry of the metatarsals is typical of sprawling taxa, like lizards.

Figure 2. Cladogram from Pritchard and Sues 2019 showing the nesting of Teraterpeton with Trilophosaurus. The yellow taxa are lepidosauromorphs and the green taxa are archosauromorphs in the LRT. Taxon exclusion folds them together like a deck of cards.

Figure 2. Cladogram from Pritchard and Sues 2019 showing the nesting of Teraterpeton with Trilophosaurus. The yellow taxa are lepidosauromorphs and the green taxa are archosauromorphs in the LRT. Taxon exclusion folds them together like a deck of cards.

The Pritchard and Sues (P+S) Teraterpeton cladogram
(Fig. 2) shuffles lepidosauromorphs (yellow) and archosaurmorphs (green) together like a deck of cards. Unfortunately the authors were following old traditional cladograms that wrongly considered Diapsida monophyletic. The large reptile tree (LRT, 1395 taxa) separates lepidosauromorphs from archosauromorphs at the first reptile dichotomy, a factor not recognized by the authors. Taxon exclusion is a problem here.

Where do we agree?

  1. Coelurosauravus and kin nest with drepanosaurs.
  2. Teraterpeton is close to Trilophosaurus, Shringisaurus and Azendohsaurus
  3. Lepidosaurs, like Huehuecuetzpalli, nest close to Rhynchocephalians
  4. Tritosaurs, like Macrocnemus, nest with Tanystropheus

Where do we disagree?

  1. The glider Coelurosauravus should nest with the gliding kuehneosaurs, not close to the aquatic Claudiosaurus.
  2. but not with unrelated basal diapsids, like Petrolacosaurus and Orovenator, which nest in the Archosauromorpha.
  3. All the protorosaurs (Prolacerta, Pamelaria, Protorosaurus, Boreopricea, Ozimek, should nest together.

Without an understanding
of the basal Lepidosauromorpha/Archosauromorpha dichotomy following the basalmost amniote, Silvanerpeton in the Viséan, taxon exclusion blurs the differences between archosauromorph-like lepidosaurs and lepidosaur-like protorosaurs, convergent with one another.

Convergence is revealed by the LRT
not by the Pritchard and Sues cladogram that suffers from taxon exclusion. Add taxa to recover the basal split between the new Archosauromorpha and the new Lepidosauromorpha.

Pritchard AC and Sues H-D 2019. Postcranial remains of Teraterpeton hrynewichorum
(Reptilia: Archosauromorpha) and the mosaic evolution of the saurian postcranial skeleton. Journal of Systematic Palaeontology, DOI: 10.1080/14772019.2018.1551249
Sues H-D 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian. Journal of Earth Science 40(4): 635-649.


Leptosaurus: another transitional taxon between Rhynchocephalia and Rhynchosauria

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Azendohsaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus pulchellus (Fitzinger 1837, Zittel 1887, Renesto and Viohl 1997; aka: Kallimodon Cocude & Michel, 1963) SCHA 40 Late Jurassic, Tithonian Stage, Germany,
155.7 to 150.8 Ma.

Holotype: Leptosaurus neptunicus Fitzinger 1837.

Rhynchocephalians are generally not so small, but this one is, likely yet another case of miniaturization at the base or transition to a major clade. In this case the SCHA 40 specimen attributed to Leptosaurus (I haven’t seen the holotype) is basal to the much larger Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus. Priosphenodon and rhynchosaurs on the other.

The large reptile tree (still not updated) keeps adding transitional taxa without changing the tree topology. That’s a measure of its strength. And more taxa using the same number of characters keeps dropping that character/taxon ratio.

Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46.

Azendohsaurus postcrania – svp abstracts 2013

Updated May 15, 2015 with a new nesting for Azendohsaurus back to a sister to the lepidosaur, Trilophosaurus.

From the abstract:
Nesbitt et al. 2013 wrote, “During the Triassic, a number of highly disparate archosauromorphs populated both terrestrial (e.g., Trilophosaurus, rhynchosaurs) and marine ecosystems (e.g., tanystropheids) across Pangea. Unfortunately, the unique and sometimes utterly bizarre body plans of these reptiles (e.g., specialized feeding adaptations) create a major challenge in understanding early archosauromorph relationships and patterns of diversification, as teasing apart homology from homoplasy has been difficult with the current sample of taxa.

“Here we present the postcranial anatomy of Azendohsaurus madagaskarensis, an early archosauromorph from the Middle-Late Triassic of Madagascar. Azendohsaurus madagaskarensis comes from a monotypic bone bed containing an ontogenetically variable sample, with preservation ranging from whole, disarticulated bones, to articulated partial skeletons. From this bonebed, the entire anatomy of the taxon is represented. Azendohsaurus madagaskarensis possessed an elongated neck, short tail, and stocky limbs. The manus and pes have unexpectedly short digits, terminating in large, recurved ungual phalanges. Together with the skull, knowledge of the postcranial skeleton elevates A. madagaskarensis to another highly apomorphic and bizarre Triassic archosauromorph.

“Even so, recovery, description and analysis of the full anatomy of A. madagaskarensis provides clues to understanding the relationships of this species and other problematic and anatomically specialized taxa, including the North American Late Triassic archosauromorphs Trilophosaurus and Teraterpeton. For example, A. madagaskarensis, Trilophosaurus, and Teraterpeton share a dorsally hooked quadrate and enlarged, trenchant unguals, whereas Trilophosaurus and Teraterpeton alone share a number of other character states (e.g., restricted scapular blade, premaxillary beak). We tested these observations in a newly constructed phylogenetic analysis centered on Triassic archosauromorphs and archosauriforms. We find that A. madagaskarensis, Trilophosaurus, Spinosuchus, and Teraterpeton form a clade within Archosauromorpha, but the relationships of this clade to other groups of Triassic archosauromorphs (e.g., archosauriforms, rhynchosaurs, tanystropheids) remains poorly supported. The newly recognized clade containing A. madagaskarensis, Trilophosaurus, and Teraterpeton demonstrates high disparity of feeding adaptations even within a closely related group of basal archosauromorphs.”

First of all,
its great to hear the postcrania of Azendohsaurus is finally on the table, soon to be published, I presume. The skull nests it as a sister to Trilophosaurus, so the short tail, short digits and stocky limbs of Azendohsaurus arrive at some surprise, except that Azhendosaurus is also related to the Priosphenodon and the rhynchosaurs.

Second of all,
Nesbitt et al. 2013 think Azendohsaurus is bizarre only because they are under the presumption that it is an archosauromorph. It is not, as documented by the large reptile tree. It’s no surprise then that Nesbitt et al. report, “relationships remains poorly supported.” Evidently Nesbitt et al. 2013 don’t have a large enough gamut in their reptile tree to recovers their featured taxon as a protorosaur and Trilophosaurus as a lepidosaur.

When Nesbitt et al. finally do figure out how to nest those taxa, they’ll also find out that their new sister taxa provide a gradual accumulation of traits that lead to all their oddball traits. It’s the same problem Nesbitt 2011 made nesting pterosaurs with archosaurs. In reality, when you don’t exclude the better candidates, tritosaur lepidosaurs provide the gradual accumulation of pterosaurian traits.

Nesbitt 2011 already made the big mistake of nesting Mesosuchus as a basal archosauromorph when it is way closer to sphenodontids. Youngina would have been a better choice as a basal archosauromorph. It’s way more plesiomorphic with regards to proterosuchids, erythrosuchids and choristorderes. 

The exception

Figure 2. Teraterpeton, a former enigma that nests here between Chanaresuchus and Tropidosuchus.

Figure 2. Teraterpeton, a former enigma that nests in the large reptile tree with Trilophosaurus despite the differences.

Nesbitt et al. found that Teraterpeton, Trilophosaurus and Azendohsaurus shared a dorsally hooked quadrate and enlarged trenchant unguals. Pamelaria has a similarly hooked quadrate and unguals of similar size.

I hope the Nesbitt team goes to a larger gamut tree and tests their taxa against other candidates before they publish another problem-filled paper like Nesbitt (2011) with strange bedfellows (sisters that don’t share very many traits) all over the place. The nestings of these featured taxa in the large reptile tree are strongly supported.

Nesbitt, S, Flynn J, Ranivohrimanina L, Pritchard A and Wyss A 2013.
Relationships among the bizarre: the anatomy of Azendohsaurus madagaskarensis and its implications for resolving early archosauromroph phylogeny. Journal of Vertebrate Paleontology abstracts 2013.

Moving Rhynchosaurs and Trilophosaurs Back into the Rhynchocephalia (Sphenodontia)

Rhynchosaurs are among the strangest reptiles that ever lived.
Characterized by a weird wide skull and protruding toothless, beak-like premaxillae, rhynchosaurs had rows of crushing teeth and giant jaw muscles for grinding food before swallowing to hasten digestion. Although the body was nothing special, no other reptile had such a skull. And evidently THAT is the cause of the current lack of a solid phylogenetic nesting.

Pre-rhynchosaurs, like Mesosuchus, appeared in the late Early Triassic to early Middle Triassic. All rhynchosaurs, including Hyperodapedon, disappeared in the Late Triassic.

Hyperodapedon in various views.

Figure 1. Hyperodapedon in various views. Note the extreme width of the skull and multiple rows of grinding teeth.

Where Did Rhynchosaurs Fit In?
Romer (1956) considered rhynchosaurs and sphenodontians to be related, but Cruickshank (1972), Benton (1983), Carroll (1988) and Dilkes (1998) split them apart, perhaps by placing too much emphasis on the lack of fusion in the tarsus and lack of acrodont teeth (see below). Caroll (1988) placed Trilophosaurus and rhynchosaurs with Prolacerta, Tanystropheus, Proterosuchus and Euparkeria. Unfortunately, no phylogenetic analysis has yet tested this nesting against a large gamut of reptiles, other than the large study.


Priosphenodon and its sphenodontid sisters, including Trilophosaurus and the rhynchosaur Hyperodapedo

Let’s Look at the Candidates
Above a selection of several rhynchocephalians is compared to three candidate diapsids. Overall Hyperodapedon, Mesosuchus and Trilophosaurus share more traits with Brachyrhinodon than with Youngina, Prolacerta or Proterosuchus. This is also demonstrated by several hundred characters and taxa in the large reptile tree. No other terrestrial reptile had such a wide skull, but Mesosuchus comes close. Brachyrhinodon and Priosphenodon come close to MesosuchusProlacerta and Proterosuchus were known for their narrow skulls filled with sharp teeth.

Here’s the Hump We Have to Get Over
According to the textbooks, lepidosaurs all have a fused astragalus and calcaneum and derived characters of bone growth with epiphyses. The problem is Trilophosaurus and rhynchosaurs don’t fuse those proximal ankle bones.

Benton (1983) reported, “Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”

These nits and picks are important, but taken as a whole (which is what we must do) currently there are no taxa more closely related to rhynchosaurs than rhynchocephalians (sphenodontians) and the trilophosaurs. Granted, all other rhynchocephalians had fused ankle bones, but having an unfused ankle is simply a matter of not fusing those bones, which develop separately in embryos. Acrodont teeth also form with fusion. Again, this would be a simple matter of switching off a gene.

Some of the Strangest Teeth You’ll Ever See
Benton (1983) discussed the placement of teeth wholly on the maxilla in rhynchosaurs. Let’s see what that looks like. The palatine (in orange) is the key bone in this controversy. In Mesosuchus the palatine is reduced and has lost its teeth. In Hyperodapedon the palatine retains teeth and extends lateral to the choanae to contact the premaxilla. In Howesia the palatine fuses to the maxillary tooth plate. In Trilophosaurus the palatine likewise fused to the maxillary tooth plate and the palatine teeth fused to the maxillary teeth, creating laterally elongated teeth with three lateral cusps. Click here for enlargement.

The palates of several rhynchocephalians, including rhynchosaurs

Figure 3. The palates of several rhynchocephalians, including rhynchosaurs. Click to enlarge.

Romer was right. Rhynchosaurs are closer to rhynchocephalians (sphenodontians). The differences noted by Benton (1983) are insufficient to outweigh a larger suite of characters that nest these taxa together.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Case EC 1928. A cotylosaur from the Upper Triassic of western Texas: Journal of Washington Academy of Science 18:177-178.
Cruickshank ARI 1972. 
The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences à Paris, Série D 275:2841-2844. 
Flynn JJ, Nesbitt, SJ, Parrish JM, Ranivoharimanana L and Wyss AR 2010. 
A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible”. Palaeontology 53 (3): 669–688. doi:10.1111/j.1475-4983.2010.00954.x
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Gregory JT 1945. Osteology and relationships of Trilophosaurus: University of Texas, Publication 4401:273-359.
Heckert AB et al. 2006. Revision of the archosauromorph reptile Trilophosaurus, with a description of the first skull of Trilophosaurus jacobsi, from the upper Triassic Chinle Group, West Texas, USA: Palaeontology 4(3):1-20.
Huxley TH 1859.
 Postscript to, R. I. Murchinson. On the sandstones of Morayshire (Elgin & c.) containing reptile remains; and their relations to the Old Red Sandstone of that country. Quarterly Journal of the Geological Society, London, 15, 138-152.
Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.
Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694. Parks P 1969. Cranial anatomy and mastication of the Triassic reptile,  Trilophosaurus [M.S. thesis]: University of Texas, 100 pp.
Romer AS 1956. Osteology of the Reptiles. University of Chicago Press, Chicago.