Shringasaurus: new rhynchocephalian lepidosaur with horns

Sengupta, Ezcurra and Bandyopadhyay 2017 bring us
a new, very large, horned rhynchocephalian lepidosaur, Shringasaurus (Fig. 1). Unfortunately, that’s not how the Sengupta team nested it (due to the sin of taxon exclusion, see below). Even so, there is consensus that the new taxon is closely related to the much smaller Azendohsaurus (Fig. 1).

Figure 1. Shringasaurus to scale with Azendohsaurus. Line art modified from Sengupta et al. Color added here. Note the anterior lappet of the maxilla over the premaxilla. The supratemporal  (dark green) remains.

Figure 1. Shringasaurus to scale with Azendohsaurus. Line art modified from Sengupta et al. Color added here. Note the anterior lappet of the maxilla over the premaxilla. The supratemporal  (dark green) remains.

From the abstract:
“The early evolution of archosauromorphs (bird- and crocodile-line archosaurs and stem-archosaurs) represents an important case of adaptive radiation that occurred in the aftermath of the Permo-Triassic mass extinction. Here we enrich the early archosauromorph record with the description of a moderately large (3–4 m in total length), herbivorous new allokotosaurian, Shringasaurus indicus, from the early Middle Triassic of India. The most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns that resemble those of some ceratopsid dinosaurs. The presence of horns in the new species is dimorphic and, as occurs in horned extant bovid mammals, these structures were probably sexually selected and used as weapons in intraspecific combats. The relatively large size and unusual anatomy of Shringasaurus indicus broadens the morphological diversity of Early–Middle Triassic tetrapods and complements the understanding of the evolutionary mechanisms involved in the early archosauromorph diversification.”

Allokotosauria
Shringasaurus was nested in the clade, Allokotosauria, According to Wikipedia, “Nesbitt et al. (2015) defined the group as a  containing Azendohsaurus madagaskarensis and Trilophosaurus buettneri and all taxa more closely related to them than to Tanystropheus longobardicus, Proterosuchus fergusi, Protorosaurus speneri or Rhynchosaurus articeps.” This definition was based on the invalidated hypothesis that rhynchosaurs and allokotosaurs were close to the base of the Archosauriformes as the addition of more taxa will demonstrate. Basically this clade equals Trilophosaurus, Azendohsaurus and now Shringasaurus. In the large reptile tree (LRT, 1049 taxa) this clade nests between Sapheosaurus + Notesuchus and Mesosuchus + Rhynchosauria all nesting within Sphenodontia (=  Rhynchocephalia), so they are all lepidosaurs. All you have to do is add pertinent taxa to make this happen in your own phylogenetic analysis.

Figure 2. Scene from the 1960 film, The Lost World, featuring a giant iguana with horns added presaging the appearance of Shringasaurus.

Figure 2. Scene from the 1960 film, The Lost World, featuring a giant iguana with horns added presaging the appearance of Shringasaurus.

Coincidentally the 1960 film,
The Lost World featured an iguana made up with horns similar to those of Shringasaurus.

References
Sengupta S, Ezcurra MD and Bandyopadhyay S 2017. A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India. Nature, Scientific Reports 7: 8366 | DOI:10.1038/s41598-017-08658-8 online here.

No Wiki page yet.

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Tulerpeton: a Devonian reptile!

This post was updated February 24, 2017, after new data on Tulerepton became available. 

This latest nesting 
of the former basal tetrapod, Tulerpeton (Fig. 2), as a Devonian reptile in the large reptile tree (957 taxa) was both anticipated (Fig. 1) and welcome.

As you may recall…
Middle Devonian tetrapod trackways (preceding and coeval with the basal bony fish Cheirolepis and the lobe fins Eusthenopteron and Osteolepis) seemed anachronistic when first announced. But it’s all coming together now. And this new nesting adds precious time for evolution to produce the variety of amphibian-like reptiles present in the Viséan, still awaiting consensus confirmation of their reptilian status.

Figure 1. The nesting of Tulerpeton in the Latest Devonian, at the base of the Lepidosauromorpha.

Figure 1. The nesting of Tulerpeton in the Latest Devonian, at the base of the Lepidosauromorpha. This taxon was added to this graphic that was published online in August 2016.

According to Wikipedia
Tulerpeton curtum
(Lebedev 1984, Fammenian, Latest Devonian, 365 mya; Fig. 1) is “one of the first true tetrapods to have arisen.” It was distinct from less derived Acanthostega and Ichthyostega by a strengthened limb structure. It was also half to an eighth the size of these basal tetrapods. A fragmented skull is known for Tulerpeton, but the only fragment I’ve seen is a vague round premaxilla on small reconstructions. Both the manus and pes have 6 digits, all provided with clawed unguals. (NOTE ADDED MARCH 6, 2017: The pes has only five digits after a fresh reconstruction)

FIgure 1. Tulerpeton compared to Eldeceeon.

FIgure 2. Tulerpeton compared to similarly-sized Eldeceeon. The loss of one digit in the manus and pes occurred between the Fammenian and Viséan.

Tulerpeton lived in shallow marine waters.
Little is known of this Eldeceeon-sized specimen, but the limbs and pectoral girdle are fairly well preserved. And these were enough to nest it with Eldeceeon (Fig. 1) out of 956 other candidate taxa in the LRT.

Coates and Ruta 2001 report:
“The most taxon-inclusive crown hypothesis incorporates the hexadactylous Late Devonian genus Tulerpeton as a basal stem amniote, thereby pegging the lissamphibian amniote divergence to a minimum date of around 360 Ma.” So there were early rumors. Only taxon exclusion prevented prior workers from recovering the reptile relationship earlier, no doubt due to the six fingers and toes on this putative basal tetrapod.

The loss of the sixth digit
occurred more than once, just as the later loss of a fifth digit occurred more than once. We should look for taxa with six fingers at the base of the Reptilomorpha and Seymouriamorpha — unless Tulerpeton developed a sixth finger on its own.

Phylogenetic analysis
originally placed Tulerpeton near the base of reptilomorphs, like Proterogyrinus and Eoherpeton. Later workers nested it as a more basal member of the Tetrapoda, between Acanthostega and Greererpeton.

Here
those long, clawed fingers and toes, and the individual proportions of the metapodials and phalanges nested Tulerpeton with Eldeceeon (Fig. 1) at the base of the Lepidosauromorpha, very near the base of the Reptilia. This clade is derived from a sister to the basalmost reptile, the late-surviving (Westphalian) Gephyrostegus bohemicus.

This new nesting of Tulerpeton pushes the origin of the Reptilia
from the Early Carboniferous back to the Late Devonian. Unfortunately, traditional phylogenetic analyses have not yet recognized the amphibian-like reptiles that were (by way of phylogenetic bracketing) laying amniotic eggs, the hallmark of the Reptilia.

Major studies do not yet recognize the reptile status
of Gephyrostegus and Tulerpeton. Hopefully someone will add them and Eldeceeon to a future taxon list to confirm or refute the present findings.

References
Coates MI and Ruta M 2001 (2002). Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.

wiki/Tulerpeton

What is Triopticus? (It’s not what they think it is…)

Updated July 13, 2017 with new bone identifications for Triopticus. These further cement the sisterhood to Tanytrachelos. 

It’s been a long time
since an interesting ‘reptile’ showed up in the literature. Especially an ‘enigma’ like this one.

A recent paper by Stocker et al. 2016
reports on a domed and expanded Late Triassic cranium that they identify as an archosaur, but it’s unlike that of any other archosaur. Triopticus primus was named for its three eyes, with a big one on top (Fig. 1). The authors compared the domed appearance of the cranium in Triopticus with a Cretaceous dome-headed ornithischian dinosaur, Stegoceras.  They also discussed convergence in general and provided a CT scan brain endocast of Triopticus.

Unfortunately 
the authors employed a prior cladogram (Fig. 2) by Nesbit et al. 2015, expanded from Pritchard et al. 2015. that was shown to not recover sister taxa that looked alike and did not provide a gradual accumulation of derived traits at several nodes. In their cladogram Triopticus nested without resolution among basal archosauriforms like Proterosuchus, which looks nothing like it. By contrast, the LRT was able nest and fully resolve Triopticus elsewhere.

Figure 1. In round 1 I added characters shown here to the LRT in two passes. One recovered a sisterhood with mesosaurs. The other nested with Tanytrachelos, among the tanystropheid tritosaur lepidosaurs. Both shown here for comparison.

Figure 1. In round 1 I added characters shown here to the LRT in two passes. One recovered a sisterhood with mesosaurs. The other nested with Tanytrachelos, among the tanystropheid tritosaur lepidosaurs. Both shown here for comparison. Triopticus would be 2x the size of the giant Tanyrachelos from New Mexico.

From the Stocker et al. abstract:  “Exemplifying this extreme morphological convergence, we present here a new dome-headed taxon from the assemblage, which further illustrates the extraordinary range of morphological disparity present early in the Late Triassic.” That ‘extraordinary range’ should be — and will be — chopped down substantially with the right sister taxa.

A few problems with the archosauriform hypothesis include:

  1. No other archosauriforms, until you get to pachycelphalosaurs in the Cretaceous, expand the cranium deleting the upper temporal fenestra.
  2. The entire rostrum and mandible is absent, so no naris, antorbital fenestra or teeth are known, even in part.
  3. They dubiously identified an antorbital fenestra and fossa at the edge of the fossil.
  4. …and they were not aware that Tanytrachelos and kin, including pterosaurs within the – Lepidosauria -, also have an antorbital fenestra, but without a fossa.
  5. A large pineal opening is present, but never present at such a size in archosauriforms.
  6. The extreme angle of the rostrum coupled with the large orbit are traits not found in basal archosauriforms that typically have a long boxy rostrum.
Figure 2. Stocker et al. 2106 cladogram nesting Triopticus uncertainly within a set of unresolved basal archosauriforms. The LRT completely resolves that node.

Figure 2. Stocker et al. 2106 cladogram nesting Triopticus uncertainly within a set of unresolved basal archosauriforms and far from the Tanystropheidae. The LRT completely resolves all nodes. Note how this cladogram mixes Lepidosauromorpha with Archosauromorpha and separates the protorosaurus, Protorosaurus and Prolacerta.

This is a perfect problem
for the large reptile tree (LRT) which now provides then 820, now 1036 opportunities for Triopticus to nest in. With that large number of taxa, unfortunately I had to split the matrix in two, even for a simple Heuristic Search. By contrast, the Stocker et al. matrix included 30 taxa and 247 characters.

Stocker et al. report,
“We chose this dataset because the following combination of character states in Triopticus are also present in some archosauromorph taxa:

  1. presence of a single occipital condyle;
  2. ossified laterosphenoid;
  3. presence of a metotic strut of the otoccipital;
  4. presence of upper and lower temporal fenestrae;
  5. presence of an antorbital fenestra and fossa formed by the lacrimal.”

They provided no reconstructions of included taxa.

First,
I tested Triopticus against basal tetrapods and the new Lepidosaurmorpha and found that Triopticus nested with the aquatic, long-necked tritosaur Tanytrachelos (Fig. 1), large specimens of which were recently found in New Mexico (Fig. 3). Like Triopticus the rostrum descends at a high angle from a tall cranium in Tanytrachelos, which also shares a large orbit and a large pineal foramen (at present known only from sister taxa). Like related fenestrasaurs and langobardisaurs, Tanytrachelos also had a small antorbital fenestra without a fossa, but that would have been beyond the rim of the broken skull in Triopticus (Fig. 5).

Figure 2. A large incomplete Tanytrachelos from New Mexico compared to the smaller more complete East Coast specimen. Triopticus would be twice as large as the New Mexico specimen.

Figure 3. A large incomplete Tanytrachelos from New Mexico compared to the smaller more complete East Coast specimen. Triopticus would be twice as large as the New Mexico specimen.

Second,
I tested Triopticus with the rest of the matrix, the new Archosauromorpha, and found that Triopticus nested with the mesosaurs (Fig. 4), an aquatic enaliosaur clade close to thalattosaurs and ichthyosaurs, all derived from basal pachypleurosaurs. It did not nest with archosauriforms. While basal mesosaurs have typical diapsid temporal regions, Mesosaurus, like Triopticus, closes up the upper temporal fenestra, then the lateral temporal fenestra with bone expansion.  Mesosaurs also retain a relatively large pineal foramen and have large eyes, but they don’t have a sharply descending preorbital region.

Mesosaurus

Figure 4. Mesosaurus, like Triopticus, has a large pineal foramen and expands the skull bones to obliterate former temporal fenestrae.

Digital Graphic Segregation
was applied to the cranial lump that is Triopticus (Fig. 5) and the skull suture patterns, perhaps overlooked by those with firsthand access due to the expansion of the cranial bones, revealed a Tanytrachelos-like morphology (Fig. 2). I illustrate this interpretation here with the hope that this hypothesis can be either confirmed or falsified. This is a tough assignment.

Figure 5. Triopticus reconstructed along the bauplan of Tanytrachelos.  The upper temporal fenestra is the top half of a divided lateral temporal fenestra. At 72 dpi this is 90 percent of actual size.

Figure 5. Triopticus reconstructed along the bauplan of Tanytrachelos. The upper temporal fenestra is the top half of a divided lateral temporal fenestra. At 72 dpi this is 90 percent of actual size.

Tanystropheids
have been reported from the Hayden Quarry of northern New Mexico (Chinle Formation) far from the west central Texas location of Otis Chalk. Stocker et al. included Tanytrachelos in their study, even though they have not provided a reconstruction of it, so it is difficult to imagine how they interpreted it. Tanystropheids, in general, have widely varying skull shapes. Triopticus appears to have expanded the morphospace just a little, not a lot.

The loss of ventral material in the Triopticus fossil
appears to have occurred at the roof the narial/oral opening.

So what other long-necked animal
expands the cranium like Triopticus? Giraffa, the giraffe. Maybe it will turn out to be a better analogy than short-necked Stegoceras?

References
Nesbitt SJ, Flynn JJ, Pritchard AC, Parrish JM, Ranivoharimanana L and Wyss AR 2015. Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. Bulletin of the American Museum of Natural History 899, 1-125.
Pritchard AC, Turner AH, Nesbitt SJ, Irmis RB and Smith ND 2015. Late Triassic tanystropheid (Reptilia, Archosauromorpha) remains from northern New Mexico (Petrified Forest Member, Chinle Formation): insights into distribution, morphology, and paleoecology of Tanystropheidae. Journal of Vertebrate Paleontology, 10.1080/02724634.02722014.02911186.
Stocker MR, NesbittSJ, Criswell KE, Parker WG, Witmer LM, Rowe TB, Ridgely R  Brown MA 2016. A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives. Current Biology (advance online publication)DOI: http://dx.doi.org/10.1016/j.cub.2016.07.066   pdf

Tridentinosaurus antiquus: a glider ancestor, not a protorosaur

I had never heard of this one before. 
Evidently this Early Permian reptile is famous for being fossilized between volcanic layers and for preserving more skin than bone. Using DGS I was able to tease out some of the bone (Fig. 1) and nest Tridentinosaurus not with the protorosaurs, as Leonardi (1959) proposed, but with basal lepidosauriforms. Tridentinosaurus nests in the large reptile tree as an Early Permian descendant of the late-surviving Palaegama and an ancestor to the Late Permian ‘rib’ glider, Coelurosauravus and the Late Triassic ‘rib’ glider, Icarosaurus along with other glider clade members.

Figure 1. Tridentinosaurus at 26.5 cm long is an Early Permian ancestor to Late Permian Coelurosauravus and Late Triassic Icarosaurus.

Figure 1. Tridentinosaurus at 26.5 cm long is an Early Permian ancestor to Late Permian Coelurosauravus and Late Triassic Icarosaurus. Here two images taken in different light conditions were superimposed, then traced. An arboreal lifestyle is suspected here, based on the long limbs and toes.

At the base of the glider clade,
Tridentinosaurus was also a sister to Jesairosaurus and the drepanosaurs. The nesting was made after the tracing. Not many traits were gleaned from the skull. More were gleaned from the hands and feet. It helps to have 693 other taxa to test it against. With such a generalized body, this specimen could have nested in several places at first glance.

Tridentinosaurus antiquus (Early Permian, Dal Piaz 1932, Leonardi 1959, 26.5cm long; Museum of Paleontology of the University of Padua 26567). Ronchi et al. described the specimen as “a beautiful but biochronologically useless specimen of which only the out−line of the soft tissues is well preserved.” The volcanic sediments in Sardinia occur in Cisuralian / Sakmarian deposits 291 million years old.

Although known for more than 50 years, 
and with quite a story to tell, this genus was not famous enough to merit its own Wikipedia page when I wrote this. Based on phylogenetic bracketing, the tail may have been twice as long originally.

Most prior workers do not nest 
Coelurosauravus and kin with Kuehneosaurus and kin (including Xianglong from the Cretaceous. Here they do nest together and Tridentinosaurus provides clues to the clade’s arboreal origin. Apparently this is a novel hypothesis, a by-product of having so many (694) taxa in the large reptile tree (subset Fig. 2).

Figure 2. Subset of the large reptile tree showing the nesting of Tridentinosaurus at the base of the gliders, close to the drepanosaurs.

Figure 2. Subset of the large reptile tree showing the nesting of Tridentinosaurus at the base of the gliders, close to the drepanosaurs.

References
Dal Piaz Gb. 1932 (1931). Scoperta degli avanzi di un rettile (lacertide) nei tufi compresi entro i porfidi quarziferi permiani del Trentino. Atti Soc. Ital. Progr. Scienze, XX Riunione, v. 2, pp. 280-281. [The discovery of the remains of a reptile (lacertide) in tuffs including within the Permian quartz porphyry of Trentino.]
Leonardi P 1959. Tridentinosaurus antiquus Gb. Dal Piaz, rettile protorosauro permiano del Trentino orientale. Memorie di Scienze Geologiche 21: 3–15.
Ronchi, A., Sacchi, E., Romano, M., and Nicosia, U. 2011. A huge caseid pelycosaur from north−western Sardinia and its bearing on European Permian stratigraphy and palaeobiogeography. Acta Palaeontologica Polonica 56 (4): 723–738.

Jesairosaurus and the drepanosaurs leave the Tritosauria :-(

My earlier reconstruction
of the basal lepidosauriform, Jesairosaurus (Fig. 1; contra Jalil 1997, not a protorosaur/prolacertiform) included several errors based on attempting to create a chimaera of several specimens of various sizes based on scale bars. In this case, scale bars should not have been used. Rather fore and hind parts had to be scaled to common elements, like dorsal vertebrae, as shown below (Fig. 2). I think this version more accurately reflects the in vivo specimen, despite its chimeric origins. All of the partial skeletons assigned to this genus were discovered at the same Early to Middle Triassic sandstone site and two were touching one another. A larger skull, ZAR 7, shows the variation in size from the skull to shoulders remains of the ZAR 6 specimen.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1997). The wide and flat ribs are interesting traits for a likely arboreal reptile.

Mother of all drepanosaurs
The Drepanosauria is an odd clade of slow-moving arboreal reptiles that includes Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus (Figs. 2, 3). Jesairosaurus was not a drepanosaur, but nested basal to this clade before the present revisions. It remains basal to the Drepanosauria now with revisions.

The revised reconstruction of Jesairosaurus 
shifts this clade away from Huehuecuetzpalli, Macrocnemus and the rest of the Tritosauria. Now Jesairosaurus and the drepanosaurs nests between Saurosternon, Palaegama and the so-called “rib” gliders, beginning with Coelurosauravus.

A short history of Jesairosaurus
Shortly after their discovery Lehman 1971 referred the several hematite encrusted specimens to the Procolophonida. Further preparation showed that they were referable to the Diapsida, according to Jalil (1990) and the, more specifically, to the Prolacertiformes (Jalil 1997) as a sister to Malerisaurus with Prolacerta as a common ancestral sister. Jalil did not include the closest sisters of Jesairosaurus as revealed by the present analysis.

With a much larger list of taxa,
the large reptile tree nests Malerisaurus between the Antarctica specimen assigned to Prolacerta (AMNH 9520) and the holotype of Prolacerta. Jesairosaurus, as mentioned above, nests with the basal lepidosauriformes. Any traits shared with protorosaurs are by convergence. Deletion of Jesairosaurus does not affect the nesting of the Drepanosauria as basal lepidosauriformes.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Arboreal
This new nesting shifts drepanosaurs closer to kuehneosaurs (Figs. 3, 4), another notably arboreal clade.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Certainly
there will someday be more taxa to fill in the current large morphological gaps in and around Jesairosaurus, but here’s what we have at present (Fig. 3) with regard to the origin of the so-called “rib” gliders (actually dermal rods, not ribs, as shown by Coelurosauravus) and the origin of the drepanosaurs.

Figure 4. Jesarosaurus to scale with sisters Palaegama and Coelurosauravus.

Figure 4. Jesairosaurus to scale with sisters Palaegama and Coelurosauravus.

The shifting of a clade
like Jesairosaurus + Drepanosauria occurred due to inaccurate reconstructions used for data. Science builds on earlier errors and inaccuracies. I let the computer figure out where taxa nest in a cladogram of 606 possible nesting sites, minimizing the negative effects of bias and tradition.

It’s sad
to see the drepanosaurs leaving the Tritosauria as it contains several oddly Dr. Seuss-ian variations on the tritosaur theme.

Also note the nesting
of the basal Rhynchocephalians, Megachirella and Pleurosaurus, between the palaegamids and the tritosaurs (Fig. 4). In the course of this study, both also received updates to their skull reconstructions. The former was difficult to interpret without knowing where it nested. What appeared to be an odd sort of a squamosal in Megachirella now appears to be a pair of displaced pleurosaur-like premaxillae. For Pleurosaurus I should not have trusted a prior line drawing by another worker. Here I used DGS to create what appears to be a more accurate skull without so many apparent autapomorphies.

References
Jalil N 1990. Sur deux cranes de petits Sauria (Amniota, Diapsida) du Trias moyen d’ Algerie. Comptes Rendus de I’ Academic des Sciences, Paris 311 :73 1- 736.
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Lehman JP 1971. Nouveaux vertebres du Trias de la Serie de Zarzai’tine. Annales de Paleontologic (Vertebres) 57 :71-93.

 

 

Opisthodontosaurus – not quite a captorhinid and definitely not a microsaur

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH 77469, here in ghosted lines. Colors represent missing bones.

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH
77469, here in ghosted lines. Colors represent missing bones. Note the concave maxilla ventral margin and the lower postorbital region compared to Cephalerpeton, its sister in the large reptile tree. These two and other taxa are sisters to captorhinids, but have narrower skulls.

A recent paper by Reisz et al. 2015 brings us a new basal reptile, Opisthodontosaurus carrolli (Fig. 1, Reisz et al. 2015; Artinskian, Early Permian ~289 mya), with teeth so robust it brought to mind a similar microsaur with thick posterior canines, Euryodus (Fig. 2).

Figure 1. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth.

Figure 2. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth.

Reisz et al. nested Opisthodontosaurus with Concordia (which it closely matches) and not far from Reiszhorhinus and Romeria primus. The large reptile tree duplicated these nestings, but recovered an excluded big-tooth taxon, Cephalerpeton (Fig. 1), closest to Opisthodontosaurus. I do not have data on another listed sister, Rhiodenticulatus, but will add it as soon as I am able to.

Reisz et al mentioned a depressed lateral dentary posterior to the tooth row. Since no large surangular was preserved and sister taxa have such a bone, it appears likely that  that depression received the missing surangular.

Like its sisters, Opisthodontosaurus is a basal lepidosaurmorph that nests with others that have a relatively narrower skull than outgroup taxa  including captorhinids and Thuringothyris. Tooth size varied a great deal in this clade.

Narrow-skulled sisters
to the captorhinids + cephalerpetontids, the larger Orobates and the smaller Milleretta, ultimately gave rise to the rest of the lepidosauromorphs, including limnoscelids, caseasaurs, diadectomorphs, pareiasaurs, turtles, lanthanosuchids, owenettids, kuehneosaurs and lepidosauriforms including pterosaurs.

Distinct from the microsaur Euryodus, Opisthodontosaurus had a taller squamosal, a greatly reduced supratemporal, a triangular postfrontal and postorbital along with a smaller basipterygoid with a more gracile cultriform process.

Thanks to Dr. Reisz for sending his paper this morning. This is a good discovery, well written and just missing one pertinent taxon.

References
Reisz RR et al. 2015. A new captorhinid reptile from the Lower Permian of Oklahoma showing remarkable dental and mandibular convergence with microsaurian tetrapods. The Science of Nature, October 2015, 102:50.

News on the Origin of Pterosaurs on YouTube

I just uploaded a pterosaur origins video on YouTube. Click here to view it.

Click to view this "Origin of Pterosaurs" video on YouTube.

Click to view this “Origin of Pterosaurs” video on YouTube. 17 minutes long.