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

Magnuviator, another basal scleroglossan.

A recent paper brings us
a Late Cretaceous “iguanomorph,” Magnuviator ovimonsensis (DeMar et al. 2017). It nested with Saichangurvel originally and here in the LRT, but both nest in the LRT with Acanthodactylus at the base of the Scleroglossa, not within the Iguania. The authors provided illustrations of the in situ fossils which I have restored to the in vivo configuration (Fig. 1) more or less.

Figure 1. Magnuviator ovimonsensis in situ from DeMar et al. 2017) and in vivo.

Figure 1. Magnuviator ovimonsensis in situ from DeMar et al. 2017) and in vivo.

DeMar et al.
added Magnuviator to the cladogram provided by Conrad 2008. Earlier we looked at the problems therein and in other earlier studies. As in the earlier Saichangurvel study, Magnuviator nests close enough to the clade Iguania that there are no intervening taxa.

References
DeMar Jr DG, Conrad JL, Head JJ, Varricchio DJ and Wilson GP 2017. A new Late Cretaceous iguanomorph from North America and the origin of New World
Pleurodonta (Squamata, Iguania). Proc. R. Soc. B 284: 20161902.

Lacerta: where is the upper temporal fenestra?

Lacerta viridis (Fig. 1) is a common extant lizard that has more skull bones than is typical for most tetrapods. It also loses the upper temporal fenestra found in other lizards, by posterior expansion of the postfrontal.

Figure 1. Lacerta viridis skull from Digimorph.org and used with permission. Here the enlargement of the postfrontal basically erases the former upper temporal fenestra. Several novel ossifications appear around the orbit and cheek.

Figure 1. Lacerta viridis skull from Digimorph.org and used with permission. Here the enlargement of the postfrontal basically erases the former upper temporal fenestra. Several novel ossifications appear around the orbit and cheek.

This Digimorph.org image
was colorized in an attempt at understanding the skull bones present here. The extant Lacerta nests with the larger extinct Eolacerta in the large reptile tree (918 taxa).

40 species are known of this genus.
Fossils are known from the Miocene (Čerňanský 2010). The tail can be shed to evade predators. This lizard is an omnivore. The curled quadrate frames an external tympanic membrane (eardrum). With the premaxillae fused, Lacerta has nine premaxillary teeth, with one in the center.

Not sure why this lizard developed extra skull bones.
It is found in bushy vegetation at woodland and field edges, and is not described as a burrower or a head basher.

Other diapsid-grade reptiles that nearly or completely lose the upper temporal fenestra include:

  1. Mesosaurus
  2. Chalcides
  3. Acanthodactylus
  4. Phyrnosoma
  5. Minmi

References
Čerňanský A 2010. Earliest world record of green lizards (Lacertilia, Lacertidae) from the Lower Miocene of Central Europe. Biologia 65(4): 737-741.
Linnaeus C 1758.
Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Lacerta viridis images online
wiki/Lacerta

Saichangurvel: not an iguanid, but very close…

This appears to be yet another case of a priori taxon exclusion.
Saichangurvel davidsoni (Conrad and Norell 2007; (IGM 3/858; Late Cretaceous) was originally considered a member of the Iguania, but here nests with Acanthodactylus, a lacertid taxon not mentioned in the original text, but nesting as a sister to the Iguania and is a basalmost scleroglossan.

Conrad and Norell report
“Iguania, like Squamata as a whole, has a rich, but patchy fossil record. Although many Cretaceous species have been identified, Saichangurvel davidsoni is the first known from a complete skeleton. Indeed, the recent revelation that none of the Euposaurus remains may be diagnosed as iguanians (Evans, 1993) renders Saichangurvel davidsoni the earliest iguanian known from complete remains.”

Contra Evans 1993
The LRT nests tiny Euposaurus with the much larger Iguana (Fig. 2) as yet one more example of phylogenetic miniaturization at the genesis of major clades. In this case the major clades are Iguania and Squamata. BTW the ResearchGate.net link for Euposaurus takes you to another SE Evans paper.

Distinct from Acanthodactylus,
the teeth of Saichangurvel have three cusps, convergent with Iguana and that may be why the specimen was originally nested with iguanids. The upper temporal fenestrae are not reduced by a posterior extension of the postfrontal. Acanthodactylus has simple cone-shaped teeth.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

The large reptile tree
(LRT) nests Saichangurvel very close to the Iguania (Fig. 2 in pink), but not in that clade. Unfortunately two of the top lizard experts in the world, Conrad and Norell, excluded taxa pertinent to the analysis, like Acanthodactylus and other basal scleroglossans (Fig 2 in green), That’s my only trump card here.

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

References
Conrad JL and Norell MA 2007. A complete late Cretaceous Iguanian (Squamata, Reptilia) from the Gobi and Identification of a new iguanian clade. American Novitates 3584:1-47.
Daza JD, Abdala V, Arias JS, Garcia-Lopez D and Ortiz P 2012. Cladistic Analysis of Iguania and a Fossil Lizard from the Late Pliocene of Northwestern Argentina”. Journal of Herpetology. 46(1):104-119.
Evans SE 1993. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios 27: 621–631.

Do gliding lizards (genus: Draco) actually grab their extended ribs?

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it.

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it. Images from Dehling 2016.

Gliding lizards
of the genus Draco (Figs. 1, 2) come in a wide variety of species. Similar but extinct gliding basal lepidosauriformes, like Icarosaurus (Fig. 2), form a clade that arose in the Late Permian and continued to the Early Cretaceous.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

A recent paper
(Dehling 2016) reported, “the patagium is deliberately grasped and controlled by the forelimbs while airborne.” Evidently this ‘membrane-grab’ behavior has not been noted before. I wondered if the rib skin is indeed grasped, or does the forelimb merely fold back against the leading edge of the patagium in a streamlined fashion? Photographs of climbing Draco specimens (Fig. 2) show that the patagium  can fully extend without the aid of the forelimbs to stretch them further forward.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut, a great place to rest the manus or grab the membrane.

A quick review of prehistoric gliding keuhneosaurs
(Fig. 3) show that the manus unguals are not quite as large and sharp as those of the pes and that the manus in gliding mode extends just beyond the shorter two anterior dermal struts so that the glider -may- have grasped the anterior struts in flight. Or may have rested the manus there. Remember, these are taxa unrelated to the extant Draco, which uses actual ribs to stretch its gliding membrane. The same holds true for the more primitive Coelurosauravus and Mecistotrachelos, which have not been traditionally recognized as basal kuehneosaurs.

* As everyone should know by now…
the so-called transverse processes in kuehneosaurs are the true ribs, only fused to the vertebrae. The ribs remain unfused to the vertebrae in the older and more primitive coelurosauravids. No sister taxa have transverse processes elongate or not.

References
Dehling M 2016. How lizards fly: A novel type of wing in animals.

Earliest(?) stem squamate – SVP abstracts 2016

Klugman and Pritchard 2016
believe they have found the earliest lepidosaur stem squamate (see below). The large reptile tree finds earlier stem squamates (Fig. 1, click here to enlarge).
Earlier we looked at the wider and narrower definitions of the term ‘stem’.
Figure 1. CLICK TO ENLARGE. Stem taxa are closest ancestors to living taxa. Here basal diapsids and marine enaliosaurs are stem archosaurs. Triceratops is a stem bird. Captorhinids are stem turtles. Pterosaurs are stem squamates.

Figure 1. CLICK TO ENLARGE. Stem taxa are closest ancestors to living taxa. Here basal diapsids and marine enaliosaurs are stem archosaurs. Triceratops is a stem bird. Captorhinids are stem turtles. Pterosaurs are stem squamates. The colors here indicate the wider definition of ‘stem’.

From the Klugman and Pritchard abstract (abridged)
“Crown group lepidosaurs are highly diverse: they comprise more than 7,000 globally distributed extant species of lizards and snakes (Squamata), plus the single rhynchocephalian genus Sphenodon. The earliest known lepidosaurs are rhynchocephalians from the Late Triassic of Europe, (1) and this group quickly diversified and achieved a global distribution by the end of the Triassic. In contrast, early squamates have a sparse fossil record; their first representatives are found in the Early-Middle Jurassic of Laurasia (2). Although Rhynchocephalia and Squamata diverged in the Middle Triassic, a 40-50 million years ghost lineage exists for Squamata. Jurassic squamates are already considerably derived, and have already diversified into their extant groups, which testifies to a substantial gap in the known fossil record. Here we report on a new lepidosaur from a Norian microvertebrate site in Petrified Forest National Park, Arizona. This fossiliferous locality is from the Upper Blue Mesa Member of the Chinle Formation, and is dated to 221 mya. The depositional environment is a shallow anoxic lake, where skeletal elements preserved are disarticulated and often fragmentary. The site has yielded a diverse small vertebrate fauna, including the new lepidosaurs and several undescribed rhynchocephalians. Skeletal elements are represented by numerous small, delicate pleurodont maxilla and dentaries. We integrated the material of the new lepidosaurs into phylogenetic analyses of Permo-Triassic Diapsida and Mesozoic Lepidosauromorpha, using maximum parsimony, maximum likelihood, and Bayesian analysis. All analyses support the new taxon as the sister taxon to all other Squamata, (3) substantially reducing the ghost lineage of Squamata. This discovery indicates that the absence of squamate fossils in their early evolutionary history could be caused in part by collection bias towards larger, more robust specimens. This taxon provides a look into the early evolutionary history of squamates. It also adds direct evidence of yet another major lineage of extant terrestrial vertebrates to originate in the Triassic.”
Notes
  1. In the LRT Megachirella (Middle Triassic) is an earlier basal rhynchocephalian. Bavariasaurus (Late Jurassic) and
  2. Lacertulus (Late Permian; Fig. 2) are basal stem squamates. TA104 (Rößler et al. 2012), an unnamed Early Permian lepidosaur close to Saniwa in the varanid clade is the earliest lepidosaur I have encountered yet, although this is based on low-rez data. Based on these nestings, the original radiation of lepidosaurs must have occurred in the Permian and then enjoyed very long period of stasis.  Lacertulus is the oldest known lepidosaur and older than any Late Triassic Petrified Forest taxa. It does not have pleurodont (fused to the jaw) teeth.
  3. The LRT is an analysis that includes a long list of pro or proto-squamates and tritosaurs that are sisters to the Squamata. Palaegama (Late Permian), Tridentinosaurus (Early Permian) and Saurosternon (Latest Permian) are sisters to the Lepidosauria and they are basal to the highly derived Late Permian taxon, Coelurosauravus. So the original radiation of lepidosaurs and their lepidosauriform sisters must have been in the Early Permian. If one deletes Sphenodon, then another stem squamate would be Macroleter (Middle Permian). Earlier than this and you get into stem turtles.
Figure 1. Lacertulus, a basal squamate from the Late Permian

Figure 2. Lacertulus, a basal squamate from the Late Permian

References
Klugman B and Pritchard AC 2016. Earliest stem-squamate (Lepidosauria) from the Late Triassic of Arizona. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism: New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834