New study on sphenodontians excludes sphenodontians

Simoes, Caldwell and Pierce 2020
bring us their views on sphenodontian phylogeny. Traditionally, Sphenodontia (= Rhynchocephalia) is the clade that includes the extant tuatara, Sphenodon (Figs. 1–3) and related taxa.

Figure 2. The dorsal spines of Tuatara (Sphenodon).

From the abstract:
“Here, we investigate the impact of a wide array of model choices on the inference of evolutionary trees and macroevolutionary parameters (divergence times and evolutionary rates) using a new data matrix on sphenodontian reptiles. Specifically, we tested different clock models, clock partitioning, taxon sampling strategies, sampling for ancestors, and variations on the fossilized birth-death (FBD) tree model parameters through time.”

“Here, we investigate the impact of a wide array of model choices on the inference of evolutionary trees and macroevolutionary parameters (divergence times and evolutionary rates) using a new data matrix on sphenodontian reptiles. Specifically, we tested different clock models, clock partitioning, taxon sampling strategies, sampling for ancestors, and variations on the fossilized birth-death (FBD) tree model parameters through time.”

“We provide a new hypothesis of sphenodontian classification, along with detailed macroevolutionary patterns in the evolutionary history of the group.”

Backstory from Simoes, Caldwell and Pierce:
“The concept of the name Rhynchocephalia was initially conceived to include Sphenodon punctuates (Fig. 1) upon the realization of its quite distinct systematic placement relative to squamates among reptiles by Günther 1867. However, the concept was later expanded and for decades it was used to include both sphenodontians and rhynchosaurs (Romer 1956, Williston 1925), which was later refuted since the first computer-based phylogeny of reptiles placed rhynchosaurs as a lineage of archosauromorphs (Benton 1985).

That Benton 1985 study was flawed due to taxon exclusion and other factors common at the genesis of software analysis in 1985. More recent work based on adding taxa overturned that aspect of Benton 1985 by returning rhynchosaurs to the lepidosauria and the sphenodontia.

Figure 2. Subset of the LRT focusing on Sphenodontia.Blue bars are taxa omitted by the authors.

Unfortunately, 
by leaving out so many sphenodontian taxa (Fig. 2) Simoes, Caldwell and Pierce bring us only 60% of a study.

Furthermore,
the authors chose an outgroup taxon that was not a lepidosaur, lepidosauriform nor lepidosauromorph. They chose Prolacerta, which, despite its name did not ‘come before Lacerta‘ (a squamate nesting with Eolacerta). Prolacerta nests in the large reptile tree (LRT, 1772+ taxa) basal to archosauriforms.

Furthermore,
by cherry-picking their inclusion set, the authors did not realize their outgroup taxon, Megachirella, was actually a in-group basalmost sphenodontian.

Furthermore,
the authors did not realize their in-group taxa Homeosaurus (2 specimens) nested outside the  Sphenodontia among the Protosquamata.

Furthermore,
two of their outgroup taxa, Ardeosaurus and Eichstättisaurus, are squamates in the ancestry of snakes in the LRT.

Furthermore, 
none of their four published cladograms agree with each other or the LRT. So, taken in concert, those are shaky phylogenetic grounds to base any study on.

Figure 1. The best data I have been able to found to document the origin of rhynchosaurs like Scaphonyx and Hyperodapedon. Despite their apparent (from the literature) commonality, there is precious little in the literature about rhynchosaurs.

How did rhynchosaurs leave the rhynchocephalia?
We looked at that many years ago. Carroll (1988) revisiting Carroll (1977) reported, “It was long thought that rhynchosaurs were closely related to modern sphendontids not the basis of general similarities of the skull and dentition. The common presence of primitive features such as the lower temporal bar only points to their common origin among early diapsids. Although the dentition appears to be vaguely similar, it is fundamentally different. Sphenodontids have only a single row of acrodont teeth in the maxilla, but rhynchosaurs have multiple rows of teeth set in sockets. Sphenodontids have a second row of teeth in the palatine, but this bone is edentulous in the rhynchosaurs. What appear to be long premaxillary teeth in the rhynchosaurs are actually processes from the premaxillary bones. Sphenodontids have true premaxillary teeth.”

Do you hear Carroll’s colleague, Larry Martin, laughing?
Clades and interrelationships are determined not by possibly convergent individual traits, but by phylogenetic analysis. The last common ancestor and all of its descendants is the only valid and irrefutable way to recognize and organize clades.

Getting back to Carroll (1977, 1988) the problem is:
the rhynchosaur outer tooth row is indeed the maxilla, the inner row is the palatine, as in rhynchocephalians, especially easy to see in Priosphenodon. That the palatine fuses to the maxilla does not take away the identity of either. Thus, the palatine is not edentulous in rhynchosaurs.

The premaxillary is also toothless
in Priosphenodon, currently considered a rhynchocephalian. Mesosuchus is considered a proto-rhynchosaur, not a rhynchocephalian, yet it has socketed teeth on the premaxilla. So there’s a transition zone developing between basal and derived rhynchocephalians, which are distinct, but decidedly related — because — no other taxa are closer to them than these two are to each other in the LRT.

At the start of his career, 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).”

At the time, and perhaps to this day,
Benton did not realize the lower temporal bar was derived in sphenodontians. Early lepidosaurs don’t have it.

Acrodont teeth are also derived from socketed teeth,
so all sphenodontids had to do was stop fusing their teeth to their skull in order to go back to the socketed teeth found in rhynchosaurs.

Rhynchosaurs stop fusing their ankles
at the same time that they stop fusing their teeth to their jaws. That’s just what they do. It doesn’t mean they get kicked out of their family. That would be “Pulling a Larry Martin.”

Figure 4. Rhynchocephalian and Rhynchosaur palates. That’s Priosphenodon in the middle leading to Mesosuchus and Howesia, to Trilophosaurus and Azendohsaurus and rhynchosaurs. That’s where the palatine grows as large as and alongside the maxilla. In derived taxa these two bones fuse creating the illusion that the maxilla has the entire tooth pad. Look at those palatine stems on Priospbenodon, which really come out on rhynchosaurs.

What can one learn from Simoes, Caldwell and Pierce 2020? 

1. Stop cherry-picking taxa
2. Stop trusting others for your cladograms and inclusion sets
3. Add more taxa to let your wider gamut cladogram tell you which taxa are in the inclusion set
4. Show fossils and reconstructions ,so readers can judge the accuracy of your scoring choices

It’s all comes down to taxon exclusion
and inappropriate taxon inclusion. Sure it’s faster and easier to trust others. But when you do, you and your team are now liable for their mistakes. Whatever your results, they depend on a valid phylogenetic context, missing in the sphenodontian study of Simoes, Caldwell and Pierce 2020.

Once you have a wide gamut cladogram,
it’s yours forever. Every worker should have their own.

The LRT has shown since 2011
that rhynchosaurs are derived sphenodontians. Additional taxa since then have only reinforced that nine-year-old hypothesis of interrelationships.

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References
Benton M J 1983. TheTriassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Phil. Trans. R. Soc. Lond. B 302, 605^717. Carroll, R. L. 1988 Vertebrate paleontology and evolution. New York: W. H. Freeman & Co.
Benton MJ 1985. Classification and phylogeny of the diapsid reptiles. Zool J Linnean Soc. 84(2):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. W. H. Freeman and Co. New York.
Günther A 1867. Contribution to the anatomy of Hatteria (Rhynchocephalus, Owen). Ann. Mag. Nat. Hist. (3) 20: 128-129.
Romer AS 1956. Osteology of the reptiles. 1st ed. Chicago: University of Chicago Press;
Simoes TR, Caldwell MW and Pierce S 2020. Sphenodontian phylogeny and the impact of model choice in Bayesian morphological clock estimates of divergence times and evolutionary rates. BMC Biol 18, 191 (2020). https://doi.org/10.1186/s12915-020-00901-5
Williston SW 1925. The osteology of the reptiles. Cambridge: Harvard University Press; 1925.

wiki/Sphenodon
wiki/Rhynchocephalia

https://pterosaurheresies.wordpress.com/2013/07/29/kaikaifilusaurus-and-the-origin-of-the-rhynchosaurs/

https://pterosaurheresies.wordpress.com/2013/03/23/sapheosaurus-bridges-the-sphenodontidtrilophosaurrhychosaur-gap/

https://pterosaurheresies.wordpress.com/2011/09/24/moving-rhynchosaurs-and-trilophosaurs-back-into-the-rhynchocephalia-sphenodontia/

https://pterosaurheresies.wordpress.com/2016/01/13/early-evolution-of-rhynchosaurs/

https://pterosaurheresies.wordpress.com/2014/02/18/the-origin-of-rhynchosaurs-revisited/

https://pterosaurheresies.wordpress.com/2014/03/20/arguments-against-the-rhynchosaurrhynchocephalian-rhylationship/

Colobops: back to Rhynchocephalia

Scheyer et al. 2020 revisit
Colobops noviportensis (unnamed in Sues and Baird 1993; Pritchard et al. 2018; Late Triassic; YPM VPPU 18835; Fig. 1) a tiny 2.5cm long skull originally considered a ‘pan-archosaur’. Using µCT scans, Pritchard et al. scored Colobops and nested it at the base of the Rhynchosauria. Pritchard et al. wrote: “Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied diapsid.”

You heard it here first in 2018. Colobops is a rhynchocephalian.

Figure 1. Colobops as originally presented and slightly restored.

That same week in 2018,
Colobops was added to the large reptile tree (LRT, now 1659+ taxa, then 1085 taxa) where it nested as a sister to the morphologically similar and size similar basal rhynchocephalian, Marmoretta (Fig. 2; Evans 1991). You can read about that nesting here.

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

This week,
Scheyer et al. nested Colobops with Sphenodon (Fig. 3), a basal extant rhynchocephalian. Sadly, the authors again omitted Marmoretta (Fig. 2).

Sues and Baird 1993 first described this specimen
without naming it and without a phylogenetic analysis, as a member of the Sphenodontia (Williston 1925), a junior synonym for Rhynchocephalia (Gunther 1867).

Marmoretta oxoniensis (Evans 1991, Waldman and Evans 1994; Middle/Late Jurassic, ~2.5 cm skull length; Fig. 2), orginally considered a sister of kuehneosaurs, drepanosaurs and lepidosaurs. Here in the LRT, Marmoretta nests between Megachirella and Gephyrosaurus + the rest of the Rhynchochephalia. Two specimens are known with distinct proportions in the skull roof.

Figure 3. Sphenodon, the extant tuatara, is close to Colobops, but Marmoretta is closer.

The LRT minimizes taxon exclusion
because it includes such a wide gamut of taxa, from Cambrian chordates to humans. The Colobops information has been online for the past two years. Colleagues, please use it. Don’t ‘choose’ taxa you think might be pertinent. Let the LRT provide you a long list of validated taxa competing to be the sister to your new discovery.

Final note: 
In the LRT (since 2011) even rhynchosaurs are lepidosaurs. Just add pertinent taxa and your tree will recover the same topology. Traditional paleontologists are taking their time getting around to testing this well-supported hypothesis of interrelationships.

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References
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Pritchard AC, Gauthier JA, Hanson M, Bever GS and Bhullar B-AS 2018. A tiny Triassic saurian from Connecticut and the early evolution of the diapsid feeding apparatus. Nature Communications open access DOI: 10.1038/s41467-018-03508-1
Scheyer TM, Spiekman SNF, Sues H-D, Ezcurra MD, Butler RJ and Jones MEH 2020. Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite. Royal Society Open Science 7:192179.
http://dx.doi.org/10.1098/rsos.192179
Sues H-D and Baird D 1993. A Skull of a Sphenodontian Lepidosaur from the New Haven Arkose (Upper Triassic: Norian) of Connecticut. Journal of Vertebrate Paleontology. 13 (3): 370–372.
Waldman M and Evans SE 1994. Lepidosauromorph reptiles from the Middle Jurassic of Skye. Zoological Journal of the Linnean Society 112:135-150.

wiki/Marmoretta
wiki/Colobops

https://pterosaurheresies.wordpress.com/2018/03/25/colobops-and-taxon-exclusion-issues/

Where would drepanosaurs nest, if Jesairosaurus was not known?

We’re getting back
to an older series today as we ‘play’ with the large reptile tree (1262 taxa, LRT) by cherry-deleting taxa.

Drepanosauromorpha are so distinct from other reptiles
that experts have been hard at work trying to figure out what they are—without success or consensus. There are so many competing ideas (which means none are convincing) that I’m going to refer you to the Wikipedia page on Drepanosauridae that lists and discusses them all with citations. The latest work (Pritchard and Nesbitt 2017) recovered a very basal diapsid nesting, but they did not realize that lepidosaur ‘diapsids’ were not related to archosaur ‘diapsids’, due to taxon exclusion at the genesis of reptiles.

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

Unfortunately,
all prior workers omitted or overlooked the widely tested closest relatives, Jesairosaurus (Jalil 1997, Fig. 1) followed by the basal lepidosauriformes, Tridentinosaurus, Lanthanolania, Sophineta and Palaegama (Fig. 1) in the LRT, which tests all prior sister candidates Megachirella (Fig. 2), at the base of the Rhynchocephalia (Fig. 3), is also closely related in the LRT. So, once again, taxon exclusion is the problem in all prior studies. Jesairosaurus was documented as the last common ancestor of drepanosauromorpha here in October 2012. This is not one of those “obvious as soon as you realize it” nestings. You really do need the wide gamut testing of the LRT to eliminate all other candidates.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

So let’s play the game of taxon exclusion…

If Jesairosaurus and all Archosauromorpha are deleted,
the remaining drepanosauromorphs do not shift to another node within the Lepidosauromorpha.

If Jesairosaurus and Hypuronector and all Archosauromorpha are deleted,
the remaining drepanosauromorphs do not shift to another node, and nest with basalmost Sphenodontia, like the BSRUG 29950-12 specimen related to Megachirella and Pleurosaurus.

If Lepidosauromorpha and Diapsida are deleted,
Jesairosaurus and the drepanosauromorphs nest with the herbivorous synapsids, Suminia and Dicynodon.

If Lepidosauromorpha and Diapsida are deleted,
Megalancosaurus alone nests between the herbivorous synapsids Venjukovia + Tiarajudens and Suminia + Dicynodon.

Figure 3. Subset of the LRT focusing on basal lepidosauriformes and Jesairosaurus at the base of the Jesairosauria. Several new clades are named here.

If only Diapsida is tested,
Jesairosaurus and the remaining drepanosauromorphs nest as a clade between the sauropterygians and mesosaurs + thalattosaurs + ichthyosaurs.

If only Diapsida is tested,
Megalancosaurus alone nests between the sauropterygians and mesosaurs + thalattosaurs + ichthyosaurs.

Nomenclature and some suggestions:

1. Jesairosauria — Jesairosaurus, Megachirella, their last common ancestor all descendants. More taxa reveal this phylogenetic pattern that has, so far, escaped the notice of professional paleontologists.
2. Rhynchocephalia — Gephyrosaurus, Megachirella, their last common ancestor all descendants.
3. Sphenodontia —  Sphenodon, Ankylosphenodon, their last common ancestor all descendants.
4. Transphenodontia — Trilophosoaurus, Mesosuchus, their last common ancestor all descendants. These taxa bridge the gap between sphenodonts and rhynchosaurs and include the latter. More taxa reveal this phylogenetic pattern that has, so far, escaped the notice of professional paleontologists.
5. Rhynchosauria — Rhynchosaurus, Hyperodapedon, their last common ancestor all descendants.
6. Pseudoribia — Coelurosauravus, Icarosaurus, their last common ancestor all descendants. These so-called ‘rib-gliders’ actually use elongate dermal ossifications to extend their gliding membranes. More taxa and a closer examination of Icarosaurus and kin reveal this clade that has, so far, escaped the notice of professional paleontologists.

The related taxa shown
in figure 3 as a subset of the large reptile tree come together by way of taxon inclusion. Prior workers missed these relationships by excluding taxa. Rhynchosaurs were once considered Rhynchocephalians, but recently that has not been accepted based on the invalidated hypothesis that rhynchosaurs were archosauriformes.

Invalidated or modified nomenclature:

1. Allokotosauria — While protorosaurs, including Pamelaria, are basal members of the new Archosauromorpha, Trilophosaurus and Azendohsaurus are members of the new Lepidosauromorpha.
2. Diapsida — The LRT documents two unrelated clades evolving diapsid skull architecture. In the LRT only archosauromorph diapsids are considered Diapsida. More taxa reveal this pattern that has, so far, escaped the notice of professional paleontologists.

I hope readers enjoy and learn from these daily blogs.
If you disagree with any of the results, I encourage you to run your own tests with similar taxon lists, then let us all know if you confirm or refute the LRT results. Don’t be like those who just hurl adjectives at the work done here. Keep up your professional demeanor and attitude and be prepared to accept new discoveries if they cannot be refuted. The strength of the LRT is that is covers all available candidates and minimizes taxon exclusion problems that plague smaller prior studies.

References
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.
Pritchard AC and Nesbitt SJ 2017. A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida. Royal Society Open Science DOI: 10.1098/rsos.170499

wiki/Jesairosaurus
wiki/Drepanosaur
wiki/Allokotosauria

New rhynchocephalian, Vadasaurus, is not a pleurosaur ancestor

Once again
taxon exclusion bites a paper on the set up and conclusion.

Bever and Norell 2017 bring us
a perfect Solnhofen (Late Jurassic) fossil of a small rhynchocephalian, Vadasaurus herzogi (Figs. 1,2) that they mistakenly promote as a pleurosaur ancestor (Fig. 5). We looked at the real pleurosaur ancestors several years ago here.

Figure 1. Vadasaurus is a perfectly preserved Solnhofen fossil rhynchocephalian. PILs and colors added. The pelvis is semi-perforate. The proximal tarsus is not co-ossified.

Vadasaurus herzogi (Bever and Norell 2017, Late Jurassic) AMNH FARB 32768, was originally nested between Sapheosaurus + Kallimodon and the aquatic pleurosaurs, Pleurosaursus and Palaeopleurosaurus. Here Vadasaurus nests very closely with Leptosaurus, a terrestrial taxon omitted originally. Close examination of photos in the literature (Fig. 2) shows that Bever and Norell overlooked the supratemporal, the jugal’s quadratojugal process and added a mandible fenestra that is not present. The lack of co-ossificiation in the astragalus and calcaneum is a trait that is retained by all later taxa, including the trilophosaurs, azendohsaurs and rhychosaurs. Priosphenodon, listed in both competing trees, is the outgroup for the Rhynchosauria.

Figure 2. The skull of Vadasaurus showing the jugal’s quadratojugal process, the portion of the postfrontal entering the upper temporal fenestra and the mandible interpreted differently than Bever and Norell 2017.

The large reptile tree (LRT, 1121 taxa, subset Fig. 3) does not include all of the taxa employed by Bever and Norell 2017. In like fashion, Bever and Norell do not include all of the rhynchocephalian taxa employed by the LRT.

Here, with high Bootstrap scores
(Fig. 3) the LRT nests Pleurosaurus with Megachirella at the base of the Rhynchocephalia (Fig. 3). Palaeopleurosaurus nests separately, with Ankylosphenodon (Fig. 5), still close to the base of the clade. Kallimodon nests close to Vadasaurus in the Bever and Norell tree, but with Sphenodon in the LRT. Other differences also occur. Homeosaurus is included in the Bever and Norell tree, but nests outside the Rhynchochephalia in the LRT.

Figure 3. Subset of the LRT nesting Vadasaurus with Leptosaurus in the Rhynchocephalia

The Bever and Norell cladogram
(Fig. 4) is very poorly supported with most nodes <50 and only one node above 80. The outgroup is wrong, based on results recovered by the LRT which tests a over 1000 possible outgroup candidates. Youngina is completely unrelated. It nests close to the archosauriform, Proterosuchus. Pristidactylus is am extant squamate also unrelated to rhynchocephalians.

By contrast,
the subset of the LRT (Fig. 3) is strongly supported with high Bootstrap scores throughout. Outgroups going back to basal tetrapods are documented.

Figure 4. Cladogram from Bever and Norell 2017 with the addition of Vadasaurus. When Bootstrap support is below 50 it is not marked. This tree does not include the correct outgroup and the Rhynchosauria + Trilophosaurus and other taxa.

The Bever and Norell paper does not provide reconstructions,
but ReptileEvolution.com does (Fig. 5). Chronology is all over the place in this clade. Megachirella and BRSUG 29950, at the base of this clade, are both Middle Triassic. Pleurosarus is Late Jurassic. Ankylosphenodon is Early Cretaceous. Sphenodon is extant.

Figure 5. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

When Megachirella, Leptosaurus and other taxa
not employed by Bever and Norell are deleted from the LRT, the topology of the tree does not change.

Figure 6. Leptosaurus was omitted by Bever and Norell. Note the triangular skull, gracile mandible, radiale and other traits reported by the authors.

Bever and Norell report that Vadasaurus is:
“Diagnosed in an exclusive clade with Pleurosauridae based on

1. a triangular skull in the dorsal view,– as in Leptosaurus (Fig. 6)
2. posteriorly tapering maxilla, – as in Leptosaurus (Fig. 6)
3. posteriorly tapering palatine, – no, it’s posteriorly round in Vadasaurus (Fig. 2)
4. moderately open interpterygoid vacuity, – not true or not visible (Fig. 2)
5. pterygoid participation in the suborbital fenestra,– as in Brachyrhindon
6. low angle of the mandibular symphysis,,– not any lower than LRT sister taxa
7. gracile lower jaw,– not any more than LRT sister taxa
8. jaw joint positioned dorsal to the maxillary tooth row, – not true in any case
9. an unossified radiale. – not true, displaced
10. a dorsoventrally compressed and elongate skull, – not true.
11. and elongate external nares.” – also in Clevosaurus and Sphenotitan, not exposed in Leptosaurus (Fig. 6).

To their credit
Bever and Norell traced the photos, probably in Photoshop. That makes the alignment of the drawing with the photo perfect. At this point, all they need to do is start coloring bones in the DGS style (Fig. 2) and expand that taxon list.

References
Bever GS and Norell MA 2017. A new rhynchocephalian (Reptilia: Lepidosauria) from the Late Jurassic of Solnhofen (Germany) and the origin of the marine Pleurosauridae. Royal Society open scence. 4: 170570. http://dx.doi.org/10.1098/rsos.170570

SVP abstracts 2017: The enigmatic New Haven Reptile

Pritchard et al. 2017
introduce the concepts of a ‘pan-archosaur’ and a ‘pan-lepidosaur’ as they describe the small, enigmatic “New Haven Reptile” (Latest Triassic; 2.5cm skull length).

From the Pritchard et al. abstract:
“The fossil record of early-diverging pan-archosaurs and pan-lepidosaurs in the Triassic is biased towards large-bodied animals (1+ meters). The Triassic Newark Supergroup of eastern North America has produced tantalizing specimens of small reptiles, hinting at high diversity on the continent. Among these is a remarkable diapsid skull (~2.5 cm length) lacking teeth and a mandible, from the Upper Triassic New Haven Arkose of Connecticut that has been referred to as one of the oldest sphenodontians from North America (referred to herein as the New Haven Reptile). 

“Following further preparation, we re-assessed the affinities of the New Haven Reptile using three-dimensional reconstruction of microCT data. The ontogenetic state of the New Haven Reptile is uncertain; despite the extensive reinforcement of the skull, the skull roof exhibits a large fontanelle between frontals and parietals. The feeding apparatus of this species is distinct from most small-bodied Triassic diapsids, with a strongly reinforced rostrum, a narrow sagittal crest on the parietals, and transverse expansion of postorbitals and jugals. The latter two conditions suggest transverse expansions of deep and superficial adductor musculature in a manner very similar to derived Rhynchosauria. This may suggest a specialized herbivorous diet similar to rhynchosaurs, although the New Haven Reptile is smaller than most modern herbivorous diapsids. 

“A phylogenetic analysis suggests that the New Haven Reptile is not a sphenodontian but an early pan-archosaur, representing a distinctive and previously unrecognized lineage. Regardless of its affinities, the New Haven Reptile differs from other small-bodied Triassic Sauria in its hypertrophied jaw musculature suggesting a greater dietary specialization in these taxa than previously understood. It underscores the importance of geographically undersampled regions in understanding the true ecomorphological diversity in the fossil record.”

So, what is the New Haven reptile?
Without seeing the fossil or the presentation, we start with what was offered:

1. a small taxon (skull = 2.5cm)
2. like a sphenodontian, diapsid temporal openings
3. lacking teeth
4. extensive reinforcement of the skull
5. large fontanelle between frontals and parietals (pineal?)
6. strongly reinforced rostrum
7. a narrow sagittal crest on the parietals
8. transverse expansion of postorbitals and jugals, like rhynchosaurs
9. hypertrophied jaw musculature

Figure 1. Priosphenodon model. Is this what the New Haven Reptile looked like? Note the dorsal fontanelle, the pineal opening that largely disappears in rhynchosaurs. 

This sounds like
Priosphenodon avelasi, (Figs. 1, 2) which is a transitional taxon more derived than sphenodontians and more primitive than rhynchosaurs. The only skull known to me is about 8cm in length, or 3x larger than the New Haven Reptile. Priosphenodon was a late-surviving Cenomian, Cretaceous taxon, more derived  than the even later-surviving extant taxon, Sphenodon.

Figure 2. Priosphenodon nests closer to rhynchosaurs than Mesosuchus does, yet it was not included in the Ezcurra et al. 2016 study.

If my guess is valid,
its no wonder that Pritchard et al. are confused. To them rhynchosaurs are not related to sphendontians. These fellow workers need to include more taxa in their analysis and a suggested list is found at the large reptile tree (LRT, 1069 taxa). 

If it is something different
please send an image or publication and I will add it to the LRT.

References
Pritchard AC, Bhullar B-A S and Gauthier JA 2017. A tiny, early pan-archosaur from the Early Triassic of Connecticut and the diversity of the early saurian feeding apparatus. SVP abstracts 2017.

SVP 2017 abstracts: Does Malerisaurus nest with Azendohsaurus?

The short answer is
no.

You might recall
we looked at Malerisaurus earlier.

A different take comes from the Nesbitt et al. 2017 SVP abstract:
“Mediation of some of these challenges is now possible with the recently recognized early
archosauromorph clade Allokotosauria. This clade contains disparate, ecologically
diverse (faunivores and herbivores), and typically larger bodied (1-3 meters in length)
archosauromorphs (Azendohsaurus, Trilophosaurus), but to this point, plesiomorphic,
early-diverging allokotosaurians have not been identified.

“Here, we recognize specimens assigned to the enigmatic taxon Malerisaurus from both present-day India and western Texas as members of Allokotosauria, and more specifically, the Azendohsauridae. The recognition of Malerisaurus as both an allokotosaur and an azendohsaurid has also helped identify other fragmentary remains of close relatives from Triassic deposits across Pangea including India, elsewhere in North America, and Africa. As such, Allokotosauria had a near Pangean distribution for much of the Middle to Late Triassic. Allokotosauria represents one of the oldest successful clades of archosauromorphs that achieved a wide geographic distribution and both taxonomic and ecomorphological diversity.”

Figure 1. Click to enlarge. The Protorosaurs, Malerisaurus, Prolacerta, Protorosaurus, Pamerlaria and Boreopricea. It is easy to see why these taxa become confused with Trilophosaurus and Azendohsaurus. More taxa solves the problem. 

In the
large reptile tree (LRT 1050 taxa) Malerisaurus nests with other protorosaurs within the new Archosauromorpha, sharing many traits by convergence with the Allokotosauria. This clade of currently three taxa (Trilophosaurus, Azendohsaurus and horned Shringasaurus) nests within the Rhynchocephalia between the derived taxa, Noteosuchus and Mesosuchus all within the new Lepidosauromorpha.

I’m guessing,
based on past performance (I was not in Calgary), that Nesbitt et al. did not add any or many basal rhynchocephalians to their cladogram, so this new odd nestings appears to join other odd nestings, likely victims of taxon exclusion.

References
Nesbitt SJ et al. (nine co-authors) 2017. The ‘strange reptiles’ of the Triassic. The morphology, ecology, and taxonomic diversity of the clade Allokotosauria illuminated by the discovery of an early diverging member. SVP abstracts 2017.

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.

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.

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.

Is Palacrodon a rhynchocephalian? – SVP abstract 2016

Originally (Broom 1906)
considered what little is known of Palacrodon browni (= Fremouwsaurus geludens; Early Triassic; Fig. 1) a member of the Rhynchocephalia. This year, Jenkins and Lewis 2016 tested Palacrodon against rhynchcephalians and procolophonids and found it nested with the former. This genus was so obscure that Wikipedia ignored it when this was first posted. The few specimens are poorly known, only a few fragments of skull + teeth from South Africa and Antarctica.

Here in a large gamut analysis Palacrodon nests
in the large reptile tree (LRT) at the base of the Placodontia (Fig. 1) between sharp-toothed and big-eyed Palatodonta + Pappochelys and the much larger, pavement-toothed, smaller-eyed Paraplacodus.

Figure 1. A comparison of basal placodonts to scale (and Paraplacodus reduced to one-third shows how Fremouwsaurus (Palacrodon) is transitional between the small spike-tooth ancestors like Palatodonta and Pappochelys and the pavement toothed Paraplacodus.

Unfortunately recent work by Jenkins and Lewis 2016
did not include basal placodonts in their limited taxon analysis. The anterior maxillary teeth are still needle-like as in ancestral taxa. One can readily wonder if this is how the transition from one tooth type to the other occurred. Note the anterior maxillary teeth of Paraplacodus are still a bit sharp. I flipped the drawing of the quadrate from its original concave posterior. We have no palatal material for Palacrodon, but ancestral taxa display short robust teeth.

From the Jenkins and Lewis 2016 abstract
“Palacrodon browni is an Early Triassic reptile found on both the South African and Antarctic continents. The taxon has been classified as a diapsid, rhynchocephalian, and procolophonid in descriptions dating from 1906 to 1999, and consensus has not been reached regarding its phylogentic relationship within Lepidosauria. A refined phylogenetic placement of this reptile would push back stem dates of Lepidosauria from the Middle to the Early Triassic. It is possible Palacrodon is part of the faunal assemblage that experienced a decrease in body size as a result of the Lilliput effect noted in several Early Triassic lineages. There is also a noted range shift which occurred within the first 20 million years of the Triassic. The change in size and range suggest Palacrodon was strongly affected by the Permian mass extinction. Using high-resolution computed tomography, two dentaries were scanned and digitally segmented using AMIRA 6.2 to examine tooth implantation type (i.e., acrodont or thecodont) and reveal characters for better resolving the phylogenetic position of Palacrodon. Thirteen additional tooth-bearing elements, made available by the Evolutionary Institute at the University of Witwatersrand in Johannesburg, were also assessed for externally visible characters. Characters were scored against known Rhynchocephalia and procolophonid specimens using MacClade 4.08 and using an apomorphy-based approach specific to characters relating to dentition and tooth-bearing bones. Preliminary data suggest rhynchocephalian association due to acrodont dentition implantation in combination with possible protothecodont dentition in posterior teeth, and additional posterior dentition typical of sphenodontians. Initial survey also exhibits extreme wear on the occlusal surface of the teeth, a pattern typical of acrodont vertebrates and certainly rhynchocephalians. Phylogenetic analysis reveals Palacrodon’s familial association to be within Lepidosauria and its close relationship to crown Rhynchocephalia. A better understanding of the taxa that survived the Permian extinction may be beneficial to understanding and predicting the survival patterns of the current extinction, which shares any similarities to the Permian event. Change in body size and range behavior may be examples of these patterns which can be assessed in Palacrodon.”

Neenan et al. 2014
looked at tooth replacement in placodonts and found, “The plesiomorphic Placodus species show many replacement teeth at various stages of growth, with little or no discernible pattern.  Importantly, all specimens show at least one replacement tooth growing at the most posterior palatine tooth plates, indicating increased wear at this point and thus the most efficient functional crushing area.”

When head-less taxa meet head-only taxa.
The nesting of head-only Palacrodon with head-less Majaiashanosaurus immediately leads to rampant speculation worthy of Dr. Frankenstein. So… what if we put the enlarged head of the former on the body of the latter. Well, it might work (Fig. 2).

Figure 2. The head of Palacrodon and the headless body of the Majiashanosaurus compared at the same scale (left) and enlarged (at right).

References
Broom R 1906. On a new South African Triassic rhynchocephalian. Transactions of the Philosophical Society of South Africa 16:379-380.
Gow CE 1992. An enigmatic new reptile from the Lower Triassic Fremouw Formation of Antarctica. Palaeontologia Africana 29:21-23.
Gow CE 1999. The Triassic reptile Palacrodon brown Broom, synonymy and a new specimen.
Jenkins KM and Lewis PJ. 2016. Triassic lepidosaur from southern Gondwana. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Neenan JM, Li C, Rieppel O, Bernardini F, Tuniz C, Muscio G and Scheyer TG 2014. Unique method of tooth replacement in durophagous placodont marine reptiles, with new data on the dentition of Chinese taxa. Journal of Anatomy 224(5):603-613.

wiki/Palacrodon

So, is it Leptosaurus? Kallimodon? Or neither?

Rauhut and Lopez-Arbarello (2016)
compare several complete specimens of Late Jurassic rhynchocephalians from Germany (Fig. 1) with a newer specimen from Schamhaupten, JME-Scha 100 (lower left of Fig. 1).  that was earlier described by Renesto and Viohl 1997 as Leptosaurus pulchellus, JME-Scha 40. (Why the number change?) The holotype, Leptosaurus neptunium (Fig. 1b, was described earlier by Fitzinger 1837, but referred to Kallimodon by Cocude-Michel 1963. So that sets the stage for the study.

We looked at this taxon earlier here when Renesto and Viohl published on it.

Figure 1. Taxa considered by Rauhut and López-Arbarello include Homoeosaurus, Leptosaurus, Kallimodon and rhynchocephaian specimen from Schamhaupten, JME-Scha 100.

From the Rauhut and Lopez-Arbarello abstract:
“Unfortunately, the taxonomy of the rhynchocephalians from these units has not been satisfactorily established so far, which hampers studies of their evolutionary importance.” 

Actually
the large reptile tree (LRT) has taken the first steps toward that goal (Fig. 2). Though not aware of the Leptosaurus holotype, I used instead the JME-Scha specimen in its place based on the work and nomenclature of Renesto and Viohl 1997. Not sure, but the holotype of Leptosaurus looks quite a bit like the Homoeosaurus specimens I used for data. 

Figure 2. Subset of the large reptile tree, the Rhynchocephalia. This clade also includes Rhynchosauria, Azendohsaurus and Trilophosaurus.

From the Rauhut and Lopez-Arbarello abstract:
“Differences to the type of Kallimodon pulchellus include the morphology of the maxillary teeth, the phalangeal formula of the manus, and the shape of the posterior process of the second sacral rib. An important difference with the type of Leptosaurus neptunius is the higher number of premaxillary teeth in the specimen from Schamhaupten (four versus two), despite a significantly larger body size, whereas there is rather a tendency to reduce the number of premaxillary teeth through fusion during ontogeny in rhynchocephalians.” 

Rauhut and Lopez-Arbarello conclude
that the JME Scha specimen cannot be referred to either Kallimodon or Leptosaurus, but they do not rename the JME Scha specimen.

Unfortunately
the authors do not realize that the tiny JME Scha specimen is the branching off point in the LRT for the toothed rhynchocephalian, Azendohsaurus and its sister Trilophosaurus, which has no premaxillary teeth because these taxa are not included on the Rauhut and Lopez-Arbarello family tree (Fig. 3). They also did not realize that Priosphenodon is the branching off point for the origin of rhynchosaurs.

Figure 3. Rhynchocephalian cladogram from Rauhut and López-Arbarello lacks many pertinent taxa and includes one, Homoeosaurus, that belongs elsewhere. The LRT nests Kallimodon with Sphenodon and Saphenosaurus with Noteosuchus.

Other problems with the Rauhut and Lopez-Arbarello family tree
include the unwarranted inclusion of Homoeosaurus. In the LRT Homoeosaurus nests within the protosquamates the only matrix to test it on a large gamut of taxa. The authors also include several taxa that were not included in the LRT, like Eilenodon, represented only by a posterior jaw fragment. On the other hand, missing taxa from the Rauhut and Lopez-Arbarello rhynchocephalian tree (Fig 3) include:

1. Megachirella
2. Marmoretta
3. Ankylosphenodon
4. Heleosuchus
5. Sphenotitan
6. Noteosuchus
7. Trilophosaurus
8. Azendohsaurus
9. Eohyosaurus
10. Mesosuchus
11. Rhynchosaurus
12. Bentonyx
13. Hyperodapedon

You might not like this, if you like traditional studies
but these taxa all nest within the clade Rhynchocephalia in the LRT. And Gephyrosaurus is no longer the most primitive of the lot.

Perhaps 
Rauhut and Lopez-Arbarello will someday expand their taxon list. That’s why the LRT is here… to make taxon selection simple, complete and verifiable, not just traditional. The hard work has already been done for you. All you have to do is focus on your clade of interest!

References
Cocude-Michel M 1963. Les Rhynchocéphales et les Sauriens des Calcaires lithographiques (Jurassique supérieur) d’Europe occidentale.– Nouvelles Archives du Muséum d’Histoire Naturelle de Lyon 7: 1–187.
Fitzinger LJF 1837. Vorläufiger Bericht über eine höchst interessante Entdeckung -Dr. Natterers in Brasil. Oken’s Isis.
von Meyer H 1850. Mittheilungen an Professor Bronn gerichtet: Neües Jahrbuch fur Mineralogie, Geologie und Palaontologie, Bd 18, p. 195-204.
Rauhut OWM and Lopez-Arbarello A 2016. Zur Taxonomie der Brückenechse aus dem oberen Jura von Schamhaupten (On the taxonomy of the rhynchocephalian from the Late Jurassic of Schamhaupten). Archaeopteryx 33: 1-11; Eichstätt 2016.
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

 

Early Evolution of Rhynchosaurs

A new open access paper
by Ezcurra, Montefeltro and Butler 2016 provides several first time ever color photos of rhynchosaur skulls and a cladogram of rhynchosaur relationships (Fig. 1). It’s a good paper, with good interrelationships. Unfortunately the wrong outgroup, the Protorosauria, was chosen.

Figure 1. Rhynchosaur cladogram by Ezcurra et al. 2016. Note the outgroup includes two protorosaurs. The large reptile tree recovers protorosaurs elsewhere and has a long list of outgroup taxa among the trilophosaurs and rhynchocephalians within the Lepidosauromorpha, not the Archosauromorpha. See figure 2. Carmel area includes taxa matching the large reptile tree among rhynchosaurs and proximal outgroups.

By contrast,
the large reptile tree nests rhynchosaurs with trilophosaurs and rhynchocephalians (sphenodontids, Fig. 2), not protorosaurs. Taxon inclusion will help you recover this relationship, too, if you wish to repeat the experiment. Ezcurra et al. (2016) relied on untested tradition, but that tradition brings with it a certain air of credulity as Prolacerta does indeed converge with Mesosuchus in several regards. But parsimony prevails when the following lepidosauromorphs (Fig. 2) are included in analysis. This is a relationship best left to software, not eyeballs and paradigms.

Figure 2. This subset of the large reptile tree nests rhynchosaurs with trilophosaurs and rhynchocephalians, not protorosaurs. Where is Priosphendon in the Ezcurra study? 

In the transition from rhynchocephalians to rhynchosaurs,
this clade had an interesting radiation that included Leptosaurus, Sapheosaurus, Trilophosaurus and Azendohsaurus (which also nests with protorosaurs when the taxa in figure 2 are excluded, before producing rhynchosaurs. Priosphenodon (Fig. 3), typically considered a Cretaceous rhynchocephalian, is a transitional taxon for some reason left off of the Ezcurra et al. 2016 taxon list that nests closer to rhynchosaurs than Mesosuchus does in the large reptile tree. Probably because all rhynchosaurs died out by the Jurassic.

Figure 3. Priosphenodon nests closer to rhynchosaurs than Mesosuchus does, yet it was not included in the Ezcurra et al. 2016 study. Perhaps because the only known fossils are a hundred million years too late. 

References
Ezcurra MD, Montefeltro F and Butler RJ 2016. The Early Evolution of Rhynchosaurs. Frontiers in Ecology and Evolution 3:142 (23 pgs) doi: 10.3389/fevo.2015.00142 http://dx.doi.org/10.3389/fevo.2015.00142