Tuatara genes provide false-positive links to mammals

Preamble:
Genomic (gene) studies think they are unlocking secret doors
to understanding vertebrate interrelationships. Sometimes they do the opposite. Wide gamut phenomic (trait) studies show that gene studies over deep time introduce invalid hypotheses of interrelationships. So, worse than useless, gene studies (like today’s example) confuse readers and workers with false positives, false hopes that claim to be true, but are not valid when put to the test.

So why are they published?
Because gene studies work great over shallow time. Ask any prosecutor or Ancestry.com.

Figure 1. The dorsal spines of Tuatara (Sphenodon).

Gemmell and Rutherford et al. 2020 report:
“The tuatara (Sphenodon punctatus)… [is] A key link to the now-extinct stem reptiles (from which dinosaurs, modern reptiles, birds and mammals evolved), the tuatara provides key insights into the ancestral amniotes.”

In a competing phenomic study (the large reptile tree, LRT, 1717+ taxa; Fig. 2) the lepidosaur, Sphenodon (Fig. 1), is simply the last living proximal outgroup taxon to living squamates. On the other hand, tuataras and mammals share a last common ancestor all the way back in the Viséan, at the last common ancestor of all reptiles, Silvanerpeton.

Figure 2. Gemmell and Rutherford cladogram compared to LRT (with taxon list greatly reduced to match Gemmell and Rutherford).

Gemmell and Rutherford et al. continue:
“Here we analyse the genome of the tuatara, which—at approximately 5 Gb—is among the largest of the vertebrate genomes yet assembled. Our analyses of this genome, along with comparisons with other vertebrate genomes, reinforce the uniqueness of the tuatara. Phylogenetic analyses indicate that the tuatara lineage diverged from that of snakes and lizards around 250 million years ago [Earliest Triassic].”

This timing is confirmed by the LRT, but fossils generally represent periods of wide radiations, not moments of origin.

“This lineage also shows moderate rates of molecular evolution, with instances of punctuated evolution. Our genome sequence analysis identifies expansions of proteins, non-protein-coding RNA families and repeat elements, the latter of which show an amalgam of reptilian and mammalian features.”

Phenomic studies do not support a mammal connection other than at the very base of the Reptilia (see the LRT).

“The sequencing of the tuatara genome provides a valuable resource for deep comparative analyses of tetrapods, as well as for tuatara biology and conservation.”

False positives are not valuable resources. They steer readers and workers wrong. Gene studies too often deliver false p;positives compared to trait-based studies over deep time.

From an online story from phys.org with quotes from the authors.
“The tuatara genome contained about 4% jumping genes that are common in reptiles, about 10% common in monotremes (platypus and echidna) and less than 1% common in placental mammals such as humans,” said Professor Adelson.

“This was a highly unusual observation and indicated that the tuatara genome is an odd combination of both mammalian and reptilian components.”

“The unusual sharing of both monotreme and reptile-like repetitive elements is a clear indication of shared ancestry albeit a long time ago,” said Dr. Bertozzi.”

Or… this is a false positive. Not sure why false positives keep creeping in to gene studies, but they do.

Colleagues: Don’t publish genomic studies unless they are confirmed by phenomic studies.

---

References
Gemmell NJ, Rutherford K., Prost, S. et al. 2020. The tuatara genome reveals ancient features of amniote evolution. Nature (2020). https://doi.org/10.1038/s41586-020-2561-9 DOI: 10.1038/s41586-020-2561-9 , www.nature.com/articles/s41586-020-2561-9

https://phys.org/news/2020-08-dinosaur-relative-genome-linked-mammals.html?fbclid=IwAR1VjTxtCI8Yd9VrUIAbuwxDmEhOM1q27WFueBbt1KIo062qKi2UqNnvzX0

https://www.researchgate.net/publication/342666056_Bird_phylogeny_false_positives_detected_in_a_gene_sequencing_study

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

Colobops and taxon exclusion issues

Too often workers fail to include the closest relatives of new specimens
in analysis and then report they have something new and different in the pantheon of tetrapods. Too often the analysis lacks the correct tree topology, also due to taxon exclusion.

The new genus, Colobops noviportensis
(Pritchard, Gauthier, Hanson, Bever and Bhullar 2018; Fig. 1) was described as a tiny (2.5 cm long skull) saurian reptile from the Triassic of Connecticut, USA. Taxonomically it suffers from taxon exclusion. It was nested by default because more closely related taxa were omitted from a previously published analysis (Pritchard and Nesbitt 2017; Fig. 2), which was an inadequate analysis to work from because it failed to show the basal dichotomy of the Reptilia (Lepidosauromorpha/Archosauromorpha; Fig. 3) revealed by increasing the number of taxa.

Figure 1. Colobops as originally presented and slightly restored. Glad to see other workers are coloring bones or identification. These are from CT scans. The postorbital processes invading the supratemporal fenestrae are unique.

From the abstract
“The taxon possesses an exceptionally reinforced snout and strikingly expanded supratemporal fossae for adductor musculature relative to any known Mesozoic or Recent diapsid of similar size. Our phylogenetic analyses support C. noviportensis as an early diverging pan-archosaur. 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.”

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs. Note the variety in the size of the supratemporal (upper) fenestrae, a variety that expands with Colobops.

Unfortunately,
their phylogenetic analysis (Fig. 3) did not include the basal sphenodontid, Marmoretta, more similar to Colobops in the large reptile tree (LRT, 1085 taxa; subset Fig. 4) than any other tested taxon. They are also the same size.

Figure 3. Cladogram from Pritchard et al. failed to include a long list of basal sphenodontians, including Marmoretta, the sister to Colobops in the LRT. Note the shuffling of lepidosauromorph and archosauromorphs in this cladogram, lacking any broad resemblance to the LRT tree topology. Pritchard et al. assume that diapsids are monophyletic, which dooms their analysis. There is so much taxon exclusion here.

Marmoretta oxoniensis (Evans 1991, Waldman and Evans 1994) Middle/Late Jurassic, ~2.5 cm skull length, orginally considered a sister of kuehneosaurs, drepanosaurs and lepidosaurs. Here Marmoretta was derived from a sister to Megachirella and Palaegama. Marmoretta was basal to Gephyrosaurus and the rest of the Sphenodontia = Rhynchochephalia. Two specimens are known (Fig. 2) with distinct proportions in the skull roof (frontal and parietal, see above). Note the variety in the supratemporal fenestrae in these closely related tiny flat-headed taxa, including Colobops.

By the way,
the Wikipedia page on Marmoretta likewise suffers from taxon exclusion.

Figure 4. Cladogram of the Sphenodontia includes Colobops and rhynchosaurs.

Pritchard et al. assumed the monophyly of the Diapsida
which doomed their cladogram to a shuffling of disparate morphologies and by-default nestings (Fig. 3). Several years ago the LRT split the Archosauromorpha from the Lepidosauromorpha at the origin of the Reptilia, and so revealed that the diapsid skull architecture evolved at least twice.

Pritchard et al. nested Colobops
at the base of the Rhynchosauria due to taxon exclusion. In the LRT (subset Fig. 4) rhynchosaurs and Colobops are separated by a long list of taxa. The authors reported, “Two additional steps produce topologies in which C. noviportensis occupies some positions with pan-Archosauria and a position nested within Sphenodontia, a clade that converged anatomically on rhynchosaurs in numerous skull characters.”

If only
Pritchard et al. had used more taxa (or the LRT) they would have known that sphenodontids did not converge with rhynchosaurs, they were basal to rhynchosaurs. The authors report, “Colobops noviportensis represents a combination of morphological traits unknown in extant amniotes, and thus a morphology that would not have been reconstructed in a macroevolutionary analysis based exclusively on extant species.” I don’t see the extant tuatara, Sphenodon. in their taxon list.

Colobops lacks teeth
and lacks alveoli as well. The authors report, “The best insights into the feeding of C. noviportensis come from the general shape of the adductor chamber. In C. noviportensis, the post-temporal process of the parietal is oriented laterally, as in Sphenodontia and Rhynchosauridae, rather than posterolaterally as in most pan-lepidosaurs and pan-archosaurs.” See how they were just peeking in at the insights revealed by the LRT? Yet they followed tradition and previously published phylogenetic analyses beset with problems from the start.

The adductor chambers for jaw muscles in Colobops
are indeed quite large. And the postorbital process that invades the supratemporal fenestra is unique (at present). Sister sphenondontids do not have such a large supratemporal fenestra until Sphenodon. Note that one of the Marmoretta specimens (Fig. 2) had developed a parietal crest, also for the enlargement of the jaw muscles. So they were trying various ways to do this.

Based on the similar sizes of the marmorettid skulls
the skull of Colobops probably represents an adult.

The authors report
“Within individual species, overall skull size appears to correlate strongly with the relative breadth of the adductor chamber; juveniles recapitulate the transition from Permian Diapsida to crown-group with a small supratemporal fossa with small proportionally modest embayments on the parietal giving way to proportionally larger fossae and deeper parietal embayments.” Good to know. Irrelevant in this case.

I’m happy to see these authors have colorize key bones
throughout their paper. That’s the best way to illustrate them.

The final takeaway:
No matter how many co-authors you have with PhDs… no matter how many diagrams you show… no matter how many irrelevant taxa you include… no matter if you have firsthand access to the specimen… no matter if you are published in Nature… if you exclude the most closely related taxa, you’re going to let bloggers report your most basic errors. The LRT is online in order to be freely used. Use it. It’s a good starting point for any new taxon because it minimizes the opportunity for taxon exclusion by including so many taxa.

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 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 4, 170499
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
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

 

 

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.

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.

The Stem-Mammals–a Brief Primer (with remarks)

Preface added the day after posting: M. Mortimer gratefully informed me that some authors consider all taxa closer to mammals than to other living taxa as ‘stem’ mammals. Perhaps that is how ‘stem’ taxa are defined. That came as news to me because I understood the term ‘stem’ to refer to immediate outgroups only based on the terms usage in other works. So you learn as you go. The broad definition quickly loses relevance and adds to confusion. In M. Mortimer’s example, Diplodocus is a ‘stem’ bird. Please read the following with these caveats in mind. 

Preface added 10/26/2016: Just found out there is are two definitions for ‘stem’ taxa, one in the wider sense and one in the narrower sense, the one is was familiar with. Learn more at Wikipedia here. 

Usually I cover published academic papers
here at PterosaurHeresies.WordPress.com. Today we’ll cover a Tetrapod Zoology blog post published online by Dr. Darren Naish a month ago. Unfortunately the post was sprinkled with traditional misconceptions.

Below
the Naish text is copied in italic and his captions are copied in their original ALL CAPS. Remarks are in red. You can see the original blogpost here. This is how all good referees mark up submitted manuscripts, with precise comments intended to help the writer improve the next draft. To that end, Naish notes he is currently writing a book that includes this subject.

The Stem-Mammals–a Brief Primer
Mammals are but the only surviving members of a far grander, older lineage
By Darren Naish on September 20, 2016

PROVISIONAL AND IN-PREP MONTAGE (FOR MY TEXTBOOK ON VERTEBRATE HISTORY) DEPICTING A SELECTION OF STEM-MAMMALS. I’VE DRAWN FAR MORE THAN THE SELECTION SHOWN HERE. CREDIT: DARREN NAISH Strangely Naish labeled this illustration “Non-synapsid-mammal-montage” Most of these taxa, caseids and Tetraceratops exempted, are indeed synapsids. The problem is, all of the red taxa are not stem mammals, nor are they in the mammal lineage at any node. Rather they represent extinct and distant offshoots. Virtually all science journalists accept what they read in publication without criticizing it. But Naish is also a PhD, so it is his duty to keep a laser focus on his headline topic, not to stray off subject, and most importantly, to clarify for his readers the inconsistencies present. Otherwise, as above, there is confusion and lack of clarity for the reader.

“For some considerable time now I’ve been promising that one day — one day — I’ll devote time and energy to coverage of that enormous, diverse, long-lived tetrapod group that we variously term the non-mammalian synapsids or stem-mammals. The most traditional term for them is ‘mammal-like reptiles’: while still in use, this term should be avoided given that the animals concerned are simply not part of the reptile lineage. Not true. According to the large reptile tree (LRT) all descendants of the first reptile/amniote, Gephyrostegus, are also reptiles, and that includes mammals and their long list of descendants. Unfortunately Naish is repeating an old and invalid tradition. The vernacular terms protomammal and paramammal have both been used for the group as well, though both have problems. Stem-mammals will be used here. If so, it is important that Naish restrict his discussion to just the immediate precursors of mammals, not the long list going back to basal synapsids, but that is not what he does.

Anyway, we’re talking about that group of tetrapods that are not mammals but are ancestral to them, and which occupy all those points on the mammal lineage outside of Mammalia. The presence of a laterotemporal fenestra (a single skull opening behind the eye socket) is a key feature distinguishing them from other amniotes. Not true. Several clades by convergence developed such a skull opening including 1. the millerettid clade and their descendants from Oedaleps to Australothyris, including the caseids. Emeroleter and Lanthanosuchus had that fenestra. So did bolosaurids. And then there are the prodiapsids from Heleosaurus to Archaeovenator and the last common ancestor of synapsids and diapsids, Vaughnictis. The early members of this segment of the mammal lineage have often been called pelycosaurs while the members of the more mammal-like segment of the lineage are termed therapsids. Actually finback pelycosaurs are an offshoot clade, not in the lineage of mammals, which proceeds from a sister to Ophiacodon to Cutleria without including finbacks. The importance of these animals concerns the fact that their comparatively excellent fossil record charts transition from an ancestral ‘reptile-like’ form to mammals via a near-perfect series of intermediates. Alas, their relative obscurity and the lack of good popular syntheses means that they are not the poster-children of evolution that they really should be… at least, not outside the palaeontological community.  Those animals were featured on both versions of Cosmos.

TETRACERATOPS FROM THE EARLY PERMIAN OF THE USA, AN EARLY SYNAPSID SOMETIMES IDENTIFIED AS ONE OF THE OLDEST THERAPSIDS BUT LATER RE-INTERPRETED AS OCCUPYING A MORE ROOT-WARD POSITION IN THE TREE. CREDIT: DMITRI BOGDANOV WIKIPEDIA CC BY 3.0. The LRT nests Tetraceratops with Tsejaia and Limnoscelis, whether it had a lateral temporal fenestra or not, far from the synapsids. Massive crushing adds doubt to that. It doesn’t look like any other synapsid and it nests with other reptiles, so why include it?

This article is not the time and place to start a group-by-group review of the many lineages concerned… I know from experience how those projects quickly expand into gargantuan multi-part monsters that can never be finished. Rather, this is just a brief primer, a placeholder. If you want to see the lineage of mammals going back to stem tetrapods, click here then peruse at your leisure the taxa that interest you.

COVER OF KEPT (1982). THE BEST BOOK ON THE GROUP OF ANIMALS SO FAR. NOW OUT OF PRINT (BUT AVAILABLE AT REASONABLE PRICES ONLINE. CREDIT: ACADEMIC PRESS LONDON. This is indeed the go-to book for synapsid data and has been for more than 30 years. See ReptileEvolution.com for updates since then. 

Before anyone asks, the one crippling, punishing problem with these animals is that – even today – there is no single, good, up-to-date, go-to volume on their diversity, history, evolution and biology. But you can go online here for the latest data. Yes, there are books on these animals, but they’re technical and mostly out of print. The best is Tom Kemp’s Mammal-Like Reptiles and the Origin of Mammals (Kemp 1982). There’s also Nick Hotton et al.’s The Ecology and Biology of Mammal-like Reptiles (Hotton et al. 1986) (a collection of papers by different authors). I have a substantial, well illustrated chapter on these animals in my giant textbook (on which go here, if you wish), but a good, dedicated, modern volume just does not exist. There are several decent review articles on the group as a whole, among the most recent being Angielczyk (2009).

MUCH-SIMPLIFIED CARTOON CLADOGRAM OF STEM-MAMMALS BASED ON TOPOLOGIES RECOVERED IN SEVERAL RECENT STUDIES. EXPANDED VERSIONS BEING PREPARED FOR MY IN-PREP TEXTBOOK (MORE HERE). CREDIT: DARREN NAISH As above, caseids are not related. Pelycosaurs are offshoots. The basal dichotomy of therapsids separated the Anomodonts from the Kynodonts.

The oldest stem-mammals date to the Moscovian part of the Carboniferous (here again, an inappropriate use of the term ‘stem’) and have conventionally been depicted as very reptilian in appearance. That’s because they are or were reptiles, as recovered by the LRT.  This is probably true in broad terms but is open to some question, there being indications that their integument and so on was not ‘reptilian’ as we conventionally imagine it. Likely without scales, based on the scant evidence at hand, but living dinosaurs are also without scales, except for those transformed from feathers. These early forms belong to those lineages conventionally lumped together as ‘pelycosaurs’ – a term that clearly refers to a paraphyletic assemblage given that therapsids evolved from somewhere among them. Not true. The LRT recovers a clade of pelycosaurs, a resurrected clade Pelycosauria. 

SOMEWHAT DATED SCHEMATIC REPRESENTATION OF SYNAPSID EVOLUTION WHICH I INCLUDE BECAUSE IT DOES A NICE JOB OF ILLUSTRATING BOTH CRANIAL VARIATION WITHIN THE GROUP, AND SOME OF THE MAIN DIFFERENCES OBVIOUS BETWEEN ‘PELYCOSAURS’, THEROCEPHALIAN-GRADE ANIMALS, AND CYNODONTS. CREDIT: PALAEOS, ORIGINALLY BY THOMAS KEMP. If Naish is trying to show us what we used to think, he’s doing a good job, but wasting time when his whole point was to update his readers on the latest, which can be found at ReptileEvolution.com.

Animals from this ‘pelycosaur’ part of the tree include the long-snouted, mostly predatory varanopids and ophiacodontids, the omnivorous and herbivorous caseasaurs, and the edaphosaurids and sphenacodontids, the latter including the famous Dimetrodon. Why waste time on these non stem-mammals? While many of these animals (especially the early members of these groups) were small (less than 50 cm long), large size (3 m or more) evolved several times independently. There are lots of other significant events here as well, including the evolution of high-fibre herbivory and the independent evolution of dorsal sails.  Why waste time on these non stem-mammals? Even in these animals there are indications of social behaviour and parental care (Botha-Brink & Modesto 2007, 2009).

RECONSTRUCTION OF AN ASSEMBLAGE (A FAMILY GROUP?) OF THE VARANOPID HELEOSAURUS, PICTURED IN THE POSE IN WHICH THEIR SKELETONS WERE DISCOVERED. CREDIT: BOTHA-BRINK & MODESTO (2009). This is Heleosaurus, which is a pro-diapsid, an outgroup to the Synapsida, but the concept is probably true of young ones nesting with an adult.

Dimetrodon – one of the most familiar and famous of all stem-mammals (Not true, merely an offshoot)– is a fascinating creature that has recently undergone something of an image change: ideas regarding the evolution, function and anatomy of its sail have all been challenged, its ecology and lifestyle have been the source of some debate, and its life appearance and gait have undergone revision in recent years. I plan to devote an article to these issues.

YOU MIGHT HAVE SEEN THIS ANIMAL BEFORE. IT’S DIMETRODON. CREDIT: D’ARCY NORMAN WIKIMEDIA CC BY 2.0 Not sure why Naish is bothering with these popular but irrelevant taxa when so many taxa much closer to mammals, the REAL stem mammals also make for good stories. Seems like he doesn’t know or doesn’t care. 

Animals close to sphenacodontids gave rise to therapsids. A more erect gait and faster metabolism occurred at the time of this transition, numerous additional changes associated with dentition, palatal structure, limb posture and so on occurring as well. It’s within this vast group (Therapsida) that we find the often herbivorous, beak-jawed dicynodonts and kin, the often predatory biarmosuchians, gorgonopsians and therocephalians, and the often striking, often large dinocephalians. That last group includes both predators and herbivores, hippo-sized animals, and species with thickened skull roofs probably used in head-butting. They dominated many continental animal communities in the Permian, being best known from the fossil records of South Africa and Russia. Still not talking about stem mammals here. When are we going to get to them? The text does not follow the headline. 

TAPINOCEPHALID DINOCEPHALIANS – LIKE TAPINOCEPHALUS DEPICTED HERE – HAD THICKENED SKULL ROOFS THAT LIKELY HAD A DISPLAY OR COMBAT FUNCTION. THE BIGGEST OF THESE ANIMALS WERE OVER 3 M LONG. CREDIT: DIBDG WIKIMEDIA CC BY SA 3.0 While fascinating, this is not a stem-mammal, but another offshoot.

Gorgonopsians and therocephalians are exciting groups that include various macropredatory, often ‘sabre-toothed’ species; both have been the subject of various recent revisions. Species within these groups have been likened to weasels, wolves and bears in approximate body form, though any resemblance would have been highly superficial. Sometime during the Late Permian, cynodonts arose from an ancestor closely related to therocephalians (both groups form the therapsid clade Eutheriodontia): Cynodontia is the group that includes mammals as well as a number of additional lineages that have their own histories and evolved their own specializations. Now we’re getting closer to the stem-mammals, members of the clade Tritylodontia within the Cynodontia!

And because this was meant to be a very, very brief primer, that is all I’ll say for now. There is so much more to do… WAIT! Naish never once wrote about or illustrated a stem-mammal here! I read this whole blog post without learning anything new about the stem-mammals, the Tritylodontidae and their immediate predecessors.. As we’ve seen before, Naish sometimes cruises on the invalid past rather than exploring today’s cutting edge data and latest discoveries. Pity, all that talent going for the low-hanging fruit. Darren, as you write your book on synapsid relationships, feel free to reference ReptileEvolution.com and the large reptile tree. It will help you understand the issues and enigmas generated in Kemp’s 1982 book.

Stem-mammals have been covered on scant occasions at Tet Zoo. But see…

• Survivors, diggers, herbivores, first giant terrestrial vertebrates: the caseids 
• http://scienceblogs.com/tetrapodzoology/2007/07/18/the-answers-we-seek-on-goodbye/ The answers we seek: on ‘goodbyes’, the necks of caseids, and weird mystery sauropods

Sometimes Dr. Naish referees manuscripts offered for academic publication. With his stuck-in-the-past bias, good luck if he referees your submission. I would not want wish that on my worst enemy, especially if you’re promoting new hypotheses.

Many scientists like to play it safe, resisting and waiting for the tide to shift on advancing new hypotheses before jumping on the bandwagon. Don’t be like that. Follow the data. Test as much as you can yourself. Be a skeptical Scientist, not a nodding Journalist. 

What do I expect from these remarks?
Based on his vocal antipathy toward the results recovered by the LRT, Dr. Naish will probably cling to his invalid traditions. After all, based on his writings, he has ‘painted himself into a corner’ from which he cannot escape without an about face apology and acknowledgment. That’s something primates, like us, do very very rarely. PhDs are not wired for it. But if Naish did run the tests he would find what I found. If not, I’d like to hear why not.

Refs – –
Angielczyk, K. D. 2009. Dimetrodon is not a dinosaur: using tree thinking to understand the ancient relatives of mammals and their evolution. Evolution: Education and Outreach 2, 257-271.
Botha-Brink, J. & Modesto, S. 2007. A mixed-age classed ‘pelycosaur’ aggregation from South Africa: earliest evidence of parental care in amniotes? Proceedings of the Royal Society B 274, 2829-2834.
Botha-Brink, J. & Modesto, S. 2009. Anatomy and relationships of the Middle Permian varanopid Heleosaurus scholtzi based on a social aggregation from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology 29, 389-400.
Hotton, N., MacLean, P. D., Roth, J. J. & Roth, E. C. 1986. The Ecology and Biology of Mammal-like Reptiles. Smithsonian Institution Press, Washington and London.
Kemp, T. S. 1982. Mammal-Like Reptiles and the Origin of Mammals. Academic Press, London.

Eohyosaurus – a new basal rhynchosaur

Eohyosaurus wolvaardti, SAM-PK-K-10159 (Butler 2015, Fig. 1) is a new basal rhynchosaur from the early Middle Triassic (Anisian) of the Karroo supergroup, known from a single skull. It is similar to Mesosuchus.

Figure 1. Eohyosaurus reconstructed from several views of a single specimen. This taxon nests between, Trilophosaurus + Azendohsaurus and the Rhychosauridae (Figs. 2, 3).

Butler et al. did a thorough and excellent job
of describing their specimen. They nested it accurately.

Unfortunately,
Butler et al. added two non-rhynchosaurian outgroups (Prolacerta broomi and Protorosaurus speneri) to their cladistic analysis and omitted many others (Figs. 2, 3).

Figure 2. Rhynchosaur tree from Butler et al. Color area added for rhynchosauridae.

In the large reptile tree (Fig. 3 subset) the protorosaurs are not related to the rhynchosaurs. And rhynchosaurs are derived from sphenodontians. That was the original assessment, but the lack of fusion in the ankles of rhynchosaurs caused Cruickshank (1972) and Benton (1983) to consider rhynchosaurs close to protorosaurs and archosaurs, like Prolacerta and Proterosuchus. Carroll (1988) considered this valid in his landmark textbook and Dilkes (1998) agreed. Details here, here and here.

They’re all wrong,
if you include the following taxa (Fig. 3) and all the 556 intervening taxa.

Figure 3. Here is where Eohyosaurus fits on the large reptile tree.

Butler et al. considered
Noteosuchus the earliest known rhynchosaur (Early Triassic). Actually it’s a transitional clade member bridging Clevosaurus, a sphenodontian, to Eohyosaurus and Mesosuchus, basal rhynchosaurs.

All you young and old scientists (paleontologists)
keep adding taxa and see what your tree recovers.

References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Butler R, Ezcurra M, Montefeltro F, Samathi A, Sobral G 2015. A new species of basal rhynchosaur (Diapsida: Archosauromorpha) from the early Middle Triassic of South Africa, and the early evolution of Rhynchosauria. Zoological Journal of the Linnean Society 10.1111/zoj.12246.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Cruickshank ARI 1972. The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dilkes DW 1995. The rhynchosaur Howesia browni from the Lower Triassic of South Africa. Paleontology 38(3):665-685.

A new nose for Azendohsaurus

When I first tested
Azendohsaurus (Flynn et al. 2010, Figs. 1,3) the large reptile tree nested it with Trilophosaurus (Fig. 2). Then when the post-crania was verbally described in an abstract (Nesbitt et al. 2013), the large reptile tree nested it with Pamelaria, a protorosaur taxon with a single median naris and a short tail. Ultimately, Azendohsaurus and Pamelaria were an odd fit, only mitigated by the fact that Azendohsaurus is an odd fit no matter where it nests.

Today
Azendohsaurus once again nests with Trilophosaurus, not far from Mesosuchus. The former has lateral nares. The latter has a medial naris. Azendohsaurus also nests not far from Noteosuchus, a taxon that shares with Azendohsaurus a short tail, but the skull is unknown.

Evidently
there is a large and varied grade of sphenodontians of which we are just becoming aware. Some of these, of course, include Priosphenodon and the rhynchosaurs.

Figure 1. The skull and palate of Azendohsaurus, a sister to Trilophosaurus.

There are many differences
between Azendohsaurus and Trilophosaurus (Fig. 2), but there are many more differences with the other 543 taxa in the large reptile tree. The presence of long teeth in Azendohsaurus set apart from all other sphenodontians. The very tall and narrow ascending processes of the premaxilla and maxilla are also oddities best matched in Mesosuchus.

Figure 2. Trilophosaurus has filled in the lateral temporal fenestra, reduced the orbit and increased the upper temporal fenestra, among other differences with Azendohsaurus.

I’m sure the definitive paper
on Azendohsaurus is ‘in press’ somewhere. Let’s see how this all turns out.

Figure 3. DGS applied to the skull of Azendohsaurus. Note the new addition of a lateral naris, not previously noted.

Despite the obvious irony,
it appears that few hypotheses in paleontology are set in stone at present. And I’m always happy to set the record straight whenever I can.

References
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences à Paris, Série D 275:2841-2844.
Flynn JJ, Nesbitt, SJ, Parrish JM, Ranivoharimanana L and Wyss AR 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible”. Palaeontology 53 (3): 669–688. doi:10.1111/j.1475-4983.2010.00954.x
Nesbitt, S, Flynn J, Ranivohrimanina L, Pritchard A and Wyss A 2013. Relationships among the bizarre: the anatomy of Azendohsaurus madagaskarensis and its implications for resolving early archosauromroph phylogeny. Journal of Vertebrate Paleontology abstracts 2013.

wiki/Azendohsaurus

Heleosuchus – the enigma has nested in the Rhynchocephalia

Figure 1. Heleosuchus, a former enigma, nests in the middle of the Rhynchocelphalia, between Planocephalosaurus and Sphenodon. Here is Heleosuchus in situ and Planocephalosaurus restored to scale. Click to enlarge.

Heleosuchus (Fig. 1) has been an enigma since first described by Owen 1876. Several heavy-hitters in paleontology (Broom 1913, Evans 1984, Carroll 1987) have taken a whack at it without resolving its relations.

According to Wikipedia, “It was originally described as a species of Saurosternon, but was later recognized as a separate taxon by R. Broom. Heleosuchus is suggested as being either an early diapsid reptile, not closely related to other lineages, or as being an aberrant and primitive lepidosauromorph. Heleosuchus shares the hooked fifth metatarsal found in some other diapsids, such as primitive turtles (Odontochelys), lepidosauromorphs, and archosauromorphs, but it also resembles ‘younginiform’-grade diapsids in its gross morphology.  Heleosuchus may also share a thyroid fenestra with these higher diapsid reptiles as well, but the identity of this feature is disputed.”

Based on tracings by Carroll (1987) the large reptile tree (not updated yet) Heleosuchus nested between Planocephalosaurus (Fig. 1) and the clade of Sphenodon and Kallimodon in the middle of the Rhynchocephalia. What was identified as a scapula must be a portion of the interclavicle instead.

However, even Carroll was not sure of the identification of several elements. Unfortunately it appears as though the last time someone published on Heleosuchus was prior to the advent of computer-assisted phylogenetic analysis. Carroll notes, “if a thyroid fenestra is present and the fifth metatarsal is hooked, Heleosuchus would definitely represent a lineage distinct from the younginoids. These features are present in Late Triassic sphenodontids and Jurassic lizards, but they are also present in other groups. In conclusion, the characters that are preserved point to a position near the base of the lepidosauromorph assemblage, possibly close to the younginoids but perhaps representing a distinct lineage.”

What appears to be bothering Carroll is the early appearance of Heleosuchus in the Late Permian of South Africa relative to the lepidosaurs known to him at the time. That early appearance doesn’t bother the large reptile tree, which nests several other Permian contemporaries just as high if not higher in the reptile family tree.

References
Broom R 1913. A revision of the reptiles of the Karroo. Annals of the South African Museum 7: 361–366.
Carroll RL 1987. Heleosuchus: an enigmatic diapsid reptile from the Late Permian or Early Triassic of southern Africa”. Canadian Journal of Earth Sciences24: 664–667.
Evans SE 1984. The anatomy of the Permian reptile Heleosuchus griesbachi. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 12: 717-727.
Owen R 1876. Descriptive and illustrated catalogue of the fossil Reptilia of South Africa in the collection of the British Museum. Trustees of the British Museum (Natural History), London, UK.

wiki/Heleosuchus