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.

The dorsal spines of Tuatara (Sphenodon).

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.

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.

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 1. 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.

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.


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/

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.

The dorsal spines of Tuatara (Sphenodon).

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 1. Gemmell and Rutherford cladogram compared to LRT (with taxon list reduced to match Gemmell and Rutherford).

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.

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.

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.

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. JesairosauriaJesairosaurus, Megachirella, their last common ancestor all descendants. More taxa reveal this phylogenetic pattern that has, so far, escaped the notice of professional paleontologists.
  2. RhynchocephaliaGephyrosaurus, Megachirella, their last common ancestor all descendants.
  3. Sphenodontia —  Sphenodon, Ankylosphenodon, their last common ancestor all descendants.
  4. TransphenodontiaTrilophosoaurus, 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. RhynchosauriaRhynchosaurus, Hyperodapedon, their last common ancestor all descendants.
  6. PseudoribiaCoelurosauravus, 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.

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

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.

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 kuehneosaursdrepanosaurs and lepidosaurs. Here Marmoretta was derived from a sister to Megachirella and PalaegamaMarmoretta 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 5. Cladogram of the Sphenodontia includes Colobops and rhynchosaurs.

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.

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.

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

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.

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 1. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

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.

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. This is the first data I've seen on the dorsal skull and postcrania. Photo courtesy of Dr. Apesteguía.

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

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.

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

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

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

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

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

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

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

No Wiki page yet.

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. This taxon nests between, Trilophosaurus + Azendohsaurus and the Rhychosauridae.

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.

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.

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. 

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.

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

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.

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