Colobops: back to Rhynchocephalia

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

Figure 1. Colobops as originally presented and slightly restored.

Figure 1. Colobops as originally presented and slightly restored.

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

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

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

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

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

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

Figure 1. Sphenodon, the extant tuatara, is close to Colobops, but Marmoretta is closer.

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

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

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


References
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Pritchard AC, Gauthier JA, Hanson M, Bever GS and Bhullar B-AS 2018. A tiny Triassic saurian from Connecticut and the early evolution of the diapsid feeding apparatus. Nature Communications open access DOI: 10.1038/s41467-018-03508-1
Scheyer TM, Spiekman SNF, Sues H-D, Ezcurra MD, Butler RJ and Jones MEH 2020. Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite. Royal Society Open Science 7:192179.
http://dx.doi.org/10.1098/rsos.192179
Sues H-D and Baird D 1993. A Skull of a Sphenodontian Lepidosaur from the New Haven Arkose (Upper Triassic: Norian) of Connecticut. Journal of Vertebrate Paleontology13 (3): 370–372.
Waldman M and Evans SE 1994. Lepidosauromorph reptiles from the Middle Jurassic of Skye. Zoological Journal of the Linnean Society 112:135-150.

wiki/Marmoretta
wiki/Colobops

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

Where would drepanosaurs nest, if Jesairosaurus was not known?

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

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

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

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

 

 

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.

So, is it Leptosaurus? Kallimodon? Or neither?

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

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

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

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

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

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

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

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

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

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

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

Figure 3. Rhynchocephalian cladogram from Rauhut and López-Arbarello lacks many pertinent taxa and includes one, Homoeosaurus, that belongs elsewhere.

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

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

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

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

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

References
Cocude-Michel M 1963. Les Rhynchocéphales et les Sauriens des Calcaires lithographiques (Jurassique supérieur) d’Europe occidentale.– Nouvelles Archives du Muséum d’Histoire Naturelle de Lyon 7: 1–187.
Fitzinger LJF 1837. Vorläufiger Bericht über eine höchst interessante Entdeckung -Dr. Natterers in Brasil. Oken’s Isis.
von Meyer H 1850. Mittheilungen an Professor Bronn gerichtet: Neües Jahrbuch fur Mineralogie, Geologie und Palaontologie, Bd 18, p. 195-204.
Rauhut OWM and Lopez-Arbarello A 2016. Zur Taxonomie der Brückenechse aus dem oberen Jura von Schamhaupten (On the taxonomy of the rhynchocephalian from the Late Jurassic of Schamhaupten). Archaeopteryx 33: 1-11; Eichstätt 2016.
Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46

 

Early Evolution of Rhynchosaurs

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

Figure 1. Rhynchosaur cladogram by Ezcurra et al. 2016. Note the outgroup includes two protorosaurs. The large reptile tree recovers protorosaurs elsewhere and has a long list of outgroup taxa among the trilophosaurs and rhynchocephalians. See figure 2.

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

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

Figure 2. This subset of the large reptile tree nests rhynchosaurs with trilophosaurs and rhynchocephalians, not protorosaurs.

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

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

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

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

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

Azendohsaurus postcrania

Figure 1. Azendohsaurus skull reconstructed with two premaxillary teeth, not four.

Figure 1. Azendohsaurus skull reconstructed with two premaxillary teeth, not four.

The new paper
on Azendohsaurus (Dutuit J-M 1972, Middle to Upper Triassic, Figs. 1-5) post-crania (Nesbitt et al. 2015, Fig. 2) has been eagerly awaited. The skull was published five years ago (Flynn et al. 2010). The description of the post-cranial bones is excellent, as was the earlier description of the cranial bones.

The is definitely a different sort of reptile…at first glance.

The big phylogenetic question is…
is Azendohsaurus closer to Pamelaria (the protorosaur archosauromorph)? Or closer to Trilophosaurus (the rhynchocephalian lepidosaur)?  Or closer to Sapheosaurus and Noteosuchus (two rhynchocephalian lepidosaurs)? Or closer to Eohyosaurus or Mesosauchus (yet other rhynchocephalians)?

Let’s test one analysis against another.

Figure 1. Reconstruction of Azhendohsaurus from Nesbitt et al. 2015. Manus on left. Pes on right.

Figure 2. Reconstruction of Azendohsaurus from Nesbitt et al. 2015. Length: a bit over one meter. Manus on left. Pes on right. Click to enlarge. No matter which clade this nests in, it is an oddity. But at present it is less odd nesting with Trilophosaurus and Sapheosaurus according to the input traits.

Unfortunately too few taxa were tested in the Nesbitt et al. study. 
Nesbitt et al. tested 29 taxa and found that Azendohsaurus nested between TeraterpetonTrilophosaurus and Pamelaria at the base of their Archosauromorpha (Fig. 3). Several mismatches occur here with great phylogenetic distances between purported sister taxa. The tree also mixes lepidosauromorphs with archosauromorphs, once again demonstrating convergence within the two major clades of reptiles.

Figure 1. The Nesbitt et al. 2015 cladogram nesting Azendohsaurus between Trilophosaurus + Teraterpeton and Pamelaria. This is not supported by the large reptile tree. Here green taxa are lepidosauromorphs. Black taxa are archosauromorphs.

Figure 3. The Nesbitt et al. 2015 cladogram nesting Azendohsaurus between Trilophosaurus + Teraterpeton and Pamelaria. This is not supported by the large reptile tree. Here green taxa are lepidosauromorphs. Black taxa are archosauromorphs. The proposed Allokotosauria is diphyletic. So is the proposed Azendohsauridae according to the large reptile tree. The black taxa are improperly included in this too small study on Azendohsaurus relationships.

By contrast,
the large reptile tree tested 610 taxa and maintained a long-standing and fully tested sisterhood between Trilophosaurus and Azendohsaurus. Furthermore, these two nested within the Rhynchocephalia at the transition to Mesosuchus, Eohyosaurus and the rhynchosaurs on the lepidosauromorph branch of the reptile (amniote) tree. Ancestral sisters include Sapheosaurus, Noteosuchus and tiny Leptosaurus (Fig. 6), taxa not listed in the Nesbitt et al. tree. Pamelaria continues to nest as a derived protorosaur on the archosauromorph branch of the reptiles.

Shifting
Azendohsaurus + Trilophosaurus + the rhynchosaurs and kin over to Pamelaria raises the MPTs from 9109 to 9127, a pretty small bump considering the great phylogenetic distance. The number drops to 9124 nesting this clade with Protorosaurus or the BPI 375 specimen of Youngina. Such similarity is due to convergence.

Notably,
Pameleria does not have two parallel rows of large teeth as in rhynchocephalians including Azendohsaurus and rhynchosaurs. Trilophosaurus does something odd with not two, but three laterally aligned cusps.

Figure 2. Rhynchocephalian subset of the large reptile tree with Azendohsaurus highlighted.

Figure 4. Rhynchocephalian subset of the large reptile tree with Azendohsaurus highlighted.

The nesting of rhynchosaurs and Trilophosaurus as basal archosauromorphs close to or within the protorosaurs has been a long standing problem in paleontology. They do indeed evolve away from the basic rhynchocephalian bauplan seen in Sphenodon.

Reducing the large reptile tree taxon list to that of Nesbitt et al. 2015
recovers a tree (Fig. 5) that again splits up archosauromorphs (inverted type) and lepidosauromorphs (black type).

Figure 5. A subset of the large reptile tree matched to the Nesbitt et al. 2015 taxon list. Here the tree mixes taxa from the two major branches demonstrating the convergence of the derived taxa and the importance of including a large gamut (610) of tested and verified taxa rather than fewer than 30 favorites or traditional guesses.

Figure 5 A subset of the large reptile tree matched to the Nesbitt et al. 2015 taxon list. Here the tree mixes taxa from the two major branches demonstrating the convergence of the derived taxa and the importance of including a large gamut (610) of tested and verified taxa rather than fewer than 30 favorites or traditional guesses. Inverted taxa are archosauromorphs. Others are lepidosauromorphs in the large reptile tree. Note that both Pamelaria and Terterpeton are only one node away from the Azendohsaurus clade here.

 

With an odd reptile like Azendohsaurus
it is necessary to use a large gamut cladogram, like the large reptile tree, to test all the possibilities and relationships, leaving out virtually no possibilities.

Figure 6. Azendohsaurus compared to sister taxa and putative sister taxa including Trllophosaurus, Pamelaria, Teraterpeton, Sapheosaurus and Leptosaurus. Diandongosaurus is ghosted as it is a tested sister to Teraterpeton. Azendohsaurus nests with Trilophosaurus in both studies. Even so it is quite distinct.

Figure 6. Azendohsaurus compared to sister taxa and putative sister taxa including Trllophosaurus, Pamelaria, Teraterpeton, Sapheosaurus and Leptosaurus. Diandongosaurus is ghosted and not related. Azendohsaurus nests with Trilophosaurus in both studies. Even so it is quite distinct.


Along the way

I learned more about Trilophosaurus (Fig. 7) by going to photographs of the material after trusting published reconstructions that combined the anterior skull specimen with a mismatched posterior skull specimen.What we’ve gotten used to  seeing is a chimaera.

Figure 4. Trilophosaurus skulls. Note the deep jugal on two and the shallow jugal on the third. Also note the postjugal bone, a novel ossification.

Figure 7. Trilophosaurus skulls, right side flipped. Note the deep jugal on two and the shallow jugal on the third. Also note the postjugal bone (deep blue), filling in the posterior jugal notch. This is a novel ossification. The asymmetry between the left and right quadrate/jugal suture appears to be natural. The palatine teeth align with the maxillary teeth, a unique trait.

I also learned
that the published Azendohsaurus premaxilla has a bit of maxilla on it (Fig. 1), reducing the premaxillary tooth count from four to two. The original researchers considered the crack the suture. No sister taxa have four teeth in the premaxilla. All have two teeth including the shallow jugal specimen of Trilophosaurus with two vestigial teeth in the premaxilla.

Figure 6. Eohyosaurus nests as a sister to the Trilophosaurus-Azendohsaurus clade.

Figure 8. Eohyosaurus nests as a sister to the Trilophosaurus-Azendohsaurus clade.

Basal rhynchocephalia
have teeth ankylosed (fused) to the bone. In some cases the teeth are bone. Apparently when rhynchocephalians became phylogenetically miniaturized in tiny Leptosaurus, neotony re-produced regular socketed teeth of the sort one also sees in Eohyosaurus, MesosuchusSapheosaurus and Azendohsaurus.

Nesbitt et al. report
“Teasing apart homology from homoplasy of anatomical characters in this broad suite of body types remains an enormous challenge with the current sample of taxa.”

Indeed that sample of taxa has to be greatly increased.
610 taxa demonstrate this amply. 29 is just too few. Too many actual sister taxa were overlooked and excluded in the Nesbitt et al. analysis. They relied on tradition rather than testing when oddly matched sister taxa nested with one another on their cladogram.

Even so,
as can be seen by the reconstructions (Fig. 5), there is still a great deal of phylogenetic distance between tested sisters. The large reptile tree minimizes this, but the distances still remain great. New discoveries will help fill these gaps, but the correct inclusion group must be used. The tree subset that includes protorosaurs and basal archosauriforms (Fig. 9) does not include Azendohsaurus, Trilophosaurus, rhynchosaurs or tanystropheids (which are all lepidosauromorphs).

Figure 7. Sapheosaurus GIF animation. This smaller ancestral sister to Azendohsaurus was overlooked and excluded by the Nesbitt et al. study.

Figure 8. Sapheosaurus GIF animation. This smaller ancestral sister to Azendohsaurus was overlooked and excluded by the Nesbitt et al. study.

Nesbitt et al. created two suprageneric clades.
Unfortunately the proposed clade Allokotosauria is diphyletic. So is the proposed clade Azendohsauridae according to the large reptile tree.

Figure 2. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes. Click to enlarge.

Figure 9.  Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and basal Archosauriformes.
Click to enlarge. Azendohsaurus, Trilophosaurus, tanystropheids and rhynchosaurs do not nest here as they do in the smaller gamut Nesbitt et al. cladogram, which improperly included them.

References
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’zhtlas 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.
Nesbitt SJ, Flynn JJ, Pritchard AC, Parrish JM, Ranivoharimanana L and Wyss AR 2015. Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. Bulletin of the American Museum of Natural History 398: 1-126.

wiki/Azendohsaurus

 

 

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.

Leptosaurus: another transitional taxon between Rhynchocephalia and Rhynchosauria

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Azendohsaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus pulchellus (Fitzinger 1837, Zittel 1887, Renesto and Viohl 1997; aka: Kallimodon Cocude & Michel, 1963) SCHA 40 Late Jurassic, Tithonian Stage, Germany,
155.7 to 150.8 Ma.

Holotype: Leptosaurus neptunicus Fitzinger 1837.

Rhynchocephalians are generally not so small, but this one is, likely yet another case of miniaturization at the base or transition to a major clade. In this case the SCHA 40 specimen attributed to Leptosaurus (I haven’t seen the holotype) is basal to the much larger Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus. Priosphenodon and rhynchosaurs on the other.

The large reptile tree (still not updated) keeps adding transitional taxa without changing the tree topology. That’s a measure of its strength. And more taxa using the same number of characters keeps dropping that character/taxon ratio.

References
Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46.

Finally, some Priosphenodon post crania!

Earlier we looked at the skull of Priosphenodon (aka Kaikaifilusaurus) No dorsal or occipital views, but plenty of data to nest it at the base of the rhynchosaurs, despite its identification as a rhynchocephalian (sphenodontian).

Now (Fig. 1), courtesy of Dr. Sebastián Apesteguía (Argentina), who wrote his thesis on Priosphenodon, an image of the skeleton as a museum model is available. I understand that the carpals are among the few imagined parts here.

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. This is the first data I’ve seen on the dorsal skull and postcrania. Photo courtesy of Dr. Apesteguía. Inset shows that the foot and manus of the model were switched based on comparisons to Hyperodapedon, a related rhynchosaur. The artist was unsupervised.

You’ll note
the wide, bulging cheeks and extremely narrow parietal (skull roof), as in rhynchosaurs. The nares had not become confluent. That comes in more highly derived forms. But look at those twin anterior dentary tips, as in rhynchosaurs. No anterior process on the ilium though. Stance probably not as sprawling as this, and not as erect as in rhyncosaurs.

References
Photo courtesy of Dr. Sebastian Apesteguía Specimen model at the new museum of Cipolletti (Rio Negro Province, Argentina), currently under construction. The sculptor is Jorge Antonio Gonzalez.