New clade of enigmatic early archosaurs? No.

Recently, Butler et al. (2014)
recovered a “new clade of enigmatic early archosaurs” comprised of Yonghesuchus, Gracilisuchus and Turfanosuchus.

Unfortunately they added the unrelated Mesosuchus (lepidosaur), Vancleavea (thalattosaur) and two pterosaurs (lepidosaurs).

And they did not add the true sisters of Gracilisuchus (Pseudhesperosuchus, Decuriasuchus, Lewisuchus, Saltopus, the SMNS 12591 specimen and Scleromochlus).

Red Flags
In the Butler et al. (2014) tree the following purported sister taxa are all “odd bedfellows” that do not look like one another.

  1. Prolacerta is derived from Mesosuchus (and presumably the rhynchosaurs)
  2. Euparkeria is derived from Tropidosuchus and Chanaresuchus.
  3. Tropidosuchus and Chanaresuchus are derived from Vancleavea.
  4. Vancleavea is derived from Erythrosuchus.
  5. Pterosaurs are derived from parasuchians!!!!!!
  6. Lagerpeton is derived from pterosaurs.
  7. Ornithosuchia is derived from Lewisuchus.
  8. Theropoda is derived from Ornithischia.
  9. Ornithosuchia is a sister to Pterosauria, also derived from Parasuchia.
  10. Revueltosaurus is a sister to the Aetosauria and derived from Ornithosuchia
  11. The new Gracilisuchus clade is derived from Revueltosaurus.
  12. Poposaurus and the poposaurs are derived from Qianosuchus, Xilosuchus and Arizonasaurus
  13. Prestosuchus and the Rauisuchidae is derived from Ticinosuchus.
  14. Hesperosuchus and the Crocodylomorpha are derived from Rauisuchidae.

Say it ain’t so!
As you can see, many of these relationships don’t make sense. Sister taxa share very few traits with one another (pterosauria and parasuchia, is the worst such example). Many relationships are upside down with basal taxa, like theropods, derived from derived taxa, like ornithischia. (M. Mortimer also had this problem a few years ago).

What is needed is a large reptile tree in which basal taxa are basal to derived taxa and all sisters look alike (share most traits). In the large reptile tree, sister taxa look quite a bit like one another. The authors should have cast a critical eye on these results, which are very similar to those of Nesbitt (2011), who also recovered many strange bedfellows.

If I had proposed that pterosaurs arose from parasuchians,
the ridicule would be endless and justified, as it is here. Taxon exclusion seems to be the culprit again, along with the tradition of using previously published matrices, even those riddled with Red Flags and strange bedfellows.

In the large reptile tree, Gracilisuchus nests with the SMNS 12591 specimen, Saltopus and Scleromochlus at the base of the Archosauria. Turfanosuchus nests at the base of the Poposauridae, between Decuriasuchus and the base of the Archosauria, not far from GracilisuchusYonghesuchus, nests between Dromicosuchus and Protosuchus.

And, because this is Science, you can repeat these experiments to see for yourself which taxa share more traits — that make sense.

References
Butler et al. 2014. New clade of enigmatic early archosaurs yields insights into early  pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evolutionary Biology  14:128. doi:10.1186/1471-2148-14-128
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

The Proterosuchus holotype – restoration and imagination

Several skulls and skeletons have been attributed to Proterosuchus, the basalmost archosauriform. Unfortunately the holotype is the worst of the lot.

Figure 1. Top and bottom images from Ezcurra et al. 2014. Middle with missing pieces imagined and restored based on other specimens.

Figure 1. Top and bottom images of Proterosuchus holotype from Ezcurra and Butler 2014. Middle with missing pieces imagined and restored based on other specimens. As you can see, the bones and impressions of bones are very difficult to see. Colorizing the bones, as I do in DGS, is an amazing way to present what those two observed in the fossil.

A recent paper by Ezcurra and Butler 2014 explores the many skulls of Proterosuchus.

From the abstract
“Based upon a comprehensive re-examination of all known specimens, as well as examination of other proterosuchid taxa in collections worldwide, we conclude that the holotype of Proterosuchus fergusi (Fig. 1) is undiagnostic… As a result, we recognize a minimum of four archosauriform species following the Permo-Triassic mass extinction in South Africa. Our results suggest a greater species richness of earliest Triassic archosauriforms than previously appreciated, but that archosauriform morphological disparity remained low and did not expand until the late Early Triassic – early Mid-Triassic.”

This skull, IMHO, cannot be used in phylogenetic analysis, and it hasn’t been used in that way. However, add a few other taxa identified by museum numbers and you’re good to go.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra, MD and Butler RJ. 2014. Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and implications for the early archosauriform radiation. Palaeontology. (advance online publication)
DOI: 10.1111/pala.12130 http://onlinelibrary.wiley.com/doi/10.1111/pala.12130/abstract
Ezcurra MD, Butler RJ and Gower D 2013. ‘Proterosuchia’: the orign and early history of Archosauriformes. Pp. 9–33 in S. J. Nesbitt, J. B. Desojo, R. B. Irmis (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin. Geological Society, London, Special Publications 379.
Welman J 1998. The taxonomy of South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18:340–347.
Welman J and Flemming  AF 1993. Statistical analysis of the skulls of Triassic proterosuchids (Reptilia, Archosauromorpha) from South Africa. Palaeontologia africana 30:113–123.

wiki/Proterosuchus

 

A closer look at Sikannisuchus huskyi

Earlier we looked at the skull roof of Sikannisuchus. Unfortunately, I ignored those long mandible bits and pieces. These give us more clues to restore the missing parts in lateral view (Fig. 1).

Sikannisuhus huskyi restored on must a view bits and pieces.

Sikannisuhus huskyi restored on must a view bits and pieces. Nesting with Postosuchus provides clues to the shapes of the missing parts. That’s a nice long skull. Must have been a BIG reptile.

If I made any errors, or the clues point in another direction, let me know.

References
Nicholls EL, Brinkman DB and Wu K-C 1998. A new archosaur from the Upper Triassic
Pardonet Formation of British Columbia. Canadian Journal of Earth Science 35: 1134–1142.

A closer look at Jesairosaurus

Earlier we looked at Jesairosaurus (Jalil 1991) and the origin of the Drepanosauridae. Today we’ll take a closer look at Jesairosaurus.

Figure 1. The ZAR 206 specimen of Jesairosaurus, nesting between Huehuecuetzpalli and the Drepanosauridae AND the Tanystropheidae.

Figure 1. The ZAR 206 specimen of Jesairosaurus, nesting between Huehuecuetzpalli and the Drepanosauridae AND the Tanystropheidae.

 

Jesairosaurus was originally considered a prolacertiform
Sure it has a long neck, but in phylogenetic analysis, it doesn’t nest with Prolacerta or Marlerisaurus, but after the basal lepidosaur Huehuecuetzpalli (described a year later) and prior to other long-necked taxa, including langobardisaurs and drepanosaurs. Note the dorsal nares and large orbit. There’s a very tall scapula here, a precursor to the tall stem in drepanosaurs. The specimen is broken up, but appears to have a tiny antorbital fenestra, a trait that has been argued about in drepanosaurs.

Distinct from most lepidosaurs,
Jesairosaurus has fairly large thecodont teeth, a trait retained by all successors, including tanystropheids and pterosaurs. Gastralia appear here for the first time in this lineage, lost in drepanosaurs, kept in langobardisaurs. The ventral pelvis isn’t fused, but the thyroid fenestra is gone.

Like most lepidosaurs,
the scapulocoracoid was fenestrated. And there’s a nice ossified sternum there.

Folks, not adding this taxon to phylogenetic analyses focused on any of the taxa mentioned above is big mistake. It’s time to clear out all the enigma taxa and nest theme where they belong.

On a side note…
As you know, I’m always attempting to improve the data here. Several months ago I mentioned to a detractor that most prior workers reported  forelimbs present in Sharovipteryx. Only Unwin et al. (2000) thought they were buried in the matrix. My detractor claimed the opposite, that I was the only one to see forelimbs. No word yet on this issue. Still waiting.

Another detractor claimed I had seen soft tissue on a Bavarian museum fossil pterosaur. When I asked which specimen, he refused to provide the number.

In a third case I asked to see a closeup of a pterosaur mandible tip that had been published. I wondered if the sharp tip might be a tooth, as it is in other sharp mandible pterosaurs. The offer was refused with the phrase, “trust us, it’s not there.” I replied “trust” is antithetical to Science. No reply and no closeup yet.

So, is it so hard to provide a museum number? A closeup of a photograph? Or a reply to a note on forelimbs? Should we trust other scientists? Or should we test and confirm or refute? There may be cooperation among other paleontologists. Or maybe they’re all very protective of their data. Evidently I also have a very bad reputation, and that may be the reason for the lack of cooperation. These things happen when paradigms are broken.

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.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle-Late Triassic of Kyrgyzstan. In: Benton M.J., Shishkin M.A. & Unwin D.M. (Eds) The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge U. Press: 177-186.

wiki/Prolacertiformes

 

 

When DNA analyses return untenable results

Sometimes DNA and RNA provide great insight into phylogenetic relationships.

Other times… not so much.

Ultimately molecule analyses have to be supported by morphological studies that enable us to see the gradual accumulation of traits in lineages. If we can’t see those gradual evolutionary changes, then we must assume there are agents in the DNA that are obfuscating relationships, rather than illuminating relationships.

Two cases in point:

Hedges & Poling (1999) argued that Sphenodon was more closely related to archosaurs than to squamates. This would require independent acquisition of a wide range of specialized features and takes no account of the fossil histories of the groups in question, according to Evans (2003).

Wiens et al., (2012) produced a molecule study of extant taxa that rearranged prior squamate trees, nesting Dibamus and gekkos at the base while nesting Anguimorpha and Iguania as derived sister clades. For those who don’t know Dibamus too well, it has no legs and a very odd skull morphology. In the large reptile tree it nests with other legless scincomorphs, with which it shares a long list of character traits.

Unfortunately these DNA studies, like ALL DNA studies, ignore fossil taxa.

But we need them.

On the other side of the coin recent work by Losos on extant anoles in the Carribbean seems to have turned up some interesting and viable results.

Not sure where to draw the line. Be careful out there.

References
Evans SE 2003. At the feet of the dinosaurs: the early history and radiation of lizards. Biological Reviews 78:513–551.
Hedges SB and Poling LL 1999. A molecular phylogeny of reptiles. Science 283, 998–1001.
Wiens JJ, et al. 2012. Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biology Letters. 2012 8, doi: 10.1098/rsbl.2012.0703.

Phylogenetic bracketing and pterosaurs – part 2

Two posts ago we looked at part 1 of this topic.

Since pterosaurs (and other tritosaurs) nest between rhynchocephalians and squamates, there are a few traits they likely shared based on phylogenetic bracketing (unless specifically excepted based on fossil evidence). Putting the rhynchocephalians aside for the moment, according to Evans (2003) squamate traits include:

(1)  a specialized quadrate articulation with a dorsal joint typically supplied by the deeply placed supratemporal, reduced squamosal, and distally expanded paroccipital process of the braincase; reduction/loss of pterygoid/quadrate overlap; loss of quadratojugal – all present in basal tritosaurs, but quadrate becomes immobile in Macrocnemus and later taxa.

(2) loss of attachment between the quadrate and epipterygoid, with the development of a specialized ventral synovial joint between the epipterygoid and pterygoid — also present up to Huehuecuetzpalli, but absent in Macrocnemus and later taxa.

(3) subdivision of the primitive metotic fissure of the braincase to give separate openings for the vagus nerve (dorsally) and the perilymphatic duct and glossopharyngeal nerve (via the lateral opening of the recesses scalae tympani ventrally). This leads to the development of a secondary tympanic window for compensatory movements and is associated with expansion of the perilymphatic system and closure of the medial wall of the otic capsule — in fossil tritosaurs these details may not be known and certainly not by me… yet.

(4) loss of ventral belly ribs (gastralia) — Basal tritosaurs, up to Homoeosaurus have gastralia. Then they don’t until Macrocnemus and all later taxa.

(5) emargination of the anterior border of the scapulocoracoid — Basal tritosaurs share this trait. Macrocnemus and tanystropheids refill the emargination. Fenestrasaurs, including pterosaurs expand the emargination resulting in a strap-like scapula and stem-like coracoid, both representing the posterior rims of these bones.

(6) hooked fifth metatarsal with double angulation — shared with tritosaurs and more complex mesotarsal joint — in tritosaurs the mesotarsal joint is simple.

(7a) a suite of soft tissue characters including greater elaboration of the vomeronasal apparatus;

(7b) a single rather than paired meniscus at the knee;

(7c) the presence of femoral and preanal organs;

(7d) fully evertible hemipenes;

(7e) and pallets on the ventral surface of the tongue tip — none of these have been noted in soft tissue fossils.

References
Evans SE 2003. At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, Cambridge 78: 513–551.

 

The many faces of Tanystropheus

Tanystropheus is well known
as the sometimes giant reptile with the hyper-elongate neck (Figs. 1, 2). Several specimens are known, all by letters in the alphabet based on Wild (1973). Few specimens have skulls.

The smaller Tanystropheus specimens (Fig. 1) have multicusp posterior teeth, and some workers consider these juveniles that change their diet and teeth as they grow. Others, including yours truly, think these are two different species, if not different genera. Remember, guyz and galz, you don’t get giant species without first going through the medium and large size ranges. We learned this earlier with Pteranodon.

Wild’s (1973) reconstruction of the skull was taken as gospel for a good long time. Then Nosotti (2007) came along and rebuilt the small skull in convincing fashion. Here we’ll take a look at a skull from a small individual (Fig. 1, Exemplar a) and compare it to two skulls from the larger forms (Fig. 2, Exemplars i and q). Then you can decide if the differences are ontogenetic or phylogenetic.

Tanystropheus exemplar a.

Figure 1. Tanystropheus exemplar a.

Exemplar a has a low rostrum and large orbit. The frontals extend over the orbits like brow ridges. The nasals are not visible on any articulated skulls, and displaced samples can be placed on the skull two different ways. The ascending process of the premaxilla is also a big question mark. It could be present or absent. The pineal opening is not large in any sister taxa, so it redevelops here. The posterior skull leans down, which, by analogy with basal synapsids indicates a bit of posterior pull on the mandible, as if Exemplar a was tugging at its meals.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar m.

Figure 2. Tanystropheus with skull reconstructions based on two specimens, exemplar i and exemplar q.

Among the giant specimens…

Exemplar i is the skull that Wild (1973) used for his ‘adult’ specimen. Like  Exemplar a, the frontals are wide, the nasals are unknown and the ascending process of the premaxilla is apparently gone. This creates quite a large confluent set of nares dorsally oriented. The posterior skull does not descend posteriorly. Only a few teeth are preserved and in dorsal view the rostrum is wide and rather flat, like a hat brim. One gets the impression that a great circle of procumbent teeth emanated from these jaws because the premaxilla appear to be quite flat in situ with no indication of any depth.

Exemplar q is lower, longer and had a reduced pterygoid and vomers. Here the nares are also very large, but divided by a slender and fragile ascending process of the premaxilla (pretty much busted up in situ). Rather than wide and flat, this rostrum is more traditionally box-like with ventrally oriented teeth. The pterygoid is greatly reduced and so are the vomers. The nasals are preserved here only as posterior rims to the large nares. The brow ridges are gone here, so Exemplar q could look up without moving its head.

The appearance of those giant nares on these tiny skulls links to that hyper-elongate neck and within, a hyper-elongate trachea that needs to be flushed of CO2 and filled with O2 every so often.

So the skulls of the big taxa are different.
It might be worthwhile to see how the post-crania also differs. There’s a PhD project waiting for someone out there, probably in Europe, where the fossils are. Or wait a few weekends and I’ll probably get around to it.

References
Bassani F 1886. Sui Fossili e sull’ età degli schisti bituminosi triasici di Besano in Lombardia. Atti della Società Italiana di Scienze Naturali 19:15–72.
Li C 2007. A juvenile Tanystropheus sp.(Protoro sauria: Tanystropheidae) from the Middle Triassic of Guizhou, China. Vertebrata PalAsiatica 45(1): 37-42.
Meyer H von 1847–55. Die saurier des Muschelkalkes mit rücksicht auf die saurier aus Buntem Sanstein und Keuper; pp. 1-167 in Zur fauna der Vorwelt, zweite Abteilung. Frankfurt.
Nosotti S 2007. Tanystropheus longobardicus (Reptilia, Protorosauria: Reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano, Vol. XXXV – Fascicolo III, pp. 1-88
Peyer B 1931. Tanystropheus longobardicus Bass sp. Die Triasfauna der Tessiner Kalkalpen. Abhandlungen Schweizerische Paläontologie Gesellschaft 50:5-110.
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus (Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-16.

wiki/Tanystropheus