Back to Vancleavea

Several years ago we looked at Vancleavea campi (Figs. 1,2 ), a Triassic aquatic reptile described by Nesbitt, et al. 2008 as an archosauriform nesting with Erythrosuchus, Euparkeria, Turfanosuchus and Doswellia (according to Wikipedia, based on published work listed above). Unfortunately, Vancleavea shares few traits with these archosauriforms. It has no antorbital fenestra, no upper temporal fenestra and no mandibular fenestra.

Figure 1. Vancleavea surrounded by purported sister taxa as figured by Nesbitt and Wikipedia. None of these taxa share more traits with Vancleavea than does Helveticosaurus, a taxon ignored since it was proposed here.

Figure 1. Vancleavea surrounded by purported sister taxa as figured by Nesbitt and Wikipedia. None of these taxa share more traits with Vancleavea than does Helveticosaurus, a taxon ignored since it was proposed here.

Not yet tested in academic publications,
the thalattosaur, Helveticosaurus, shares more traits with Vancleavea than 569 other tested taxa in the large reptile tree.

Figure 2. Vancleavea with its sister, Helveticosaurus.

Figure 2. Vancleavea with its sister, Helveticosaurus.

This counter argument
was made more than 4 years ago. To date no one else has supported or refuted the argument. Nevertheless, in the last four years Vancleavea has appeared in several cladograms without Helveticosaurus. Unfortunately this demonstrates that paleontologists are really not interested in its correct nesting node, but would rather just add new taxa to existing flawed analyses and cladograms. Testing prior work is not their strong suite. Discovery is.

Vancleavea campi  (Nesbitt et al. 2009) Late Triassic,~210 mya, ~1.2 meters in length, was originally considered a very weird archosauriform close to DoswelliaTurfanosuchusChanaresuchus and Erythrosuchus, but that’s because the authors did not compare it to Helveticosaurus with which Vanclevea shares more traits. It turns out that Vanclevea was a not-so-weird thalattosaur and a prime example of what happens when the gamut of the inclusion set is decided prior to the analysis. Vancleavea was the last in its lineage. Unlike other thalattosauriforms, Vancleavea was armored with a variety of ossified scales covering the body.

There must be dozens
of Vancleavea-like thalattosaurs yet to be discovered, judging by the variation present between it and Helveticosaurus. Even so, after adding hundreds of taxa to the large reptile tree, these two still nest together.

Not the only time a taxon’s correct nesting ignored.
These taxa are also traditionally incorrectly nested based on the results of the large reptile tree.

  1. Turtles
  2. Pterosaurs
  3. Fenestrasauria and Tritosauria
  4. Snakes
  5. Caseasauria
  6. Mesosauria
  7. Poposauria
  8. Rhynchosauria
  9. Synapsida
  10. Chilesaurus and Daemonosaurus
  11. Gephyrostegus
  12. Procolophon
  13. Cartorhynchus
  14. Youngina and Youngoides
  15. Xianglong
  16. Tetraceratops
  17. Eudibamus
  18. Doswellia
  19. Revuletosaurus
  20. Scleromochlus
  21. Pseudhesperosuchus
  22. Marasuchus
  23. Lagerpeton
  24. Ticinosuchus
  25. and whatever else I’ve forgotten to list here

References
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
Parker WG and Barton B 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11 (3): 20p.

wiki/Vancleavea

Update on the Rossman 2002 “Brazilosaurus”

Figure 1. The nesting of Rossman's "Brazilosaurus" (the PIMUZ AIII 0192 specimen) at the base of the Thalattosauria is confirmed with the addition of post-cranial and new cranial data.

Figure 1. Click to enlarge. The nesting of Rossman’s “Brazilosaurus” (the PIMUZ AIII 0192 specimen) at the base of the Thalattosauria is confirmed with the addition of post-cranial and new cranial data.

Today: Some new data and a new reconstruction of the skull and postcrania of the intriguing and potentially important postcrania of PIMUZ A/III 0192. This mesosaur-ish reptile was attributed by Rossman 2002 to Brazilosaurus sanpauloensis. 

Earlier the only data I had on this specimen was a line drawing of a skull from Rossman 2002. This data resulted in a nesting outside of Brazilosaurus + Stererosternum + Mesosaurus, at the base of the Thalattosauria. Notably, with the additional data, the nesting did not change.

Crushed skulls are often the best Because all the parts are crushed into a single plane and you can rebuild that “house of cards” or “crushed eggshell” in many views. Some parts are visible through the orbit. The occiput often flips to the side.

Mesosaurs are key
Workers have attempted to nest mesosaurs based on its lack of temporal fenestration — and they (Modesto 2006) end up with pareiasaurs and millerettids and procolophonoids. But with it’s hyper-long teeth, Mesosaurus is clearly a derived form. What we’re looking for is a basal taxon that looks like Mesosaurus with small plesiomorphic teeth. Then perhaps we’ll see more evidence for the diapsid skull morphology. And that’s exactly what we find.

Figure 2. Click to enlarge. The Rossman "Brazilosaurus" PIMUZ AIII 0192. This is a basal thalattosaur and a derived mesosaur. Due to severe crushing elements from the other side of the skull made it appear that the skull lacked fenestration following the generally accepted but mistaken hypothesis that all mesosaurs lacked temporal fenestra.

Figure 2. Click to enlarge. The Rossman “Brazilosaurus” PIMUZ AIII 0192. This turns out to be THE  basal thalattosaur as well as a basal mesosaur. Due to severe crushing elements from the other side of the skull made it appear that the skull lacked fenestration following the generally accepted but mistaken hypothesis that all mesosaurs lacked temporal fenestra. Note the tiny forelimbs and deep tail chevrons. Low dorsal spines and gracile ribs are also noteworthy.

Here (Fig. 1) the Rossman (2002) “Brazilosaurus” nests at the base of the Thalattosauria, whether using the Rossman data as is, or pulling slightly different traits out (Fig. 2).

Rossman (2002) presented photos of several interesting mesosaurs. Among them was the SMF-R-4710 specimen attributed to Stereosternum (Fig. 3). This one does nest with Stereosternum, but with more open temporal fenestrae, its nests at the base of the mesosaurs, close to the base of the ichthyosaurs and thalattosaurs.

Figure 3. The SMF-R-4710 specimen attributed to Stereosternum, but with larger temporal fenestrae, smaller teeth and other distinct traits.

Figure 3. Click to enlarge. The SMF-R-4710 specimen attributed to Stereosternum, but with larger temporal fenestrae, smaller teeth and other distinct traits. The high unfused dorsal processes are also seen on Hupehsuchus and Utatsusaurus.

If you think this Stereosternum specimen is starting to look a lot like Wumengosaurus, you’d be right. And Wumengosaurus now nests at the base of Hupesuchus + Ichthyosaurs, so we’re getting closer and closer to the common origin of both. One keeps its teeth, the other does not.

Figure 3. Stereosternum SMF-R-4710 reconstructed from traced image (in color below). Here temporal fenestration is clearly diapsid.

Figure 3. Stereosternum SMF-R-4710 reconstructed from traced image (in color below). Here temporal fenestration is clearly diapsid.

Lest you doubt
Running the large reptile tree with all temporal fenestration traits deleted recovers a single tree unchanged from the full character list tree. If anyone wants to come up with better data or a better tracing, please use specimen numbers.

There are so many specimens of mesosaurs
and so many variations and only three names for them (Mesosaurus, Brazilosaurus, Stereosternum). Someone needs to put it all together and catalog some of the important specimens (e.g. the holotypes). We’ll need new generic names for the specimens above.

If someone has a good photo of the Brazilosaurus holotype (Shikama and Ozaki 1966), please let me know.

References
Cope ED 1886. A contribution to the vertebrate paleontology of Brazil. Stereosternum tumidum, gen. et sp. nov. Proceedings of the American Philosophical Society 23(121):1-21.
Modesto S 2006.
 The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology. Zoological Journal of the Linnean Society, 2006, 146, 345–368.
Shikama T and Ozaki T 1966. On a Reptilian Skeleton from the Palaeozoic Formation of San Paulo, Brazil” Transactions and Proceedings of the Palaeontological Society of Japan, New Series 64: 351–358.

 

Hescheleria and Nectosaurus: odd hook-nose thalattosaurs

Thalattosaurs were aquatic diapsids that had lost the upper temporal fenestra and were most closely related to ichthyosaurs, according to the large reptile tree. Postcranially, some thalattosaurs had paddles. Others had fingers and claws. Thalattosaurs appear to have differed principally in the skull, especially the preorbital portion of the skull, probably as a reflection of their various diets.

Straight
Several thalattosaurs have a long straight rostrum. Think Askeptosaurus, Endennasaurus and Xinpusaurus (Fig. 2).

Hooked
Hescheleria rubeli (Middle Triassic (Anisian/Landinian) and Nectosaurus halius (Late Triassic) don’t. These hook-nose thalattosaurs (Fig. 1, from Rieppel et al. 2005) expand the morphological diversity of this increasingly varied clade of ichthyosaur sisters.

Figure 1. Nectosaurus and Hescheleria, two odd hook-nose thalattosaurs

Figure 1. Nectosaurus and Hescheleria (upper left), two odd hook-nose thalattosaurs. That deep set of fused vomers on Nectosaurus may be unique to it and its sisters.

Hescheleria (Rieppel et al. 2005) was twice the size of Nectosaurus, based on the skull alone (Fig. 1). Not sure what the post-crania looked like. Apparently it isn’t well known. The vertically descending premaxillary rostrum is a unique morphology shared by Hescheleria and Nectosaurus, perhaps also Paralonectes, amongst known thalattosaurs. Not so much in Thalattosaurus and Miodentosaurus.

Figure 2. The Thalattosauria and outgroups (Wumengosaurus and Stereosternum) to scale.

Figure 2. The Thalattosauria and outgroups (Wumengosaurus and Stereosternum) to scale.

Thalattosaurs started with a pretty long rostrum. It became shorter with Helveticosaurus and Vancleavea. (Fig. 2).

References
Rieppel OC, Müller J and Liu J 2005. Rostral structure in Thalattosauria (Reptilia, Diapsida). Canadian Journal of Earth Sciencies: Vol. 42, pp. 2081-2086

Anshunsaurus (thalattosaur) juvenile notes

Anshunsaurus (Liu 1999) was a late middle Triassic (Landinian) thalattosaur close to Askeptosaurus. It is known from an adult and a juvenile.

From the abstract: “A marine reptile from the Ladinian deposits near Xingyi is described and identified as a juvenile of Anshunsaurus wushaensis on the basis of similar skull proportions and many postcranial characters. Based on this specimen and observations of the holotype of A. wushaensis, there is no distinct ontogenetic differentiation in the length of the jugal. The absence of an astragalus in the holotype, and the greater length of metacarpal V relative to metacarpal IV, could be due to intraspecific variation. Ossification is not synchronous for corresponding elements on both sides of the body.”

This asymmetry is the key point to this post, and something to consider when thinking about adult/juvenile matching.

Figure 1. The two Anshunsaurus skull, adult and juvenile.

Figure 1. The two Anshunsaurus skull, adult (from Liu and Rieppel 2005) and a  juvenile (from Liu 2007). Scale bar is 10cm. So on a 72dpi screen the skulls are shown at 0.8 scale or 20 percent smaller.

What are thalattosaurs?
Liu and Rieppel 2004 wrote, “The phylogenetic position of thalattosaurs within amniotes is controversial: They have been suggested to be diapsids with possible affinities to the Lepidosauromorpha (Romer, 1956; Rieppel, 1998), Archosauromorpha (Evans, 1988), to be Neodiapsida inc. sed. (Benton, 1985), or else to be the sister taxon of Sauria (Mu¨ller, 2004) or of Ichthyopterygia (Müller, 2003).”

According to the large reptile tree, Müller is correct.

The Triassic marine reptile Anshunsaurus huangguoshuensis was originally described by Liu (1999) as a sauropterygian (likely a plesiosaur or nothosaur) on the basis of a dorsal view of a skull. The specimen was recognized as thalattosaurian by Rieppel et al. (2000). So errors happen.

Figure 2. The manus and pes of the large and small Anshunsaurus specimens.

Figure 2. The manus and pes of the large and small Anshunsaurus specimens. In the manus note the difference in metacarpal/digit proportions along with carpal ossification. In the pes note similar differences, and also a lengthening of mt4 and a narrowing of its proximal articulation. Individual variation or speciation?

Genus differences
Anshunsaurus differed from the previously known but similar Askeptosaurus by the maxilla forming part of the  anteroventral orbital margin; fusion of the postorbital and postfrontal; the posterolateral process of the frontal extending posteriorly far beyond the anterior margin of lower temporal fossa, narrowly approaching but not contacting the supratemporal; the long and slender ventral process of the squamosal extending to the lower margin of the cheek; jugal with an elongate posterior process; lateral exposure of the angular equal to that of the surangular; deltopectoral crest on the humerus developed; fibula expanded.

Species differences
A. wushaensis
 was slightly smaller and differed from the holotype A. huangguoshuensis in the following characters (Rieppel et al., 2006):

  1. relatively smaller skull relative to the glenoid-acetabulum length;
  2. short posterior process of the jugal that does not extend backward beyond the midpoint of the lower temporal fossa;
  3. neural spines in the posterior dorsal region that are not taller than their anteroposterior width and with a distinct ornamentation of vertical grooves and ridges near their dorsal margin;
  4. cruciform interclavicle with a broad-based anterior process;
  5. ectepicodylar groove and notch on humerus distinct;
  6. entepicondyle well developed, with ridge on ventral side of medial margin but no foramen;
  7. metacarpal V slightly longer than metacarpal IV;
  8. loss of one phalanx in fourth digit;
  9. iliac blade posterodorsally expanded; 
  10. seven ossified tarsals.

In the skull, the major difference between A. huangguoshuensis and A. wushaensis is the degree of extension of the posterior process of the jugal.

Rieppel et al. (2006) report on the new species, “The specimen here described is remarkable with respect to the asymmetry of the maxillae, scapulae, and ilia. The scapular and iliac asymmetry is due to different degrees of ossification. It indicates that the corresponding elements on two sides are not synchronous in the process of ossification.”

Worth remembering.

References
Liu J 1999. New discovery of sauropterygian from Triassic of Guizhou, China. Chinese Science Bulletin 44: 1312–1315.
Liu J 2007. A Juvenile Specimen of Anshunsaurus (Reptilia: Thalattosauria). American Museum Novitates 3582, 9 pp.
Liu J and Rieppel O 2005. Restudy of Anshunsaurus huangguoshuensis (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou, China. American Museum Novitates 3488, 34 pp.
Rieppel O, Liu J and Li C 2006. A new species of the thalattosaur genus Anshunsaurus (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou Province, southwestern China. Vertebrata PalAsiatica 44: 285–296.

Brazilosaurus and something like it at the base of the Thalattosauria

Brazilosaurus holotype – Shikama (1966)
Brazilosaurus (Fig. 1) was described by Shikama (1966) as a sort of mesosaur with a longer neck, shorter teeth and other minor differences. From the available online pdf (created from photocopies), I can only read the line drawing, but photos were published originally (if anyone has them, I’d like to see them, they’re too dark on the pdf).

Figure 2. The holotype Brazilosaurus from Shikama (1966, above) and bones colorized (below) based on sister taxa. The apparent giant cheek region may represent the occiput crushed into the bedding plane as it is the right size and shape and no sister taxa have anything similar. The gracile jugal indicates the presences of a lateral temporal fenestra, as in mesosaurus.

Figure 2. The holotype Brazilosaurus from Shikama (1966, above) and bones colorized (below) based on sister taxa. The apparent giant cheek region may represent the occiput crushed into the bedding plane as it is the right size and shape and no sister taxa have anything similar. The gracile jugal indicates the presences of a lateral temporal fenestra, as in mesosaurus. These are the problems working with line drawings rather than fossils or photos. No giant teeth here, as in Mesosaurus.

The illustrated cheek region is much too large compared to all sister taxa, so it may represent the occiput, which it is the right size to be. The jugal looks similar to those in Stereosternum and Mesosaurus, so likewise probably framed a lateral temporal fenestra. Guesswork at this point.

Brazilosaurus referred specimen – Rossman (2002) 
published this image (Fig. 1) of a specimen he attributed to Brazilosaurus. While not too far off from each other phylogenetically, no one would ever confuse the two. They’re just too different. Note the scale bars. Those tells us the Rossman specimen is not just a short-rostrum juvenile. Overall it’s the same size but has a shorter/taller rostrum and larger orbit.

My re-interpretation of the Rossman bones is in color. The reinterpretation is closer to the interpretation of sister taxa. The parietal goes on top of the head, not posterior to the orbit, for instance. And an unidentified bone sticks up from the cranium and that bone has what appears to be half of a pineal / parietal opening. When I see hirez photos I’ll revisit this if necessary.

Figure 1. Specimen referred to Brazilosaurus by Rossman (2002, above), colorized with bones reidentified below. Although sharing many traits with Brazilosaurus (Fig. 2), it also shares many traits with Xinpusaurus suni (Fig. 3).

Figure 2. Specimen referred to Brazilosaurus by Rossman (2002, above), colorized with bones reidentified below. Although sharing many traits with Brazilosaurus (Fig. 2), it also shares many traits with Xinpusaurus suni (Fig. 3). Apparently this diapsid resealed its temporal fenestrae, but a good look at the fossil itself is needed to confirm.

The referred specimen is likewise known to me only as a drawing with flaws (Fig. 2). Again, I wish I had access to the original specimen, or to a good photo. Or to the post-crania. All attempts at contacting Rossman have failed. I understand he is in poor health.

Xinpusaurus suni (Fig. 3) is a basal thalattosaur (close to ichthyosaurs like Utatsusaurus) sharing many traits with the Rossman specimen. It has no upper temporal fenestra, but it has a large lateral temporal fenestra. So these fenestra appear to come and go, as they do in basal diapsids like Araeoscelis.

Figure 3. Xinpusaurus suni, a basal thalattosaur sharing many traits with the Rossman specimen.

Figure 3. Xinpusaurus suni, a basal thalattosaur sharing many traits with the Rossman specimen. This specimen suggests the parietal of Rossman might be the postorbital. Here the septomaxilla are no longer indicated. The tiny bones above the nares are reduced nasals. It is important to see the original materials to solve these problems.

Adding Brazilosaurus to the large reptile tree nests it with Mesosaurus. Adding the Rossman specimen nests it basal to all thalattosaurs and therefore close to Xinpusaurus. Hupehsuchus + Utatsusaurus are outgroups.

So, one more mesosaur – thalattosaur connection.

References
Rossmann T 2002. Studien an Mesosauriern (Amniota inc. sed., Mesosauridae): 3. Neue Aspekte zur Anatmie, Erhaltung und Paläoökologie aufgrund der Exemplare im Paläontologischen Institut der Universität Zurich. Neues Jahrbuch fur Geologie und PaläontologieAbhandlungen 224, 197-221.
Shikama T 1966. On a reptilian skeleton from the Palaeozoic formation of San Paulo, Brazil. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 64:351-358.

What is Hupehsuchus? Another “Platypus of the Triassic”

Yesterday we looked at a new “platypus of the Triassic,” the basal thalattosaur, Concavispina and noted some traits shared with Hupehsuchus (Fig. 1), another “platypus of the Triassic,” by convergence.

Nesting Problems
Paleontologists have had trouble figuring out what Hupehsuchus (Middle Triassic) was. This marine reptile nearly stymied Carroll and Dong (1991) who found it shared 32 derived traits with ichthyosaurs and 29 with the completely unrelated mosasaurs, 26 with plesiosaurs and 22 with nothosaurs. Mesosaurs were not included, but they are further removed than ichthyosaurs. Wumengosaurus, the current outgroup taxon, was unknown at the time.

Figure 1. Click to enlarge. Hupesuchus, a close relative of Concavispina and ichthyosaurs, derived from Wumengosaurus and Stereosternum.

Figure 1. Click to enlarge. Hupesuchus, a close relative of Concavispina and ichthyosaurs, derived from Wumengosaurus and Stereosternum.

Wikipedia (Feb. 2013) reported, “It is unknown exactly what Hupehsuchus is related to. It is fairly clear that it shares a close relationship with Nanchangosaurus, but other relations are unknown. Many features, including the discovery of polydactyly, suggest that Hupehsuchus is related to the ichthyosaurs, but the fact that Hupehsuchus’ extra digits include more bones in the hand, rather than just the fingers as in the ichthyosaurs, may discredit that theory. It along withNanchangosaurus seem to be so different from any other reptile that a new order has been constructed for the two genera called Hupehsuchia.”

Motani (1999) correctly nested Hupehsuchus at the base of the Ichthyosauria, but nothing beyond the base, leaving that a great unknown.

This is lunacy. Or lethargy.
All it takes is a phylogenetic analysis to figure out what Hupehsuchus is and where it nests.  The large reptile tree nested Hupehsuchus at the base of the Ichthyosauria. Both taxa were sisters to Thalattosauria. All three were derived from a sister to Wumengosaurus and the mesosaur, Stereosternum. You can trace the lineage all the way back to the first tetrapods, but we’ll stop here with Petrolacosaurus (Fig. 2).

One of the big problems that the large reptile tree overcame
was the nesting of mesosaurs within the Diapsida. Mesosaurs largely, but not completely, roofed over their temporal fenestrae, which caused them to be seriously mislabeled with the pareiasaurs and millerettids. By focusing on a single trait (temporal fenestrae) while ignoring a similar absence of a lateral temporal fenestra in a known diapsid, Araeoscelis, AND ignoring a suite of other traits, paleontologists essentially painted themselves into a corner they then could not escape from.

(The same sort of academic blindfold also exists with poposaur ankles.)

 

Figure 2. Click to enlarge. The origin of ichthyosaurs and thalattosaurs from basal diapsids and basal mesosaurs. Relationships are rather apparent when seen in this context.

Figure 2. Click to enlarge. The origin of ichthyosaurs and thalattosaurs from basal diapsids and basal mesosaurs. Relationships are rather apparent when seen in this context.

Permian marine reptiles
Evidently there was a huge and rapid diversification of reptiles following the return of mesosaurs to the water. We’re just now getting twigs from that bush. That’s why Hupehsuchus looks so different form Wumengosaurus and Utatsusaurus. Then again, it looks even _less_ like anything else on the large reptile tree, and that tells the tale.

So what was behind that increase in marine diversification?
Were mesosaur descendants competing with any other tetrapods in the water? Some mesosaurs were able to handle hyper-saline waters. Living amphibians like fresh waters. But temnospondyls, the big amphibians of the Carboniferous, Permian and Triassic, are found in both fresh and coastal marine sediments. So the amphibians were there first and they were bigger.

Mesosaurs, plesiosaurs and ichythyosaurs were all live bearers, so that may have been a factor. Amphibians were all still laying eggs in water. So mother mesosaurs protected her embryos until birth, but the young were fewer in number as amphibians typically produce large amounts of eggs.

Mesosaurs, plesiosaurs and ichythyosaurs are not found in coal deposits, but in sediments that once formed sea floors. So perhaps more open seas further from shore gave early Permo/Triassic marine reptiles a playing field in which to evolve quickly and successfully, away from the Early and Middle Triassic amphibians.

Of course the great Permo-Triassic extinction event might have helped.

Remember, when we find a fossil taxon, it can be millions of years older than the original specimen of that species, having spread and multiplied, thereby multiplying our chances of finding it. Then again, the species and its fossil could be just a flash in the pan, of its own time only. Phylogenetic analysis helps in this regard, finding specimens millions of years younger than their phylogenetic descendants, or not, helps determine the longevity of a species. But I digress.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

By the way the Feb. 5 blog on phylogenetic analysis was hugely popular despite its farcical nature. 

References
Carroll RL and Dong Z-M 1991. Hupehsuchus, an enigmatic aquatic reptile from the Triassic of China, and the problem of establishing relationships. Philosophical Transactions of the Royal Society London B 28 331:131-153.
Motani R 1999. Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology 19(3):473-496.
Young C-C and Dong Z-M 1972. On the aquatic reptiles of the Triassic in China. Vertebrate Paleontology Memoirs. 9-1-34.

wiki/Hupehsuchus

Concavispina – A Platypus of the Triassic

Concavispina biseridens (Zhao et al. 2013) is a new thalattosaur (Fig. 1) that nests with the two Xinpusaurus specimens (Figs. 2, 3), but at the base of their clade. Rather than having a sharp-pointed rostrum, Concavispina had a broad, nearly spoon-bill premaxilla. The low blunt maxillary teeth appeared in two rows on each side, an inner and right next to it, an outer. The rostrum and mandible both tilted up. One can imagine this genus was a bottom-feeder, crushing small prey items with that bill and teeth, convergent, perhaps, with the living platypus (Ornithorhynchus anatinus). 

Concavispina biseridens, a new thalattosaur with twin blunt teeth and a wide, platypus-like bill.

Figure 1. Click to enlarge. Concavispina biseridens, a new thalattosaur with twin blunt teeth and a wide, platypus-like bill. The forelimbs were tiny. The hind limbs were weak. At least five sacral vertebrae locked the pelvis to the spine. The narrow clavicle was taller than the short scapula. Here the jugal is broken into several pieces, but extended to the quadrate in life. The mandible appears to have curved upwards, matching the premaxilla. Here the specimen, including its ribs and gastralia, are traced in situ following crushing. Not much shifted prior to burial, but the premaxilla and cruciform interclavicle twisted from transverse to parasagittal during crushing. 

Atypical for thalattosaurs, many of the vertebral spines were embayed dorsally, producing two spikes per spine fore and aft. This concave dorsal spine trait inspired the generic name. The twin teeth inspired the specific name. By convergence, there is an almost pre-snake-like morphology here, with such small limbs and so many ribs. Curious that so many sacral transverse processes were present on that odd-shaped ilium. I count five.

Xinpusaurus suni, the short rostrum species.

Figure 2. Xinpusaurus suni, the short rostrum species.

Xinpusaurus kohi, the swordbill species.

Figure 3. Xinpusaurus kohi, the swordbill species.

Concavispina is certainly a derived taxon, but it nests at the base of the even more derived sword-bills in the genus Xinpusaurus. Odd that all three of these oddballs nest so close to the base of the thalattosauria, just outside of Ichthyosauria and another platypus-like oddball (apparently by convergence), Hupehsuchus (Fig. 4).  All these taxa had their origins near the derived mesosaur, Wumengosaurus, which we looked at earlier.

Hupesuchus, a close relative of Concavispina and ichthyosaurs.

Figure 4. Hupesuchus, a close relative of Concavispina and ichthyosaurs, but not a thalattosaur and not far from Wumengosaurus.

We’ll take a closer look a Hupehsuchus and Xinpusaurus in future posts.

And what was it about Utatsusaurus that helped transform it, over time, into the variety of ichthyosaurs we now recognize?

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Zhao L-J, Liu J, Li C and He T 2013. A new thalattosaur, Concavispina biseridens gen. et sp. nov. from Guanling, Guizhou, China. Vertebrata PalAsiatica 24-28.

The Palate of Endennasaurus

Reconstructing the palate of Endennasaurus.

Figure 1. Reconstructing the palate of Endennasaurus. Here the visibly preserved portions of the pterygoids are beige in color. The invisible portions are restored in dark beige or tan and they probably were dorsal to the palatines which appear to fuse in Renesto’s drawing. The palatines are purple. Restored portions in dark violet. The vomers are orange. The ectopterygoids, completely hypothetical, are brown. Despite the presence of mandibles, the rest of the palate can be approximated by looking at the rest of the skull and making comparisons to other taxa.

The palate of toothless Endennasaurus is distinct. Similar enough to other thalattosaurs, the palate has its own morphology based on basic palate “rules.” A line of matrix separates the front of the palate from the rear. The edges are covered by the mandibles, so some parts need to be restored. Taking all these clues together, plus comparisons to sister taxa, permits an approximation of the palate of Endennasaurus.

Distinct from other thalattosaurs, the anterior pterygoid is dorsal to the joined palatines.

If I’ve made any mistakes, please bring them to my attention. We’ll look at a series of sauropterygian palates next.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Renesto S 1992. The anatomy and relationships of Endennasaurus acutirostris (Reptilia: Neodiapsida) from the Norian (Late Triassic) of Lombardy. Rivista Italiana di Paleontologia e Stratigrafia, 97:409-430.
Müller J, Renesto S and Evans SE 2005. The marine diapsid reptile Endennasaurus(Reptilia: Thalattosauriformes) from the Late Triassic of Italy. Palaeontology 48:15-30.

wiki/Endennasaurus

A New Palatine for Askeptosaurus

Askeptosaurus italicus (Nopcsa 1925) Middle Triassic ~225 mya, ~2 m long, is known from several crushed, largely complete skeletons. It was a mesosaur/thalattosaur derived from a sister to StereosternumWumengosaurusand Xinpusaurus and phylogenetically preceded other thalattosauriformes, such as Miodentosaurus and Endennasaurus.

Müller (2005) reported, The palatine is only poorly preserved. In specimen PIMUZ T 4846 (Fig. 5A), the posterolateral portion is exposed [in dorsal view] slightly in the anterior half of the left orbit. It possesses a concave posterior margin, which indicates that the palatine formed the anterior border of the suborbital fenestra. Müller did not identify a palatine in PIMUZ T4832, a skull preserved in ventral (palatal) view.

The palatine of Askeptosaurus.

Figure 1. Click to enlarge. The palatine of Askeptosaurus. Upper left: Reconstruction by Müller 2005 with a generic palatine identified. Upper right: insitu ventral view of PMIZ with overlooked palatine colored violet. Upper right inset: palatine identified by Müller 2005 in anterior orbit in dorsal view, PMIZ. Lower left reconstruction with new palatine in place. Lower right: Clarazia palate with palatine identified in violet.

Let’s Look for Palatines in Related Taxa
Clarazia provides a clear palatine, a ‘Y’-shaped element in the anterior palate. A similar structure was traced by Müller 2005 but not recognized as a palatine. It’s a match for the palatine in Clarazia and a perfect fit against the rim of the pterygoid.

We’ll look at a series of enaliosaurian (Sauropterygia + Ichthyopterygia + Thalattosauriformes) palates next time.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Nopcsa F 1925. Askeptosaurus, ein neues reptil der Trias von Besano: Centralblatt für Mineralogie, Geologie und Paläontologie, p. 265-2
Kuhn E 1952. Die Triasfauna der Tessiner Kalkalpen. XVII. Askeptosaurus italicus Nopsca. Abhandlungen der Schweizerischen Paläontologischen Gesellschaft, 69, 1–73.
Kuhn-Schnyder E 1971. Über einen Schädel von Askeptosaurus italicus Nopcsa aus der Mittleren Trias des Monte San Giorgio (Kt Tessin, Schweiz). Abhandlungen des Hessischen Landesamtes für Bodenforschung, 60, 89–98
Müller J 2005. The anatomy of Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio and the interrelationships of thalattosaurs (Reptilia, Diapsida). Canadian Journal of Earth Science 42: 1347–1367.

wiki/Askeptosaurus

Nesbitt (2011) and his Characters – part 3 – Vancleavea + Archosauria

Following remarks from fellow paleontologists asking for my study to include more Nesbitt (2011) characters in the large reptile study, I thought we should dive right into them, taking a few days to digest them all — a bite at a time. Earlier we considered more basal clades in part 1 and part 2.

Nesbitt Characters for Vancleavea + Archosauria
Sterling Nesbitt (SN) reported, (1) Postparietal(s) absent (146-1). Postparietals are absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(2) Postaxial intercentra absent (177-1). Postaxial intercentra are absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(3) Ectepicondylar flange of the humerus absent (234-1). An ectepicondylar flange is absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(4) Distal condyles of the femur not projecting markedly beyond shaft (318-1). Distal condyles of the femur not projecting markedly beyond shaft in basal pterosaurs.
Note: As in certain lepidosaurs, including all fenestrasaurs.

Long time readers will remember that Vancleavea nests as a thalattosaur close to Helveticosaurus, not an archosauriform, as recovered by the large reptile tree.

Tomorrow: Crurotarsi (Phytosauria + Crocodylomorpha)

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
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.