SVP abstracts 14: Phylogeny of the Eosauropterygia reviewed

Lin et al. 2020 bring us a new phylogeny
of the Eosauropterygia (defined as: Pachypleurosaurus (Fig. 1) and descendants, or Sauropterygia sans Placodontia).

Pachypleurosaurus had more than two sacrals all converging on a tiny ilium.

Figure 1. Pachypleurosaurus had more than two sacrals all converging on a tiny ilium.

From the Lin et all 2020 abstract:
“During the last two decades, abundant Triassic sauropterygians have been reported from Europe and southwestern China, which greatly improve our understanding of the diversity and stratigraphic, as well as paleogeographic, distribution of Triassic sauropterygians. The phylogeny of Sauropterygia was also repeatedly analyzed with the description of each new species. Except for Placodontia, however, various analyses of sauropterygian interrelationships have yielded incongruent results, especially with regards to the monophyly of Pachypleurosauridae and Eusauropterygia (= Eosauropterygia sans Pachypleurosauridae) which were alternatively supported or rejected by different analyses.”

“The incongruent results of these analyses were probably caused by the implementation of different character codings, based primarily on the same data matrix taken from a global parsimony analysis by Rieppel about 20 years ago, which was based almost exclusively on European material. Since we have a large number of new specimens from the rest of the world, it is high time to reexamine the phylogeny of the entire group, or at least of the eosauropterygians, in order to assess whether and how the newly described taxa affect overall tree topology.”

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 2. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Continuing from the Lin et all 2020 abstract:
“Given that the ingroup relationships of Placodontia is well established, we herein focus on reanalyzing the interrelationships of Eosauropterygia, which is the sister clade of the Placodontia within the Sauropterygia. We present a comprehensive phylogenetic hypothesis for Eosauropterygia based on a cladistic analysis of 137 characters coded for four outgroup and 49 ingroup taxa, including nearly all currently recognized Triassic eosauropterygian genera. This is the most inclusive phylogenetic analysis of Eosauropterygia to date.”

Does it include the taxa listed above (Fig. 1). If not, add them.

“The new phylogenetic hypothesis of Eosauropterygia suggests that Pachypleurosauridae is the sister taxon of Eusauropterygia, and their monophyly as traditionally upheld is reestablished.”

Which taxon is the last common ancestor? In the large reptile tree (LRT, 1751+ taxa, subset Fig. 2) indicates that Eusauropterygia is indeed monophyletic and arises from a series of pachypleurosaurs. This is distinct from the Lin et al. results which recovers a monophyletic Pachypleurosauridae.

“Furthermore, the monophyly of the genus Nothosaurus as traditionally conceived is not supported, whereas the monophyly of Lariosaurus is obtained if the lariosaurian affinity of N. juvenilis, N. youngi, and N. winkelhorsti is accepted. In this study, the monophyletic Pistosauroidea excludes Corosaurus and Cymatosaurus. The latter two genera are found to form a clade that represents the basal-most members of Eusauropterygia. The new phylogenetic hypothesis is mostly in good accordance with the stratigraphic distribution of the genera.”

I cannot comment further on a cladogram I have not seen. Overall the LRT recovers a traditional cladogram, with the exception of a short list of non-tradtional outgroups, like the Mesosauria, Thalattosauria and Ichthyosauria along with a long list of basal aquatic diapsids. The clade Enaliosauria is traditionally considered obsolete, but the LRT recovers it as a monophyletic clade. Turtles are not closely related when the valid, tested turtle sisters and ancestors are included in the taxon list. The initial radiation of sauropterygians evidently occurred prior to the Early Triassic given the diversity present in the Early Triassic and the diversity of mesosaurs in the Late Permian.


References
Lin W, Jiang D, Rieppel O, Motany R, Tintori A, Sun Z and Zhou M 2020. Phylogeny of the Eosauropterygia (Diapsida: Sauropterygia) incorporating recent discoveries from South China.  SVP Abstracts 2020.

wiki/Sauropterygia

SVP abstracts 5: New Thalattosauriformes from China

Chai J, Jiang D and Sun Z 2020 introduce
a few new thalattosauriformes (Fig. 1) We looked at thalattosaurs here back in 2011, 2013, when they entered the LRT.

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

Figure 1. The Thalattosauria and outgroups (Wumengosaurus and Stereosternum) to scale. Do you see why Vancleavea makes a better thalattosaur than an archosauriform?

From the abstract:
“Thalattosaurifomes is one of the important marine reptiles found in Middle to Late Triassic. It can be classified into two clades, namely Askeptosauridae and Thalattosauridae.”

The large reptile tree (LRT, 1749+ taxa) also documents two large clades within Thalattosauria, one that includes Askeptosaurus (Fig. 1) and another that includes Thalattosaurus (Fig. 1).

“They were discovered in North America and Europe, and more recent discovery in Xingyi Fauna, southwest China had provided new information about their evolution. XNGM WS-22-R5, a newly prepared specimen, had a different type of rostrum with the local Xinpusaurus. Its strongly ventrally deflected contour assembles the same type found in North America and Europe, and it’s the first thalattosaur with this design found in China.”

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

Figure 2. Xinpusaurus suni, a basal thalattosaur sharing many traits with the Rossman specimen.

Xinpusaurus kohi, the swordbill species.

Figure 3. Xinpusaurus kohi, the swordbill species.

The LRT currently nests two specimens attributed to Xinpusaurus (Figs. 2, 3).

“Phylogenetic analysis indicates that this specimen forms a polytomy with Hescheleria ruebeli and Clarazia schinzi.”

In the LRT Clarazia (Fig. 4) nests close to the Xinpusaurus clade, but closer to other thalattosaurs.

Figure 4. Clarazia, a thalattosaur sister to the new Oregon specimens.

Figure 4. Clarazia, a thalattosaur sister to the new Oregon specimens.

“As the turned-downward rostrum appear in XNGM WS-22-R5, Hescheleria ruebeli and Nectosaurus halius, and the resolution of current phylogenetic tree is low, it’s hard to determine whether this feature is related to phylogeny. It is more likely an adaptation as Nectosaurus did not has a close affinity with this new specimen, as while as the similar design occurred in Proterosuchid.”

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

Figure 5. Nectosaurus and Hescheleria, two odd hook-nose thalattosaurs

“A complete specimen, XNGM XY-PVR2013-R2, is described. According to the characters of jugal, surangular, angular, humerus, dorsal neural spines and carpals etc, it can be identified as Anshunsaurus cf. A.huangguoshuensis.”

Anshunsaurus is similar to long-snouted Askeptosaurus (Fig. 1), transitional to Miodentosaurus (Fig. 1).

“We compared the currently known three species of Anshunsaurus, and found that the previous diagnosis is not diagnostic enough. The ratio in diagnosis varies among the specimens of the same species. The only distinct diagnostic character is the development of ec- and entepicodylar on the humerus of A,wushaensis. As this is the most unambiguous character among Anshunsaurus and it’s related to the locomotion of forelimbs, we suppose that this difference maybe a sexual dimorphism.”

Try to avoid “Pulling a Larry Martin”. Don’t cherry-pick one to a dozen subtle or stand-out traits. Instead, add taxa, run the analysis and let the software decide. After phylogenetic analysis of several specimens, then decide if any traits are sexually dimorphic or otherwise important as an afterthought.

Wonder if they included Vancleavea (Fig. 1) in their analysis? Among 1749 taxa, Vancleavea would rather nest with thalattosaurs than with archosauriforms.


References
Chai J, Jiang D and Sun Z 2020. New specimens found in Xingyi Fauna provide evolution information of Thalattosauriformes. SVP abstract

 

SVP abstracts – Origin of aquatic reptiles?

Sobral and Schoch 2019
bring us news on a taxon at the genesis of aquatic reptiles.

I presume that means
no sea turtles, no marine iguanas, no mosasaurs, no sea crocs, no penguins. If so, the LRT already provides a long list of diapsid taxa at the base of the Enaliosauria (Fig. 1; including mesosaurs, ichthyosaurs, thalattosaurs, placodonts, pachypleurosaurs and plesiosaurs) along with other basal aquatic marine younginiforms (Fig. 2), a monophyletic clade distinct from terrestrial younginiforms that gave rise to protorosaurs and archosauriforms.

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 1. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

From the abstract:
“The Middle Triassic was a time of major changes in terrestrial tetrapod faunas, but the fossil record of this interval is largely obscure.”

Why do paleontologists always paint themselves into a corner like this? To make their discoveries more newsworthy?

“This is unfortunate, since many modern groups originated or diversified during this time. However, recent excavations in the upper Middle Triassic of Germany have revealed several new taxa, most of which are much smaller than those found in other tetrapod-bearing basins of similar age.”

Here’s Galesphyris (Fig. 2) at the base of the aquatic younginiforms in the LRT.

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge.

Sobral and Shoch continue:
“Here, we report a new taxon from the Vellberg limestone quarry comprised of skull bones distinct from other diapsids from this locality. It is diagnosed by a long maxilla with a far posteriorly reaching tooth row; a long and stout ventral process of the postfrontal; exclusion of the postorbital from the lower temporal fenestra due to a contact between the anteroventral process of the squamosal and the dorsal process of the jugal; and a tall quadrate + quadratojugal complex.”

“Some anatomical aspects of the new taxon are similar to stem diapsids such as Elachistosuchus huenei from similar deposits of Northern Germany and of uncertain phylogenetic affinity.”

In the LRT Elachistosuchus (Fig. 3) nests certainly between proterosuchids and choristoderes (Fig. 4). Neither are related to aquatic younginiforms.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 3. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

“A phylogenetic analysis retrieved both taxa in an “ichthyosauromorph” clade, included in an almost exclusively aquatic group. The new taxon, Hupehsuchus, and Elachistosuchus appear as successive sister-taxa to Ichthyopterygia.”

This is not supported by the LRT where Hupehsuchus (Fig. 5) and Elachistosuchus (Fig. 3) are not related  to one another. The outgroups to the Ichthyopterygia (Fig. 1) are the Thalattosuchia, Mesosauria and basal Sauropterygia (pachypleurosaurs).

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 5. Basal Ichthyosauria in the LRT, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and ThesaurusFigure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

“It is interesting to note that many of the autapomorphic characters of the new taxon pertain to elements related to the lower temporal fenestra. In particular, the contact between the jugal and squamosal is unusual, but is also found in sauropterygians, saurosphargids, Hupehsuchus, and Wumengosaurus, as well as in rhynchocephalians.”

Oh, why did they have to add rhynchocephalians? They were doing so well! Readers beware, convergence is rampant (= everywhere) in the Reptilia. Don’t rely on one, two or a dozen traits. If you do, you’ll be pulling a Larry Martin. Only rely on the last common ancestor in a valid cladogram to determine relationships.

“Derived ichthyosaurs show the typical jugal-quadratojugal contact, but via an unusual dorsal contact between the two. The jugal–squamosal contact may thus represent a transitional state to the anatomy observed in later ichthyosaurs, reinforcing the interpretation of the ‘ventral cheek embayment’ of basal ‘euryapsids’ as a ventrally open lower temporal fenestra.”

“Thus, the new taxon has implications for the origin of secondarily aquatic groups, and therefore also paleobiogeographic significance. The appearance of placodontians has been traced to central Europe, but ichthyopterygians are believed to have originated in the Eastern Tethys. The new taxon indicates that the earliest evolutionary history of these groups may have occurred in the Western Tethys, associated with the Germanic Basin. This new material emphasizes the importance of sampling small-bodied taxa in the understanding of reptile evolution.”

The Lower Keuper is Carnian, early Late Triassic. Galesphyris is older. It comes from the Late Permian, perhaps representing an early Early Permian genesis.


References
Sobral G and Shoch R 2019. A small diapsid from the Lower Keuper of Germany and the origin of aquatic reptiles. Journal of Vertebrate Paleontology abstracts.

Sachicasaurus: the first giant nothosaur, not a pliosaur

Páramo-Fonseca, Benavides-Cabra and Gutiérrez 2018
described Sachicasaurus (Figs. 1-3, MP111209-1, Barremian (Early Cretaceous) Columbia; estimated 10m in length, 2m skull length), a taxon they thought was a giant pliosaur related to Brauchauchenius (Fig. 2).

Unfortunately
the authors did not consider comparing their discovery to Nothosaurus. The short flippers are the first clue that perhaps they should have done so. Misidentifying several bones was a problem. The large reptile tree (LRT, 1420 taxa) tests each new taxon against all prior taxa, thereby largely avoiding the paleo-sin of taxon exclusion.

Figure 1. Sachicasaurus skull from Páramo-Fonseca et al. 2018, colors added.

Figure 1. Sachicasaurus skull from Páramo-Fonseca et al. 2018, colors added. Some skull bones restored in color. Note the differences in the preorbital region of the skull between the original interpretation drawing and the DGS color applied to the skull photo.

Sachicasaurus vitae (Páramo-Fonseca, Benavides-Cabra and Gutiérrez 2018, 10m in length) was originally considered a short-flippered pliosaur related to long-flippered Brachauchenius characterized by two autopomorphic characters: a very short mandibular symphysis ending at the mid length of the fourth mandibular alveoli and reduced number of mandibular teeth (17-18). Here this giant nests with Nothosaurus (above). Originially several bones were misidentified. The ilium is uniquely bifurcated with a dorsal and posterior process. In dorsal view the mandibles are convex while the maxillae are concave, leaving quite a gap between them.

Figure 2. Sachicasaurus was the size of the pliosaurs, Kronosaurus and Brauchenia, but was related to Nothosaurus. This is the first known giant nothosaur.

Figure 2. Sachicasaurus was the size of the pliosaurs, Kronosaurus and Brauchenia, but was related to Nothosaurus. This is the first known giant nothosaur.

Several bones were originally misidentified.
The former left ‘scapula’ is really the clavicle. The former right ‘scapula’ is really the coracoid. The former sock-shaped ‘radius’ is the tiny scapula.

Figure 3. Sachisaurus pectoral girdle and flippers reconstructed with new identities provided here.

Figure 3. Sachisaurus pectoral girdle and flippers reconstructed with new identities provided here. Pectoral elements are digitally duplicate and flipped left to right.

Real plesiosaurs have long flippers
with more than the usual number of phalanges per digit. By contrast, Sachicasaurus does not have long flippers and It has the plesiomorphic number of phalanges. Yes, the skull is huge and the neck is short. In the LRT those pliosaur-like traits are not enough to attract Sachicasaurus toward the pliosaurs. Note the different interpretations of the skull bones presented here (Fig. 1). The nasals, in particular, are nothosaurian, not pliosaurian.

Figure 4. Data for Nothosaurus for comparison with Sachicasaurus. The interclavicle could easily be lost.

Figure 4. Data for Nothosaurus for comparison with Sachicasaurus. The interclavicle could easily be lost. Note the plesiomorphic number of phalanges on both the manus and pes. Compare these to those in figure 3.

From the same Early Cretaceous formation
three real pliosaurs have been discovered. This would have been the fourth one, except it’s a nothosaur with pliosaur size and proportions by convergence. Earlier we looked at a similar convergence between toothed whales and baleen whales.

Figure 5. Subset of the LRT focusing on the Eusauropterygia, including Sachicasaurus.

Figure 5. Subset of the LRT focusing on the Eusauropterygia, including Sachicasaurus.


References
Páramo-Fonseca ME, Benavides-Cabra CD and Gutiérrez IE 2018. A new large Pliosaurid from the Barremian (Lower Cretaceous) of Sáchica, Boyacá, Colombia. Earth Sciences Research Journal 220(4):223-238. eISSN 2339-3459. Print ISSN 1794-6190.

wiki/Sauropterygia
wiki/Sachicasaurus

Cartorhynchus: rebuilding the small ichthyosaur mimic

Mistakes were made here
earlier while reconstructing Cartorhynchus, the basal sauropterygian ichthyosaur-mimic. Those mistakes are corrected here (Figs. 1, 2) and already updated in earlier posts. All of these repairs further cement the relationship of Cartorhynchus to its sister, Sclerocormus  (Fig. 3) and its ancestral sister, Qianxisaurus (Fig. 4), taxa nesting near the base of the Eosauropterygia, not the Ichthyopterygia in the large reptile tree (LRT, 1401 taxa).

Figure 1. New tracing and reconstruction of the basal sauropterygian with flippers, Cartorhynchus.

Figure 1. New tracing and reconstruction of the basal sauropterygian with weak flippers, Cartorhynchus. Note the flipped maxilla, now convex ventrally. The pectoral girdle is rebuilt based on that of Qianxisaurus. See text for details. Compare pectoral elements to Qianxisaurus in figure 5.

Cartorhynchus lenticarpus (Motani et al. 2014; Early Triassic) was originally considered a strange basal ichthyosauriform and a suction feeder. Here it nests with Sclerocormus and Qianxisaurus as a basal eosauropterygian representing a new clade of ichthyosaur-mimics with a very early appearance of flipper-like limbs. Neotony played a part in the appearance of a short rostrum, large eyes, short neck, poorly ossified phalanges and small size. The supratemporal was large here, and the splenial can be seen in lateral view, though just barely. These are also results of neotony as most sauropterygians lack them. The outgroup taxon, Pachypleurosaurus, fuses the large supratemporal and squamosal

Ichthyosaurs have the following traits by convergence.
Ichthyosaurs have robust scleral rings (eyeball bones) while most eosauropterygians do not. Distinct from most eosauropterygians and like ichthyosaurs, Qianxisaurus has small supratemporals and gracile scleral rings. The splenials are not visible in the present exposure. Like Cartorhynchus, the digits of Qianxisaurus are not well developed. 

Figure 2. Cartorhynchus reconstruction in lateral and dorsal views with new lateral view skull and pectoral girdle.

Figure 2. Cartorhynchus reconstruction in lateral and dorsal views with new lateral view skull and old invalid dorsal view skull. The new pectoral girdle is in place here. The flippers seem to be relatively immobile. The tail was the main propulsive organ. Neotony created this sauropterygian with large eyes, short snout, short neck and digit-less limbs.

The premaxilla
of Cartorhynchus was tiny, ideal for nipping small food items. Small teeth were present, contra the original interpretation. The naris and orbit were quite large, distinct from all candidate sister taxa. The in situ maxilla was taphonomically flipped, so Cartorhynchus actually had a ventrally convex maxilla. The heavy ribs and flat bottom make Cartorhynchus look like a bottom feeder. The elevated dorsal neural spines suggest a dorsal fin (Fig. 2). The small scapula and coracoid suggest a weak, passive pectoral flipper. A long tail was probably present, as in its larger sister, Sclerocormus (Fig. 3). This would have been the primary propulsive organ. Note the lack of large flippers in Sclerocormus. Qianxisaurus is the last known common ancestor.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Figure 3. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Qianxisaurus chajiangensis (Cheng et al. 2012; Fig. 4) is a Middle Triassic basal eosauropterygian based on a virtually complete articulated skeleton with all digits poorly ossified. Cheng et al. 2012 nested Qianxisaurus as derived from a sister to Wumengosaurus, a taxon that nested closer to thalattosaurs, ichthyosaurs and mesosaurs in the LRT. The Cheng et al. (2012) study had some odd nestings including Kuehneosauridae (rib gliders) a little too close to turtles and thalattosaurs. The LRT widely separated these taxa, as befitting their utterly distinct morphologies.

Figure 4. Slight changes to the temple region of Qianxisaurus shows the reappearance of the suptratemporal, which had been lost in more primitive taxa only to be reacquired here and further elaborated in Cartorhynchus.

Figure 4. Slight changes to the temple region of Qianxisaurus shows the reappearance of the suptratemporal, which had been lost in more primitive taxa only to be reacquired here and further elaborated in Cartorhynchus.

The LRT
nests Qianxisaurus between Pachypleurosaurus and LariosaurusPistosaurus nests as an outgroup in the Cheng et al. (2012) tree, but closer to Simosaurus in the LRT.

The upper temporal fenestrae of Qianxisaurus
were smaller than in Pachypleurosaurus. The supratemporal formed the posterior rim without fusion to the squamosal. In Qianxisaurus the retroarticular process of the mandible was smaller than in related taxa. The teeth of Qixiansaurus were unusual with a slightly constricted cylinder and short conical crown.

Despite the small size of the ilium
at least four sacrals were present.

The Cartorhynchus-like pectoral girdle of Qianxisaurus.
The scapula (green Fig. 5) had a slim strap-like morphology. The clavicles were broader laterally, meeting medially in an arch shape, as in Cartorhynchus (Fig. 1).

Figure 5. The Qianxisaurus pectoral girdle is ancestral to the Cartorhynchus pectoral girdle with similarly shaped elements. Compare to figure 1.

Figure 5. The Qianxisaurus pectoral girdle is ancestral to the Cartorhynchus pectoral girdle with similarly shaped elements. Compare to figure 1. Interclavicle is hidden in situ and hypothetical here based on phylogenetic bracketing. 

Mimic taxa
appear occasionally in the LRT, which, so far, has been able to lump and split mimics by testing them against all available candidate sisters. Motari et al. 2014, for all his experience and expertise in ichthyosaurs, failed to add basal eosauropterygians, like Qianxisaurus, to their taxon lists and so was not able to consider this possibility. Better not to assume things, but to let the software perform an unbiased analysis starting with a wide gamut of taxa like the LRT.

Correcting mistakes
is part of the scientific process, whether they be internal or external. 

References
Cheng YN, Wu XC, Sato T and Shan HY 2012. A new eosauropterygian (Diapsida, Sauropterygia) from the Triassic of China. Journal of Vertebrate Paleontology. 32 (6): 1335. doi:10.1080/02724634.2012.695983
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

wiki/Qianxisaurus
wiki/Cartorhynchus
wiki/Sclerocormus

 

Libonectes enters the LRT

After applying colors to
the bones in a photograph of the skull of Libonectes (Fig. 1, Turonian, early Late Cretaceous, Welles 1949, originally Elasmosaurus morgani), the Carpenter 1997 drawing was added to gauge similarities and difference. A transparent GIF makes this easy. Comparisons to the earlier (Late Triassic) Yunguisaurus and Thalassiodracon are instructional. These taxa also rotate the orbits anteriorly, providing binocular vision. The pterygoid (dark green) pops out slightly behind the jugal.

Figure 1. The skull of Libonectes. Freehand drawing from Carpenter xxxx. DGS colors added here. Some parts of the original fossil may be restored.

Figure 1. The skull of Libonectes. Freehand drawing from Carpenter 1997. DGS colors added here. Some parts of the original fossil may be restored. The fossil may be more fully prepared than this now. Note the slight differences between the fossil and drawing. The orbits appear to permit binocular vision.

Libonectes morgani, (Welles 1949, Elasmosaurus morgani, Carpenter 1997) an elasmosaur of the Turonian, early Late Cretaceous. In the large reptile tree (LRT, 1399 taxa) this skull nests with the skull-less Albertonectes (Fig. 2) and Plesiosaurus (Fig. 3) at first with no resolution owing to the lack of common traits between the skull-only and skull-less taxa.

Figure 3. Plesiosaurus skull in several views alongside the pectoral girdle.

Figure 2. Plesiosaurus skull in several views representing two specimens alongside the pectoral girdle. Data comes only from this drawing, not the fossil itself, which I have not yet seen.

Later the post-crania of Libonectes is added
and the two elasmosaurs now nest together sharing fore limbs slightly longer than hind limbs (Fig. 3) among several other less obvious traits. Neck length, much longer with more vertebrae than in Plesiosaurus, scores the same, “Presacral vertebrae, 31 or more” in the LRT.

Figure 1. Libonectes flippers. 2nd frame shows PILs. Terrestrial tetrapods flex and extend along continuous PILs. The in vivo misalignment of phalanges in Libonectes largely prevents flexion and extension, creating a large stiff flipper at misaligned PILs. Those that are more proximal are continuous, permitting a limited amount of flexion and extension.

Figure 3. Libonectes flippers. 2nd frame shows PILs. Terrestrial tetrapods flex and extend along continuous PILs. The in vivo misalignment of phalanges in Libonectes largely prevents flexion and extension, creating a large stiff flipper at misaligned PILs. Those that are more proximal are continuous, permitting a limited amount of flexion and extension.

Sachs and Kears 2017
bring us images and descriptions of the post-crania of Libonectes, a Late Cretaceous elasmosaur, one of the sauropterygian plesiosaurs, similar in most respects to the other tested elasmosaur, Albertonectes, which we looked at earlier here.

Distinct from terrestrial tetrapods
that flex and extend their phalanges along continuous PILs, the in vivo misalignment of phalanges in Libonectes largely prevents flexion and extension, creating a stiffer flipper at the misaligned PILs. Note, those that are more proximal are continuous, permitting more flexion and extension.

PILs were first documented
in Peters 2000. Many taxa may be distinguished by their fore and hind PIL patterns as also shown for pterosaurs in Peters 2011.

It is worth noting (and scoring)
that the forelimbs are slightly larger than the hind limbs in elasmosaurs, distinct from other sauropterygians, convergent with many ichthyosaurs, sea turtles and perhaps other taxa I am overlooking presently (overlooking some birds and all bats and pterosaurs for the moment, because they fly).

Figure 5. Elasmosaurid origins. The long neck preceded the flippers in this clade of vertical feeders.

Figure 4. Elasmosaurid origins. The long neck preceded the flippers in this clade of vertical feeders.

We looked at hypothetical elasmosaur swimming techniques
a few months ago here.

References
Carpenter K 1999. Revision of North American elasmosaurs from the Cretaceous of the western interior. Paludicola, 2(2): 148-173.
Sachs S and Kear BP 2017. Redescription of the elasmosaurid plesiosaurian Libonectes atlasense from the Upper Cretaceous of Morocco. Cretaceous Research 74:205–222.
Welles SP 1949. A new elasmosaur from the Eagle Ford Shale of Texas. Fondren
Science Series, Southern Methodist University 1: 1-28.

wiki/Albertonectes
wiki/Libonectes

Paludidraco and Cymatosaurus in the LRT

It’s been awhile since we looked at anything wet.
A new robust-ribbed sauropterygian, Paludidraco ( Fig. 1, Middle Triassic) does indeed share many traits with Simosaurus, as described by Chaves et al. 2018.

A welcome confirmation!
Due to its tiny dentition, Paludidraco was originally considered a likely filter feeder, distinct from related, long-toothed nothosaurs and plesiosaurs. Simosaurus also has relatively tiny teeth, but on a larger skull and fewer in number. That’s evolution at work!

Isn’t it great to see these two related taxa together? Doesn’t it make compare and contrast so much easier? See the evolution of the human ear bones from primitive jaw bones illustration here for another great example of comparative anatomy.

Figure 1. Simosaurus compared to Paludidraco.

Figure 1. Simosaurus compared to Paludidraco. Isn’t it great to see these two related taxa together? Doesn’t it make compare and contrast so much easier? 

Chaves et al. 2018 provided
a cladogram of marine reptile relationships (Fig. 2). Most of these taxa are also included in the large reptile tree ( LRT, 1261 taxa, subsets Figs. 3, 4), which includes many times more taxa and more marine reptiles. Missing from the Chavez team cladogram (Fig. 2) is the genus/taxon Anningsaura, which links nothosaurs to pistosaurs + plesiosaurs in the LRT. The Chaves et al. cladogram, nests Cymatosaurus (Fig. 4) and Corosaurus basal to Pistosaurus + plesiosaurs.

Figure 2. Paludidraco cladogram with arrows showing how taxa nest in the LRT. Taxon exclusion is the problem here.

Figure 2. Paludidraco cladogram from Chaves et al. 2018 with arrows showing how taxa nest in the LRT. Taxon exclusion is the problem here. See figure 3.

The Chaves et al. 2018 cladogram
(Fig. 2) excludes many pertinent taxa, so much so that important interrelationships were missed, based on the authority of the LRT (Fig. 3), which minimizes taxon exclusion due to its wider gamut of taxon inclusion. Several taxa in the Chaves et all cladogram would shift positions when tested with more taxa (arrows in Fig. 2) as the LRT shows (Fig. 3).

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria). Paludidraco was not added when this graphic was created, but has since been added. Sharp-eyed readers will see Vancleavea here.

Cymatosaurus
had to be added to the LRT (Fig. 4) to test it fairly against the Chavez team cladogram (Fig. 2). Only the skull is known (AFAIK) from three different species.

FIgure 4. The addition of Cymatosaurus is more of an insertion, that changes nothing else in the tree topology. Here it nests on the nothosaur side of Simosaurus.

FIgure 4. The addition of Cymatosaurus is more of an insertion, that changes nothing else in the tree topology. Here it nests on the nothosaur side of Simosaurus, not close to plesiosaurs.

Despite the many offshoot traits
found in Anningsaura, the rest of its traits nest it firmly at the base of the pistosaurs + plesiosaurs, where Chaves et al. nests Cymatosaurus. In the LRT Cymatosaurus nests close to Paludidraco, but more on the nothosaur side than the plesiosaur side.

References
Chaves C de M, Ortega F and Pérez‐García A 2018. New highly pachyostotic nothosauroid interpreted as a filter-feeding Triassic marine reptile. Biology Letters. 14 (8): 20180130.
Maisch MW 2014. A well preserved skull of Cymatosaurus (Reptilia: Sauropterygia) from the uppermost Buntsandstein (Middle Triassic) of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen272 (2): 213–224.

wiki/Paludidraco

Turtle origins: Pappochelys STILL not the best candidate

Schoch and Sues 2017
bring us more details about Pappochelys, and pull a ‘Larry Martin‘ or two to force fit this taxon into a false narrative: the origin of turtles story. What little they report and show is indeed intriguing. What more they don’t report and show invalidates their hypothesis. A wider gamut phylogenetic analysis has the final say.

As a reminder,
many paleontologists try to find one, two or a dozen traits that look like they link one taxon to a clade, but avoid testing those hypotheses in a wide gamut phylogenetic analysis, like the large reptile tree (LRT, 1048 taxa). This technique of force-fitting and ignoring other candidate sisters never turns out well. It’s not pseudoscience, but it does remind one of early attempts at flying that did not include sufficient power, rudders, ailerons and horizontal stabilizers. Those attempts were all doomed to crash.

A wide gamut phylogenetic analysis
remains the only tool that always delivers a correct tree topology because  taxon exclusion is minimized. The LRT worked with Diandongosuchus. It worked with Lagerpeton. It worked with Chilesaurus. It worked with turtles, whales and seals. And it worked with pterosaurs. The LRT works!

Let’s just make this short and painful
Schoch and Sues ignored:

  1. the sister of Pappochelys in the LRT, Palatodonta
  2. other proximal relatives of Pappochelys in the LRT, Diandongosaurus, Anarosaurus, Palacrodon and Majiashanosaurus
  3. the sister to hard shell turtles in the LRT, Elginia
  4. the sister to soft shell turtles in the LRT, Sclerosaurus
  5. basalmost hard shell turtles in the LRT, Niolamia and Meiolania.
  6. the proximal relatives of Eunotosaurus in the LRT, Acleistorhinus, Delorhynchus, Australothyris and Feeserpeton.

Figure 1. Shoch and Sues cladogram of turtle origins. Look at that loss of resolution!

Figure 1. Shoch and Sues cladogram of turtle origins. Look at that loss of resolution! Gliding kuehneosaurs nest between aquatic taxa? Really? Add about 300 taxa and let’s see if this tree resolves itself. 

Schoch and Sues employed only 29 taxa
many of which were suprageneric, compared to 1048 specimens in the LRT. Schoch and Sues lament, “the currently available data fail to support any of the three more specific hypotheses for the diapsid origins of turtles (sister group to Sauria, Lepidosauria or Archosauria, respectively). We found no support for earlier hypotheses of parareptilian relationships for turtles hypothesized by Laurin & Reisz (1997) and Lee (1997), respectively, nor for the hypothesis that captorhinid eureptiles were most closely related to turtles (Gaffney & McKenna 1979; Gauthier et al. 1988).” Schoch and Sues published a cladogram (Fig. 1)  in which the following taxa could not be resolved:

  1. Acerosodontosaurus (swimming diapsid)
  2. Kuehneosauridae (gliding lepidosauriforms)
  3. Claudiosaurus (swimming diapsid)
  4. ‘Pantestudines’ = Eunotosaurus, Pappochelys, Odontochelys, Proganochelys (turtles and turtle mimics)
  5. Trilophosaurus + Rhynchosauria + Prolacerta + Archosauriformes (a paraphyletic mix)
  6. Squamata + Rhynchocephalia (terrestrial lepidosaurs)
  7. Placodus + Sinosaurosphargis + Eosauropterygia (swimming enaliosaurs)

In other words
Schoch and Sues have no idea how these taxa are related to each other. Their data fails to lump and separate 29 taxa completely. They report, “[Papppochelys] shares various derived features with the early Late Triassic stem-turtle Odontochelys, such as T-shaped ribs, a short trunk, and features of the girdles and limbs.” See what I mean about pulling a ‘Larry Martin’? They’re trying to save their hypothesis by listing a few to many traits. Unfortunately Schoch and Sues do not have the data that documents this suite is unique to Pappochelys and turtles. Actually these traits are found elsewhere within the Reptilia and sometimes several times by convergence.

Figure 1. Pappochelys comes to us from several specimens, all incomplete and all disarticulated. These are the pieces of the skull we will use in Photoshop to rebuild the skull. Schock and Sues made a freehand cartoon, a practice that needs to be discouraged.

Figure 2. Pappochelys comes to us from several specimens, all incomplete and all disarticulated. These are the pieces of the skull we will use in Photoshop to rebuild the skull. Schock and Sues made a freehand cartoon, a practice that needs to be discouraged. They had the nasals backwards and the lacrimal upside down and labeled a prefrontal. The failed to recognized the quadratojugal. And they changed the squamosal. The postorbital looks to be so fragile that the orbit might instead have been confluent with the lateral temporal fenestra.

Freehand reconstructions
Shoch and Sues created their reconstructions not by tracing bones, but freehand. That never turns out well. They created cartoon bones and modified them to be what they wanted them to be when they could have used Photoshop and real data.

Figure 2. Shoch and Sues compared Pappochelys to Odontochelys and Proganochelys, but deleted the more primitive Eunotosaurus. And it's easy to see why. Eunotosaurus has wider ribs than its two purported successors. That and the LRT tell you its not a turtle, but a turtle mimic. Note the inaccuracy Schoch and Sues applied to their Odontochelys. The version from ReptileEvolution.com appears in frame 2 of this GIF animation.

Figure 3. In dorsal view Shoch and Sues compared Pappochelys to Odontochelys and Proganochelys, but deleted the more primitive Eunotosaurus. And it’s easy to see why. Eunotosaurus has wider ribs than its two purported successors. That and the LRT tell you its not a turtle, but a turtle mimic. Note the inaccuracy Schoch and Sues applied to their Odontochelys. The version from ReptileEvolution.com appears in frame 2 of this GIF animation. Since Pappochelys is know from 4 or more scattered and incomplete specimens, we really don’t know how many dorsal ribs it had.

Why didn’t they show Eunotosaurus
(in Fig. 3)? This turtle mimic has wider and more extensive dorsal ribs. That could be one reason. We’re all looking for a gradual accumulation of traits and Eunotosaurus, one of many turtle mimics, does not provide the primitive state.

Figure 6. Pappochelys compared to placodont sister taxa and compared to the Schock and Sues reconstruction, which appears to have several scale bar errors and underestimated the number of dorsal vertebrae. Click to enlarge. So few ribs and vertebrae are known for Pappochelys that their order, size and number could vary from that shown here. Note the ribs of Paraplacodus are also expanded. The number of dorsal vertebrae is unknown and probably more than nine based on sister taxa.

Figure 4. From two years ago. Pappochelys compared to placodont sister taxa and compared to the Schoch and Sues reconstruction, which appears to have several scale bar errors and underestimated the number of dorsal vertebrae. So few ribs and vertebrae are known for Pappochelys that their order, size and number could vary from that shown here. 

The ‘Probably’ weasel word
Pappochelys is not known from any complete or articulated fossils. Even so Shoch and Sues report, “The vertebral column of Pappochelys comprises probably eight cervical, probably nine dorsal, two sacral, and more than 24 caudal vertebrae.” This is wishful thinking… They should have said ‘unknown’ not ‘probably’.

Dredging up false data to support a diapsid relationship
Schoch and Sues reference Bever et al. (2015) when they show a Eunotosaurus juvenile purportedly lacking a supratemporal and in its place, an upper temporal fenestra. Earlier that ‘missing’ supratemporal was identified as a nearby bump on the cranium of the juvenile.

Gastralia
Turtle ancestors in the LRT have no gastralia. So the origin of the plastron is still not known. According to Schoch and Sues, “The gastralia of Pappochelys are unique in their structure and arrangement.” Unfortunately Palatodonta is only known from cranial remains.    All other proximal relatives in the LRT have slender gastralia, not broad like those in Pappochelys. Some Pappochelys gastralia are laterally bifurcated, similar to the plastron elements in Odontochelys. That’s intriguing, but ultimately yet another Larry Martin trait. What we’re looking for is maximum parsimony, a larger number of traits shared by sister taxa and proximal relatives than in any other taxa.

Scapula
The Pappochochelys scapula is dorsally small and slender, like those of other placodonts and basal enaliosaurs. Shoch and Sues compared it to the basal turtle scapula, which is relatively much larger. Comparable pectoral elements are documented in the outgroups Bunostegos and Sclerosaurus, but these were ignored by Shoch and Sues. We don’t know of any post-crania for the hard shell turtle sister, Elginia, which might or might not have had a Meiolania-like carapace.

Shoch and Sues made some great observations,
but they kept their blinders on with regard to other candidates. A wide gamut analysis really is the only way to figure out how taxa are related to one another. Hand-picking traits and cherry-picking a small number of taxa is not the way to understand turtle origins. However, once relationships are established and all purported candidates are nested in a large gamut analysis, THEN it’s great to describe and compare how various parts of verified sister taxa evolved.

The LRT
nests turtles with pareiasaurs. Hardshell turtles arise from the mini-pareiasaur Elginia to Niolamia. Softshell turtles arise from the mini-pareiasaur Sclerosaurus to Odontochelys. Pappochelys nests with Palatodonta at the base of the Placodontia.

References
Bever GS, Lyson TR, Field DJ and Bhular B-A S 2015. Evolutionary origin of the turtle skull. Nature published online Sept 02. 2015.
Schoch RR and Sues H-D 2017.
Osteology of the Middle Triassic stem-turtle
Pappochelys rosinae and the early evolution of the turtle skeleton. Journal of Systematic Palaeontology DOI: 10.1080/14772019.2017.1354936

Juvenile articulated Eusaurosphargis discovered

Scheyer et al. 2017
bring us a new largely articulated juvenile Eusaurosphargis specimen (PIMUZ A/III 4380; Figs. 1–3) very similar to the adult disarticulated specimen described by Nosotti and Rieppel 2003 (BES SC 390; Middle Triassic, ~240 mya, ~20 cm snout to vent length). Scheyer et al. had trouble nesting Eusaurosphargis correctly as a derived thalattosaur largely due to taxon exclusion (see below).

Figure 1. Adult and juvenile Eusaurosphargis specimens to scale.

Figure 1. Adult and juvenile Eusaurosphargis specimens to scale. The adult was disarticulated.

The old ‘adult’ specimen
was considered more closely related to Helveticosaurus (Fig. 4) than to placodonts. Here both Eusaurosphargis and Helveticosaurus nest within the Thalattosauriformes close to armored Vancleavea. Here Eusaurosphargis does not nest close to turtle-like Sinosaurophargis. The adult skeleton is completely disarticulated. That makes reconstruction particularly difficult. Thus the order of the traced vertebrae in dorsal view (Fig. 1) is largely guesswork. Likewise, the skull included some guesswork helped by phylogenetic bracketing.

Figure 2. The in situ juvenile specimen of Eusaurosphargis, the original tracing and DGS tracing of dorsal ribs (blue) and sternal ribs (green).

Figure 2. The in situ juvenile specimen of Eusaurosphargis, the original tracing and DGS tracing of dorsal vertebrae and elongated transverse processes (blue) and dorsal ribs (green). The specimen was exposed from below, but preserved right side up, hence the slight disarticulation of dorsal elements and the skull in marine sediments. CT scans indicate the buried sacral ribs were longer than traced here. 

The new ‘juvenile’ specimen
has a disarticulated skull, but most of the elements appear to be present, though some were originally unidentified and the squamosal, now a jugal, was misidentified.

Figure 3. Eusaurosphargis juvenile skull, pectoral and pelvic girdles reconstructed.

Figure 3. Eusaurosphargis juvenile skull, pectoral and pelvic girdles reconstructed. GIF animation second frame shows two views of the in situ skull. The juvenile includes articulated extremities. Boxed elements are the purported squamosals, here identified as jugals. Scheyert et al. did not attempt a skull reconstruction.

Scheyer et al. report
the armor and other elements “support an essentially terrestrial lifestyle for Eusaurosphargis and and that within the marine reptile ‘superclade’ E. dalsassoi potentially is the sister taxon of Sauropterygia.” Neither are supported by the large reptile tree (LRT 1027 taxa), which resurrected the clade, Enaliosauria for Scheyer’s ‘superclade.’

The elongated dorsal transverse processes
and osteoderms are convergent with those in placodonts and sinosaurosphargids.

The jugals are much larger than the squamosals
as in Helveticosaurus and Vancleavea. For reasons unknown, Scheyer et al. erroneously compared these elements with those of the more distantly related Askeptosaurus, which ALSO has tiny squamosals, like most, if not all, thalattosaurs.

Phylogenetic analysis
The Scheyer et al. inclusion set excludes so many pertinent taxa that it nests turtles with archosaurs and lepidosaurs. It also nests Eusaurosphargis close to placodonts. Correctly it nests Eusaurosphargis close to Helveticosaurus and Thalattosauriformes. Vancleavea was not included. It is clear that Scheyer et al. have no idea how the major taxa are actually arranged as documented in the LRT for the last seven years. They also employed suprageneric taxa. There’s no reason for such unprofessional  guessing to continue in professional studies.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly. It was also much larger than Eusaurosphargis but was coeval. Vancleavea is shown to scale and to the same length.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly. It was also much larger than Eusaurosphargis but was coeval. Vancleavea is shown to scale and to the same length.

‘Homologies’ reported by Scheyer et al.:
“PIMUZ A/III 4380 shares with Palatodonta bleekeri (and placodonts such as Paraplacodus broilii and Placodus gigas) the deep skull shape and wide snout with large external nares, as well as the double tooth row in the upper jaw (on the maxillae and palatines) and a single row in the lower jaw.” These traits are likewise found by homology in Helveticosaurus and Vancleavea where known. Scheyer et al. feel the freedom to make these comparisons to placodonts because their incorrect (based on massive taxon exclusion) cladogram nests Eusaurosphargis close to placodonts. This is the authority of the LRT and its large gamut, specimen-based taxon list at work. When Scheyer et al. have a comparable taxon list, then we can discuss differences in scoring, if they arise.

Terrestrial?
Scheyer et al. report, “Given the large number of pachypleurosaurs of similar size range, among a plethora of thousands of other fossils, we corroborate the previous idea that E. dalsassoi had a terrestrial habitat preference.” This makes no sense. In the LRT pachypleurosaurs arise from marine taxa and give rise to marine taxa. Thus, based on phylogenetic bracketing. pachypleurosaurs are marine (or at least aquatic), too,

Scheyer et al. report, “the short and proximally dorso-ventrally wide tail would be similarly inefficient in providing propulsion.” You don’t have to get around fast in order to be aquatic. The flattened turtle-like appearance of several saurosphargids and placodonts have similar short-comings. And look at Helveticosaurus, the acknowledged sister (Fig. 4).

Scheyer et al. report,The stylopodial elements (humerus and femur) are tubular, moderately thin-walled bones with large marrow cavities” typical of terrestrial, not marine diapsids. They do not report similar tests on the universally accepted sister taxon, Helveticosaurus (and Vancleavea), but the proximal limb elements look similar from the outside (Fig. 4).

The All-Aquatic Superclade of Chen et al. 2014
does not include mosasaurs, but does include a few representatives of most other marine clades (but not nearly the number of taxa as in the LRT). While this is confirmation of the results first reported here in 2011, the topology of the Chen et al. cladogram has serious problems all based on taxon exclusion. Such problems are minimized in the LRT based on its large gamut where there is no need to ‘delete problematic characters’ in order to achieve a result that makes sense. 

A larger gamut phylogenetic analysis
nests Helveticosaurus, Vancleavea and Eusaurosphargis within the Thalattosauriformes, despite over 1020 opportunities to nest elsewhere. Their disparate morphologies hint at further transitional and unusual morphologies to come.

Congeneric? Yes. Conspecific? No.
The smaller Eusaurosphargis nests with the larger one in the LRT. So they could be congeneric. However, comparing the reconstructions of the two shows several differences in the skull bones that preclude the two from being conspecific. Such juvenile/adult conspecific relationships in fossils found years apart and miles apart are, by their very nature, very rare, but they do occur.

References
Chen X-H, Motani R, Cheng L, Jiang D-Y and Rieppel 2014. The Enigmatic Marine Reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the Phylogenetic Affinities of Hupehsuchia. PlosOne online.
Nosotti S and Rieppel O 2003. Eusaurosphargis dalsassoi n.gen. n.sp., a new, unusual diapsid reptile from the Middle Triassic of Besano (Lombardy, N Italy). Memories of the Italian Society of Natural Science and the Museum of Natural History in Milan, XXXI (II).
Scheyer T et al. (5 other authors) 2017. A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny. Nature.com/scientific reports online.

wiki/Eusaurosphargis

At the nothosaur/plesiosaur node

A cover story and rapid communication in the latest Journal of Vertebrate Paleontology features Wangosaurus (Ma et al. 2015, Fig. 1), a long-necked, short-faced sauropterygian with short fingers and toes.

[Unfortunately, Wangosaurus in the urban dictionary is “a complete jackass.”] But let’s concentrate on the fossil, which is virtually complete and wonderfully preserved.

Figure 1. Wangosaurus. Click to enlarge.

Figure 1. Wangosaurus. Click to enlarge. Note the short fingers and toes.

Sister taxa
In the Ma et al paper, Wangosaurus nested as a sister Yungisaurus (Figs. 2, 3) and both were considered pistosaurids, the clade transitional between nothosaurs and plesiosaurs, despite their morphological differences.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

In the large reptile tree (subset Fig. 4), Yungisaurus also nests between Pistosaurus and Plesiosaurus, but Wangosaurus nests in a much more basal node, between nothosaurs and Simosaurus, still close to the nesting in the Ma et al. paper (Fig. 2).

Figure 3. Yungisaurus in situ and closeups of the skull and flippers.

Figure 3. Yungisaurus in situ and closeups of the skull and flippers. This is a much larger sauropterygian with longer toes transformed into flippers. Interesting to see the rear flippers larger than the forelimbs. So does that tell us something about their swimming technique?  

The Ma et al. tree is based on earlier work by Jiang et al. (2014 – featuring the basal placodont Majianshanosaurus), which is an updated version of Neenan et al. (2013). Note the differences in the skulls of Wangosaurus and Yungisaurus. Those don’t look like close relatives to me and their scores confirm those suspicions.

 

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

The Ma et al. tree employs suprageneric taxa (always a problem). You’ll note that turtles and lepidosauriformes are the proximal outgroup taxa to sauropterygians here. That is not supported by the large reptile tree. I also find it odd that the marine reptiles Claudiosaurus and Hovasaurus nest so far from the rest of their natural clade in the Ma et al. tree, and separate from one another.

References
Cheng Y-N,  Sato T, Wu X-C and Li C 2006. First complete pistosaurid from the Triassic of China. Journal of Vertebrate Paleontology 6(2):501-504.
Ma L-T, Jiang D-Y, Rieppel O, Motani R and Tintori A 2015.
A new pistosaurid (Reptilia, Sauropterygia) from the late Landinian Xingyi marine reptile level, southwestern China. Journal of Vertebrate Paleontology 35(1): e881832.