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

 

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