Revised taxonomy of Xinpusaurus and other thalattosaurs

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Michael W. Maisch (2024)
Notes on thalattosaurs (Reptilia, Triassic) with special reference to the genus Xinpusaurus, from the Upper Triassic of SW-China
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 311(3): 229 - 280
DOI: 10.1127/njgpa/2024/1191
https://www.schweizerbart.de/papers/njgpa/detail/311/105464/Notes_on_thalattosaurs_Reptilia_Triassic_with_special_reference_to_the_genus_Xinpusaurus_from_the_Upper_Triassic_of_SW_China

Concavispina xingyiensis n. comb.

 
Xinpusaurus suni (= X. bamaolinensis jun. syn.)


The thalattosaur genus Xinpusaurus Yin in Yin et al. 2000 from the Upper Triassic (Carnian, Tuvalian) Xiaowa Formation of Guizhou, People’s Republic of China, is represented by several well-preserved skulls and skeletons. Although its osteology is relatively well known, the taxonomy of the genus is complicated by a lack of a full description of the holotype of the type species, Xinpusaurus suni Yin, 2000, and an inadequate description of X. bamaolinensis Cheng, 2003. In this paper, additional data are presented on several referred specimen of Xinpusaurus suni and on X. kohi. Previous attempts to differentiate species of Xinpusaurus from the Xiaowa Formation are discussed. A new phylogenetic analysis of the Thalattosauria is performed to evaluate the observable morphological differences, including all relevant specimens of Xinpusaurus as separate OTU’s. It demonstrates that specimens hitherto referred to X. suni are conspecific. X. bamaolinensis shows no differences to X. suni, and is regarded as a junior subjective synonym. X. kohi differs from X. suni in the completely straight rostrum, a contact between frontal and supratemporal, a well-developed deltopectoral crest of the humerus, a hatchet-shaped instead of reniform radius and ossification of the distal carpals and tarsals. It is a diagnosable taxon and the second valid species of Xinpusaurus. Xinpusaurus xingyiensis is the sister-taxon of Concavispina biseridens. It is referred to that genus as Concavispina xingyiensis n. comb. There is thus no Middle Triassic record of the genus Xinpusaurus. Specimen HFUT GL-17-006, referred to X. suni as a juvenile specimen, is also different from Xinpusaurus and possibly represents a new genus and species. The genus Xinpusaurus as redefined is monophyletic. A close phylogenetic relationship of Xinpusaurus and Nectosaurus is re-confirmed. The Askeptosauroidea is monophyletic, with Askeptosaurus holding the most basal position, but otherwise askeptosauroid interrelationships remain unresolved, including the three named species of Anshunsaurus, which is not found to be monophyletic. Thalattosauroidea and Thalattosauridae, but not Claraziidae, are confirmed as monophyletic groups. Thalattosauridae includes Thalattosaurus and Nectosaurus, as originally envisaged by Merriam, as well as Concavispina, Xinpusaurus, Gunakadeit, and the currently unnamed HFUT GL-17-00. Concavispina is the most basal thalattosaurid. Within Thalattosauridae, the recently described Gunakadeit is the sister-taxon of Nectosaurus. Gunakadeit and Nectosaurus are highly derived thalattosaurids, which form the sister-group of Xinpusaurus.

===