A new basal hupehsuchian from the Early Triassic of South China and its implication to the phylogenetic relationships of Ichthyosauromorpha (Reptilia: Diapsida)

ABSTRACT

The endemic Hupehsuchia from the Early Triassic of South China is generally accepted as the sister group of ichthyosauriforms and represents the only ichthyosauromorph that lived mainly in the shallow aquatic environment. Therefore, the detailed morphological study of basal hupehsuchians is important to elucidate the relationships of Ichthyosauromorpha with other reptiles. However, Nanchangosaurus, the most basal hupehsuchian taxon, is represented by only two skeletons, and the morphology of its palate and most of the appendicular skeleton remains unknown, limiting its role in resolving the phylogenetic relationships of Ichthyosauromorpha. Here we report a new hupehsuchian specimen from the Early Triassic of South China, which we have identified as a new morphotype of Nanchangosaurus. The new skeleton shows for the first time the morphology of the palate, zeugopodium and autopodium in Nanchangosaurus. Phylogenetic analyses including new morphological information from this skeleton support the recent recovery of an aquatic clade that includes the three major Triassic marine reptile groups. A clade comprising Helveticosaurus and Sauropterygomorpha forms the sister group to Ichthyosauromorpha, and Thalattosauria occupies the most basal position in this large aquatic clade. Archosauromorpha is recovered as a sister group to this aquatic clade, and together they form part of a monophyletic Archelosauria.

KEYWORDS:

• Nanchangosaurus
• Ichthyopterygia
• Archelosauria
• aquatic adaptation

Acknowledgments

We thank L.Y. Li and F.Z. Huang for preparing the specimen and A.S. Wolniewicz for discussing the specimen and helping with the phylogenetic analysis discussed in the paper. E. Maxwell and another anonymous reviewer carefully reviewed an earlier version of the paper and helped to improve it.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/08912963.2024.2354791.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under Grant numbers 42172026 and 41772003.