# Taxonomy, morphology, and phylogeny of a nearly complete nanhsiungchelyid specimen from the Upper Cretaceous of the Nanxiong Basin, China

## TL;DR

A nearly complete fossil of an ancient turtle from China reveals new details about its skull, shell, and evolutionary relationships.

## Contribution

A new nearly complete Nanhsiungchelys specimen is described, offering insights into its morphology and phylogeny.

## Key findings

- The specimen has a skull similar to Nanhsiungchelys yangi but with unique carapace features.
- The plastron morphology suggests the specimen may be male.
- Phylogenetic analysis shows Nanhsiungchelys spp. and Anomalochelys angulata form a monophyletic group.

## Abstract

Nanhsiungchelys, the type genus of Nanhsiungchelyidae, is an extinct turtle taxon that lived during the Late Cretaceous in southern China. Despite having a relatively abundant fossil record, the plastral morphology of Nanhsiungchelys is not well understood. Here, we describe a large specimen of Nanhsiungchelys with an associated skull and shell (SNHM 1558) from the Upper Cretaceous of Nanxiong Basin, China. The skull of SNHM 1558 is similar to that of Nanhsiungchelys yangi, but the carapace bears a pair of stick-like anterolateral processes. For this reason, we tentatively refer SNHM 1558 to Nanhsiungchelys cf. yangi. A concave plastron and a narrower posterior lobe indicate that SNHM 1558 may be a male. Nanhsiungchelys spp. was previously regarded as the most advanced taxa of Nanhsiungchelyidae, but some morphological characteristics suggest plesiomorphic similarities with the outgroup Adocus spp. A phylogenetic analysis using Adocus spp. as the outgroup suggests that Nanhsiungchelys spp. and Anomalochelys angulata form a monophyletic group at the base of Nanhsiungchelyidae. However, this phylogenetic result is not conclusive, as Nanhsiungchelys spp. is found deeply nested within the tree when Sinaspideretes wimani is employed as the outgroup.

The online version contains supplementary material available at 10.1186/s13358-025-00385-2.