Tuesday, February 19, 2019

[Paleontology • 2019] Cyamodus orientalis • A New Species of Cyamodus (Placodontia, Sauropterygia) from the early Late Triassic of south-west China

Cyamodus orientalis
Wang, Li, Scheyer & Zhao, 2019

The Triassic eastern Tethyan faunas have continued to yield numerous specimens of marine reptile taxa in recent years. Nevertheless, compared with other sauropterygian clades, the diversity of placodonts in these faunas is low, and remains of this group are relatively rare in the fossil assemblages. Here, we report a new cyamodontoid specimen (ZMNH M8820) from the early Late Triassic of Guizhou, south-west China. This specimen is a nearly complete skeleton lacking only the forelimbs. It is distinct from other known Chinese placodonts as it features a large skull with remarkably enlarged supratemporal fenestrae and a small and less regularly arranged carapace. Interestingly, this new specimen resembles the European Cyamodus more than any Chinese cyamodontoid genera, particularly when considering the dentition and other cranial morphology. However, it differs from known Cyamodus species in some cranial features (e.g. epipterygoid fully ossified, posttemporal fenestra large, dentition derived) and the absence of a separate pelvic shield. Furthermore, based on an updated data matrix of placodonts, our phylogenetic results support the affinity of this new Chinese specimen with European Cyamodus species, and a new species, Cyamodus orientalis sp. nov., is erected here. This new material represents the first reported Cyamodus specimen in the world that preserves a three-dimensional skull with an associated postcranial skeleton and it extends the distribution of this genus into the early Carnian of the eastern Tethys. The existence of Cyamodus, a nearshore taxon, in south-west China at this time reveals greater similarity and more rapid intercommunication than previously known between western and eastern Tethyan vertebrate faunas, although the palaeobiogeographical origin and migration history of Cyamodontidae – and of other clades of placodont reptiles – are still obscure due to the scarcity of material from the northern and southern margins of the Palaeotethys.

Keywords: Placodontia, Guanling Biota, dentition, carapace, biogeography

Figure 2. Photographs and line drawings of the skull of Cyamodus orientalis sp. nov. (ZMNH M8820) in A, dorsal view; B, ventral view; C, left lateral view; D, occipital view.

Figure 1. Skeleton of Cyamodus orientalis sp. nov. (ZMNH M8820) with skull in original position.

Superorder Sauropterygia Owen, 1860 
Order Placodontia Cope, 1871 
Family Cyamodontidae Nopcsa, 1923 

Genus Cyamodus Meyer, 1863 
Type species. Cyamodus rostratus M€unster, 1839.

Cyamodus orientalis sp. nov.

Derivation of name. The species name is derived from the Latin word ‘oriens’ (East), referring to the Triassic marine reptile fauna in south China being located in the eastern Tethys, while all other known species of Cyamodus are from the western Tethys. 

Wei Wang, Chun Li, Torsten M. Scheyer and Lijun Zhao. 2019. A New Species of Cyamodus (Placodontia, Sauropterygia) from the early Late Triassic of south-west China. Journal of Systematic Palaeontology.  DOI: 10.1080/14772019.2018.1535455