The cranial anatomy of Chinese placodonts and the phylogeny of Placodontia (Diapsida: Sauropterygia)

Abstract

Placodonts are Triassic marine reptiles that inhabited the eastern and western margins of the Tethys Ocean (modern South China and Europe/Middle East). Although the crania of European taxa are relatively well understood, those of Chinese taxa have not been extensively studied, and most of them have not been incorporated into a comprehensive phylogeny. Here we present the first reconstructions of all known Chinese placodont holotype skulls using micro-computed tomographic (μCT) scanning and/or detailed anatomical study. We also present the first phylogenetic analyses that incorporate all placodont genera using a general diapsid matrix that includes postcranial characters, and a placodont-only cranial matrix. Results vary between the matrices; however, both support a monophyletic Placodontia with eastern taxa interspaced throughout, indicating no major separation between the eastern and western Tethyan realms. Support is strong for a western Tethyan origin of Placodontia, although the highly nested Placochelyidae first appear in the upper Middle Triassic of the eastern Tethys. Thus, all placodont clades appear to have originated in a period of intense speciation during the Middle Triassic. © 2015 The Linnean Society of London