A new cryptodire from the Eocene of the Na Duong Basin (northern Vietnam) sheds new light on Pan-Trionychidae from Southeast Asia

Abstract

Striatochelys baba gen. et sp. nov. is a new pan-trionychid from the middle–upper Eocene (late Bartonian–Priabonian, 39–35 Ma) of the Na Duong Basin in northern Vietnam. It represents one of the best documented and most completely known Palaeogene pan-trionychid species from Asia. Striatochelys baba can be diagnosed by: (1) its relatively small size; (2) the absence of a preneural; (3) the presence of well-developed straight ridges on the costals and neurals in adults; (4) ridges more strongly developed posteriorly than anteriorly; and (5) entoplastron callosity in the shape of a bulge. A phylogenetic analysis recovers S. baba within Pan-Trionychinae in an unresolved polytomy with species of the genus Nilssonia. In addition, comparisons of the new taxon with plastomenids, pan-trionychids from the Palaeogene and extant trionychids from Asia demonstrate a particularly close resemblance to Nilssonia spp. Based on the close resemblance between S. baba and ‘Trionyx’ impressus (a pan-trionychid from the Maoming Basin of southern China), we here assign the latter species to the new genus Striatochelys. The close relationship between S. baba gen. et sp. nov. from the Na Duong Basin and S. impressa comb. nov. from the Maoming Basin further supports the hypothesis that a close connection between both localities existed, as already exemplified by other faunal elements such as pan-geoemydids and crocodylians. http://zoobank.org/urn:lsid:zoobank.org:pub:E8E5C4DE-E52A-43FB-B9C1-CE3ED2ED66C1.