Basal turtle material from the Lower Cretaceous of Yakutia (Russia) filling the gap in the Asian record

Abstract

© 2019 Elsevier Ltd This paper describes fragmentary turtle material (isolated basisphenoid, shell bones, humerus and ilium) from the Lower Cretaceous (Berriasian–Barremian) Teete locality in Yakutia (Eastern Siberia, Russia). All the material is attributed to one taxon of basal turtles (Mesochelydia indet.), based on the morphology of the basisphenoid, shell bones and humerus, as well as microanatomy and histology of the shell bones and humerus. Canals and foramina of the basisphenoid of this taxon revealed by CT scanning show an unusual pattern, which allows various interpretations and suggests a higher diversity of carotid and/or vidian systems in basal turtles than hitherto believed. Mesochelydia indet. from Teete fills an Early Cretaceous gap in the record of Asian basal turtles and represents the northernmost Asian non-marine turtle occurrence of the Mesozoic. All in all, the record of Asian basal turtles appears to be wider geographically and more complete temporally than previously thought. The Asian basal turtles are represented by at least three phylogenetic lineages: primitive Testudinata in the Late Triassic, primitive Mesochelydia from the Early Jurassic to the Early Cretaceous and primitive Perichelydia from the Middle Jurassic to the Late Cretaceous. The presence of such a primitive (Jurassic level) turtle in Teete supports the hypothesis that the vast territory of Siberia was a refugium for Jurassic vertebrate faunal elements. Details of the external morphology and histology of the Teete turtle material as well as its high paleolatitude occurrence argue in favor of its aquatic lifestyle.