The Early Jurassic clevosaurs from China (Diapsida: Lepidosauria)

Abstract

The Lufeng Formation of Yunnan Province, China has provided an important contribution to the understanding of Early Jurassic terrestrial vertebrate faunas. Here, previously described rhynchocephalian skull material is reassessed and new information is provided regarding the dentition. Unfortunately, poor preservation obscures a number of morphological features and is, in places, misleading. No significant characters can be found to warrant prior taxonomic separations. Affinity to Clevosaurus is supported by the presence of a lateral ectopterygoid-palatine contact that excludes the maxilla from the suborbital fenestra and a jugal with a long dorsal process that extends posteriorly. As in other clevosaurs, the snout is short and rounded, and all specimens demonstrate a large and steeply inclined coronoid process of the dentary. The taxon possesses a greater number of teeth than the type species Clevosaurus hudsoni and in this respect more closely resembles C. bairdi, C. convalis, or C. minor. Flanges, if at all present on the dentary teeth, are small. Differences from other described species of Clevosaurus include a palatine tooth row that is strongly curved rather than straight, and there is evidence of an additional row of teeth on the pterygoid, making three in all. Due to the lack of reliable autapomorphies the material is probably best treated as Clevosaurus sp. but further material may provide enough evidence to resurrect “Clevosaurus petilus” or the generic name “Dianosaurus.” Nevertheless, the Lufeng material represents the earliest known lepidosaur material from Asia and confirms the presence of the Rhynchocephalia in China during the Jurassic. The latter is significant because they are notably absent from productive younger localities.