Chirotherium and first Asian Rhynchosauroides tetrapod trackways from the Middle Triassic of Yunnan, China

Abstract

ABSTRACT The Middle Triassic (Anisian) Guanling Formation in Yunnan and Guizhou provinces, southwestern China, is well-known for its marine-reptile fauna with numerous well-preserved skeletons. Tetrapod footprints from this unit have been reported of both terrestrial and marine forms documenting a marginal marine environment in the eastern Tethys region. In particular Chirotherium barthii, an ichnospecies that is characteristic of the Middle Triassic (Anisian), was formerly described from the Guanling Formation of Guizhou Province. Recently chirotheriid tracks were also reported from deposits of this unit in Yunnan Province. Here we provide the first detailed documentation of this tracksite. Furthermore, we assign these trackways to the ichnospecies Chirotherium barthii, based on identical features in footprint morphology. Additionally, from the same surface, we describe the first tracks and trackways of the lacertoid ichnogenus Rhynchosauroides from the Asian continent. Trackmakers of C. barthii are non archosaurian archosauriforms or members of the archosaur crown-group, while Rhynchosauroides can be attributed either to lepidosauromorph or archosauromorph diapsids. The environment was a coastal area along the eastern Tethys, with marine, semi-aquatic and terrestrial tetrapods leaving their footprints in the carbonatic sediment of mudflats and lagoons when searching for food, that possibly consisted of small marine invertebrates or the small lacertoid forms being the prey of the larger archosaurs.