A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China

ABSTRACT

A new Middle Triassic archosaur, Diandongosuchus fuyuanensis, gen. et sp. nov., is described on the basis of a skeleton from the Zhuganpo Member (Ladinian) of the Falang Formation, eastern Yunnan Province, China. It is primarily characterized by the nasal process of the premaxilla extending posteriorly well beyond the external naris, the super-sized coracoid foramen laterally bordered by the scapula, the ischium with a strongly expanded medial portion anteroposteriorly longer than the proximodistal height of the bone, and anteriorly notched cervical osteoderms. D. fuyuanensis is a pseudosuchian on the basis of the crocodile-normal tarsal joint and other features, such as the distal end of the ulna in posterolateral view squared off, osteoderms with a distinct anterior process, the presacral vertebrae dorsally covered by more than one osteoderm, dorsal osteoderm alignment dorsal to presacrals 10–24 staggered, the pubis-ischium contact reduced to a thin proximal contact, and the medial contact of the ischia extensive but the dorsal margins separate. It is from a marine deposit but shows few morphological adaptations of the postcranial skeleton for a semiaquatic way of life when compared with Qianosuchus from the Anisian limestone of the same area. A phylogenetic analysis derived from an existing data matrix suggests that the new archosaur occupies the basal-most position in Poposauroidea and further confirms the poposauroid status of Qianosuchus. On the basis of current information, the discovery of Diandongosuchus does not firmly underscore the affinity of the semiterrestrial vertebrate faunas between the eastern and western regions along the northern coastline of the Tethys.

ACKNOWLEDGMENTS

We are grateful to J. Ding (IVPP) for skillful preparation of the specimen used in this study, to W. Gao (IVPP) for photographic work, and M. Gilbert (CMN) for highlighting the elements of Figure 4A. S. Brusatte (American Museum of Natural History), R. Schoch (Staatliches Museum für Naturkunde), J. Desojo (Museo Argetino de Ciencias Naturales), and P. Dodson (University of Pennsylvania, Philadelphia) kindly provided information. X.-C.W. particularly wishes to thank the IVPP for hospitality during his visits. W. Parker and S. Nesbitt carefully reviewed the manuscript, offering critical comments and suggestions that led to its great improvement. Editors P. Barrett and R. Irmis provided more than editorial assistance. This work was supported by research grants from the National Natural Science Foundation (NNSFC-41072014, 41172027) of China, and the CAS/SAFEA International Partnership Program for Creative Research Teams of China (to C.L., L.-J.Z, and X.-C.W.); from the CMN (to X.-C.W.); from the ZMNH (to L.-J.Z.); and from Tokyo Gakugei University (to T.S.).

Handling editor: Randall Irmis