Earth and Environmental Science Transactions of the Royal Society of Edinburgh

Research Article

A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China

Sterling J. Nesbitta1a2 p1, Jun Liua3 and Chun Lia3

a1 Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA

a2 Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA

a3 Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China

ABSTRACT

The two major lineages of extant archosaurs, crocodylians and avians, diverged in the Triassic, but the details and timing of this event are incompletely understood. Fragmentary and phylogenetically uninformative specimens, in addition to poor temporal constraints on rock units from the Early and Middle Triassic, typify obstacles in identifying early archosaurs. This paper re-describes the partial skeleton of the only known specimen of Xilousuchus sapingensis Wu, 1981 from the Early Triassic Heshanggou Formation in north-central China. Originally assigned to the non-archosaurian archosauriform clade Proterosuchidae, an extensive phylogenetic analysis posits X. sapingensis as a crown-group archosaur within Suchia, thus making this taxon the unequivocally oldest known member of Archosauria. The age and phylogenetic position of X. sapingensis indicate that many archosaurs, including all major clades of non-archosaurian archosauriforms, the avianline, ornithosuchids, aetosaurs and paracrocodylomorph lineages, must have diverged by the end of the Early Triassic. X. sapingensis is part of a possible clade of sail-backed poposauroids that were common components of archosaur assemblages during the Early to Middle Triassic.

Key Words:

  • anatomy;
  • Archosauria;
  • Archosauriformes;
  • Ctenosauriscidae;
  • Mesozoic;
  • Poposauroid

Correspondence:

p1 Department of Biology, University of Washington, Seattle, WA 98195, USA