New cranial material of Simocyon from China, and its implications for phylogenetic relationship to the red panda (Ailurus)

Abstract

ABSTRACT A well-preserved skull of Simocyon, an extinct hypercarnivorous procyonid, is described from a late Miocene (Baodean; approximately 5.3–9 Ma) locality in north Shaanxi, China. New knowledge about its cranial morphology allows insight into its phylogenetic position among musteloid camivorans. A sister-group relationship between the simocyonines and the ailurines (the East Asian red panda) is proposed on the basis of cranial and dental evidence. Shared derived characters in support of this relationship include: highly arched zygomatic arch; posteriorly extended posterior palatine border; long bony external auditory meatus; a posterolateral process of promontorium; ventrally ridged paroccipital process; anteriorly inclined coronoid crest; and lateral grooves on canines. The simocyonine-ailurine clade is in turn postulated to be within the procyonid clade because of its common possession of an enlarged M2 and an elongated talonid on m2. The new fossil evidence contradicts several recent phylogenetic studies (both morphological and molecular) that place the red panda (Ailurus) in various basal positions within the ursoid clade (including ursids, amphicyonids, and pinnipeds) instead of the musteloid clade. Analysis of the primitive morphotype at the base of the simocyonine-ailurine clade suggests that many of the characters in support of the ursoid relationship for Ailurus are primitive conditions or were independently derived within more restrictive clades.