The cranial morphology of an early Eocene didymoconid (Mammalia, Insectivora)

Abstract

An early Eocene didymoconid skull with perfect basicranial region from Hubei Province of China is described. Important cranial features include a small orbit, a broad temporal region, a maxilla–frontal contact in the orbit, absence of the jugal–lacrimal contact, a broad dorsal process of the alisphenoid, an extensive squamosal, absence of the postglenoid foramen, a transversely elongate glenoid fossa, a fully ossified bulla, an external auditory canal floored by the squamosal and mastoid of the petrosal, a greatly expanded mastoid of the petrosal, and a large foramen for the epitympanic sinus in the tympanic roof. In addition, the internal carotid artery may be reduced, although the stapedial artery is well developed. Analyses of the cranial features reveal that this skull is already highly specialized. The analyses also indicate that the North American genus Wyolestes and the Asiatic didymoconids form a paraphyletic group and that derivation of both Wyolestes and didymoconids from a Paleocene Yantanglestes-like mesonychid is not supportable. Instead, on the basis of cranial evidence, a didymoconid-insectivore relationship is suggested.