Leptarctus is a poorly known fossil carnivore that ranges through the Miocene of North America and Inner Mongolia, China (Lim, 1996; Zhai, 1964). Though it has been one of the least studied carnivores, more than 20 localities in North America have produced Leptarctus (Lim, 1999). The characters diagnosing Leptarctus as a mustelid include absence of M2, absence of a notch between the blades of the upper carnassial, and a reduced dentition with loss of PI and pi. Though Leptarctus is a mustelid, the teeth bear many similarities to those of procyonids, Procyon lotor and Nasua nasua and stand as a remarkable example of dental convergence (Leidy, 1856; Lim, 1999). Unlike other mustelids, Leptarctus has prominent double sagittal crests, heavy zygomatic arches, a prominent occipital crest, a well-developed hypocone on P4, labially curved upper canines, grooved lower canines, raccoon-like mandibles, elongated metatarsals, and unique bony projections on the tympanic bullae (Lim, 1999).