THE FIRST OCCURRENCE OF POSTCRANIAL ELEMENTS OF A LEPTARCTINE (MAMMALIA: CARNIVORA: MUSTELIDAE) AND NEW CRANIAL MATERIAL OF LEPTARCTUS OREGONENSIS: IMPLICATIONS FOR THE ECOLOGY OF THIS EXCEPTIONALLY RARE CARNIVORAN TAXON

No consensus has yet been reached about the paleoecology of any of the genera of the Leptarctinae, a diverse Miocene subfamily of Mustelidae from North America and Eurasia. Differing interpretations of dental and cranial features and a previous lack of available postcranial elements have left the diet and locomotor habits of this subfamily uncertain. Initial interpretations of leptarctines as coati-like omnivores or badger-like carnivores were rejected on the basis of dentition. Leptarctines have also been compared to the kinkajou, a mostly frugivorous procyonid; the raccoon, an omnivore that eats fruit, nuts, eggs, and small vertebrates; and the arboreal, strictly herbivorous koala. The comparison to a koala-like diet implied a strongly arboreal lifestyle for leptarctines. Most recently, the cranial and dental morphology have been interpreted as evidence for a crushing omnivorous diet. A lack of available material for functional morphology studies has left the idea of an arboreal leptarctine to conjecture.

We here present a partial skeleton of a late leptarctine from the UCMP collections. This late early Hemphillian (7.5 – 6.7 Ma) specimen from the Rome fauna of Malheur County, Oregon, includes most of the skeleton as well as the lower right dentary. Presence of the humerus, ulna, and radius as well as femur and tibia shed light on the locomotor habits of leptarctines. These elements, with the addition of the pectoral and pelvic girdles, the vertebral column (represented by cervical vertebrae including atlas and axis, thoracic, lumbar, and caudal vertebrae) and podial elements preliminarily support a rather generalized ambulatory ecology for this leptarctine, with no strong adaptations to an arboreal or fossorial way of life.

In addition, recent fieldwork in the Mascall Formation of central Oregon (early Barstovian, 15.9 – 14.8 Ma) produced a nearly complete skull of Leptarctus oregonensis, a small Leptarctus. This specimen compliments previous work on cranial morphology of the Leptarctinae. The generalized dentition, strong temporal crests and robust zygomatic arches corroborate previous research that suggests a strong bite force and a crushing omnivorous diet. Taken together, these two specimens greatly add to our understanding of Oregonian Miocene faunas.