A new fossil mustelid from the Miocene of South Dakota, USA.

Abstract

A skull from the Barstovian of South Dakota has typical leptarctine characteristics, including robust zygomatic arches, double sagittal crests, grooves on the lingual side of the lower canines, and bony projections from the tympanic bullae. The robust mandibles and expanded masseteric fossa of this specimen indicate that it had large jaw muscles. Dental morphology and other characters lead us to agree with earlier suggestions that Hypsoparia is a valid genus. The morphology of Hypsoparia suggests that leptarctines were more herbivorous than most other Carnivora. Mustelids vary greatly in size and include 67 extant species in 25 genera. These species occupy many habitats, including fresh and salt water, and all land areas of the world except the West Indies, Madagascar, Sulawesi, Antarctica, and most oceanic islands (Nowak 1999). Qiu and Schmidt-Kittler (1982) considered Leptarctinae to be a subfamily of mustelids including Craterogale (North America, Middle Miocene), Trocharion (Europe, Middle Miocene), Hypsoparia (North America, Upper Miocene), and Leptarctus (North America and Asia, Lower to Upper Miocene). Leptarctus ranges from basal Hemingfordian strata to the Early Hemphillian (Lim 1999). The characters diagnosing Leptarctus as a mustelid include absence of M2, absence of a notch between the paracone and the metacone of the upper carnassial, and a reduced dentition with loss of P1 and p1. Among mustelids, Leptarctus also has many unique characters, including prominent double sagittal crests, a well-developed hypocone on P4, grooved lower canines, heavy zygomatic arches, and bony projections on the tympanic bullae (Lim 1999). Dorr (1954) erected a new genus and species of leptarctine mustelid from the Late Miocene of Montana, USA: Hypsoparia bozemanensis. Qiu and Schmidt-Kittler (1982) confirmed it as a taxon separate from Leptarctus. However, McKenna and Bell (1997) and Baskin (1998) synonymized H. bozemanensis with Leptarctus primus. The new specimen from the Miocene of South Dakota, USA, provides evidence that Hypsoparia is a separate genus from Leptarctus. We can describe this animal as follows: Systematic paleontology: class, Mammalia; order, Carnivora; family, Mustelidae (Fischer von Waldheim 1817); subfamily, Leptarctinae (Gazin 1936); genus Hypsoparia (Dorr 1954). Emended diagnosis: the muzzle short, deep, and wide compared with that of Leptarctus; small, round infraorbital foramen; relatively greater height of zygomatic arch; upper canine with anterior wear; P2 and P3 unicuspid with complete cingula; P4 and M1 longer than wide; labial side longer than lingual side on P4; anterior margin of M1 curving inward; mandibles larger and more robust than in L. primus; mandible deep with two mental foramina located below p2 and p3; masseteric fossa enlarged; m2 longer than wide; m1 with a broadly basined talonid; p3 and p4 with prominent cingula.