223 Paludicola 12(4):223-246 March 2020 © by the Rochester Institute of Vertebrate Paleontology MUSTELIDAE FROM OBSERVATION QUARRY (EARLY BARSTOVIAN) OF NEBRASKA, WITH COMMENTS ON SHEEP CREEK AND LOWER SNAKE CREEK MUSTELIDS Jon A. Baskin Department of Biological and Health Sciences, Texas A&M University–Kingsville, Kingsville, TX 78363 jon.baskin@tamuk.edu ABSTRACT Seven species of mustelids (Carnivora, Mustelidae) occur in the middle Miocene Observation Quarry, Dawes County, Nebraska. These include Skopelogale melitodes, new genus and species. Leptarctus oregonensis is also known from the early Barstovian Mascall Formation of Oregon and the Olcott Formation (Lower Snake Creek Fauna) of Nebraska. Plionictis ogygia, Plionictis parviloba, “Martes” glareae, and Sthenictis dolichops also occur in the Olcott Formation. Miomustela madisonae is elsewhere known from the early Barstovian of Montana and the late Hemingfordian and Barstovian of California. The mustelids of Observation Quarry support an early Barstovian (Ba1) age assignment, coeval with the Lower Snake Creek Fauna. INTRODUCTION The Observation Quarry Local Fauna (LF) is from the “Sand Canyon Beds”, Dawes County, Nebraska. Ted Galusha of the AMNH, who worked for Childs Frick (Frick, 1937; Galusha, 1975a), collected almost all of the mammals from this locality and described the regional geology (Galusha, 1975b). Korth and Evander (2016) described four new species of small mammals from there. They provided complete locality information and faunal lists and assigned the fauna to the early Barstovian North American Land Mammal Age (NALMA). Small carnivorans previously reported from Observation Quarry include the procyonids Arctonasua minima (Baskin, 1982), Bassariscus minimus (Baskin, 2004), and Probassariscus matthewi, (Matthew and Cook, 1909; Baskin, 2004), and the mustelid Miomustela madisonae (Douglas, 1904; Lofgren et al., 2016; Lofgren and Abersek, 2018). This paper adds the mustelids Skopelogale gen. nov., Leptarctus, “Martes”, Plionictis, and Sthenictis to Observation Quarry. Additional mustelids that are discussed are Dinogale, Mionictis, and Brachypsalis from the Sheep Creek Formation and/or Lower Snake Creek Fauna of the Olcott Formation. MATERIALS AND METHODS The mustelids from the Sheep Creek Fauna, Lower Snake Creek Fauna, and Observation Quarry LF are in the collections of the American Museum of Natural History. Measurements were taken with dial calipers to the nearest 0.1 mm. Dental Abbreviations—L = length, Le = external length, Li =internal length, W = width; tr = trigonid; tl = talonid; D = depth of mandible between p4 and m1. Institutional Abbreviations—AMNH FM, Fossil mammal collection of the American Museum of Natural History, New York, New York; AMNH F:AM, Frick Collections of fossil mammals in the AMNH; ANSP, Academy of Natural Sciences, Philadelphia, Pennsylvania; CM, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania; LACM (CIT), Natural History Museum of Los Angeles County (former California Institute of Technology collection), Los Angeles, California; MNHN, Muséum national d’Histoire naturelle, Paris, France; PU, Princeton University, Princeton, New Jersey; UCMP, University of California Museum of Paleontology, Berkeley, California; UOMNH, University of Oregon Museum of Natural and Cultural History, Eugene, Oregon. SYSTEMATIC PALEONTOLOGY Order CARNIVORA Bowdich, 1821 Family MUSTELIDAE Fischer, 1817 Subfamily LEPTARCTINAE Gazin, 1936 Leptarctus Leidy, 1857 Genotypic Species—Leptarctus primus Leidy, 1857. Holotype—ANSP 11293, left P4. Horizon—Bijou Hills, Fort Randall Formation, South Dakota, U.S.A.; late Barstovian (Ba2) NALMA. Leptarctus oregonensis Stock, 1930 (Figures 1A, 2A, B; Tables 1-3) Holotype—LACM (CIT) 206, partial left maxilla with P4 and M1, right P4, and part of the skull.