Journal of Paleontology, 92(2), 2018, p. 289–304 Copyright © 2017, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.78


Craniodental morphology and diet of Leptarctus oregonensis (Mammalia, Carnivora, Mustelidae) from the Mascall Formation (Miocene) of central Oregon


Jonathan J. Calede,1* Winifred A. Kehl,2 and Edward B. Davis3


1Department of Biology, University of Washington, 24 Kincaid Hall, Box 351800, Seattle, Washington 98195-1800, USA ⟨caledj@uw.edu⟩ 2Department of Museology, University of Washington, Box 359485, Seattle, WA 98195-9485, USA ⟨kehlw@uw.edu⟩ 3Department of Geological Sciences and Museum of Natural and Cultural History, University of Oregon, 1272 University of Oregon, Eugene, Oregon 97403-1272, USA ⟨edavis@uoregon.edu⟩


Abstract.—The Leptarctinae are an enigmatic subfamily of mustelids present in North America and Eurasia during the Miocene (Arikareean to Hemphillian North American Land Mammal Ages). Their diet and ecology have been particularly controversial. Some workers have suggested they were similar to koalas, whereas others suggested they were crushing omnivores analogous to raccoons. Leptarctus oregonensis Stock, 1930, a poorly known leptarctine from the early Barstovian, is represented by fragmented cranial elements and isolated teeth from the Mascall Forma- tion of Oregon, and some fairly complete but undescribed material from the Olcott Formation of western Nebraska. Herein, we describe the first well-preserved skull of L. oregonensis from the type formation. Based on this new speci- men, we confirm that L. oregonensis is a distinct species from L. primus Leidy, 1856 and L. ancipidens White, 1941 that is characterized by a distinct morphology of its tympanic projections and first upper molars. We are also able to describe intraspecific variation within L. oregonensis coinciding with the geographic distribution of the specimens (Oregon and Nebraska). The most variable characters are concentrated in the morphology of the frontals and the upper fourth premolar. Additional specimens will be needed to settle the debate over sexual dimorphism in this species, but this new specimen suggests that Leptarctus oregonensis, despite being one of the smallest members of the Leptarctinae, was an animal-dominated omnivore with considerable crushing ability.


Introduction


The extinct subfamily Leptarctinae includes Miocene mustelids that are sister taxon to the clade including crown mustelids (i.e., neomustelids) and their close relatives (Plesiogale and Paragale) (Wang et al., 2004; Bever and Zakrzewski, 2009). They are found from the early Hemingfordian to early Hemphillian North American Land Mammal Ages (18.8– 6.7 Ma; Baskin, 1998; Limet al., 2001; Tedford et al., 2004) and known primarily from cranial and dental material. Most of the diversity of leptarctines is found in North America, but the


Asian fossil record of this subfamily has grown through recent finds (e.g., Wang et al., 2003; Wang et al., 2004). Leptarctines are also found in European faunas from the early to mid- Miocene (17–15 Ma) of France, Germany, Luxembourg, and Spain (e.g., Robles et al., 2010). The subfamily Leptarctinae includes at least five, possibly six, genera (Trocharion, Kinometaxia, Schultzogale, Craterogale, Leptarctus, and possibly Hypsoparia). All leptarctines share prominent features of the skull, including a short face, parasagittal crests,


* Current address: Department of Evolution, Ecology, and Organismal Biology, The Ohio State University at Marion, 1461 Mount Vernon Avenue, Marion, Ohio 43302-5628, USA ⟨calede.1@osu.edu⟩


roughened parietals, robust zygomatic arches, grooves on the lingual side of the lower canines, and unusual projections on the tympanic bullae (Baskin, 1998; Lim and Martin, 2002; Wang et al., 2004). Leptarctus was erected by Leidy (1856) on the basis of an


isolated upper fourth premolar (P4), but subsequent finds have produced enough fossil material to characterize the genus by a number of distinct features of the skull and dentition. These diagnostic dental characters include: a large P4 with a prominent parastyle, an internal cingulum, a large hypocone, a quadrate upper first molar (M1) with widely separated paracone and metacone and a posterointernal hypocone, and numerous features of the lower dentition including m1 with a strong metaconid, a long talonid, and a notch between the metaconid and the cingulum of the talonid (Baskin, 1998; Wang et al., 2004; Bever and Zakrzewski, 2009). The holotype of Leptarctus oregonensis (LACM CIT 206) was collected in the Mascall Formation (Barstovian: 15.77–14.80 Ma; Tedford et al., 2004) of Oregon and described by Stock (1930). It consists of a partial maxilla with the left P4–M1, the right P4, a partial zygomatic arch, and a cranial fragment including part of the lateral temporal crest. Leptarctus oregonensis was distinguished from the previously identified species of Leptarctus (L. primus, L. wortmani, Matthew, 1924 and L. progressus Simpson, 1930)


289


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204