Paludicola 14(2):57-74 April 2023 © by the Rochester Institute of Vertebrate Paleontology 57 ADDITIONAL SMALL MAMMALS FROM THE OLIGOCENE BRULE FORMATION (LATE ORELLAN-WHITNEYAN) OF SOUTHWESTERN NORTH DAKOTA William W. Korth 1 , Clint A. Boyd 2 , Robert J. Emry 3 , and Jeff J. Person 2 1 Rochester Institute of Vertebrate Paleontology, 265 Carling Rd., Rochester, NY 14610 and Rochester Museum & Science Center, 657 East Avenue, Rochester, NY 14607 2 North Dakota Geological Survey, 600 East Boulevard Ave., Bismarck, ND 58505 3 Department of Paleobiology, Smithsonian Institution, National Museum of Natural History, PO Box 37012 MRC 121, Washington, DC 20013. ABSTRACT Several recently published studies documented much of the micromammal portion of the Oligocene faunae recovered from the Fitterer Ranch and Obritsch Ranch localities in Stark County, North Dakota. That work identified four stratigraphically segregated faunae that range in age from latest Orellan to late Whitneyan. This study reviews the remaining micromammals from those localities, the leptictids and lipotyphlans, recognizing the presence of ten taxa. One species, Mystipterus austinae (Talpidae, Uropsilinae), is new and represents the earliest occurrence of the genus. In addition to Leptictis dakotensis, the presence of a new leptictid taxon is documented but is not named pending a detailed revision of that group. The recognition of the erinaceid Amphechinus horncloudi represents the earliest occurrence of this species, which was previously restricted to the Arikareean. Four other taxa previously known from older faunae are identified, extending their known ranges into the Whitneyan ( Centetodon marginalis, Cryptoryctes sp., cf. C. kayi, Domnina gradata, and Oligoscalops galbreathi). With the incorporation of the data from this study, the well-sampled micromammal faunae from Fitterer Ranch and Obritsch Ranch provide important information for evaluating broader patterns of micromammal evolution, dispersal, and extinction within the Great Plains region of North America. INTRODUCTION The stratigraphy and age of Fitterer Ranch and Obritsch Ranch localities in southwestern North Dakota is described and detailed sections provided elsewhere (Skinner, 1951; Stone, 1973; Murphy et al., 1993; Korth et al., 2019a, 2019b, 2021a; Boyd et al., in press). Both localities are stratigraphically situated within the Brule Formation (White River Group) and are predominantly Whitneyan in age with only the basal stratum at Fitterer Ranch being questionably latest Orellan or earliest Whitneyan (Korth et al., 2019a, 2019b). In a recent series of papers, the marsupials (Korth et al., 2021a), rodents (Korth et al., 2019a, 2019b) and lagomorphs (Boyd et al., in press) from these localities have been described in detail. The only groups of micromammals that remain undescribed are those discussed here: the leptictids and lipotyphlans. Terminology—Dental terminology follows that of Rich (1981). Stratigraphic Terminology: Sampling intervals cited in this study correspond to those used by Korth et al. (2019a, 2019b, 2021a) and were based on the stratigraphic units first defined by Skinner (1951) for the White River Group at Fitterer Ranch. The discreet, temporally segregated faunae defined by Korth et al. (2021a) in the study area are applied in this study, though we modify Obritsch Ranch Fauna B to include specimens from Fitterer Ranch sampling interval 7 for the purposes of this study. Biostratigraphic Terminology: The North American Land Mammal Ages (NALMA) used in this study follow the terminology and definitions of Prothero and Emry (2004). Measurements—All measurements taken with optical micrometer to nearest 0.01 mm. Abbreviations—(for dentitions) C/c, upper/lower canine; P/p, upper/lower premolar; M/m upper/lower molar. (for institutions) NDGS, North Dakota Geological Survey; USNM, United States Museum of Natural History (Smithsonian). SYSTEMATIC PALEONTOLOGY Order Leptictida McKenna, 1975 Family Leptictidae Gill, 1872 Genus Leptictis Leidy, 1868 Leptictis dakotensis (Leidy, 1868) Figure 1; Table 1 Referred Specimens—NDGS 9905, cranium lacking anterior rostrum, orbital walls, and zygomatic arches with left P4-M3 and right P5-M3; NDGS 9593, left maxilla with M1-M2; NDGS 9579, right P4; NDGS 9585, left M1; NDGS 9666, right M3; NDGS 9665, partial right M3; NDGS 9575, left dentary with p4, m1- m2, partial m3; NDGS 9573, dentary fragment with dp5 (p5 erupting); NDGS 9907, partial right dentary with p4- m1; NDGS 9906, partial left dentary with m2-m3;