Pipestone Springs Main Pocket (PSMP) (Renova Formation, Jefferson County, Montana) has yielded an unusually rich concentration of mostly small-bodied Chadronian (late Eocene) mammals. Coprolites are common at PSMP and indicate which taxa and skeletal elements were consumed, as well as provide insight as to which carnivore species were likely to have deposited their feces at the site. Two distinct coprolite groupings were recognized based on differences in diameter, morphology, and abundance of bone. The sample of larger coprolites ranges in diameter from 16–29 mm and lacks a distinct mode. Some of the larger coprolites contain bone, but if present, it is sparse, poorly preserved, and unidentifiable. The sample of smaller coprolites varies in diameter from 4–15 mm and has a prominent mode at 10–11 mm. Many of the smaller coprolites contain abundant bone that is often highly fragmented. Osteoderms, bone ends, or dental elements identified to taxon in smaller coprolites indicate that marsupials, lizards, lagomorphs, and rodents were prey of smaller PSMP carnivores. Most elements identified as lagomorph or rodent probably represent Palaeolagus temnodon and Ischyromys veterior based on their high abundance in surface collections. Undigested bone from disaggregated carnivore feces did contribute to the large number of small dentigerous elements recovered from surface collections at PSMP, but it probably was not a major source because only two smaller coprolites had an exposed partial dentary or maxilla. The remains of mammalian carnivores are comparatively rare at PSMP and nine taxa are described, 52% of which represent Hesperocyon gregarius and 21% Brachyrhynchocyon dodgei. If the percentage of surface collected specimens for each carnivore taxon at PSMP is a reflection of activity at the depositional site, most of the smaller coprolites probably represent Hes. gregarius. To test this hypothesis, the ratios between feces diameter and body mass, as well as average lower first molar, (m1), length and body mass in an extant canid were applied to m1s of Hes. gregarius and the smaller coprolites from PSMP. Results indicate a mass of 3.3 kg for the smaller PSMP carnivore and 2.9 kg for Hes. gregarius from PSMP, both similar to the mass of Hesperocyon based on skeletal material. Also, the mode of smaller diameter coprolites is more prominent than the mode of the diameter of feces from an extant canid, which suggests that most of the smaller PSMP coprolites represent the activity of a single species, in this case Hes. gregarius. Many larger coprolites at PSMP probably represent Br. dodgei based on its high relative abundance, but the lack of a prominent mode for the larger coprolites suggests that one or more other species also contributed to the sample.

The composition of the basicranial axis has been reported in the comparative literature in numerous extant and extinct mammals. The primary components are unpaired endochondral bones: the ethmoid, presphenoid, basisphenoid, and basioccipital. Ventral to these are several dermal elements: included are the unpaired vomer, which is widely present, and three bones with more limited distributions, the paired palatines, the paired pterygoids, and the unpaired parasphenoid. Here, we describe novel dermal structures on the dorsal aspect of the basicranial axis in the rock hyrax, Procavia capensis. This taxon has a medial process of the paired frontal bones that meets on the midline and overlies the presphenoid at its juncture with the ethmoid; we term this the presphenoid process of the frontal. Ventral to the presphenoid process is a second smaller process that is off the midline and presents a facet contacting a boss on the presphenoid; we term this the presphenoid facet of the frontal. Occupying the notch between these two structures is the ethmoidal nerve. We sampled the taxonomically diverse collections of the Section of Mammals, Carnegie Museum of Natural History, and the literature. We found additional instances of interfrontal contact dorsal to the ethmoid and presphenoid in the artiodactyl Neotragus and in various platyrrhine and catarrhine primates resembling the presphenoid process of the frontal of P. capensis. However, we did not find a presphenoid facet of the frontal in Neotragus and the primates, which, therefore, thus far is unique to P. capensis. Additionally, we report the presence of a midline suture on the ventral surface of the presphenoid of neonatal P. capensis, which, to our knowledge, is also unique to this mammal.

Eleven species of rodents are described from the Diamond O Ranch local fauna from the Beaverhead Basin, southwestern Montana. Of the species recognized, seven have been previously reported from the Chadronian of Montana or adjacent Wyoming and Saskatchewan or Texas: Ardynomys occidentalis Burke, 1936; Pseudocylindrodon sp., cf. Pseudocylindrodon neglectus Burke, 1935; Eutypomys parvus Lamb, 1908; Adjidaumo minimus (Matthew, 1903); Paradjidaumo disjunctus Korth, 2013; Paradjidaumo nanus Emry and Korth, 2013; and Aulolithomys vexilliames Korth and Emry, 1997. Isolated molars of two different indeterminate species of Ischyromys Leidy, 1856, are also recognized. Two new species are described: the ischyromyine Spurimus hoffmani and the eomyid Metanoiamys norejkoi. Both these species represent the latest occurrence of these genera, which are elsewhere limited to the earlier Eocene. The rodents from Diamond O Ranch suggest an early Chadronian age for the fauna; however, other components of the fauna make this age determination uncertain (Tabrum et al. 1996:295; Fostowicz-Frelik and Tabrum 2009).

Nine rodents are described from the Whitneyan (middle Oligocene) White Hills fauna of Montana. Of these, three new genera are described: the aplodontid Altasciurus, the cylindrodontid Lophicylindrodon, and the castorid Montanacastor. Prosciurus relictus (Cope, 1873) is named as the type species of Altasciurus. The other genera are unique to this fauna and are based on new species; Lophicylindrodon expiratus and Montanacastor simplicidens. In addition, two more new species are described: the eomyid Orelladjidaumo exiguus and the cricetid Willeumys argosorus. The rodent fauna from White Hills is believed to be Whitneyan in age because of the occurrence of Eumys brachyodus Wood, 1937, and Leptodontomys douglassi (Burke, 1934); both elsewhere known from the Whitneyan. The rodent fauna is unique for several reasons: 1) a much lower diversity of rodents than in comparably aged faunas; 2) the number of unique species (four of nine); 3) the relict occurrence of a cylindrodontid (otherwise latest occurrence in the Chadronian); and 4) the extremely high proportion of a single species (A. relictus makes up over 70% of the number of specimens in the fauna). The uniqueness of this fauna may be explained by the fact that the other well-known Whitneyan faunas are from the Great Plains, whereas the White Hills fauna was likely from an isolated intermountain basin. However, taphonomic factors may have controlled the relative numbers of specimens of each species.