Ochotona sp.

Christopher, Jass, N., Usa, J. J. & Usa, 2009, Pleistocene lagomorphs from Cathedral Cave, Nevada, PaleoBios 29 (1), pp. 1-12 : 2-3

Ochotona sp.

Referred Specimens —See Appendix 1.

Description —The p3s of Ochotona sp. from Cathedral Cave exhibit some variation in size ( Fig. 2) and are characterized by the presence of at least three enamel reentrant folds (anterointernal, anteroexternal, and posteroexternal; Figs. 3a,b). The folds are simple and lack the crenulated enamel patterns seen in many leporid species. The degree to which enamel reentrant folds are developed varies in some specimens and depends on how far the enamel penetrates from the margin towards the midline of the tooth. Some specimens (e.g., TMM 43693-1857) display weak development (i.e., little or indistinct enamel penetration towards the midline) of the anterointernal reentrant, as in the ‘ Ochotona sp. near Trout Cave form’ from Porcupine Cave, Colorado ( Mead et al. 2004). Several specimens retain at least some development of a fourth, posterointernal reentrant fold. A strongly developed posterointernal reentrant fold, in which there is distinct penetration of enamel towards the midline, is apparent in both occlusal and ventral views of specimen TMM 43693-1856 ( Fig. 3c).

Ochotona dentaries lacking the p3 were identified on the basis of diminutive size and general shape similarity to those of modern pikas. Whenever possible, the shape of the m3 or m3 alveolus was evaluated because it is triangular in leporids, but anteroposteriorly short in ochotonids ( Heaton 1985). Dentaries of Ochotona sp. from Cathedral Cave that preserve the m3 or m3 alveolus retain a flattened posterior margin that gives the tooth and alveolus a more rectangular appearance than those of leporids.

Discussion —Two species of pika, O. collaris and O. princeps inhabit North America today. Ochotona collaris is geographically restricted to portions of Alaska and northwestern Canada, while O. princeps inhabits portions of southwestern Canada and the western United States ( Wilson and Ruff 1999). Fossil specimens, mainly attributed to O. princeps , are known from eastern and western portions of the United States and Canada ( Mead 1987). Two extinct species of pika are also known from North America. Ochotona spanglei occurs in the late Miocene-early Pliocene of Oregon ( Shotwell 1956), and the larger O. whartoni was found in the Pleistocene of Alaska and Canada ( Guthrie and Matthews 1971, Mead and Grady 1996). Other morphological variants are recognized in the fossil record but their taxonomic status is uncertain ( Mead et al. 2004).

The average length of the p 3 in Cathedral Cave specimens is 1.23 mm (n = 75; SD = 0.11; range = 1.0–1.5) and the average width is 1.32 mm (n = 74; SD = 0.16; range = 1.0–1.7). Although there are size differences among individual specimens, the scatterplot of measurements for the p3 (i.e., length versus width; Fig. 2) is not clearly bi- or polymodal. This might suggest the presence of a single species exhibiting intraspecific variation at Cathedral Cave. However, Mead and Grady (1996) presented scatterplots (length versus width) of the m1 and P 3 in extant and fossil pikas that show species “clusters”. If this result can be extrapolated to the p3s from Cathedral Cave, several species might be represented by the size range found here.

The amount of variation occurring in quantitative and qualitative morphologic characters of the p 3 in fossil and extant pikas needs further study. There is some indication that morphological variants occur in the fossil record (e.g., Mead and Grady 1996, Mead et al. 2004), but the taxonomic level at which that variation is expressed remains uncertain. It is possible that most, if not all, of the specimens from Cathedral Cave are Ochotona princeps ; however, the presence of a few unique morphological variants suggests that other species might be represented in the fauna. Because our understanding of morphologic variation in the individual teeth of Ochotona is rudimentary, assigning the specimens from Cathedral Cave to O. princeps would, by default, be partially based on the assumption that fossil Ochotona occurring within or near the modern range of O. princeps are that species. As noted elsewhere, assumptions about geography during the identification process may lead to circularity in subsequent hypotheses concerning regional faunal dynamics (e.g., biogeography; Bell et al. 2004a). Therefore, I restricted my identifications to Ochotona sp. but provide an illustration of a specimen (TMM 43693-1856) with a morphotype that might be outside of the natural range of variation in the p3 of O. princeps ( Fig. 3c).

TMM 43693 - 1856 has a well-developed postero-internal fold that is unique among North American pikas examined in this study. Erbajeva’s (1994) review of the phylogeny and evolution of ochotonids includes an illustration of a p3 of Ochotona antiqua that exhibits four reentrant folds as in TMM 43693 - 1856. Ochotona antiqua is known only from late Miocene-early Pliocene deposits in the Old World ( Erbajeva 1994). I am hesitant to assign TMM 43693 - 1856 to any particular species prior to a thorough review of variation in the p3 of New and Old World species of Ochotona . The occurrence of this p3 morphology in Cathedral Cave specimens could represent a new species or a new record of an Old World species, or it may fall within the natural, but as yet undocumented, range of variation exhibited by extant North American pikas.