Description of a new species of the North American archaic pika Hesperolagomys (Lagomorpha: Ochotonidae) from the middle Miocene (Barstovian) of Nebraska and reassessment of the genus Hesperolagomys

Andrea R. Bair

ABSTRACT

Hesperolagomys niobrarensis (Lagomorpha, Ochotonidae; new species) is described from a large sample from the late Barstovian (Miocene) of Nebraska. Along with new specimens of H. galbreathi and H. fluviatilis, this sample provides a context for reassessment of taxonomy and understanding of morphological variation in Hesperolagomys. I introduce a new method for determining the relationship between occlusal width and wear stage in isolated lagomorph upper cheek teeth. Cranial and dental characters of Hesperolagomys, including presence of a premolar foramen in the maxilla, place it within Ochotonidae. The P3 of Hesperolagomys is unique among North American lagomorphs in possessing two persistent cement-filled lingually oriented striae, and an anteriorly-directed stria paralleling the outer curve of the tooth. Hesperolagomys additionally differs from Russellagus in smaller size and presence of a deep, persistent lingual hypostria in P4-M2. Hesperolagomys species differ primarily in size and in lower cheek tooth shape; ANOVAs of tooth dimensions strongly support three size groups corresponding to three species. H. fluviatilis (late Barstovian) is smallest in most dimensions, with p3 lacking a cement-filled anterolingual groove and lower molariform teeth with relatively narrow, asymmetrical talonids. H. niobrarensis (late late Barstovian) is largest in most dimensions; p3 has a weak but cement-filled anterolingual groove and lower molariform teeth have moderately wide, asymmetrical talonids. Transverse width of upper cheek teeth of H. niobrarensis is anomalously variable and has a statistically highly significant linear relationship with wear. H. galbreathi (late Clarendonian) is intermediate in size; lower molariform teeth have relatively wide and buccolingually symmetrical talonids, and p3 is short with a prominent cement-filled anterolingual groove.

Andrea R. Bair. Department of Geological Sciences, University of Colorado, Boulder, CO, 80309, U.S.A. 

Key words: North America; Lagomorpha; Ochotonidae; Miocene; Barstovian; Clarendonian; new species