North American archaic ochotonids Hesperolagomys and Russellagus (Mammalia: Lagomorpha) and geometric constraints on the evolution of hypsodonty in lagomorphs

TL;DRAbstract

New specimens of Russellagus and Hesperolagomys (Mammalia, Lagomorpha, Ochotonidae), reexamination of type material, and new information from topotypic specimens provide a context for reassessment of these taxa. Hesperolagomys niobrarensis (new species) is described from a large sample from the late Barstovian (Miocene) of Nebraska. Cranial and dental characters of Hesperolagomys and Russellagus, including presence of a premolar foramen in the maxilla, place these genera within Family Ochotonidae. These taxa share characters including: rooted cheek teeth, talonids narrower than trigonids in lower molariform teeth and having an anterior projection, persistent crescentic valley in P4-M2, and p3 with deep buccal fold and slender trigonid. Hesperolagomys P3 is unique among North American lagomorphs. Hesperolagomys is smaller than Russellagus and has a deep, persistent lingual hypostria in P4-M2; Russellagus additionally differs from Hesperolagomys in having wider anterior projections of th

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