Early Pleistocene leporids (Mammalia, Lagomorpha) of Roland Springs Ranch Locality 1 and the rise of North American Quaternary leporines

Abstract

Roland Springs Ranch Locality 1 (RSR-1) is an early Pleistocene vertebrate faunal locality on the Rolling Plains of Scurry County, Texas. Leporid remains are common among material recovered from ongoing, systematic excavations at RSR-1. The size and morphology of collected lower third premolars were utilized to identify the leporid taxa present at RSR-1. The resulting sample assemblage is unique in composition, including: Hypolagus gidleyi, Hypolagus spp. (small form), Notolagus lepusculus, Nekrolagus progressus (including forms with the Lepus pattern), and Aztlanolagus agilis. The biochronology of such a combination of taxa indicates placement near the boundary between the early and late subdivisions of the Blancan Land Mammal Age, generally consistent with the current interpretation of RSR-1.The RSR-1 sample is considered against the backdrop of Neogene-Quaternary faunal turnover that included the extinction of the Archaeolaginae and radiation within the extant subfamily, Leporinae. Leporid abundance during the late Pliocene-early Pleistocene (Blancan Land Mammal Age) of North America marks peak species richness for the rabbit family. Late Miocene-early Pleistocene changes in climate and grassland composition and structure in North America coincide with this pivotal period of leporid natural history. Environmental shifts potentially created a period of expanded physical heterogeneity and niche diversification that provided the ecological conditions for archaeolagines, Blancan leporines, and emerging derived, modern type (Lepus pattern) leporines to widely coexist. The Lepus pattern of extant cottontails and jackrabbits, is hypothesized as a competitive advantage initiated by grassland change and particularly suited for the arid and open Quaternary Great Plains.