Preliminary Systematic Analysis of An Avifaunal Assemblage from Roland Springs Ranch of Western Texas

The Plio-Pleistocene is of great interest in regard to avian evolution, as the climatic fluctuations of the Pleistocene impacted avian biodiversity significantly. By the late Pliocene, virtually all modern avian families and genera were present and species diversity had peaked in excess of 20,000. The glaciation events of the Pleistocene reduced this number to fewer than 10,000. As few described North American avifaunal assemblages are available, the overall pattern of avian systematics and biogeography is poorly understood. This research is focused on a systematic and biogeographical analysis of the avifaunal component of a fossil assemblage from the Roland Springs Ranch of Snyder, Texas. This locality, RSR1, is in the Rolling Plains region of westernTexas. Deposition appears to have occurred in a low-energy fluvial environment without apparent taphonomic bias resulting in the preservation of a diverse fauna. Preliminary biostratigraphic dating using non-avian taxa suggests this assemblage represents a transitional period between the Blancan and Irvingtonian North American Land Mammal Ages (ca. 1.8 mya). As such, the RSR1 avifauna should compare well with others from contemporaneous North American sites, and is hypothesized to be similar to those from localities located in the early to middle Blancan-age Rexroad Formation in the High Plains of Kansas. This avifaunal assemblage numbers over 30 specimens and consists of various elements representing at least two orders. The fauna fills an important spatial gap in the avifaunal record and will help to resolve avian systematic and biogeographical issues from the important period just prior to the Pleistocene.