Sciurid rodents (Mammalia) from the Chadronian and Orellan (Oligocene) of Nebraska

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Abstract
Upper dentition of Protosciurus mengi Black, from the Orellan Brule Formation, Nebraska, is described for the first time. The zygomatic plate is tilted anterodorsally, showing the beginnings of sciuromorphy as in the Arikareean species of this genus. A new genus of sciurid, Oligospermophilus, is named for the species originally identified as ?Protosciurus douglassi (Korth), based on additional material including a skull and upper dentitions. The zygomasseteric structure of O. douglassi is unlike any previously described Tertiary sciurid. The range of O. douglassi is extended from the late Chadronian to the Whitneyan. Three distinct lineages of sciurids, distinguished on dental morphology and zygomasseteric structure, can be traced in the Oligocene in North America; they are represented by the genera Protosciurus, Oligospermophilus, and ?Protosciurus.

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