Phylogeny of Nearctic Sciuridae

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Abstract
External morphology, osteology, myology and paleontology are studied comparatively. Morph. features are segregated as cenotelic or paleotelic. Paleotelic features are mentioned under the accounts of the genera or other appropriate systematic categories. Cenotelic features are mentioned under the accounts of the respective morph. structures, where the adaptive nature of selected characters is mentioned, as for example 4 instead of 3 sacral vertebrae in fossorial forms, and better developed mystacial vibrissae and longer radius and ulna with smaller distal ends in arboreal forms. In the skull, characters significant phylogenetically are principally associated with the masticatory mechanism and with the differential development of parts of the brain. The presence or absence of cheek pouches has broad evolutionary significance. The evidence concerning pouches in fossil forms is indicated by the attachments on the skull of the associated facial musculature. The absence of the clavobrachialis muscle in Ammospermophilus seems to be a paleotelic character. New spp. are Sciurus tecuyensis* from the Lower Miocene, Citellus primitivus* from the Upper Miocene, and S. venturus* from the Lower Pliocene. ARCTOMYOIDES, from the Upper Miocene, is based on Sciurus arctomyoides Douglass. The Tertiary spp. malheurensis, angusticeps and tephryus are transferred from Sciurus to Protospermophilus. Ammospermophilus is given generic rank and Eutamias is reduced to a subgenus of Tamias. Nearctic Sciuridae are placed in 3 divisions: (1) flying squirrels, (2) tree squirrels and (3) chipmunks and terrestrial squirrels. The Paramyidae is more closely related to the Sciuridae than is any other family. Probably the Sciuridae originated in the Eocene from the protogomorphs.

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