Master's Theses



Degree Name

Master of Science (MS)


Geographic variation among populations of Onychomys leucogaster in western North America was investigated using morphometric, karyotypic, and fossil data. Populations previously considered to represent O. l. utahensis, as well as those from the southern portion of the range of O. l. fuscogriseus, are regarded as color variants of O. l. brevicaudus that do not warrant separate subspecific status. Populations in northeastern Oregon and eastern Washington are described and named as a distinct subspecies. O. l. brevicaudus in the Great Basin is more similar morphologically to O. l. arcticeps in the Wyoming Basin than to O. l. melanophrys or O. l. pallescens on the Colorado Plateau although all four have the same standard karyotype. Late glacial/early Holocene fossils indicate that O. leucogaster was a component of a "cold" desert refuge in the location of the present Mohave "hot" desert during the last glacial episode. It progressed northward into the Great Basin during late glacial time, and then eastward into the Wyoming Basin and farther northward onto the northern Columbia Plateau during early Holocene time.


Jerry R. Choate

Date of Award

Summer 1984

Document Type

Thesis - campus only access


© 1984 Brett R. Riddle


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