28.6  Jan. 5  Systematic Revision and Biogeography of North American Tortoises (Testudinidae:Gopherus) JONES, CB; San Diego State University jonesc@rohan.sdsu.edu

Gopherus is one member of a clade of tortoises that are endemic to North America. Gopherus arose sometime in the late Eocene or early Oligocene. During the Cenozoic, three other named genera of tortoises existed in North America: Hadrianus, Stylemys, and Hesperotestudo. The earliest confirmed gopher tortoise, G. laticunea, is known from the White River Formation of the central U.S. However, gopher tortoises have also been reported from Eocene and Oligocene sediments of San Diego County, California.

Until this project most systematic analyses of North American tortoises have not coded for individual species of tortoises of all fossil genera. This study hopes to clarify relationships between later diverging Hadrianus and very early diverging Gopherus, such as G. utahensis. Also including individual species from Stylemys and Hesperotestudo will aid in resolving relationships between them as well as with Gopherus.

Fossils from Southwest North America have been analyzed and have added much to the zoogeographical and systematic understanding of gopher tortoises. Correct identification and careful analysis of these specimens have expanded the temporal and spatial distribution of G. laticunea, as well as the extant G.berlandeiri, which has been confirmed in Pleistocene sediments from the Sonoran Desert of Mexico. Futher examination of the undescribed Eocene Gopherus from San Diego will either expand the known range of G. utahensis or confirm the existence of another early diverging Gopherus in the region. This study builds on previous work on North American tortoises with the addition of numerous postcranial characters. This aids in resolving the placement of fossil specimens from which only postcranial elements are known.