Small rodents (Mammalia) from Eocene deposits of San Diego County, California. Bulletin of the AMNH ; v. 158, article 4

Supplemental Materials
Journal Title
Journal ISSN
Volume Title
New York : American Museum of Natural History
"Four genera (Microparamys, Sciuravus, Griphomys, and Pareumys) and seven species of small rodents are discussed from Eocene deposits in two areas of San Diego County, California. Fossils from the greater San Diego area (Friars and Mission Valley formations) suggest an earliest 'Uintan' (roughly mid Eocene) age. Specimens from the northwesternmost corner of San Diego County in Camp Pendleton Marine Corps Base (?Santiago Formation) suggest a significantly younger assemblage, time-correlative with the Uintan part of the Sespe Formation of Ventura County, California. Sciuravus does not occur in the Pendleton-Sespe localities nor does Griphomys in the greater San Diego area. One species (Griphomys toltecus) is described as new from Camp Pendleton. Detailed comparisons of the San Diego fauna with taxa from the Rocky Mountain region suggest that widespread overland dispersal of land vertebrates across western North America was possible during at least some part of the earlier Eocene, even by the rodents for which strong edaphic controls on range extension might have been expected. Microparamys sp. cf. M. minutus from San Diego cannot be distinguished from M. minutus from the Powder Wash Bridgerian section of Utah and cannot be ruled out as an ancestor for M. tricus from the Pendleton and Sespe deposits. 'Microparamys sp. D' from the Sespe is a distinct species but is not here formally named. Deciduous premolars in Microparamys and Sciuravus may have been retained well into adulthood. 'Sciuravus powayensis' is probably a complex species that in reality included two extremely closely related species; the complexity is not formalized by a new name. The ancestry of Griphomys may lie near Namatomys fantasma. Similarity is great between Pareumys sp. near P. grangeri (considered a cylindrodontid) from San Diego and Spurimus scotti (considered an ischyromyid) from Wyoming, thus further suggesting the close phylogenetic affinities of the two families"--P. 225.
p. 223-261 : ill. ; 26 cm.
Includes bibliographical references (p. 259-261).