Lomas Las Tetas de Cabra fauna

88 p. : ill. (1 col.), maps ; 26 cm.Includes bibliographical references (p. 64-70)."Fossil mammal and other vertebrate remains from the Lomas Las Tetas de Cabra in Baja California Norte, Mexico, provide an opportunity to examine the utility of continental scale geochronologies based on land mammal faunas. Early reports proposed a late Paleocene to early Eocene age for this fauna. Recent fieldwork and considerations of cumulative fossil discoveries strongly indicate that the Baja fauna represents the Wasatchian Land Mammal Age (early Eocene) and is strikingly similar to faunas of this age from the western interior of the United States. Wasatchian-age taxa represented in the Baja assemblage include Hyracotherium, Hyopsodus, Meniscotherium (also possibly from Clarkforkian assemblages), Diacodexis, and Prolimnocyon. Also present in the fauna are excellent specimens of Wyolestes and Esteslestes, a new genus of didelphid marsupial, as well as a badly distorted skull of a pantodont. An early Eocene age assignment is supported by analysis of the marine section adjacent to the Tetas de Cabra sequence. The marine organisms are consistent with a middle Ypresian (early Eocene) age assignment. Paleomagnetic analyses of both the terrestrial and marine sections also corroborate this age assignment. These new results substantiate the validity of the Wasatchian as a discrete temporal interval that can be applied at a continental scale. The Wasatchian thus fulfills the expectations for a mammal-based chronology. Similarities, rather than differences, between the Baja assemblage and other Wasatchian-age faunas is the dominant pattern. A choice among dispersal theories for the sources of Wasatchian mammals is not clearly indicated by the faunal evidence"--P. 3

New Fossil Rodents from the Early Oligocene Rancho Gaitan Local Fauna, Early Chadronian, Northeastern Chihuahua, Mexico

Contents: Abstract -- Introduction -- Paramyidae -- Cylindrodontidae -- References CitedOne new genus and three new species of rodents are described from the early Oligocene of Chihuahua. Mytonomys gaitania is a paramyid slightly more advanced than species from the late Eocene of Utah and California. Jaywilsonomys, new genus, with two new species, is a cvlindrodont apparently descended from the late Eocene Pareumys. The Chihuahua deposits are probably slightly later than the late Eocene Mvton of Utah and probably appreciably earlier than the early Oligocene Capote Mountain Tuff of Trans- Pecos Texas.Texas Memorial Museu

The Xochixtlapilco dinosaur ichnofauna, Middle Jurassic of Oaxaca, southeasten Mexico: description and paleontologic significance

Volume: 515Start Page: 1End Page: 4