Oligocene mammals from the Andes of central Chile

More than 1400 fossil mammal specimens have been collected over the past 20 years through a series of US-Chilean paleontological expeditions in the central Chilean Andes. These fossils derive from volcaniclastic intervals of the Abanico Formation, mostly between 33.5° and 35.5°S latitude. Mammal assemblages from this formation appear to sample at least six late Eocene to early Miocene South American Land Mammal "Ages", including two from Oligocene, the Tinguirirican (early) and Deseadan (late). The hardness of typical Abanico matrix preserves many specimens in excellent condition, but has limited the number available for taxonomic studies due to the extensive preparation time required. The first -discovered and best- characterized Abanico assemblage is Tinguiririca. Nearly half of the species from Tinguiririca have been described, and studies of two groups are forthcoming: notohippid notoungulates and caviomorph rodents. The notohippids include: two new species of Eomorphippus Ameghino; another species, likely new, but poorly represented; and "E." pascuali Simpson, a species distinct from others of that genus. The caviomorphs include a new chinchillid and a new dasyproctid. Several other Abanico assemblages may be at least partly contemporaneous with Tinguiririca. One, in the valley of the Río Cachapoal, includes: Polydolops mckennai Flynn and Wyss (Polydolopidae); Johnbell hatcheri Hitz, Flynn and Wyss (Interatheriidae); Trachytherus Ameghino (Mesotheriidae); Archaeotypotherium Roth, and Protarchaeohyrax Reguero, Croft, Flynn and Wyss ("Archaeohyracidae"); plus several xenarthrans and at least one rodent. Two others, in the Río Maipo drainage, include Santiagorothia Hitz, Reguero, Wyss and Flynn (Interatheriidae), Archaeotypotherium, a mesotheriid notoungulate, possibly an isotemnid notoungulate, and a rodent. Another locality in the same region appears to be younger, potentially Deseadan in age; rodents are present and abundant, and armadillos, hegetotheriid notoungulates, and interatheriid notoungulates also have been identified.Simposio V: Los mamíferos oligocenos de América del Sur: explosión evolutiva de los mamíferos nativos y llegada de los emigrantes africanosFacultad de Ciencias Naturales y Muse

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