Portal de Periódicos da CAPES

Chapter 12

2003; American Museum of Natural History; Volume: 279; Linguagem: Inglês

10.1206/0003-0090(2003)279 2.0.co;2

1937-3546

Gary Morgan, Spencer G. Lucas,

Species Distribution and Climate Change

Significant mammalian faunas of Pliocene (Blancan) and early Pleistocene (early and medial Irvingtonian) age are known from the Rio Grande and Gila River valleys of New Mexico. Fossiliferous exposures of the Santa Fe Group in the Rio Grande Valley, extending from the Española basin in northern New Mexico to the Mesilla basin in southernmost New Mexico, have produced 21 Blancan and 6 Irvingtonian vertebrate assemblages; three Blancan faunas occur in the Gila River Valley in the Mangas and Duncan basins in southwestern New Mexico. More than half of these faunas contain five or more species of mammals, and many have associated radioisotopic dates and/or magnetostratigraphy, allowing for correlation with the North American land-mammal biochronology. Two diverse early Blancan (4.5–3.6 Ma) faunas are known from New Mexico, the Truth or Consequences Local Fauna (LF) from the Palomas basin and the Buckhorn LF from the Mangas basin. The former contains five species of mammals indicative of the early Blancan: Borophagus cf. B. hilli, Notolagus lepusculus, Neotoma quadriplicata, Jacobsomys sp., and Odocoileus brachyodontus. Associated magnetostratigraphic data suggest correlation with either the Nunivak or Cochiti Subchrons of the Gilbert Chron (4.6–4.2 Ma), which is in accord with the early Blancan age indicated by the mammalian biochronology. The Truth or Consequences LF is similar in age to the Verde LF from Arizona, and slightly older than the Rexroad 3 and Fox Canyon faunas from Kansas. The Buckhorn LF has 18 species of mammals, including two rodents typical of the early Blancan, Mimomys poaphagus and Repomys panacaensis. The Buckhorn LF also is similar in age to the Verde LF and has affinities with the Panaca LF from Nevada. Although the Buckhorn and Truth or Consequences LFs have few taxa in common, the similarities of both faunas with the Verde LF suggest they are close in age.Eight faunas from the central and southern Rio Grande Valley are medial Blancan in age (3.6–2.7 Ma), including the Pajarito and Belen faunas from the Albuquerque basin, the Arroyo de la Parida LF from the Socorro basin, the Cuchillo Negro Creek and Elephant Butte Lake LFs from the Engle basin, the Palomas Creek LF from the Palomas basin, the Hatch LF from the Hatch-Rincon basin, and the Tonuco Mountain LF from the Jornada basin. These faunas are characterized by the presence of taxa absent from early Blancan faunas, including Geomys (Nerterogeomys) paenebursarius, Equus cumminsii, E. scotti, and Camelops, and the absence of South American immigrant mammals found in late Blancan faunas. The Pajarito LF is directly associated with a pumice dated at 3.1 Ma. The Cuchillo Negro Creek and Elephant Butte Lake LFs are in close stratigraphic association with a basalt flow of 2.9 Ma. Magnetostratigraphy constrains the age of the Tonuco Mountain LF between 3.6 and 3.0 Ma.The Mesilla A fauna from the Mesilla basin and the Pearson Mesa LF from the Duncan basin are late Blancan in age (2.7–2.2 Ma). Both record the association of Nannippus with a South American immigrant, Glyptotherium from Mesilla A and Glossotherium from Pearson Mesa, restricting their age to the interval after the beginning of the Great American Interchange at about 2.7 Ma and before the extinction of Nannippus ca. 2.2 Ma. Magnetostratigraphy further constrains the Mesilla A and Pearson Mesa faunas to the upper Gauss Chron, just prior to the Gauss/Matuyama boundary. The Mesilla B and Virden faunas occur higher in the same stratigraphic sequences as the Mesilla A and Pearson Mesa faunas, respectively, and are latest Blancan in age (2.2–1.8 Ma). Both faunas contain taxa restricted to the Blancan, including the camels Blancocamelus and Gigantocamelus from Mesilla B, and Canis lepophagus from Virden. The absence of Nannippus, and of Mammuthus and other genera that first appear in the Irvingtonian, support the age.The Tijeras Arroyo fauna from the Albuquerque basin and the Tortugas Mountain and Mesilla C fa