Chapter 18. A NEW MAMMAL FAUNA AT THE TOP OF THE GRAN BARRANCA SEQUENCE AND ITS BIOCHRONOLOGICAL SIGNIFICANCE

KRAMARZ, ALEJANDRO A.; VUCETICH, MARÍA G.; CARLINI, ALFREDO A.; CIANCIO, MARTÍN R.; ABELLO, MARÍA A.; DESCHAMPS, CECILIA M.; GELFO, JAVIER N.

The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia

Cambridge University Press

Lugar: Cambridge, UK; Año: 2010; p. 264 - 277

ABSTRACTThe top of the stratigraphic sequence of the fossil-bearing Sarmiento Formation atGran Barranca has yielded a distinctive assemblage of mammalian taxa. Fossils occur instrata located 25m above the upper-most level bearing typical Colhuehuapian mammals.This association is represented by fragmentary remains of small to middle sized mammalsbelonging to paucituberculatan marsupials, dasypodids, glyptodonts, tardigrades,hegetotheres, interatheres, proterotheriids and hystricognath rodents. Although this faunacontains at least two new rodent species not recorded in other faunas, it is more similar tothat recorded at the lower and middle sections of the Pinturas Formation at NW Santa CruzProvince (the Ameghino’s Astrapothericulan fauna) than to any other known fossilmammal assemblage. The strata yielding this fauna (Upper Fossil Zone—UFZ—) isestimated to be in Chron C6n (19.7 to 18.7 Ma), but the taxic similarity with the youngerAstrapothericulan fauna (dated between 17.5 and 16.5 Ma) suggests that the UFZ is placedat the youngest extreme of the Chron C6n. The Astrapothericulan and the UFZ assemblageswould correspond to a single post Colhuehuapian - pre Santacrucian biochronological unit(the “Pinturan”) which would span from ca. 18.75 to ca. 16.5 Ma. This is the youngestfaunal unit within the standard sequence of the middle Cenozoic SALMAs at GranBarranca. The assignment to this unit of other early Miocene faunas elsewhere in SouthAmerica (at present poorly o partially known) depends on further descriptions and futurefindings.