Chronostratigraphy and “Land-Mammal Ages” in the Cenozoic of southern South America: principles, practices, and the “Uquian” problem

Abstract

The concept of “land-mammal age” as developed in South America is examined. The “Uquian Land-mammal age” is used as a study case. “Land-mammal age” parataxonomy is here considered methodologically but not conceptually different from chronostratigraphic taxonomy. “Land-mammal ages” in South America are based on stages. However, we consider that accurate biostratigraphic studies must be done in South America for establishing the biostratigraphy and precise boundary stratotypes of most stages-ages. The Uquia outcrops are here considered inadequate as a stratotype. A new South American continental stage-age is proposed. This stage is based on a biostratigraphic scheme. The stratotypes of the stage and biozones are located in the fossiliferous southeastern Buenos Aires Province marine cliffs. The lower boundary stratotype is proposed. The stage-age is probably correlated with the Gauss Chron and the lower Matuyama Chron. Additionally, some major units of Ameghino are validated and a different timing for the arrival of North American mammals to southern South America is presented.

Las sucesiones sedimentarias continentales expuestas en Centinela del Mar, provincia de Buenos Aires, Argentina (Pleistoceno Inferior-Holoceno)

“…Sobre la unidad precedente, identifican un nivel litológicamente similar a la Formación La Postrera (sensu Fidalgo et al, 1973a), al que dividen en dos subniveles. El subnivel inferior (Lf M) es el portador de la asociación mamaliana sobre la que establecen la Fauna Local «Centinela del Mar», provisoriamente referida a una nueva Unidad Mamífero denominada «Centinelense», asignable al Pleistoceno Superior y anterior a la Unidad Mamí-fero Lujanense (para una definición de estas unidades bioestratigráficas véase Tonni et al, 1985Tonni et al, , 1987; para una crítica a las mismas véase Cione & Tonni, 1995). El subnivel superior (Lf N) es referido a la Unidad Mamífero Lujanense por la presencia de Equus (Amerhippus) cf.…”

“…Cabe destacar, al menos como antecedente, que E.P. Tonni (apreciación personal en Cione & Tonni, 1995) manifiesta la presencia de fauna ensenadense en los niveles inferiores de CdM.…”

The fossil record of South American short-faced bears (Ursidae, Tremarctinae)

“…In South America, the oldest records of fossil bears are Ensenadan, the 'Puelchan' record could be Ensenadan in age (Cione and Tonni, 1995), and the youngest are latest Lujanian (Early Holocene). According to 14 C dates, the two youngest records in South America are A. tarijense (UMAG 53643, 11,210G50 14 C yr BP, San Roman et al, 2000; GALY s/n, 11,600G130 14 C yr BP, Ubilla and Perea, 1999).…”

“…Three specimens (MMMP 162S, 26S, 48S) came from these marine cliffs north of Mar del Plata City. In this area, sediments have been referred to the Ensenadan, Bonaerian, Lujanian, and Platan (Tonni et al, 1992;Cione and Tonni, 1995;1999). Recent magnetostratigraphic studies by Bidegain et al (1998) show that a change from chron C1r to C1n can be identified 7 m above the top of the cliff (3 m from the base).…”

Evolutionary and biogeographic history of weasel-like carnivorans (Musteloidea)

“…sorgentinii (Cione and Tonni, 1995) known from a partial mandible described in Reig (1957). This fossil is referred to the Vorohuean, a subage of the Marplatan South American Land Mammal Age (Cione and Tonni, 1995). Woodburne et al (2006) correlate the Vorohuean to ~3.0-2.4 MYA.…”