BOND mariano
capítulos de libros
The Mustersan Age at Gran Barranca: A Review
The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic
Cambridge University Press
Lugar: Cambridge,UK; Año: 2010; p. 255 - 263
Abstract The Mustersan South American Land Mammals Age (SALMA), based on the ?Astraponote´en? of Ameghino (late Eocene), represents the first moment when native ungulate mammals showed an increase in the number of high-crowned taxa. Ameghino initially distinguished two levels in his ?Astraponote´en?: the ?Astraponote´en? and an ?Astraponote´en le plus supe´rieur,? but later abandoned this subdivision. After Ameghino, other faunas came to be included in the ?Astraponote´en,? such as those from Cerro del Humo and La Gran Hondonada. New collections made at Gran Barranca with precise stratigraphic control, isotopic dates, and magnetostratigraphy allow resuscitation of the ?Astraponote´en le plus supe´rieur? and demonstrate its equivalence to the Tinguirirican of Chile, in both content and age. New studies show that many Mustersan ungulates with high-crowned cheek teeth come from the ?Astraponote´en le plus supe´rieur.? This explains the mixture of faunas of notoungulates with different degrees of hypsodonty. The Mustersan SALMA is represented at Gran Barranca by assemblages from both the Rosado and Lower Puesto Almendra members, dated between 39.0 and 36.5 Ma. These members are separated by unconformities from the underlying Gran Barranca Member and the overlying VeraMember, containing faunas ascribed to the Casamayoran and ?Astraponote´en le plus supe´rieur,? respectively. The classical Mustersan site at ?Colhue-Huapi Norte? where several Mustersan taxa were found (among them the type of Astraponotus assymmetrus) is the same site as Cerro del Humo. The RosadoMember at Profile J (Gran Barranca) is here proposed as the source of the assemblage of taxa that serve as the type fauna of the Mustersan SALMA, because it has the characteristic taxa, precise upper and lower boundaries, and is placed within a well-dated and very complete mammal sequence.