Biostratigraphy of the Casamayoran, Early Eocene of Patagonia. American Museum novitates ; no. 2820

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New York, N.Y. : American Museum of Natural History
"The Casamayoran, presumed to pertain to the early Eocene, is the most diverse and best known of South America's early to middle Tertiary land mammal ages. Because the composition of local faunas and the stratigraphic position of assemblages at any given locality have not been evaluated, however, the Casamyoran has remained a dimensionless age, despite its seminal importance to understanding the early radiations of mammals on the South American continent. Preliminary analysis of field data and collections obtained by G.G. Simpson in 1930-1931 suggests a faunal succession in the Casamayoran of Patagonia. Large, well documented samples are available from two localities with relatively wide stratigraphic distributions of Casamayoran mammals: Cañadón Vaca and the Gran Barranca south of Lago Colhué Huapí, central Chubut. The compositions of these two local faunas differ markedly, and lithostratigraphic, biostratigraphic, and paleontologic evidence suggests that these differences are temporal and not ecological in nature. Faunal composition of the two localities is compared qualitatively and statistically with respect to the magnitude of difference seen in preceding and succeeding South American land mammal ages and to roughly equivalent North American land mammal ages. Two new subdivisions of the Casamayoran, the Barrancan and the Vacan, are defined on this basis. In addition, a composite stratigraphic plot of taxa from the younger of the two localities (the Gran Barranca) produced a number of non-overlapping range zones within the Barrancan; statistical analysis indicates that the probability these observations are due to sampling error is small in most, but not all, cases. The other Patagonian local faunas are briefly considered with respect to this scheme, and an hypothesis of their relative ages is presented"--P. [1].
26 p. : ill., 2 maps ; 26 cm.
Includes bibliographical references (p. 25-26).