( Middle and Lower) The upstream end of the conglomeratic horizons end abruptly at a fault, immediately to the left of #3 to #5. All of the labeled conglomeratic horizons in this outcrop produce fossils. The primary portion of the outcrop extends from #3 to #11, and it is ∼100 m in length, as shown here, but it is underwater during the rainy season. ( Upper) The entire outcrop, showing the isolated upstream exposures (#1 and #2) of the fossil-bearing conglomeratic horizons. Wide-angle and close-up views of the Santa Rosa outcrop. The regional stratigraphy is poorly exposed and known only rudimentarily.įig.
2) is located in a remote, isolated corner of eastern Perú where access is solely by chartered aircraft and there has been little to no modern geologic work. Third, there have been no means to date the paleofauna accurately using stratigraphy. This makes biogeographic and biostratigraphic correlation difficult, if not impossible, in most cases. Second, all of the identified mammalian taxa present have been new to science at the species level, most at the generic level, many at the family level, and some possibly even at the ordinal level. Moreover, there are few mammalian maxillary or mandibular fragments with more than one tooth, which makes associating teeth of different loci within a species’ tooth row difficult. First, it is mostly a microvertebrate paleofauna comprising primarily isolated teeth, the majority of which are only a few millimeters in size. Three major factors have hindered studies of the Santa Rosan vertebrates. We conclude that the ∼41 Ma age proposed for CTA-27 is incorrect, and that there are currently no compelling Eocene records of either rodents or primates in the known fossil record of South America. These analyses produced mean age estimates for Santa Rosa that closely approximate the maximum 29.6 ± 0.08 Ma composite date provided by detrital zircons, but predict that CTA-27 is much younger than currently thought (∼30 Ma).
To further test the Middle Eocene age estimate for CTA-27, we ran multiple Bayesian tip-dating analyses of Caviomorpha, treating the ages of all Paleogene species from Perú as unknown. However, the presence of the same caviomorph species and/or genera at both CTA-27 and at Santa Rosa is now difficult to reconcile with a >11-My age difference. The first appearance datum for Caviomorpha in South America is purported to be the CTA-27 site in the Contamana region of Perú, which is hypothesized to be ∼41 Ma (Middle Eocene) in age. Here, we present detrital zircon dates that indicate that the maximum composite age of Santa Rosa is 29.6 ± 0.08 Ma (Lower Oligocene), although several zircons from Santa Rosa date to the Upper Oligocene. This diverse paleofauna was originally assigned an Eocene age based largely on the stage of evolution of the site’s caviomorph rodents and marsupials. The Santa Rosa fossil locality in eastern Perú produced the first Paleogene vertebrate fauna from the Amazon Basin, including the oldest known monkeys from South America.
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