Asphaltic deposits, or "tar pits," present a unique opportunity to investigate the paleobiology and paleoecology of Quaternary mammals due to their tendency to accumulate and preserve remains of numerous taxa, along with associated materials that can aid in paleoenvironmental and chronological analyses. This role is especially important in areas with low preservation potential or incomplete sampling, such as the Neotropics.
Fossil deposits in the asphaltic sediments of the Santa Elena Peninsula in southwestern Ecuador contain some of the largest and best-preserved assemblages of Pleistocene megafaunal remains known from the neotropics, and thus represent an opportunity to greatly expand our knowledge of Pleistocene paleoecology and the extinction of Quaternary megafuana in this region. This dissertation reports data from excavations at Tanque Loma, a new late-Pleistocene locality on the Santa Elena Peninsula that preserves a dense assemblage of megafaunal remains in hydrocarbon-saturated sediments along with microfaunal and paleobotanical material.
Chapter 1 details the results of three years of excavations and associated sedimentological, stratigraphic, systematic, taphonomic, and chronological studies at Tanque Loma. Remains of extinct Pleistocene megafauna are encountered within and up to one meter above a laterally extensive asphalt-saturated sandstone layer along with abundant plant material. Several meters of presumed-Holocene sediments overlying the megafauna-bearing strata are rich in microvertebrate remains including birds, squamates, and rodents, most likely representing raptor assemblages. While over 1,000 megafaunal bones have been identified from the Pleistocene strata at Tanque Loma, more than 85% of these remains pertain to a single species, the giant ground sloth Eremotherium laurellardi . Only five other megafauna taxa have been identified from this site, including Glossotherium tropicorum, Holmesina occidentalis, cf. Notiomastodon platensis, Equus (Amerhippus) santaelenae, and a cervid tentatively assigned to cf. Odocoileus salinae based on body size and geography.
Taken together, the taxonomic composition, taphonomy, geologic context, and sedimentology of Tanque Loma suggest that this site represents a bone bed assemblage in a heavily vegetated, low-energy riparian environment with secondary infiltration of asphalt that helped preserve the bones.
The large accumulation of one taxon, Eremotherium laurillardi, at Tanque Loma offers a unique opportunity to investigate the ecology and behavior of this species. Chapter 2 uses data from this and other paleontological localities as well as modern African ecosystems to investigate the formation of the E. laurillardi assemblage at Tanque Loma and the behavioral ecology and life history of this species.
Chapter 3 endeavors to offer context for the Tanque Loma locality by combining data from these excavations with analyses of other asphaltic vertebrate localities in the region. The most well known asphaltic paleontological locality in tropical South America is the Talara tar seeps in northwest Peru, which has yielded a great diversity of microfossils as well as extinct megafauna. In addition, two other highly productive asphaltic localities have been excavated on the Santa Elena Peninsula -- the La Carolina locality excavated by Robert Hoffstetter in the 1940's, and the Coralito locality excavated by Franz Spillmann in the 1930's and A. Gordon Edmund in the 1960's.
Finally, the radiocarbon dates so far obtained on extinct taxa at Tanque Loma and the other asphaltic localities examined here are consistent with a model positing earlier extinctions of megafauna in tropical South America than of related taxa further south on the continent, although this observed pattern may be an artifact of low sampling in the region. (Abstract shortened by UMI.)
|Advisor:||Barnosky, Anthony D.|
|Commitee:||Brashares, Justin, Kirch, Patrick, Lindberg, David R.|
|School:||University of California, Berkeley|
|School Location:||United States -- California|
|Source:||DAI-B 75/08(E), Dissertation Abstracts International|
|Subjects:||Ecology, Paleontology, Paleoecology|
|Keywords:||Asphaltic deposits, Ecuador, Megafauna, Paleoecology, Quaternary, Taphonomy|
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