Abstract

Late Quaternary Megafaunal Extinctions in South America:

Chronology, environmental changes and human impacts at regional scales

by

Natalia Andrea Villavicencio Figueroa

Doctor of Philosophy in Integrative Biology

University of California, Berkeley

Professor Anthony D. Barnosky, Chair

By the end of the Pleistocene the world lost most of its species of large mammals in what is known as the Late Quaternary Extinction event. The debate about the possible causes of extinction revolves around the impacts caused by modern humans migrating around the world, the climate changes associated with the glacial-interglacial transition happening at the time of the extinction and combinations of both. South America was one of the most severely impacted continents losing over eighty percent of all its species of mammals with an average body weight exceeding forty four kilograms. In this continent, human arrival and late glacial climate changes were not far separated in time and previous analyses have shown interesting regional differences in the timing and pattern of extinction inside the continent.

A critical step to understand the extinction event at regional and continental scales is the development of robust radiocarbon-based chronologies of megafaunal presence and extinction which can be compared to the timing of arrival of humans and of environmental changes. This dissertation addresses the Late Quaternary Extinction event debate in South America by developing analyses of the extinction at regional scales, and improving the chronology of extinction for some regions of the continent by radiocarbon dating bone specimens of extinct megafauna following high standard procedures for radiocarbon dating bone.

Chapter one consists of a bestiary of the Pleistocene megafauna of South America. It describes each species and genera of megafauna giving details about their geographic distribution and general paleoecology. A final synthesis of the information shows regional differences in megafaunal diversity that can be explained by sampling bias. While regional differences in diversity persist in time when the Late Pleistocene is compared to the present, regions are today more similar than in the past, which suggests that a considerable amount of regional megafaunal endemism was lost during the Late Quaternary Extinction event.

Chapter two is a regional scale analysis of the megafaunal extinction in Southern Patagonia. Using published information it was possible to build a robust chronology of magefaunal extinction and human arrival into this region. When comparing these chronologies with the timing of major environmental changes it seems that a combination of human impacts and vegetation changes were behind most of the megafaunal extinctions.

Chapter three describes the process of radiocarbon dating bone specimens of extinct megafauna following high-standard procedures of bone treatment. It was possible to produce fifty four radiocarbon dates from which twenty seven are reported in this chapter. The new data improves the chronology of extinction for some areas, particularly for the Central Andes and for Southern Chile. These new chronologies of extinction showed that in the Central Andes extinct megafauna disappears at the time of human arrival while the megafauna present in Southern Chile coexisted with humans for thousands of years. In the second case the megafaunal extinction happens at a time of major environmental changes. These differences highlight the need of developing regional analyses, rather than continental-scale analyses, in order to have a more comprehensive understanding of the extinction event in South America.