Rapid body size decline in Alaskan Pleistocene horses before extinction

• Published in: Nature Vol. 426; no. 6963; pp. 169 - 171
• Main Author: Dale Guthrie, R
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 13-11-2003; Nature Publishing Group
• Subjects: Alaska; Animals; Biodiversity; Body Constitution; Body size; Carbon dating; Climate; Climate change; Earth sciences; Earth, ocean, space; Endangered & extinct species; Exact sciences and technology; Fossils; Geographical distribution; Holocene; Horses; Horses - anatomy & histology; Horses - physiology; Human Activities; Mammals; Models, Biological; Paleontology; Pleistocene; Predatory Behavior; Radiocarbon dating; Time Factors; Vertebrate paleontology; United States; Alaska; United States > US; Chordata; Quaternary; Equidae; Eutheria; Hippomorpha; North America; upper Pleistocene; Vertebrata; C-14; biologic evolution; extinction; Mammalia; climate modification; Theria; dating; Perissodactyla; Cenozoic; Phanerozoic; Pleistocene; Tetrapoda; dimensions
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature02098

About 70% of North American large mammal species were lost at the end of the Pleistocene epoch. The causes of this extinction-the role of humans versus that of climate-have been the focus of much controversy. Horses have figured centrally in that debate, because equid species dominated North American late Pleistocene faunas in terms of abundance, geographical distribution, and species variety, yet none survived into the Holocene epoch. The timing of these equid regional extinctions and accompanying evolutionary changes are poorly known. In an attempt to document better the decline and demise of two Alaskan Pleistocene equids, I selected a large number of fossils from the latest Pleistocene for radiocarbon dating. Here I show that horses underwent a rapid decline in body size before extinction, and I propose that the size decline and subsequent regional extinction at 12,500 radiocarbon years before present are best attributed to a coincident climatic/vegetational shift. The present data do not support human overkill and several other proposed extinction causes, and also show that large mammal species responded somewhat individualistically to climate changes at the end of the Pleistocene.