Origin and Extinction of Megafauna

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• published: 28 Apr 2014
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The term megafauna refers to an array of animals whose ancestors and descendants had significantly smaller body masses. Widely accepted thresholds are animals weighing 40kg (88 pounds) 100kg (220 pounds) or more. By this definition, today's elephants and rhinoceroses are considered modern megafauna. Commonly, however, the term megafauna refers to animals from the Pleistocene epoch, ranging from roughly 2.6 million years ago to 11,700 years ago. A few examples of Pleistocene megafauna include giant beavers, cave bears, dire wolves, wooly rhinos, Megaloceros, giant sloth, Diprotodon, Smilodon, Mastodon, Procoptodon, Glyptodont, Megladon, and the Moa. Many have hypothesized as to the cause of these large animals, and climate has often been attributed as a major contributing factor. According to Bergmann's Rule, there is a correlation between the body size of mammals and the climate in which that mammal lives. Larger body mass allows mammals to retain more body heat, which would correspond to larger animals living around the poles, in cooler climates, and smaller animals living directly along the equator. There have also been correlations between precipitation values and seasonality, which also supports the idea that larger animals were able to grow in areas of lower precipitation and with higher seasonality. Animals in areas of lower precipitation would have to adapt to store water for longer periods of time and through droughts that may occur due to high seasonality, and would therefore need to have larger body masses. While the origination of megafauna is still commonly questioned, four consistent extinction theories have been developed. The Overkill Hypothesis is the idea that widespread migration of humans led to the overhunting of many megafauna, leading to kinks in the ecosystem and ultimately the extinction of many megafauna. Other theories includes massive climate change, the spread of disease from one mammal to another, and a possible impact.