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Megafauna refers to large animals, with varying weight thresholds. It includes extinct Pleistocene species, such as mammoths and saber-toothed tigers, and any largest animal in Earth’s history. The cause of their extinction is unknown, but human hunting and competition is a factor.
Megafauna is an informal term for large animals, especially very large animals such as elephants and hippos. The threshold for an animal to be “megafauna” is variously defined as 44 kg (97 lbs), 100 kg (220 lbs), and 250 kg (551 lbs). Megafauna is sometimes divided into three categories: “small” (250-500 kg, 551-1102 lb), medium (500-1,000 kg, 1102-2204 lb), and large (over 1,000 kg/2204 lb). Intuitively, it appears that megafauna includes animals significantly larger than humans, including cows and horses.
The term megafauna is especially popular to describe the many large Pleistocene species that went extinct as a result of hunting or competition with humans: dire wolves, short-faced bears, mammoths, moas, saber-toothed tigers, etc. May refer to Pleistocene (1.8 million to 10,000 years BP) animals that went extinct in the last two million years or so: ground sloths, megalodon sharks, “terror birds”, etc., or more generally, any largest animal in the history of the Earth.
The Pleistocene was a particularly distinctive period for megafauna as it contained many animals that resemble, are closely related to, or are actually larger versions of the species that survived today. For example, although the mammoth was not particularly larger than an elephant, it was closely related to it. The dire wolf was a larger version of today’s gray wolf. The cave bear was a larger version of other living bears. There were giant eagles in New Zealand, 10-foot carnivorous birds in South America, even dog-sized rodents on Mediterranean islands, and cow-sized hamsters in Uruguay!
About 2 million years ago, there was a massive die-off in megafauna worldwide, followed by another surge when humans spread across the globe just 100,000 years ago. This latter extinction drive is obviously caused by human hunting and competition, but the source of the former is unknown. Ice age is sometimes singled out as the culprit, but these species have survived many ice age cycles before then without incident. Interspecies pandemics have been considered, but the extinction model is too long and complex to support this hypothesis. More research is needed to determine why much of the Late Pleistocene megafauna has disappeared.
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