Giants of the ice age, including mastodons and woolly mammoths, may have gone extinct due to the combined effects of ice age and human hunters, a new study reveals. Previously, many paleontologists had attributed the loss of these species to the rise of early human beings, while others placed the blame with the end of the ice age.

Climate change in the form of warmer, drier conditions could have combined with significant hunting by our distant ancestors to create a perfect storm, driving these ice age giants to extinction. Among the species lost at this time were massive beasts such as the large ground sloth, giant jaguars and saber-toothed cats. Megafauna are considered to be animals which weigh more than 100 pounds when fully grown. Bears of this era were 10 times as large as grizzlies seen in the modern age.

Traditional thinking held that humans first entered the New World, en masse, just as megafauna began to disappear 13,000 years ago. However, new evidence suggests that our distant ancestors arrived in the Western Hemisphere 2,000 years before that time. Despite a plethora of fossils showing signs of hunting and butchering, it now appears ancient humans did not, on their own, drive these animals to extinction. Researchers believe climate change may have weakened animal populations, sending their numbers into oblivion. This realization still leaves several questions unanswered.

"It's a really nice example of a key study where humans and climate seem to be intersecting in some way. It's clear that without human impacts, there wouldn't have been an extinction. Is it human populations growing rapidly once it warms, and hunting? Or is it humans disrupting the way the animals migrate and the way they use habitats?" Paul Koch, a paleontologist and geoscientist from the University of California, Santa Cruz, asked.

Mitochondrial DNA from 89 samples of bones and teeth from ice age giants was compared to temperature records measured from examination of ice cores. Radiocarbon dating was carried out on 71 fossil remnants, also recovered in Patagonia. This study showed that a vast number of animals in the region died at nearly the same time - 12,300 years ago.

"[This is] the first time we've had any idea of the timing of the South American extinctions," said Alan Cooper of the Australian Centre for Ancient DNA at the University of Adelaide in Australia.

Human beings colonized two continents - North and South America - in just 1,500 years. This provides paleontologists with a unique history of human impacts on the environment.

Photo: Rob Pongsajapan | Flickr 

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