By Jason G. Goldman
Around 13,000 years ago North America had a more diverse mammal community than modern-day Africa. There were multiple horse species, camels, llamas and a now-extinct animal called Glyptodon, which looked something like a Volkswagen bug–size armadillo. Smilodon, a saber-toothed cat around the size of today’s African lion, skulked across the grasslands in search of ground sloths and mammoths. Seven-foot-long giant otters chowed down on massive trees. And such massive creatures were not just found in North America. On every continent mammals on average were a lot larger in the late Pleistocene, the geologic epoch spanning from around 2.5 million until about 11,700 years ago.
Scientists have long debated what caused all these large-bodied critters to go extinct while many of their smaller counterparts survived. A team of researchers led by University of New Mexico biologist Felisa Smith analyzed evidence from millions of years’ worth of mammalian extinctions and found that on each continent large mammals started to die out around the same time humans first showed up. They announced their findings Thursday in Science.
If the extinction trend continues apace, modern elephants, rhinos, giraffes, hippos, bison, tigers and many more large mammals will soon disappear as well, as the primary threats from humans have expanded from overhunting, poaching or other types of killing to include indirect processes such as habitat loss and fragmentation. The largest terrestrial mammal 200 years from now could well be the domestic cow, Smith’s research suggests.
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