The Incredible Shrinking Kangaroo
Scientists studying the bones of long-dead kangaroos and other marsupials in Australia have discovered an astonishing fact: Nearly all of the larger animals have shrunk. Over the past 40,000 years, kangaroo teeth have gradually shortened. The teeth--and presumably the body sizes--of kangaroos now hopping through the bush are 30 percent smaller than those of their ancestors.
It's as if for thousands of years, something has been removing the biggest animals of each species and leaving ever-smaller ones to reproduce. One of Australia's best-known paleontologists, Tim Flannery of the Australian Museum in Sydney, contends he knows what is causing the phenomenon. "I think it's due to human hunting pressure," Flannery says. "There's no doubt that the shrinkage has occurred. The larger they were, the more they have shrunk."
Some time after aborigines first arrived in Australia--at least 40,000 and perhaps as long as 140,000 years ago--some 50 species of large mammals disappeared. Meanwhile, kangaroos and other surviving marsupials began shrinking. To get the most meat for their hunting efforts, aboriginal hunters likely took the biggest animals.
Flannery has dubbed Australia's surviving marsupials "time dwarfs," and he thinks modern hunters might even now be perpetuating the ancient trend.