Dog Extinctions Show Why Bigger Isn't Better

Link : http://story.news.yahoo.com/news?tmpl=story&cid=583&ncid=583&e=20&u=/nm/20041001/od_nm/science_carnivores_dc


WASHINGTON (Reuters) - Fossils from extinct dogs show why bigger is not better -- giant meat-eating animals died out because they relied too heavily on hunting other big animals, scientists reported on Thursday.



Smaller, quicker carnivores could vary their diet more, hunting small rodents and mixing in berries, roots and other food sources, said Blaire van Valkenburgh and colleagues at the University of California Los Angeles.


But once a carnivore reached a certain size, it would spend more energy hunting than it would get from small prey, and had to rely on big game, they report in this week's issue of the journal Science. And that made them less adaptable.


"Among living meat eaters, almost all species larger than about 21 kg (45 pounds) prey on species as large or larger than themselves, whereas smaller carnivores can subsist on much smaller prey (such as invertebrates and rodents)," the researchers wrote.


This could help explain the mass extinctions of many giant animals called megafauna that dominated and then disappeared from North America over the last 50 million years.


Van Valkenburgh's team studied a range of fossils from extinct canids, a grouping or "clade" of animals that includes wolves, foxes, coyotes and dogs.


Canids that fed on large prey tended to have deeper jaws, long shearing teeth and few molars for grinding food. They ranged in size from that of a small fox to about the size of a very large wolf.


As they got bigger, their teeth adapted more and more for ripping flesh and crushing bone and became less suited for chewing other foods. Some species developed massive jaws.


"As mean body size increased, species evolved into specialized hypercarnivores," Van Valkenburgh's team wrote.


"Did this result in an increased susceptibility to extinction? Such 'hypercarnivores' seem to have disappeared, based on fossil evidence, more quickly than other animal species."


None of the hypercarnivores lasted for more than six million years, while more omnivorous species endured for as long as 11 million years, they found.