Washington, Nov 26 (ANI): The extinction of dinosaurs 65 million years ago resulted in the size of mammals increasing - by about a thousand times bigger than they had been.

Basically, the dinosaurs disappear and all of a sudden there is nobody else eating the vegetation.
That's an open food source and mammals start going for it, and it's more efficient to be an herbivore when you're big, said Dr. Jessica Theodor, associate professor in the Department of Biological Sciences at the University of Calgary.

You lose dinosaurs 65 million years ago, and within 25 million years the system is reset to a new maximum for the animals that are there in terms of body size. That's actually a pretty short time frame, geologically speaking, she added.

That's really rapid evolution.

Researchers collected data on the maximum size for major groups of land mammals on each continent, including Perissodactyla, odd-toed ungulates such as horses and rhinos; Proboscidea, which includes elephants, mammoth and mastodon; Xenarthra, the anteaters, tree sloths, and armadillos; as well as a number of other extinct groups.

The results give clues as to what sets the limits on mammal size on land; the amount of space available to each animal and the climate they live in.

The colder the climate, the bigger the mammals seem to get, as bigger animals conserve heat better. It also shows that no one group of mammals dominates the largest size class - the absolute largest mammal belongs to different groups over time and space.

The study is published in Science. (ANI)