The Independent: A worldwide study of fossilized mammals has demonstrated beyond any doubt that it was the extinction of the dinosaur some 65 millions years ago that was the key trigger leading to the explosive growth of the warm-blooded mammals...
The study found that for the first 40 million years or so of their existence, the mammals were mostly small, shrew-like creatures that lived in a narrow range of habitats. However, after the dinosaur disappeared, larger creatures capable of exploiting a wide variety of ecological niches, from leaf-eating giant sloths to tundra-munching mammoths.
'Basically, the dinosaur 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 a herbivore when you're big,' said Jessica Theodor of the University of Calgary in Canada... 'Within 25 million years the system is reset to a new maximum... That's actually a pretty short time frame, geologically speaking. That's really rapid evolution.'...
The study in the journal Science found that many different types of mammals grew into gigantic forms on different continents... John Gittleman of the University of Georgia, who took part in the study, said... 'Having so many different lineages independently evolve to such similar maximum sizes suggests that there were similar ecological roles to be filled by giant mammals across the globe.'
