Mammals 'exploded' in size after dinosaurs' demise - The size of mammals "exploded" after the sudden demise of the dinosaurs 65 million years ago, say biologists.
They did so because there were no other animals around to eat the plants, according to research published in the journal Science.
The biggest mammals jumped in size 1,000-fold from a maximum of about 22lb (10kg) at the time of the dinosaurs to some 17 tons (17 tonnes) within 25 million years.
Dr. Jessica Theodor, associate professor of biology at Calgary University in Canada, said: "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."
She added: "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. That's really rapid evolution."
She and colleagues came to their conclusions after documenting maximum size for major land mammal groups on each continent.
The largest mammal ever to have walked the earth was a hornless rhinoceros-like herbivore that stood about 18ft (5.5m) high at the shoulder, which lived in Eurasia almost 34 million years ago.
However, even they are dwarfed by today's blue whales, mammals that can weight more than 200 tons. ( telegraph )
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