How did the megafauna come about?
Until the dinosaurs were wiped out, the mammals were all rat-sized things. There were a few that were cat-sized, but very, very few. At the time that the dinosaurs get wiped out, most of the mammals get wiped out as well by the asteroid impact, 65 million years ago. After that, just a few species are left. The slate is sort of wiped clean. Animals start diversifying very rapidly because there are lots of open ecological niches. So the mammals start getting larger pretty quickly, and within half a million years you’ve got mammals the size of calves. And by 55 million years ago, you’ve got mammals as big as anything living on earth today, for example the uintatheres. They’re these enormous mammals whose fossils were first found in the Unita Mountains in Utah. Four or 5 tons in body weight, they have three sets of horns on their head, with these long, dagger-like canines, even though they’re herbivores. But were they really megafauna? Well, what we normally talk about as megafauna is real
