Many people mistakenly believe that mammals “succeeded” the dinosaurs 65 million years ago, appearing suddenly on the scene to occupy the ecological niches rendered vacant by theK/T Extinction.
The fact is, though, that early mammals lived alongside dinosaurs (usually high up in trees, out of harm's way) for a large part of the Mesozoic Era. Most of these early furballs were about the size of mice, but a few (like the dinosaur-eating Repenomamus) grew to respectable sizes of 50 pounds or so, tiny by T. Rex standards but huge for an ancient mammal.
