Imagine – by an unforeseen temporal slip or a time machine accident – that you find yourself in western Canada, circa 75 million years ago. You might need a few moments to realize that something has gone horribly wrong. Between towering stands of sequoia just sparse enough to let the sun shift on the forest floor, swaths of ferns and small herbs cover the ground, interrupted here and there by mulberry-like shrubs. Watching a dinosaur amble out of the forest onto the carpet of greenery would probably be your first clue that something had gone awfully wrong.

By virtue of their numbers, chances are that you’d spot a megaherbivore first. (Or at least you’d hope – out in the open, you’d