The elephant, the rhino and the hippo are the biggest terrestrial mammals on earth.
They differ from one another and do not belong to the same family yet they share one trait: these vegetarian giants are non ruminants and have appeared before the ruminants. The latter have developed very specific ecosystems while the former have survived adopting a generalist behavior, i.e. using a large spectrum of habitats and vegetation.
That strategy happens to be the only sustainable one to cover their gigantic feeding needs.