Protoceratops

Protoceratops seems to have been so common in the Mongolian desert, that some paleontologists have nick-named it 'the sheep of the Cretaceous'.
Protoceratops was about the size of a large pig (400kg). Its stout frame would have provided it some protection against the sun and against water loss in the heat of the desert. It would have needed it, as we know that Protoceratops was living amongst the hot and dry giant sand dunes of the ancient Mongolian desert.
As a herbivore, Protoceratops would have had a hard time finding fresh leaves and shoots in the arid desert. So it may have preferred to feed on buried roots and tubers, using its sharp beak to slice through their toughened exterior.
Finding water supplies would also have been a problem. Protoceratops might have got some of its water from plants, but sometimes it would have needed to find a pond or stream to drink from.
Given its small size and abundance, Protoceratops would have sat firmly near the bottom of the food chain. The small dinosaur Velociraptor hunted Protoceratops so it is likely that other, larger dinosaurs, including Tarbosaurus, did too. Protoceratops had very few means of defending itself, though its powerful beak, stocky body and bony head armour would have afforded it some degree of protection.

Aside from predation, Protoceratops would also have faced the daily threat of being buried alive in the treacherous sand dunes of the desert.
Examine the evidence at BBC.co.uk/dinosaurs