Did it occur to anyone?

They show the scene to be rocky and barren. very little vegetation. Yet they show a Brontosaurous with a full belly. That animal could out eat an elephant, who can chomp down 1000 pounds of leafy food in one day. Just what would the Herbivores have to eat? And if the Herbys had nothing to eat, what would the Carnys have to eat. By the way, what did the tribe do with the T-rex Tumak killed? Did they use the hide, eat the flesh, use the teeth as weapons, aquire a taste for dino flesh? As I remember, when the movie came out, it pushed Miss Welch in fur skins more than anything else. In the original it was the concept that was pushed not the personalities.