Did those meat-eating dinosaurs become so by accident?

Question

What I mean is, in the beginning, they wouldn't have been meat eaters, would they?

Answer 1

Meat-eaters in general would have evolved long before dinosaurs ever walked the earth.  Some dinosaurs would have been meat eaters from the start as they evolved from other meat eating critters, and some would have started as plant eaters who evolved to be meat eaters through environmental pressure.

I don't know where meat-eating originally started but I'm guessing it came from scavengers/decomposers.

Answer 2

I think they were just born with that instinct

Answer 3

out of hunger

Answer 4

Carnivorous behaviour probably originates in animals that are either omnivorous, or are not specialised for any particular type of food. Take chimpanzees, for example. They mainly eat plants, but often supplement their diets with meat. It doesn't take a wild stretch of imagination to see a population of chimpanzees, under environmental pressure, eating nothing but meat. Under those circumstances, the chimpanzees that are better suited to eating meat would flourish and multiply. The others would dwindle and die.

I can imagine similar environmental pressures led to the evolution of carnivorous dinosaurs.