Animals in the past

Have you ever watched a jurasic park movie?
The film is about the revival of ancient animals in the present. The animals can be recreated with the help of very modern technology. The animals that exist in the movie jurasic park is indeed never lived in the past.

From where did the filmmakers know the shape, size, place of living, to the food of these early animals? You can see the existence of the animals of the past from the fossils left by these animals.