Prehistoric Planet - Season 1 (2002)

Meet the animals of the Triassic with a lesson on how to distinguish reptiles from dinosaurs from proto-mammals. Problem is, several critters are somewhere in between.

A diplodocus wanders into a forest where she lays as many as a hundred eggs. Even in the relative safety of the forest the young diplodocus are at risk from various carnivores such as ornitholestes and allosaurus even before they hatch. But in a few year some grow large enough on the lush forest vegetation to join the herd migrating on the prairie.

With the land full of dinosaurs and the sea full of fish some reptiles returned to the sea when they grew to dinosaur proportions to become top predators. Still, life has it's challenges.