Summary

This chapter explored the origins of the first dinosaurs, their rapid diversification, and the reasons for their sudden prosperity in the fossil record.

1. The earliest known dinosaurs are found in fossil deposits from the early part of the Late Triassic Epoch, about 228 million years ago.

2. Dinosaurs were already diverse and widespread by the Late Triassic, suggesting that their true origins date back to the Middle Triassic.

3. The small "proto-archosaur" Euparkeria dates from the borderline between the Early and Middle Triassic Epochs and appears to have been closely related to the ancestral roots of the dinosaurs.

4. Lagerpeton and Marasuchus, from the Middle Triassic Epoch, were early members of the archosaur group Ornithodira, the same group that includes dinosaurs and pterosaurs.

5. The first dinosaurs included the Staurikosaurus from Brazil and Herrerasaurus and Eoraptor from Argentina. They were predatory saurischian dinosaurs.

6. "Prosauropods" were large, saurischian herbivores from the Late Triassic Epoch, the first wave of important dinosaurian plant eaters.

7. Pisanosaurus is the earliest known ornithischian dinosaur and dates from the early Late Triassic of Argentina.

8. The rapid rise of the dinosaurs in the Late Triassic Epoch was likely due to their opportunistic expansion into ecological niches left vacant by the extinction of other, once-dominant vertebrates.

SECTION TWO:

Dinosaurs of the Early Mesozoic Era k4J

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