Dinosaur

Dinosaurs were a diverse group of reptiles that first appeared in the Triassic Period and dominated terrestrial ecosystems for much of the Mesozoic Era.

Dinosaurs were a diverse group of reptiles that first appeared in the Triassic Period and dominated terrestrial ecosystems for much of the Mesozoic Era. Non-avian dinosaurs went extinct about 66 million years ago, while birds are their living descendants.

Evolution and age

Dinosaurs first appeared in the Triassic Period and became a dominant group during the Mesozoic Era. Fossil evidence shows they existed for at least 230 million years before the end-Cretaceous extinction.

Extinction

Non-avian dinosaurs disappeared about 66 million years ago at the Cretaceous–Paleogene boundary. The leading explanation is a large asteroid impact, with possible added effects from volcanism and long-term climate change.

Diversity and diet

Dinosaurs occupied many ecological roles and included herbivores, carnivores, and likely omnivores. Their body sizes ranged from very small species to the largest land animals known.

Birds and dinosaurs

Modern birds are dinosaurs in the evolutionary sense, belonging to the only dinosaur lineage that survived the mass extinction at the end of the Cretaceous.