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ALL ABOUT DINOSAURS!
What is a Dinosaur? Dino Info Pages Dinosaur Coloring Print-outs Name That Dino Biggest, Smallest, Oldest,... Evolution of Dinosaurs Dinos and Birds Dino Myths

Eoraptor
Dinosaur Evolution

Dinosaurs evolved from other reptiles (socket-toothed archosaurs) during the Triassic period, over 230 million years ago. Dinosaurs evolved soon after the Permian extinction, which was the biggest mass extinction that ever occured on Earth. During this time (the Triassic period), the mammals also evolved.

Dinosaur timeline

Thecodonts: Crocodile-like Archosaurs:
Chasmatosaurus
Chasmatosaurus, a crocodile-like, meat-eater (a thecodont) from the Triassic period.
Thecodonts may have been ancestors of the dinosaurs. Thecodonts (like Chasmatosaurus) were socket-toothed reptiles that were the ancestors of dinosaurs, birds, pterosaurs, and crocodilians. These archosauriforms were low-slung, meat-eating quadrupeds had long jaws and a long tail (they looked a lot like crocodiles).

Reptilia cladogram

This is a cladogram of the clade Reptilia (reptiles), tracing the ancestry of these groups.


The Earliest Dinosaurs:
The first dinosaurs were small and lightly built, mostly about 10-15 feet long (3 to 4.5 m). They were bipedal carnivores or omnivores, and probably very agile and fast.

The world's oldest-known dinosaurs have been found on Madagascar, an island off the coast of SE Africa. These dinosaur fossils date from about 230 million years ago during the Triassic period.

EoraptorUntil recently, the earliest-known dinosaur was Eoraptor lunensis (meaning"dawn raptor") which lived about 228 million years ago. It was a small, primitive theropod (a bipedal meat-eater) about 3 feet (1 m) long. It lived in what is now Argentina, South America (fossils were found at the Ischigualasto Formation).


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