Dinosaurs Ruled for 165 Million Years, Yet Only About 700 Species Are Known

Dinosaurs ruled Earth for about 165 million years, yet scientists have identified only about 700 extinct species, and the fossil record is far from complete.

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Dinosaurs were around for roughly 165 million years before non-avian dinosaurs disappeared about 66 million years ago. Yet only around 700 extinct dinosaur species have been discovered and named. That number is not a complete count of all the dinosaurs that ever lived. The fossil record is naturally patchy, because an animal has to die in the right setting, become buried, survive geological change, and eventually be exposed where people can find it. Some kinds of rock and some periods of Earth history are also much better represented at the surface than others. Scientists therefore expect that many dinosaur species left no fossils that can be found today. Modern estimates also change as new fossils are discovered and as researchers decide whether previously named fossils really represent separate species. This makes the known 700 species a record of what has been found and recognized so far, rather than a final count of dinosaur diversity.

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