Evolution of the Dinosaurs

Dinosaur Ancestors

How did life evolve after the early one-celled organisms?

Over hundreds of millions of years after the evolution of single-celled organisms, the oceans abounded with a huge variety of life. The first soft-bodied animals, such as worms and jellyfish, evolved toward the close of the Pre-Cambrian (also seen as Precambrian) era roughly 600 million years ago; the first animals with hard parts, such as shelled mollusks, evolved during the first period after the Pre-Cambrian known as the Cambrian period of the Paleozoic era.


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