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In the Middle Jurassic, Pangaea began to split apart. It began to separate into Laurasia and Gondwana, and the Atlantic Ocean formed. Tectonic activities closed the Paleo-Tethys Ocean. A subduction zone on the coast of western North America continues to create the ancestral Rocky Mountains.
Life of the epoch
The cynodont therapsids flourished with the dinosaurs, but they were only shrew-sized. None grew larger than a badger. One group of cynodonts, the Trithelodonts were becoming rare and eventually became extinct at the end of this epoch. The Tritylodonts were still common, though. In this epoch "true" mammals evolved from a group of cynodonts.
- The Tethys Ocean: an ancient seaway approximately in the position of the Mediterranean.
- Formed by an oceanic plate sliding under a continental plate.
- "Cetiosaurus." In: Dodson, Peter et al. The Age of Dinosaurs. Publications International, p65. ISBN 0-7853-0443-6.
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