Middle Jurassic
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The Middle Jurassic, called the Dogger in the European system of classification, is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago.
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[edit] Paleogeography
Pangaea began to separate into Laurasia and Gondwana and the Atlantic Ocean formed. Tectonic activities are active on eastern Laurasia as the Cimmerian plate continues to collide with Laurasia's southern coast, completely closing the Paleo-Tethys Ocean. A subduction zone on the coast of western North America continues to create the Ancestral Rocky Mountains.
[edit] Life
[edit] Marine life
During this time, marine life (including ammonites and bivalves) flourished. Ichthyosaurs, although common, are reduced in diversity; while the top marine predators, the pliosaurs, grew to the size of killer whales and larger (e.g. Pliosaurus, Liopleurodon). Plesiosaurs became common at this time, and metriorhynchid crocodilians first appear.
[edit] Terrestrial life
New types of dinosaurs evolved on land (including Cetiosaurs, brachiosaurs, megalosaurs and hypsilophodonts).
Descendants of the therapsids, the cynodonts were still flourishing along with the dinosaurs even though they were shrew-sized; none exceeded the size of a badger. A group of cynodonts, the Trithelodonts were becoming rare and eventually became extinct at the end of this epoch. The Tritylodonts were still common though. Mammaliformes, who evolved from a group of cynodonts were also rare and less significant at this time. It was at this epoch that the "true" mammals evolved.
[edit] Flora
Conifers were dominant in the Middle Jurassic. Other plants, such as ginkgoes, cycads, and ferns were also common.
| Jurassic period | ||
|---|---|---|
| Lower/Early Jurassic | Middle Jurassic | Upper/Late Jurassic |
| Hettangian | Sinemurian Pliensbachian | Toarcian |
Aalenian | Bajocian Bathonian | Callovian |
Oxfordian | Kimmeridgian Tithonian |
