Middle Jurassic

The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 161.5 million years ago. During this time, Earth was a very different place compared to today, with a warm climate and high sea levels that covered many land areas.

Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare. However, important geological formations containing fossils of these animals have been found in many parts of the world. Examples include the Forest Marble Formation in England, the Kilmaluag Formation in Scotland, the Calcaire de Caen of France, the Daohugou Beds in China, the Itat Formation in Russia, the Tiourarén Formation of Niger, and the Isalo III Formation of western Madagascar.

Rocks from the Middle Jurassic were once called Dogger or Brown Jurassic in Europe until the 1980s. Studying these rocks and fossils helps scientists understand how life evolved and how Earth’s landscapes changed millions of years ago.

Paleogeography

During the Middle Jurassic Epoch, Pangaea started to break apart into Laurasia and Gondwana, and the Atlantic Ocean began to form. Eastern Laurasia was very active as the Cimmerian plate bumped into Laurasia's southern edge, closing the Paleo-Tethys Ocean completely.

A subduction zone along the coast of western North America kept building up the Ancestral Rocky Mountains. Subduction zones around the edges of Pangaea helped create new seabeds in the early Atlantic Ocean and formed mountain ranges like the Rockies and the Andes along the western coasts of North America, Central America, and South America.

Fauna

The Middle Jurassic was an important time for life on Earth. Many groups, such as dinosaurs and mammals, diversified during this period.

During this time, marine life like ammonites and bivalves flourished. Ichthyosaurs were common but less diverse, while pliosaurs grew very large. Plesiosaurs became more common, and many types of fish swam in the Jurassic seas.

On land, many major groups of dinosaurs appeared, including cetiosaurs, brachiosaurs, megalosaurs, and early ornithopods. Cynodonts, descendants of the therapsids, were still around along with dinosaurs. Though mammals were small, they were diverse and found worldwide.

Flora

Conifers were the most common plants during the Middle Jurassic. Other plants, such as ginkgoes, cycads, and ferns, were also widespread during this time.