The Jurassic World (200-140 million years ago)

Pangaea started to break apart during the Jurassic Period.  The Atlantic Ocean opened to the west of Britain and the Americas drifted away from Europe.  The Earth was relatively warm, sea levels were high and there were hardly any polar ice caps.  The Jurassic rocks of Dorset and East Devon record marine conditions during the Jurassic Period - conditions that fluctuated from relatively deep seas to coastal swamps.  Sea levels rose and fell in a series of cycles, depositing deep water clays, followed by sandstones and finally shallow water limestones.  Seas were shallower in the Middle Jurassic, creating an environment of islands surrounded by shallow shoals, similar to the Caribbean of today.  Seas then deepened again, and finally shallowed towards the end of the Jurassic, creating the conditions for a forest to flourish in a tropical swamp environment.

Jurassic Life

Ammonites were molluscs related to the modern squid, but usually had hard spiral shells.  Many species of ammonite fossils are found on the Dorset and East Devon Coast.  The giant ammonite, comes from Portland. 

The expansion of shallow seas encouraged an explosion of life in the Jurassic, and many animals evolved rapidly in order to take advantage of the new habitats available.  Reptiles were the ‘top predators' on land, sea and in the air.  Dinosaurs walked the Earth and the dominant carnivores in the seas included ichthyosaurs, plesiosaurs and crocodiles.  This reconstruction shows the seas of the Jurassic coast, around 195 million years ago, and is drawn from local fossil finds.