Triassic Period

The Triassic Period represents a period of time 250 – 200 million years ago.
During this period the world was very different, consisting of one large super-continent known as Pangaea. England lay near the equator where hot desert conditions prevailed. Mountains in the West were eroded by huge rivers that flowed north, depositing pebbles and sands across southern England that later solidified to form the Aylesbeare Mudstones, Otter Sandstone and Budleigh Salterton Pebble Beds. The desert lakes that formed around the rivers were subject to intense evaporation, creating a concentrate of minerals and salts that remain in the cliffs today as gypsum deposits.

Triassic life largely consisted of survivors from a mass extinction at the end of the previous Period, the Permian. These first dinosaurs evolved and went on to dominate life during the following Jurassic and Cretaceous Periods that together with the Triassic, form the Mesozoic Era. One of the most numerous of creatures were Beaked Lizards, the Rynchosaurs, which grazed on the vegetation growing alongside the rivers.

By the end of the Triassic Period many early living groups of four legged animals had developed, including creatures such as frogs, turtles and crocodiles.
On land some reptiles evolved to become warm blooded, creating the first mammals.

The Jurassic Period

The Jurassic Period represents a period of time 200 – 140 million years ago.
During this period the super-continent of Pangaea started to break up to form separate, smaller continents. England gradually drifted North with the Atlantic Ocean widening as the Americas drifted away from Europe. The earth was warm and as there was very little ice at the polar caps the sea levels were high and the desert landscape of southern England was submerged beneath a tropical sea.

The sea levels fluctuated in a series of cycles during the Jurassic Period. Clays were deposited on the deepest ocean floors, followed by Sandstones and finally shallow water Limestones. The sea was shallowest during the Mid-Jurassic, creating and environment of islands surrounded by shallow shoals, similar to the Caribbean today. The sea levels rose again before becoming shallow enough in the Late Jurassic for trees to grow on exposed areas of land. These tropical forests grew in swampy conditions and their remains can be seen in the layer of Jurassic Sediment, Dirt Bed at Lulworth and Portland.

Jurassic life was dominated by the sea, with ammonites, belemnites and fish being hunted by predatory air breathing marine reptiles such as Ichthyosaurs and Plesiosaurs. Above the waves soared flying reptiles. Dimorphodon hunted by using the sharp teeth on the bottom part of its beak to scoop up prey from the sea.

The Cretaceous Period

The Cretaceous Period represents a period of time 140 – 65 million years ago.
During this period the gulf between America and Europe continued to grow as the continents drift further apart, opening up the expanse of the Atlantic Ocean.
The Early Cretaceous Period marked a time when shallow lagoons and slat flats similar to the sabkhas found in the Gulf of Arabia today.
Later lush swamps developed, providing a hunting ground for dinosaurs, but all that changed in the Mid-Cretaceous when tectonic plate movements under south-west England tilted the rocks to the east, and a vast sea developed over the area. The water was clear and warm allowing plankton to flourish. Over millions of years their tiny skeletons sank to the ocean floor and solidified to form Chalk.

Cretaceous life within southern England is mainly represented by marine creatures such as fish, sea urchins, crocodile and turtle. Although the seas also contained air breathing marine reptiles like the Plesiosaur, and Pterosaurs flew overhead in the skies, remains of these are rarely found within the World Heritage Site. But dinosaur footprints from the Early Cretaceous have been found, showing where they crossed shallow lagoons between flooded sections of land.