The Triassic Period represents a period of time
250 – 200 million
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
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
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
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
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
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.
All pictures on this page are copyrighted
to professional illustrator, John Sibbick