Uncovered during the Victorian age, at a time when paleontology itself first began, the Blue Lias of Dorset represents a thriving community of Jurassic marine life. During this period, huge parts of Europe were a chain of isolated islands in a warm, shallow epicontinental sea. Such seaways covered large parts of the Mesozoic globe, often caused when sea levels were at their highest and they flooded the interiors of continents.
The Blue Lias is part of an immense Lias Group composed of shales, marls and clays. The formations stretch across Europe and run from the end of the Triassic to the beginning of the Jurassic. Ranging from 215 to 190 million years old, the Lias covers the Rhaetian Stage of the Triassic, as well as the Sinemurian, Pliensbachian, Hettangian and Toarcian Stages of the earliest Jurassic.
Some of the countries it encompasses include Germany, the UK and parts of the North Sea. The Posidonia Shale of Germany's Holzmaden is a Liassic rock formation and also has many marine fossils. The Blue Lias covers an area made up of parts of England, most famously in Dorset, and South Wales.
Here, quarrying has been done for centuries and it is through this quarrying that many workers and paleontologists have uncovered the fossilized remains of a huge marine ecosystem. Among these fossils are those of coil-shelled ammonites. These mollusks fill the rocks of the Lias in vast numbers, and help to date the site. They are index fossils in this respect and in life they were pelagic drifters that ranged far and wide through the open oceans.
Dimorphodon is possibly the best-known pterosaur from England's Lias beds. It was not the marine hunter that it was once imagined to be. Instead, it used its powerful limbs to hunt overland, searching out small animals to shred apart with its cutting teeth. This early pterosaur, despite being a non-pterodacyloid, was a very adept terrestrial hunter and walker.
Most Liassic dinosaurs are small and primitive. One of the better-known and oft-reconstructed is Scelidosaurus. It was a small and early armored dinosaur that still had just a set of spikes and plates rather than the ornate body armor of his descendants. For its time though, the small Scelidosaurus was a powerful adversary for the little hunters of the low-lying Lias islands. Named and described in 1859 by Richard Owen, Scelidosaurus is the most completely known British dinosaur plus the earliest known find of a complete dinosaur skeleton.
The animal is known from an especially well-preserved and highly complete skeleton that had once drifted out to sea after the animal's death. In life it was around 4 meters long and weighed 270 kilograms. It was a four-footed animal that browsed on low-growing vegetation. Scelidosaurus used its narrow jaws to pick out ferns, horsetails, cycads and conifers at a height of a meter or so off the ground. This excellent preservation allows for a complete look at Scelidosaurus as an animal.
The native predator is not as well-known. Called Sarcosaurus, this small predator is of uncertain classification. It is certainly very primitive, being classified as either a ceratosaur or a coelophysoid. Whatever it was, it may have been a speedy, lightweight hunter that may have tackled prey smaller and lighter than itself. It was once named as a species of Megalosaurus, the same way that many old theropod finds were. Known from a leg bone, Sarcosaurus is estimated to have been 3.5 meters long, a mere nothing among its later kin but a fair size for an animal of its time.
Marine reptiles are very common here and the most common among these are the plesiosaurs. These four-flippered marine hunters had diversified into an incredible variety, with the standard body form having been set down.
This design consisted of a narrow but powerful body, four large flippers, a short tail and a fair-sized neck. The animal's head could be either large or small, and the necks varied in length according to the creature's habits.
Among the first discovered was Plesiosaurus dolichodeirus. This smallish plesiosaur was one of the first ever discovered, courtesy of Mary Anning herself. The animal was named by William Conybeare and Henry De La Beche in 1824. They classified it as an "antediluvian reptile", the same as the other odd Mesozoic reptiles discovered during the Victorian age. Plesiosaurus was once a huge wastebasket taxon that encompassed a great number of other Early Jurassic plesiosaurs/ Only recently was the animal split apart.
