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Reptiles
Reptiles developed from one branch of the amphibians in Permian times. The major change was that they laid eggs that were protected by a shell. This allowed them to live entirely on land.
The early Permian and Triassic reptiles were quite small. Some were hunters, others grazed
and browsed the vegetation. But, by the Jurassic and Cretaceous periods, evolutionary trends had produced an extraordinary variety of reptiles, some still small, but others of gigantic size. Thus, this time is called the Age of the Reptiles.
The dinosaurs (meaning terrible lizards) are a very varied group and include the largest land- based hunters of all times. The most massive of these hunters, Tyrannosaurus rex, weighed up to 8 tonnes and was over 12 metres long. The plant eaters were even bigger, the swamp-dwelling Diplodocus weighed up to 50 tonnes and could be 25 metres long.
Swimming reptiles included the ichthyosaurs, whose streamlined bodies made them look like porpoises, except that they carried fearful rows
of teeth in their jaws. Another marine group was the plesiosaurs, adapted with long necks and paddle-like feet. There were also flying reptiles, the pterosaurs, with membranes between their limbs to act as wings.
(Above and below) Vertebrae from dinosaurs, showing the dished discs with knobbly protrusions.
(Above) A complete skeleton of
an ichthyosaur (Ichthyosaurus quadriscissus). Great skill was needed to pare away the sediment that surrounded it.