Ichthyosaurs are a group of Mesozoic marine reptiles that were completely adapted to the aquatic environment. Their hydrodynamic bodies were similar in shape to those of sharks and dolphins. They had an inverted heterocercal tail with the spine extending to the lower part of the caudal fin. Most ichthyosaurs were predators, feeding on fish, molluscs (mainly cephalopods), arthropods and marine reptiles, including smaller ichthyosaurs. Fully adapted to marine life, ichthyosaurs never reached the mainland and were viviparous, giving birth to live offspring that developed in the mother’s body, as evidenced by the fossilised female ichthyosaurs with their newborn babies or with embryos still in their abdomens. The average length of ichthyosaurs was 2 metres, but much larger specimens are known, such as the Lower Jurassic Temnodontosaurus sp. from England exhibited in the museum.