Fossil Keichousaurus 'Marine Reptile' Skeleton Triassic Period, 250-200 million years B.P. A complete fossil Keichousaurus hui skeleton in a veined rectangular matrix. 1.28 kg, 25 x 18 cm (9 7/8 x 7 in.). From a Lincolnshire, UK, collection. Keichousaurus was a late-Triassic marine reptile. It was a member of the Pleurosaur family, which became extinct 250 million years ago during the Triassic-Jurassic extinction event. They were specialised fish eaters, and were highly unusual amongst marine reptiles in that they gave birth to live young rather than laying eggs. [No Reserve]