Discoveries of fossil reptiles in the sea cliffs of south-western England helped to consolidate ideas of 'deep time' and extinction by revealing ancient worlds whose unfamiliar and bizarre inhabitants had no living counterparts. Many of these fossils were from the Lower and Upper Lias Groups, suites of rocks laid down in the shallow seas that covered much of southern England during the Early Jurassic period (around 201-174 million years ago). Sir Richard Owen (1804-92) was one of several anatomists who provided extensive descriptions of these animals. His monograph on the Liassic Reptilia (published in three parts in 1861-81) includes the first, and so far only, detailed description of the early armoured dinosaur Scelidosaurus (the first dinosaur known from an almost complete skeleton), an important account of Dimorphodon (the first flying reptile named from the United Kingdom), and critical information on two marine reptile groups, the plesiosaurs and ichthyosaurs.