Silurian eurypterid fossils, 19th-century illlustration. Eurypterids (sea scorpions) were arthropods that existed from the Ordovician to the Permian, from around 470 to 252 million years ago. They were among the first large predators to evolve in the Earth's oceans. They could reach sizes of up to 2.5 metres, but most were under 20 centimetres long. These specimens dates from the Silurian. At top is Pterygotus bilobus. At bottom is an upper (left) and lower (right) view of Eurypterus remipes. This artwork was published in an 1864 edition of 'The World Before the Deluge' by Louis Figuier.