Eurypterdis Looking like a cross between a lobster and a giant scorpion, eurypterdis (yu-RIP-ta-rid) were terrors of the ancient Paleozoic seas. These predators could reach sizes as big as a human and used giant pincers to grab and crush victims. Among the largest arthropods that ever lived, eurypterdis were probably the first sea creatures to venture onto land. Scientists have founf more than 300 species of this ancient creature. Eurypterdis had two sets of gills, one for breathing underwater and another to help them breath air. These ancient creatures could crawl onto beaches and riverbanks and hunt for prey there as well as in the water.

Family: Eurypteracea

Size: 1 in. to 6.5 ft

Where: Most fossils have been found in North America and Europe

When: From 510-245 mya, in the Paleozoic era