The Big Bang of July. The Ordvician(Paleozoic Era) Trilobites

Palaeontologists have identified more than 20,000 different trilobites, an amazingly diverse group of animals. They all lived in the sea: some burrowed in the mud, some crawled on the surface of the seabed and others swam about in open water or inhabited reefs. Although some types of trilobites were blind, most had well developed eyes with very sophisticated lenses that had a great depth of field. Some species had eyes on stalks and these are believed to have buried themselves in the mud, with only their eyes sticking out like periscopes.