The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443 million years ago, to the beginning of the Devonian period. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by 5-10 million years. The base of the Silurian is set at a major extinction event when 60% of marine species were wiped out.

Silurian period sees the appearance of the first plants on land. Algae is in abundance in the seas, as well as marine invertebrates.

Coral reefs made their first appearance during this time, built by extinct tabulate (an extinct form of coral) and rugose corals (are an extinct order of coral). The first bony fish, the Osteichthyes (superclass of fish) appeared, represented by the Acanthodians (sometimes called spiny sharks) covered with bony scales; fishes reached considerable diversity and developed movable jaws, adapted from the supports of the front two or three gill arches.

A diverse fauna of Eurypterus (Sea Scorpions) - some of them several metres in length, prowled the shallow Silurian seas of North America; many of their fossils have been found in New York State. Brachiopods (also known as lamp shells), bryozoa (tiny colonial animals), molluscs (these range from tiny snails, clams, and abalone to squid, cuttlefish and the octopus), and trilobites (Trilobites are extinct arthropods) were abundant and diverse.

Myriapods became the first proper terrestrial animals. The terrestrial ecosystems included the first multicellular terrestrial animals that have been identified, relatives of modern spiders and millipedes whose fossils were discovered in the 1990s.

Myriapods - four groups of arthropod - the centipedes, millipedes, pauropods, and symphylans - share a number of common features such as a similar body plan consisting of a head followed by an elongate trunk with many legs.