Trilobites are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last trilobites disappeared in the mass extinction at the end of the Permian about 251.9 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described.
Redlichiida, such as this Paradoxides, may represent the ancestral trilobites.
Fossil Prochuangia from the Cambrian period of Darnjal Formation, Tabas, Iran
Meroperix, from the Silurian of Wisconsin
Walliserops trifurcatus, from Jebel Oufatene mountain near Fezzou, Morocco
Extinction is the termination of a taxon by the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" after a period of apparent absence.
Extinction
The thylacine (Thylacinus cynocephalus) is an example of an extinct species.
External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio
The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction.