Trilobite fossils

Trilobites

Trilobites ("three-lobes") are extinct arthropods that form the class Trilobita. They appeared in the Middle Cambrian epoch and flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Late Devonian extinction, all trilobite orders, with the sole exception of Proetida, died out. The last of the trilobites disappeared in the mass extinction at the end of the Permian about 250 million years ago.

Trilobite fossils are very well-known, and possibly the second-most famous fossil group, after the dinosaurs. When trilobites appear in the fossil record of the Lower Cambrian they are already highly diverse and geographically dispersed. Because of their diversity and an easily fossilized exoskeleton, they left an extensive fossil record with some 17,000 known species spanning Paleozoic time. Trilobite fossils have been important in biostratigraphy, paleontology, and plate tectonics research. For example, trilobite fossils have been important in estimating the rate of speciation during the period known as the Cambrian Explosion because they are the most diverse group of metazoans known from the fossil record of the early Cambrian (Lieberman, 1999), and are readily distinguishable because of complex and well preserved morphologies. The trilobites are often placed within the arthropod subphylum Schizoramia within the superclass Arachnomorpha (equivalent to the Arachnata) (e.g., Cotton & Braddy 2004), although several alternative taxonomies are found in the literature.
Different trilobites made their living in different ways. Some led a benthic life as predators, scavengers or filter feeders. Some swam (a pelagic lifestyle) and fed on plankton. Still others (particularly the family Olenidae) are thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived food.

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