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Trilobites were extinct arthropods that appeared in the Cambrian Era and went extinct at the end of the Permian. They are an iconic fossil group and have been used as a reference point for research in paleontology, biostratigraphy, and plate tectonics. Trilobites had a shield-shaped body divided into three sections and filled a variety of ecological niches. Over 17,000 trilobite species have been identified, and they may underlie all other arthropods.
Trilobites are extinct arthropods, one of the most famous fossil groups outside of dinosaurs. Trilobites appeared at the very dawn of the Cambrian Era, 542 million years ago, and became extinct at the end of the Permian 250 million years ago, making trilobites iconic of the Paleozoic fauna. Early genera include Fallotaspis, Profalloptaspis and Eofallotaspis. Trilobite fossils are so common that you can buy one on eBay for $10 US dollars or less. Numerous trilobite fossils have been found in Utah and Morocco, although collectors should be careful, as there is a serious counterfeiting problem with trilobite fossils.
Trilobites were shield-shaped arthropods, particularly interesting because they do not resemble living arthropods. Trilobites are the only arthropod subphlyum that has gone extinct. During the Late Devonian extinction 364 million years ago, all trilobites became extinct except the order Proetida, represented by smaller trilobites. Trilobites had difficulty managing the diversity of predators throughout the Devonian. In all, over 17,000 trilobite species have been identified, including later spiny forms, which evolved to cope with increased predation.
Because trilobite fossils are so numerous and well understood, they serve as an excellent reference fossil, informing research in paleontology, biostratigraphy, and plate tectonics. Because of their diversity, trilobites have been used as a reference point for speciation rates during the Cambrian explosion, an episode of adaptive radiation during the Cambrian period. The trilobites themselves are a prototypical example of the evolutionary successes of the Cambrian explosion. Trilobites may underlie all other arthropods. If so, all insects, arachnids, crustaceans, mites and scorpions all evolved from trilobite ancestors.
The body of trilobites is divided into three sections: head, thorax and tail. In early trilobites, the tail is very short and vaguely pronounced. Trilobites had antennae, and some had horns resembling those seen on modern beetles. Trilobites filled a variety of ecological niches and included predators, scavengers, or filter feeders. Some just walked on the ocean floor, while others swam and ate plankton. Some have even developed a symbiotic relationship with sulfur-eating bacteria.
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