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.
Paradoxides is a genus of large to very large trilobite found throughout the world during the Middle Cambrian period. One record-breaking specimen of Paradoxides davidis, described by John William Salter in 1863, is 37 cm (15 in). The cephalon was semicircular with free cheeks ending in long, narrow, recurved spines. Eyes were crescent shaped providing an almost 360° view, but only in the horizontal plane. Its elongate thorax was composed of 19–21 segments and adorned with longish, recurved pleural spines. Its pygidium was comparatively small. Paradoxides is a characteristic Middle-Cambrian trilobite of the 'Atlantic' (Avalonian) fauna. Avalonian rocks were deposited near a small continent called Avalonia in the Paleozoic Iapetus Ocean. Avalonian beds are now in a narrow strip along the East Coast of North America, and in Europe.
Redlichiina is a suborder of the order Redlichiida of Trilobites. The suborder contains three superfamilies: Emuelloidea, Redlichioidea and Paradoxidoidea. These trilobites are some of the oldest trilobites known. They originated at the beginning of the Cambrian Period and disappeared at the end of the middle Cambrian.
Kootenia is a genus of trilobites of the family Dorypygidae. 118 specimens of Kootenia are known from the Greater Phyllopod bed, where they comprise 0.22% of the community. Its major characteristics are that of the closely related Olenoides, including medium size, a large glabella, and a medium-sized pygidium, but also a lack of the strong interpleural furrows on the pygidium that Olenoides has.
Olenoides was a trilobite from the Cambrian period. Its fossils are found well-preserved in the Burgess Shale in Canada. It grew up to 10 cm long.
Naraoia is a genus of small to average size marine arthropods within the family Naraoiidae, that lived from the early Cambrian to the late Silurian period. The species are characterized by a large alimentary system and sideways oriented antennas.
Holyoakia is a genus of very small trilobites of the family Dorypygidae, from the late Lower Cambrian of South Australia and Antarctica.
Meteoraspis is an extinct genus of ptychopariid trilobites of the family Tricrepicephalidae. The various species lived from 501 to 497 million years ago during the Dresbachian faunal stage of the late Cambrian Period. Fossils of Meteoraspis are characteristic of Late Cambrian strata in North America, though they are found in Late Cambrian strata elsewhere in the world, such as M. nevensis from Victoria Land, Antarctica.
Ogygopsis is a genus of trilobite from the Cambrian of Antarctica and North America, specifically the Burgess Shale. It is the most common fossil in the Mt. Stephen fossil beds there, but rare in other Cambrian faunas. Its major characteristics are a prominent glabella with eye ridges, lack of pleural spines, a large spineless pygidium about as long as the thorax or cephalon, and its length: up to 12 cm.
Pagetia is a genus of small trilobite, assigned to the Eodiscinid family Pagetiidae and which had global distribution during the Middle Cambrian. The genus contains 55 currently recognized species, each with limited spatial and temporal ranges.
Oryctocephalus is a genus of trilobite known from the Middle Cambrian Burgess Shale. 24 specimens of Oryctocephalus are known from the Greater Phyllopod bed, where they comprise 0.42% of the community. This small- to medium-sized trilobite's major characteristics are prominent eye ridges, pleural spines, long genal spines, spines on the pygidium, and notably four furrows connecting pairs of pits on its glabella. Juvenile specimens have been found with only 5 or 6 thoracic segments and about one eighth of adult size, as well as about 2 mm wide.
Alokistocaridae is a family of ptychopariid trilobites that lived from the Botomian epoch of the Early Cambrian until the Late Cambrian. Alokistocarids were particle feeders and left small furrows which are occasionally preserved. Their remains are found worldwide. Elrathia kingii, one of the most collected trilobites in the world, is a typical alokistocarid.
Chancia is an extinct genus of Cambrian trilobite. It was a "fast-moving epifaunal detritivore" from Canada and the United States. Chancia was a particle feeder. Its major characteristics are a normal glabella but an enlarged cephalon due to a pre-glabellar field in front of the glabella, as well as developed eye ridges, medium-sized genal spines, and an extremely small pygidium.
Zacanthoides is an extinct Cambrian genus of corynexochid trilobite. It was a nektobenthic predatory carnivore. Its remains have been found in Canada, Greenland, Mexico, and the United States. Its major characteristics are a slender exoskeleton with 9 thoracic segments, pleurae with long spines, additional spines on the axial rings, and a pygidium that is considerably smaller than its cephalon.
Lotagnostus is a genus of very small trilobites in the order Agnostida, which lived on the outer continental shelves worldwide, during the late Upper Cambrian. It was described by Whitehouse in 1936, and the type species is Lotagnostus trisectus, which was originally described as a species of Agnostus by Salter in 1864.
Burlingia is a rare and diminutive genus of trilobite, that lived during the early to middle Middle Cambrian. Species assigned to Burlingia have been found in Norway, Sweden, Northern Siberia, and South-eastern China.
Biceratops is an extinct genus of olenelloid redlichiid trilobites, of average size, with the largest specimen 8 centimetres or 3.1 inches long, not including the huge pleural spines of the 3rd segment of the thorax. It lived during the Toyonian stage, in what is today the South-Western United States. Biceratops can easily be distinguished from other members of Biceratopsidae by the absence of genal spines, in combination with effaced features of the raised axial area of the head shield, that is bordering the two horn-like projections that carry the eyes. Biceratops nevadensis is the only known species in this genus.
Ptychoparia is a genus of ptychopariid trilobites, and is the type genus of the family Ptychopariidae, and the order Ptychopariida.
Thoracocare is a minute to very small trilobite, that lived during part of the Middle Cambrian in what are today the states of Idaho, Nevada and Utah. It is the only trilobite known with just two thorax segments outside most members of the Agnostida order. It can be distinguished from Agnostida by the very wide subquadrate glabella, parallel-side or widening forward in the largest specimen, with the full front side touching the border. Two species are known, one, T. idahoensis, only from pygidia.
Tricrepicephalus is an extinct genus of ptychopariid trilobites of the family Tricrepicephalidae with species of average size. Its species lived from 501 to 497 million years ago during the Dresbachian faunal stage of the late Cambrian Period. Fossils of Tricrepicephalus are widespread in Late Cambrian deposits in North America, but is also known from one location in South America. Tricrepicephalus has an inverted egg-shaped exoskeleton, with three characteristic pits in the fold that parallels the margin of the headshield just in front of the central raised area. The articulating middle part of the body has 12 segments and the tailshield carries two long, tubular, curved pygidial spines that are reminiscent of earwig's pincers that rise backwards from the plain of the body at approximately 30°.
