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 is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficulty to relate sediments in different areas, there remains some discussion, but among the earliest are Fallotaspis, and Lemdadella, both belonging to this order. The first representatives of the orders Corynexochida and Ptychopariida also appear very early on and may prove to be even earlier than any redlichiid species. In terms of anatomical comparison, the earliest redlichiid species are probably ancestral to all other trilobite orders and share many primitive characters. The last redlichiid trilobites died out before the end of the Middle Cambrian.
Microdictyon is an extinct armoured worm-like panarthropod coated with net-like scleritic plates, known from the Early Cambrian Maotianshan shale of Yunnan China and other parts of the world. Microdictyon is part of the ill-defined taxon – Lobopodia – that includes several other odd worm-like animals that resembling worm with legs, such as Hallucigenia, Onychodictyon, Cardiodictyon, Luolishania, and Paucipodia. The isolated sclerites of Microdictyon are known from other Lower Cambrian deposits. Microdictyon sclerites appear to have moulted; one sclerite seems to have been preserved during ecdysis.
Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian of the East Gondwana supercontinent, in what are today South-Australia and Antarctica.
Meniscuchus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Botomian stage, which lasted from approximately 522 to 516 million years ago. This faunal stage was part of the Cambrian Period. Meniscuchus has been found in the USA, Canada, Russia and Australia.
Resserops is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the middle of the Atdabanian or the early part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. It has been found in Spain and southern Morocco. It can be recognised by the sabre-like spines of the headshield that are a smooth continuation of the frontal edge, and the enlarged spines on the 9th segment of the thorax.
Olenelloides armatus is an extinct, small sized olenelloid redlichiid trilobite arthropod. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. The most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..
Egyngolia is a genus of very small sized Trilobites, that lived during the Lower Cambrian in what are today the Russia Federation, Mongolia, and South Australia.
Tsunyidiscus is a trilobite belonging to the Suborder Eodiscina. Tsunyidiscus appeared near the end of the Lower Cambrian, during the late Atdabanian stage of geologic time and some collections suggest it may have survived into the Botomian. The genus is very small, oculate and isopypous with a narrow dome-shaped glabella and a narrow bullet-shaped pygidial axis. Thorax consists of three segments. Tsunyidiscus is the only genus currently attributed to the family Tsunyidiscidae.
Lemdadella is an extinct genus of redlichiid trilobites that lived during the late Atdabanian stage, which lasted from 521 to 514 million years ago during the early part of the Cambrian Period.
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.
Eoredlichia is an extinct genus of trilobite of average to large size. It lived during the early Cambrian in the Chengjiang fauna of Yunnan, China, and in Australia and Thailand. Eoredlichia is compounded of the Greek ἠώς and Redlichia, a later but related genus, so it means "early Redlichia". The species epithet intermedia means intermediate, indicating it is morphologically intermediate between other species. Eofallotaspis gives rise to Lemdadella, and thence to Eoredlichia and the other Redlichiidae.
Holmiidae is a family of trilobites, that lived during the Lower Cambrian (Atdabanian). The Holmiidae is a diverse family of eight genera containing at least 17 species. It includes some of the earliest trilobites of Baltica. Holmiidae occur throughout Baltica and Western Laurentia, and also in Morocco.
Kangacaris is an extinct genus of soft-shelled trilobite-like arthropod of the nektaspid order from the Lower Cambrian (Botomian). K. zhangi is known from South Australia, and K. shui from South-West China.
Ptychoparia is a genus of ptychopariid trilobites, and is the type genus of the family Ptychopariidae, and the order Ptychopariida.
Richterops is an extinct genus of trilobite arthropods. The genus lived during the middle of the Atdabanian or the early part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the second half of the Lower Cambrian. It has been found in southern Morocco. It can be recognised by the long spines of the headshield that are a smooth continuation of the frontal edge, and the enlarged spines on the 11th segment of the thorax.
Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Lower Cambrian period and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or three segments. Eodiscina includes six families classified under one superfamily, Eodiscoidea.
Delgadella is a diminutive trilobite that lived during the late Lower Cambrian and has been found in Russia, Mongolia, Spain, Italy (Sardinia), Portugal, Morocco and Canada (Newfoundland). It can be recognized by its strongly effaced headshield and tailshield, with narrow but distinct furrows and borders along its margins, and three thorax segments.
Orygmaspis is a genus of asaphid trilobite with an inverted egg-shaped outline, a wide headshield, small eyes, long genal spines, 12 spined thorax segments and a small, short tailshield, with four pairs of spines. It lived during the Late Cambrian in what are today Canada and the United States.
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°.
