Trilobites are a group of 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 extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 20,000 species having been described.
Phacopida ("lens-face") is an order of trilobite that lived from the Late Cambrian to the Late Devonian. It is made up of a morphologically diverse group of related suborders.
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Silurian extinction event.
The Phacopina comprise a suborder of the trilobite order Phacopida. Species belonging to the Phacopina lived from the Lower Ordovician (Tremadocian) through the end of the Upper Devonian (Famennian). The one unique feature that distinguishes Phacopina from all other trilobites are the very large, separately set lenses without a common cornea of the compound eye.
Dalmanitoidea is a superfamily of trilobites in the order Phacopida, containing the three families Dalmanitidae, Diaphanometopidae and Prosopiscidae.
Dalmanitidae is a family of trilobites in the order Phacopida that lived from the Floian (Ordovician) to the Devonian and includes 33 genera.
Eldredgeia is a genus of trilobites in the order Phacopida, suborder Phacopina, family Calmoniidae. This genus comes from the Devonian of South America and South Africa, usually found in nodules. The trilobite Eldredgeia venusta, from Bolivia, is the most common South American trilobite on today's fossil market, and even then it is not all that common. This genus has a spiny pygidium and usually the eye facets are well preserved.
Calymenina is a suborder of the trilobite order Phacopida.
Eophacops is a genus of trilobites from the order Phacopida, family Phacopidae. These trilobites lived during the Middle Silurian in what now are North America and North-West Europe. Species assigned to this genus can be distinguished from Phacops by their small size (2–3 cm). Eophacops has very large eyes compared to the rest of its body.
Acastoidea is a superfamily of trilobites from the order Phacopida, suborder Phacopina. This superfamily is divided into two families, Acastidae and Calmoniidae. This superfamily is distinguishable from the Phacopidae in that eyes are closer to the glabella and that the glabella has lobes, unlike the genera in Phacopidae.
Acastidae is a family of trilobites in the order Phacopida, suborder Phacopina, superfamily Acastoidea, containing the following genera:
Acastava is an extinct genus of trilobite in the order Phacopida, from the upper Pragian to Emsian period of the Devonian.
Deltacephalaspis is an extinct genus of trilobites in the order Phacopida. It contains four species, D. comis, D. magister, D. retrospina, and D. tumida. Fossils of the genus have been found in the Belén, Icla and Gamoneda Formations of Bolivia and the Gydo Formation of South Africa.
Hadromeros is an extinct genus of trilobite in the order Phacopida.
Kozlowskiaspis is a genus of trilobites in the order Phacopida, that existed during the lower Devonian in what is now Bolivia. It was described by Branisa and Vanek in 1973, and the type species is Kozlowskiapsis superna. It also contains the species K. australis and K. borealis. The type locality was the Icla Formation.
Encrinuridae is a family of trilobite within the order Phacopida that lived in what would be Africa, Asia, Australia, Europe, North America, and South America from the middle Ordovician to the early Devonian from 479 to 412.3 million years ago, existing for approximately 66.7 million years.
Morocconites malladoides is an average size trilobite, which lived during the Devonian period, in what is now southern Morocco. This species is assumed to be a close relative of Acastoides. The most conspicuous feature is the very long upcurved frontal medial spine, a bit like an avocet bill. It is the only known species in this genus.
Pilekiidae is a family of trilobites in the order Phacopida, specifically within Suborder Cheirurina. It includes the following genera:
Bouleia is a genus of trilobites in the order Phacopida which existed during the lower Devonian in what is now Bolivia. It was described by Kozlowski in 1923, and the type species is B. dagincourti, which was originally described under the genus Phacops by Ulrich in 1892. It also contains the species B. sphaericeps, originally described by Kozlowski, also in 1923, as Dereimsia sphaericeps. The type locality was the Icla Formation in Padilla.
Cheirurina is a suborder of the trilobite order Phacopida. Known representatives range from the uppermost Cambrian to the end of the Middle Devonian (Givetian). Cheirurina is made up of a morphologically diverse group of related families.
