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.
John William Salter was an English naturalist, geologist, and palaeontologist.
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.
Triarthrus is a genus of Upper Ordovician ptychopariid trilobite found in New York, Ohio, Kentucky, and Indiana, eastern and northern Canada, China and Scandinavia. It is the last of the Olenid trilobites, a group which flourished in the Cambrian period. The specimens of T. eatoni that are found in the Beecher's Trilobite Bed, Rome, New York area are exquisitely preserved showing soft body parts in iron pyrite. Pyrite preservation has given scientists a rare opportunity to examine the gills, walking legs, antennae and digestive systems of trilobites, which are rarely preserved. Triarthrus is therefore commonly used in science texts to illustrate trilobite anatomy and physiology.
Flexicalymene Shirley, 1936, is a genus of trilobites belonging to the order Phacopida, suborder Calymenina and Family Calymenidae. Flexicalymene specimens can be mistaken for Calymene, Gravicalymene, Diacalymene and a few other Calymenina genera. They are used as an index fossil in the Ordovician. Ohio and North America are particularly known for being rich with Flexicalymene fossils.
Gravicalymene Shirley, 1936, is a genus of trilobites belonging to the order Phacopida, suborder Calymenina and family Calymenidae. Species included in this genus have previously been allocated to Calymene Brongniart 1822,Flexicalymene Shirley, 1936. and Sthenarocalymene Siveter 1977.
Gyrometopus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Arenig stage of the Ordovician Period, approximately 479 to 472 million years ago.
Cloacaspis is an extinct genus of Olenid Ptychopariid trilobite. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago. Richard Fortey has proposed that these particular trilobites lived in anoxic regions of the ocean floor, and cultivated symbiotic, sulfur-metabolizing bacteria.
Benthamaspis is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago.
Aspidaeglina is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 473 to 470 million years ago.
Merlinia is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago. These trilobites were named after the Welsh wizard Merlin, as the fossilised tails (pygidia) of trilobites were often mistaken for petrified butterflies, and were hence linked with mythological tales involving Merlin.
Priceaspis is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago. Fossils of the genus have been reported from the Emanuel Formation of Western Australia.
Thysanopyge is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived in what is now South America during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago.
Globampyx is an extinct genus raphiophorid trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago. Species of the genus are known from Canada, Norway (Svalbard) and Sweden.
Ceratolithus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago.
Megalaspidella is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago.
Megalaspides is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago.
Bumastus is an extinct genus of corynexochid trilobites which existed from the Early Ordovician period to the Late Silurian period. They were relatively large trilobites, reaching a length of 6 in (15 cm). They were distinctive for their highly globular, smooth-surfaced exoskeleton. They possessed well-developed, large compound eyes and were believed to have dwelled in shallow-water sediments in life.
Angelina Salter, 1859, is a genus of ptychopariid trilobite belonging to the Family Olenidae, Suborder olenina. It lived during the Tremadocian Stage, lowermost of the two standard worldwide divisions forming the Lower Ordovician Series and lowest of the seven stages within the Ordovician System. It encompasses all rocks formed during Tremadocian times, which spanned the interval between 485.4 million and 477.7 million years ago. Fossilized remains of Angelina are known from Wales, Central and South America. It differs from most other Triarthrinae in being larger, with a relatively narrow glabella, the occipital ring poorly defined, and lateral glabellar furrows relatively obscure. Eyes are placed midlength that of the cephalon and the facial sutures converge on the front border at the midline. Species also have long genal spines.
Olenidae is a family of ptychopariid trilobites. Some genera, Balnibarbi and Cloacaspis, are thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived nutrition.
