Ptychopariida is a large, heterogeneous order of

trilobite Trilobites (; meaning "three lobes") 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 ...

containing some of the most primitive species known. The earliest species occurred in the second half of the Lower

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

, and the last species did not survive the

Ordovician–Silurian extinction event The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 443 Mya. It ...

. Trilobites have facial sutures that run along the margin of the

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior t ...

and/or fixigena to the shoulder point where the

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino s ...

meets the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the c ...

. These sutures outline the cranidium, or the main, central part of the head that does not include the librigena (free cheeks). The eyes are medial along the glabella on the suture line (and some species have no eyes). The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s of the moults of trilobites can often be told from the fossils of the actual animals by whether the librigena are present. (The librigena, or cheek spines, detach during moulting.) In ptychopariids, short bladelike genal spines are often present on the tips of the librigena. The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border. The Subclass Librostoma was recently erected to encompass several related orders, including Ptychopariida,

Asaphida Asaphida is a large, morphologically diverse order of trilobites found in marine strata dated from the Middle Cambrian until their extinction during the Silurian. Asaphida contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, ...

, Proetida,

Harpetida Harpetida is one of the eleven orders of the extinct arthropod class Trilobita. The first harpetid trilobites appear in the Upper Cambrian, and the last species die out at the end of the Devonian period. Harpetid trilobites are characterized am ...

, and possibly Phacopida. These are now known as the "Librostome Orders". Trilobites of the orders Proetida, Harpetida, and of the family Damesellidae were originally placed in Ptychopariida.

Taxonomy

Suborder Olenina *Superfamily Olenoidea **Family Ellipsocephaloididae **Family Olenidae *Superfamily ''Incertae sedis'' **Genus '' Triarthrus'' Suborder Ptychopariina *Superfamily Ellipsocephaloidea **Family Agraulidae **Family Aldonaiidae **Family Bigotinidae **Family Chengkouiidae **Family Ellipsocephalidae **Family Estaingiidae **Family Palaeolenidae **Family Yunnanocephalidae *Superfamily Ptychoparioidea **Family Acrocephalitidae **Family Alokistocaridae **Family Antagmidae **Family Asaphiscidae **Family Atopidae **Family Bolaspididae **Family Cedariidae **Family Changshaniidae **Family Conocoryphidae **Family Conokephalinidae **Family Crepicephalidae **Family Diceratocephalidae **Family Elviniidae **Family Eulomidae **Family Holocephalinidae **Family Ignotogregatidae **Family Inouyiidae **Family Isocolidae **Family Kingstoniidae **Family Liostracinidae **Family Llanoaspididae **Family Lonchocephalidae **Family Lorenzellidae **Family Mapaniidae **Family Marjumiidae **Family Menomoniidae **Family Nepeidae **Family Norwoodiidae **Family Papyriaspididae **Family Phylacteridae **Family Proasaphiscidae **Family Ptychopariidae **Family Shumardiidae **Family Solenopleuridae **Family Tricrepicephalidae **Family Utiidae **Family Wuaniidae *Superfamily ''Incertae sedis'' **Genus '' Tonopahella'' Suborder ''incertae sedis'' *Family Avoninidae *Family Catillicephalidae *Family Ityophoridae *Family Plethopeltidae

References

Order Ptychopariida

By Sam Gon III Trilobite orders Cambrian first appearances Late Ordovician extinctions {{Ptychopariida-stub

Taxonomy

See also

References