Ptychopariida is a large, heterogeneous order of

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

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

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

, and the last species did not survive the Ordovician–Silurian extinction event. 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 ...

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., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...

meets the

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of 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 di ...

. 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 preserve ...

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,

Proetida Proetida is an order of trilobite that lived from the Ordovician to the Permian. It was the last surviving order of trilobite, dying out in the Permian-Triassic extinction event. Description These typically small trilobites resemble those of ...

, Harpetida, 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 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