Late Cambrian – Middle Permian
Ptychopariida is an extinct order of fast-moving, low-level epifaunal carnivores.
Characteristics of the Order
- Cephalon typically with opisthoparian facial sutures, and a gently forward-tapering simple glabella bearing a broad, rounded front.
- Thorax large, with more than 8 segments.
- Pygidium are quite variable and can be small bearing a border or large with or without border.
Treatise on Invertebrate Paleontology (1959):
- A large order of trilobites having more than three thoracic segments. A few are proparian (some Ptychopariina) and some modified forms have marginal or submarginal sutures (some Ptychopariina, most Harpina and Trinucleina), but a large majority are opisthoparian. The glabella is primarily of simple, generalized type, tapering forward, and glabellar furrows, if present, (many Ptychopariina) are commonly simple subparallel linear depressions. In some modified forms, the glabella deviates in shape (Illaenina, Harpiana, Trinucleina, most Asaphina, some Ptychopariina) and the different pairs of lateral glabellar furrows, if present, are more or less dissimilar. A preglabellar field commonly is present but may be secondarily reduced. A rostral plate and connective sutures are present or absent; if a rostral plate is lacking (modified forms) the librigenae are either separated by a median suture or fused together (Asaphina, Harpina, Trinucleina, some Ptychopariina). The hypostoma is separated from the cephalon by a hypostomal suture or uncalcified membrane. Most early forms have a relatively large thorax and small pygidium, whereas later forms especially have fewer thoracic segments and a large pygidium.
- Early representatives of the Ptychopariida resemble Redlichiina, but many of these later have eye lobes that are longer or less separated from the eye ridges, or they are characterized by a glabella that expand forward. The Corynexochida differ from the Ptychopariida in having the hypostoma fused with the rostral plate; also, many of the Corynexochida differ from contemporaneous Cambrian Ptychopariida in having more divergent lateral glabellar furrows, and in having a glabella that expands forward. The Lichida and Odontopleurida differ from the Ptychopariida, among various features, in their peculiar types of glabella and glabellar furrows. Among the Phacopida, early forms, especially of the Calymenina, resemble the Ptychopariida, but most differ in the pattern of the glabellar furrows and are predominantly proparian or gonatoparian.
- The Ptychopariida seem to be closely related to the Redlichiina, and probably gave rise to most or all post-Cambrian trilobite groups (except, of course, post-Cambrian agnostids).