Trilobite Order Ptychopariida
Ptychopariid Trilobites |
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Also see: Class Trilobita - Trilobite Classification |
| Ptychopariida (pronounced Pity-cho-pa-ree-da) is a huge and morphologically diverse order of trilobite that has largely defied science's attempts to unravel its phylogeny through cladistics. Many ptychopariids were among the most primitive trilobites dating to the early Cambrian. The order persisted through to the late Ordovician. Fortey (2001), posited that Ptychopariida arose out of the paraphyletic suborder Redlichiina. Ptychopariida is a critical grouping in that the order likely gave rise to the great plurality of post-Cambrian trilobites (Edgecombe, 1992; Eldredge, 1977; Fortey and Chatterton, 1988; Fortey and Owens, 1997; Fortey, 2001; Jell and Adrain, 2003). Order Ptychopariida is often described as a catch-all bucket for trilobites from the middle through upper Cambrian.
What are now trilobite Orders Ptychopariida, Asaphida, Proetida, and Harpetida were grouped together as Order Ptychopariida in the 1959 Treatise on Invertebrate Paleontology. The subclass Librostoma was erected in 1990 by Fortey (1990) to unite these orders that are allied at least in more primitive genera by a natant hypostomal condition where the Hypostome is free of the anterior doublure, and aligned with anterior edge of glabella. Subsequently, Ebach & McNamara (2002) raised Harpetida to an order status because its members lack a rostral plate and have a marginal facial suture. The thorax is usually large, much longer than the normally small pygidium and has eight or more segments. In some species the pygidium has a flattish border. Ptychopariida trilobites typically have opisthoparian facial sutures, with a forward angled simple glabella with a rounded front. Order Ptychopariida includes what is arguably the most common trilobite, Elrathia kingii that is prodigious in the House Range of Utah.
(Pity-cho-pa-ree-da)
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