Proetida

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Proetida
Temporal range: Early Ordovician – End Permian, 488–251Ma
Aulacopleura konincki.jpg
Aulacopleura konincki 14mm, collected near Kosovu Beruna, Czech Republic, Silurian
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Subclass: Librostoma
Order: Proetida
Fortey & Owens, 1975

Proetida is an order of trilobite that lived from the Ordovician to the Permian. It was the last order of trilobite to go extinct, finally dying out in the Permian extinction.[1]

These typically small trilobites resemble those of the order Ptychopariida, from which the new order Proetida was only recently separated in 1975 by Fortey and Owens. Like the order Phacopida, the proetids have exoskeletons that sometime have pits or small tubercles, especially on the glabella (middle portion of the head). Because of their resemblance to the Ptychopariida in some features, the proetids are included in the subclass Librostoma.

Unlike the trilobites of the Phacopid suborder Phacopina, whose eyes are schizochroal, the proetids have the more common holochroal eyes. These eyes are characterized by close packing of biconvex lenses beneath a single corneal layer that covers all of the lenses. Each lens is generally hexagonal in outline and in direct contact with the others. They range in number from one to more than 15,000 per eye. Eyes are usually large, and because the individual lenses are hard to make out, they look smooth and sometimes bead-like.

The thorax of proetids was made up of anywhere between 8–22 segments, but most commonly 10. Many also have genal spines coming off either side of the head, though in some they are blunted. These two features can aid in distinguishing proetids from some Phacopid trilobites in the suborder Phacopina, to which they can be very similar.

Cummingella belisama, Family Proetidae, 18mm, from the Kohlenkalk of Tournai, Belgium, Lower Carboniferous/Missisippian (Tournaisian)

The following superfamilies and families are recognised:[2]

References[edit]

  1. ^ Paleobiology Database. "PBDB: Proetida". Retrieved December 4, 2011. 
  2. ^ Sam Gon III (April 21, 2008). "Order Proetida". A Guide to the Orders of Trilobites. Retrieved November 9, 2010.