Ptychopariida

From Palaeos

o Arthropoda
`--o TRILOBITA
   |?-Agnostina
   `--+--o Redlichiida
      |  |--Olenellina
      |  `--Redlichiina
      |--Corynexochida
      |--Phacopida
      |--Lichida
      `--o Librostoma
         |--Proetida
         |--Harpetida [Harpoidea]
         |--Ptychopariida
         |?-Eodiscina
         `--Asaphida

Various ptychopariid trilobites from the Weeks Formation of Upper Cambrian Utah. The uppermost is Tricephalus coria. The center is Meteoraspis dis. To the lower left of M. dis is Democephalus granulatus. To the lower right is Gerospina schachti. For size reference, M. dis is approximately 1 inch long. ©Stanton Fink

Introduction

This section is copied from Wikipedia:

Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian period, but the order was extant through the Late Ordovician period. Many of the offshoot species are difficult to classify in this single order.

These trilobites have facial sutures that run along the margin of the glabella (central portion of the head) to the shoulder point where the cephalon meets the thorax. These sutures outline the glabella, or the main, central part of the head that doesn't include the free cheeks. The eyes are medial along the glabella on the suture line (however, some species have no eyes). Genial spines stretching back from either side of the cephalon are often present. The fossils of the moults of these trilobites can often be told from the fossils of the actual animals by whether or not the free cheeks are present, as in the moults, the free cheeks are no longer attached. Bladelike genial spines are often present.

The thorax is large, and is typically made up of eight or more segments. The thorax is usually much longer than the tail section (pygidium), which is usually small. In some species, the pygidia are outlined with a flat border.

Phylogeny

<==Ptychopariida [Ptychopariina]
   |  i. s.: Cyclolorenzella
   |         Lisaniidae
   |         Onchonotinidae
   |           |--Onchonotina Lu 1961
   |           `--Onchonotus Raymond 1924
   |         Quebecaspis
   |         Taenicephalites Rasetti 1961 [Parabolinoididae]
   |           |--*T. macrops Rasetti 1961
   |           `--T. plerus Shergold 1980
   |         Taenicephalus
   |           |--T. megalops Kobayashi 1938
   |           `--T. polyaricus Rosova 1963
   |         Shumardiidae
   |         Guizhoucephalina Chien 1961
   |           `--*G. longispina Chien 1961
   |         Onchonotellus
   |         Leiostegiacea
   |         Elrathia kingi
   |         Triarthrus
   |--+--Olenacea
   |  `--Phacopida
   `--+--Calymenina
      |    |--Flexicalymene meeki
      |    `--Calymene
      |--+--Ptychoparioidea
      |  `--Basidechenella [Corynexochida]
      |       `--B. lucasensis
      |--Asaphida [Asaphina]
      |    |  i. s.: Isotelus gigas
      |    |--Asaphacea
      |    |--Ceratopygidae
      |    |--Cyclopygidae
      |    `--Dikelocephalacea
      `--Illaenida [Illaenina]
           |--Scutellum
           `--Bumastus
                |--B. insignis
                `--B. ioxus

* Type species of genus indicated

References

Eckert, J. D., & C. E. Brett. 2001. Early Silurian (Llandovery) crinoids from the Lower Clinton Group, western New York State. Bulletins of American Paleontology 360: 1-88.

Hong, P. S., J. G. Lee & D. K. Choi. 2003. Trilobites from the Lejopyge armata zone (upper Middle Cambrian) of the Machari Formation, Yongwol Group, Korea. Journal of Paleontology 77 (5): 895-907.

Owens, R. M. 2002. Cyclopygid trilobites from the Ordovician Builth-Llandrindod Inlier, central Wales. Palaeontology 45 (3): 469-485.

Prothero, D. R. 1998. Bringing Fossils to Life: An introduction to paleobiology. WCB McGraw-Hill: Boston.

Shergold, J. H. 1980. Late Cambrian trilobites from the Chatsworth Limestone, western Queensland. Bureau of Mineral Resources, Geology and Geophysics – Bulletin 186: 1-111.

Links

• Order Ptychopariida
• A Guide to the Orders of Trilobites By Sam Gon III

Credits

CKT071122 (phylogeny and references); Wikipedia (Introduction)