Phacopida

From Palaeos

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

Dalmanites limulurus from the Silurian of New York.

Introduction

This section from Wikipedia:

Phacopida is an order of trilobite that lived from the Ordovician to the Devonian. It is made up of a morphologically diverse group of related suborders.

The origin of the Phacopida order is uncertain. It comprises three suborders (Phacopina, Calymenina, and Cheirurina) which share a distinctive protaspis (developmental stage lacking segments) type. The Cheirurina and Calymenina retain a rostral plate (an apomorphy) but in virtually all Phacopina the free cheeks are yoked as a single piece. This sort of similarity in development suggests phylogenetic unity. The suborder Calymenina is the most primitive of the Phacopida order and shares some characteristics with the order Ptychopariida, though it is not included in the subclass Libristoma.

Phacopida had 8 to 19 thoracic segments and are distinguishable by the expanded glabella, short or absent preglabellar area, and schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina) eyes. Schizochroal eyes are compound eyes with up to around 700 separate lenses. Each lens has an individual cornea which extended into a rather large sclera.

The development of schizochroal eyes in phacopid trilobites is an example of post-displacement paedomorphosis. The eyes of immature holochroal Cambrian trilobites were basically miniature schizochroal eyes. In Phacopida, these were retained, via delayed growth of these immature structures (post-displacement), into the adult form.

Phacops rana and Dalmanites limulurus are two well-known represnetatives of this order. Other phacopids include Cheirurus, Deiphon, Calymene and Ceraurinella.

o Trilobita
`--o PHACOPIDA
   |--o Calymenina
   |  |--Pharostomatidae
   |  |--Homalonotidae
   |  |--Bavarillidae
   |  `--Bathycheilidae
   |--o Phacopina
   |  |--o Dalmanitoidea
   |  |  |--Dalmanitidae
   |  |  |--Prosopiscidae
   |  |  `--Diaphanometopidae
   |  `--o Acastoidea
   |     |--Acastidae
   |     `--Calmoniidae
   `--o Cheirurina
      |--Cheiruridae
      |--Pliomeridae
      |--Pilekiidae
      `--Encrinuridae

Information

Linnaean taxonomy:

• Phylum: Arthropoda
  • Class: Trilobita
    • Order: Phacopida

Author: Salter, 1864

Phylogeny

Dendrogram

<==Phacopida
   |--Cheirurina
   |    |--Cheiruridae
   |    |    |  i. s.: Krattaspis Öpik 1937
   |    |    |--Eccoptochilinae
   |    |    |    |--Eccoptochile Hawle & Corda 1847
   |    |    |    |    |--*E. clavigera (Beyrich 1845)
   |    |    |    |    |--E. almadenensis Romano 1980
   |    |    |    |    |--E. impedita Hammann 1972
   |    |    |    |    |--E. mariana (Verneuil & Barrande 1855)
   |    |    |    |    |--E. perlata Hawle & Corda 1847
   |    |    |    |    |--E. quillieri (Tromelin in Guillier 1873)
   |    |    |    |    `--E. scrobiculata (Angelin 1854)
   |    |    |    |--Eccoptochiloides Prantl & Přibyl 1947
   |    |    |    |    |--E. scuticauda (Barrande 1846) [incl. *E. tumescens (Barrande 1852)]
   |    |    |    |    |--E. henryi Přibyl, Vaněk & Pek 1985
   |    |    |    |    `--E. octacantha (Angelin 1854)
   |    |    |    |--Foulonia Přibyl & Vaněk in Přibyl, Vaněk & Pek 1985
   |    |    |    |    `--*F. peregrina (Dean 1966) [=Ceraurinella peregrinus]
   |    |    |    `--Placoparina Whittard 1940
   |    |    |         `--*P. sedgwickii (McCoy 1849)
   |    |    |              |--P. s. sedgwickii
   |    |    |              `--P. s. shelvensis Hughes 1969
   |    |    |--Sphaerexochinae
   |    |    `--+--Pilekiinae
   |    |       `--Cheirurinae
   |    `--Pliomeridae
   |         |  i. s.: Emsurella Rosova 1960
   |         |           `--E. humilla Rosova 1960
   |         `--Protopliomeropinae
   |              |--Protopliomerops Kobayashi 1934
   |              `--Rossaspis Harrington 1957
   `--Phacopina
        |--Phacops rana
        |--Dalmanites
        `--Greenops

* Type species of genus indicated

References

Conway Morris, S. 1998. The Crucible of Creation. Oxford University Press: Oxford.

Crawford, R. L. 1992. Catalogue of the genera and type species of the harvestman superfamily Phalangioidea (Arachnida). Burke Museum Contributions in Anthropology and Natural History 8: 1-60.

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.

Fletcher, T. P. 2005. Holaspid variation in the solenopleurid trilobite Parasolenopleura gregaria (Billings, 1865) from the Cambrian of Newfoundland. Palaeontology 48 (5): 1075-1089.

Miller, S. A., & J. P. Harley. 1996. Zoology (3rd ed.) Wm. C. Brown Publishers: Dubuque (Iowa).

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

Přibyl, A., J. Vaněk & I. Pek. 1985. Phylogeny and taxonomy of family Cheiruridae (Trilobita). Acta Universitatis Palackianae Olomucensis Facultas Rerum Naturalium Geographica-Geologica XXIV 83: 107-193.

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

Rong, J.-Y., R.-B. Zhan & J. Jin. 2004. The Late Odovician and Early Silurian pentameride brachiopod Holorhynchus Kiaer, 1902 from north China. Journal of Paleontology 78 (2): 287-299.

Sánchez, T. M., & N. E. Vaccari. 2003. Ucumariidae new family (Bivalvia, Anomalodesmata) and other bivalves from the Early Ordovician (Tremadocian) of northwestern Argentina. Ameghiniana 40 (3): 415-424.

Shu, D.-G., L. Chen, J. Han & X.-L. Zhang. 2001. An Early Cambrian tunicate from China. Nature 411: 472-473.

Links

• Order Phacopida

Credits

CKT070122 (Phylogeny) ; DanielCD Wikipedia(Introduction)