Eodiscidae

Eodiscidae
Temporal range: Lower and Middle Cambrian
Pagetia taijiangensis, 6mm, from Kaili, Guizhou, China, Middle Cambrian
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Order: Agnostida
Suborder: Eodiscina
Superfamily: Eodiscoidea
Family: Eodiscidae
Raymond, 1913
genera
  • Eodiscus
  • Dawsonia
  • Helepagetia
  • Kiskinella
  • Macannaia
  • Opsidiscus
  • Pagetia
  • Pagetides
  • Sinopagetia[1]
Synonyms

Dawsoniidae, Pagetidae, Aulacodiscidae, Opsidiscidae, Pagetiellinae

The Eodiscidae are a family of trilobites belonging to the order Agnostida that lived during the final Lower Cambrian (late Toyonian) and the Middle Cambrian. They are small or very small, and have a thorax of two or three segments. The Eodiscidae include nine genera (see box).

Taxonomy

The Eodiscidae probably descended from the Yukoniidae.[2]

Description

Internal moult of the cranidium of Pagetia fossula, 2mm, showing scrobiculate border and glabellar spine

Like other Agnostida, the body of the Eodiscidae is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are of approximately same size, with 2 or 3 thoracic segments in-between, each consisting of a horizontal inner portion that abruptly passes into an inclined outer portion (fulcrate). The central raised area of the cephalon (or glabella) is narrow, usually with parallel sides and rounded front. The furrow between the occipital ring and the more frontal parts of the glabella are a pair of pits low on its sides beneath a large median spine extending from the glabella backwards. The distance between the glabella and the border (or preglabellar area) is usually long. This border has dozens of small furrows radiating inward (a so-called scrobiculate border), but this defining feature may be absent in effaced species or destroyed by poor preservation. The axis of the pygidium has four to ten rings.[1]

References

  1. ↑ 1.0 1.1 Whittington, H. B. (1997). Treatise on Invertebrate Paleontology Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.
  2. ↑ Jell, P.A. (1975). "Australian Middle Cambrian Eodiscoids with a review of the superfamily". Palaeontographica Abteilung A 150: 1–97. cited in H.B. Whittington et al., eds. (1997). Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.