Eodiscidae

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Eodiscidae
Temporal range: Lower and Middle Cambrian
Pagetia taijiangensis 2.jpg
Pagetia taijiangensis , 6mm, from Kaili, Guizhou, China, Middle Cambrian
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita (?)
Order: Agnostida
Superfamily: Eodiscoidea
Family: Eodiscidae
Raymond, 1913
Genera
Synonyms
  • Aulacodiscidae
  • Dawsoniidae
  • Opsidiscidae
  • Pagetidae
  • Pagetiellinae

Eodiscidae is a family of agnostid trilobites 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. Eodiscidae includes nine genera (see box).

Contents

Taxonomy

The Eodiscids probably descended from the agnostids of family Yukoniidae. [2]

Description

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

Like other agnostids, the body of eodiscids 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]

Related Research Articles

<i>Acimetopus</i>

Acimetopus Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943), Order Agnostida Salter (1864). It lived during the Botomian stage. = late Lower Cambrian Stage 4 ; the upper Botomian boundary corresponds to base of the Middle Cambrian, Miaolingian Series and Wuliuan stage.

<i>Analox</i>

Analox Rasetti, 1966 is a genus of Eodiscinid trilobites belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida It lived during the Botomian stage. It can easily be distinguished from other trilobites by the two furrows that extend forwards and sidewards from the front of the glabella.

Meniscuchus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Botomian stage, which lasted from approximately 522 to 516 million years ago. This faunal stage was part of the Cambrian Period. Meniscuchus has been found in the USA, Canada, Russia and Australia.

Parapagetia is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period.

<i>Dicerodiscus</i> Extinct genus of trilobites

Dicerodiscus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Botomian stage, in China. Four species have been assigned to it. Dicerodiscus is unique for an eodiscoid in having conspicuous and curved spines that are attached anteriorly, and at their base are directed outward perpendicular to the midline, before gradually bending further backwards.

Semadiscus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It has been collected from the Lower Cambrian of Canada (Newfoundland), Russia, and the United States. Only the headshield is known, and it may well be that it would be better to include it in Serrodiscus.

Egyngolia is a genus of very small sized Trilobites, that lived during the Lower Cambrian in what are today the Russia Federation, Mongolia, and South Australia.

Yukoniidae S. Zhang, 1980 [nom. transl. et emend. Jell, in Whittington et al., 1997 ex Yukoniinae S. Zhang in W. Zhang, Lu et al., 1980] is a small family of trilobites, belonging to the Eodiscina.

Acmarhachis is a genus of trilobite in the order Agnostida, which lived in what are now Australia, Canada, China (Anhui), Kazakhstan, Russia (Kharaulakh), and the US. It was described by Resser in 1938, and the type species is Acmarhachis typicalis.

<i>Phalagnostus</i>

Phalagnostus is a genus of small trilobites, in the order Agnostida. It lived during the Middle Cambrian, in what are now Canada, China, the Czech Republic, Denmark, England, France, the Russian Federation, Wales, Sweden, and possibly the United States (Vermont). The headshield is almost entirely effaced and wider than the tailshield. The pygidium is also very effaced, but the ovate pygidial axis is well defined and a border furrow is also present.

<span class="mw-page-title-main">Eodiscina</span>

Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Lower Cambrian period and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or three segments. Eodiscina includes six families classified under one superfamily, Eodiscoidea.

<i>Litometopus</i> Extinct genus of trilobites

Litometopus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Botomian stage.

<i>Mallagnostus</i>

Mallagnostus Howell, 1935, is a trilobite genus belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida Salter (1864) according to Whittington et al. 1997. It lived during the late Lower Cambrian, with remains found in USA, Canada (Newfoundland), Spain, England, Russia, Mongolia, and the early Middle Cambrian as reported from China and Russia (Yakutia).

<i>Galbagnostus</i>

Galbagnostus is an extinct genus of agnostid trilobite. It lived during the Lower and Middle Ordovician.

<i>Tchernyshevioides</i> Genus of trilobite

Tchernyshevioides is a diminutive trilobite that lived during the early Middle Cambrian (Amgaian) and has been found in the Russian Federation and the Jbel Wawrmast Formation of Morocco.

<i>Toragnostus</i>

Toragnostus is a genus of trilobites restricted to the late Middle Cambrian. Its remains have been found in the United States, Greenland, Denmark, China, Sweden, the Russian Federation, and Kazakhstan. Its headshield and tailshield are almost completely effaced and it has two thorax segments.

The Hebediscidae Kobayashi, 1944, are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian. They are small or very small, and have a thorax of two or three segments. The Hebediscidae include five genera.

The Calodiscidae Kobayashi, 1943 [nom. transl. Öpik, 1975 ex Calodiscinae Kobayashi, 1943] are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian. They are small or very small, and have a thorax of two or three segments. The Calodiscidae includes five genera.

<i>Cedaria</i>

Cedaria is an extinct genus of trilobites from the late Cambrian.

Anabaraspis is a genus of redlichiid trilobite. A. splendens occurs in the uppermost Lower Cambrian and lowest Middle Cambrian of Russia. In Anabaraspis there is a long area in front of the glabella which is not differentiated in a border and a preglabellar field. This is a unique character in the family Paradoxididae. The frontal lobe of the central raised area of the headshield is slightly pointed, rather than rounded or truncate, a character shared with Plutonides, though, in Plutonides it hangs over the short anterior border.

References

  1. 1 2 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.