Acimetopus

Last updated

Acimetopus
Temporal range: Botomian (Olenellus-zone)
Acimetopus linedrawing.jpg
Acimetopus bilobatus
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Trilobita
Order:
Agnostida
Family:
Weymouthiidae
Genus:
Acimetopus

Rasetti, 1966
Type species
Acimetopus bilobatus
Rasetti, 1966  [1]

Acimetopus Rasetti, 1966, [2] is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943), [3] Order Agnostida Salter (1864). [4] It lived during the Botomian stage. [1] = late Lower Cambrian Stage 4 (upper of two stages subdividing the un-named Series 2); the upper Botomian boundary corresponds to base of the Middle Cambrian, Miaolingian Series and Wuliuan stage.

Contents

Type species

Acimetopus bilobatus Rasetti, 1966, from his locality cs-4 in limestone beds which form several outcrops on a hillside at Griswold Farm, about 1 mile southeast of North Chatham, Columbia County, New York State, USA; the associated faunule is referred to as the Acimetopus bilobatus faunule due to the nominate species being one of the most common and characteristic trilobites.

Distribution

Acimetopus is known from the Lower Cambrian of the United States (unnamed formation, East Chatham Quad, Columbia County, New York State 42°24′N73°30′W / 42.400°N 73.500°W / 42.400; -73.500 ), [5] and England. [6]

Description

Like in all Agnostida, the body of Acimetopus is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are approximately the same size (or isopygious). The thorax is unknown but all weymouthiids where it is known have 3 thoracic segments. Acimetopus has no eyes. Its cephalic border is strongly convex, with a pair of lateral marginal spines. The entire exoskeleton of Acimetopus is covered in granules. The central raised area of the cephalon, called the glabella, is strongly divided by two deep furrows that merge when crossing the midline. The large and inflated anterior lobe is isolated from border furrow. Behind it is a pair of small, separated, subtriangular lobes. The posterior part of the glabella is large and carries an inflated spine that is directed upwards and backwards. Genal spines are present. The axis of the pygidium (or rhachis) has nine rings that are strongly inflated, with the second ring carrying a vertical spine. The border surrounding the pygidium is defined by a deep furrow, is narrow, and lacks spines. [6]

Ecology

Acimetopus bilobatus occurs in association with other Weymouthiidae including ( Acidiscus , Analox , Bathydiscus , Bolboparia , Leptochilodiscus , Serrodiscus ), Calodiscus , and several species of Olenellus Billings, 1861, and Bonnia Walcott, 1916 (Family Dorypygidae). [5]

Related Research Articles

<i>Acidiscus</i>

Acidiscus Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi T. (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.

<i>Bathydiscus</i>

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

<i>Bolboparia</i>

Bolboparia is an extinct genus of eodiscinid agnostid trilobites. It lived during the late Lower Cambrian in what today Canada and the United States.

Leptochilodiscus Rasetti, 1966 [= Kerberodiscus Bassett et al., 1976] is a genus of Lower Cambrian Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943), Order Agnostida. It lived during the Botomian stage = late Lower Cambrian Stage 4 ; the upper Botomian Stage boundary corresponds to base of both the Middle Cambrian Wuliuan stage and Miaolingian Series.

<i>Ninadiscus</i>

Ninadiscus Korobov, 1980, 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 the base of the Middle Cambrian, the Miaolingian Series and Wuliuan Stage.

<i>Oodiscus</i>

Oodiscus is an extinct genus of small size trilobite, with three known species. It lived during the Toyonian in what are now Canada and the USA.

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

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>

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.

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>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.

Weymouthiidae

The Weymouthiidae Kobayashi 1943 are an extinct family of eodiscinid agnostid trilobites. They lived during the late Lower Cambrian and earliest Middle Cambrian in the so-called Olenellus- and Eokochaspis-zones in the former paleocontinents of Laurentia, Avalonia, Gondwana. The Weymouthiidae are all blind and lack free cheeks.

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>Jinghediscus</i>

Jinghediscus Xiang & Zhang, 1985 is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida It lived during the lower Middle Cambrian, with remains found in China (Xinjiang) and Australia (Queensland).

<i>Serrodiscus</i>

Serrodiscus Richter and Richter 1941. is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida. It lived during the late Lower Cambrian, with remains found in Canada, China (Gansu), The United Kingdom (England), Germany (Silesia), Poland, the Russian Federation, and the United States. It is named for the spines on the ventral side of the pygidium, which give it a serrated impression.

References

  1. 1 2 SEPKOSKI, J. (2002). "A compendium of fossil marine animal genera (Trilobita entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 5 September 2006. Retrieved 12 January 2008.
  2. ↑ RASETTI, F., 1966. New Lower Cambrian trilobite faunule from the Taconic sequence of New York. Smithsonian Miscellaneous Collections 148, 1-52.
  3. ↑ KOBAYASHI T. 1943. Brief notes on the Eodiscids 1, their classification with a description of a new species and a new variety. Proceedings of the Imperial Academy, Tokyo, Volume 19, pp. 37-42.
  4. ↑ SALTER, J. W. 1864: On some new fossils from the Lingula-flags of Wales. Quarterly Journal of the Geological Society of London, 20, 233–241.
  5. 1 2 Paleobiology Database. "East Chatham Quad, unnamed fm., NY (Cambrian of the United States) (trilobite)" . Retrieved 19 December 2012.
  6. 1 2 WHITTINGTON, H. B. (1997). Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.


Agnostus-pisiformis.png

This Agnostida-related article is a stub. You can help Wikipedia by expanding it.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.