''Acidiscus'' Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family

Weymouthiidae The Weymouthiidae Kobayashi 1943 are an extinct family of eodiscinid agnostid trilobites. They lived during the late Lower Cambrian and earliest Middle Cambrian (Botomian to Delamaran) in the so-called ''Olenellus''- and ''Eokochaspis''-zon ...

Kobayashi T. (1943), Order Agnostida Salter (1864). It lived during the Botomian stage = late Lower Cambrian Stage 4 (upper of two stages subdividing the unnamed Series 2); the upper Botomian boundary corresponds to base of the Middle Cambrian,

Miaolingian The Miaolingian is the third Series of the Cambrian Period, and was formally named in 2018. It lasted from about to million years ago and is divided in ascending order into 3 stages: the Wuliuan, Drumian, and Guzhangian. The Miaolingian is prec ...

Series and

Wuliuan The Wuliuan stage is the fifth stage of the Cambrian, and the first stage of the Miaolingian Series of the Cambrian. It was formally defined by the ICS in 2018. Its base is defined by the first appearance of the trilobite species ''Oryctocephalu ...

stage.

Etymology

* ''A. birdi'' is named for Dr. John M. Bird who collected the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

. * ''A. hexacanthus'' is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

hexa "six" and acanthos "spine", for having two pairs of border spines in addition to one pair of genal spines. * ''A. theristes'' is named after a Greek in the

Iliad The ''Iliad'' (; grc, Ἰλιάς, Iliás, ; "a poem about Ilium") is one of two major ancient Greek epic poems attributed to Homer. It is one of the oldest extant works of literature still widely read by modern audiences. As with the ''Odysse ...

(an epic poem written by

Homer Homer (; grc, Ὅμηρος , ''Hómēros'') (born ) was a Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Homer is considered one of the ...

around 800 B.C.E.) who accused

Agamemnon In Greek mythology, Agamemnon (; grc-gre, Ἀγαμέμνων ''Agamémnōn'') was a king of Mycenae who commanded the Greeks during the Trojan War. He was the son, or grandson, of King Atreus and Queen Aerope, the brother of Menelaus, the husb ...

of greed and

Achilles In Greek mythology, Achilles ( ) or Achilleus ( grc-gre, Ἀχιλλεύς) was a hero of the Trojan War, the greatest of all the Greek warriors, and the central character of Homer's ''Iliad''. He was the son of the Nereid Thetis and Peleus, k ...

of cowardice during the Trojan War.

Taxonomy

A cladogram showing the relationship between several species of the genera ''Acidiscus'', '' Bolboparia'' and '' Stigmadiscus'' ''Acidiscus'' is most closely related to ''Bolboparia'' and slightly more distantly to ''Stigmadiscus''.

Synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

for ''Acidiscus-Bolboparia'' include anterolateral cephalic spines and a large preoccipital glabellar tubercle or spine. Both of these features have been considered as being diagnostic of ''Acidiscus'' (e.g., Rushton, 1966; Rasetti, 1966;) but they are shared with ''Bolboparia''. Synapomorphies of ''Bolboparia'' include a sharply tapered and pointed glabella, no occipital spine, tubercles confined to posterior part of the cephalic border, strongly inflated genae, and a sculpture of tightly packed coarse granules. ''Stigmadiscus'' is characterised by an inflated posterior part of the glabella, the loss of anterolateral cephalic spines and a preoccipital glabellar node, and in having a very narrow cephalic border. Among genera currently assigned to Weymouthiidae Kobayashi, 1943 (Jell ''in'' Whittington ''et al''. 1997), Rushton (1966, p. 12) noted that, “''Acidiscus'' Rasetti differs from ''Serrodiscus'' but slightly”, although several of the characteristics in the former genus that he listed, include the preoccipital glabellar and anterolateral cephalic spines, and the configuration of the lateral glabellar furrows.

Distribution

* ''A. birdi'' is known from the Lower Cambrian of the United States (unnamed formation, East Chatham Quad, Columbia County, New York State ), Canada (Newfoundland) and England (Purley Shales of Warwickshire). WHITTINGTON, H. B. ''et al''., 1997. Part O, ''Treatise on Invertebrate Paleontology''. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. * The

Holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of ''A. theristes'' Rushton, 1966, RUSHTON, A.W.A. 1966. The Cambrian Trilobites from the Purley Shales of Warwickshire. ''Palaeontographical Society Monographs'' (1): p. 16, pl. 1, figs. 20 a, b. is A 57082, held at the

Sedgwick Museum of Earth Sciences The Sedgwick Museum of Earth Sciences, is the geology museum of the University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledg ...

, University of Cambridge and was collected by Rushton from about 450' above base of the Purley Shale Formation (''Protolenus'' Biozone) at Camp Hill, St. Paul's Church, Stockingford, Nuneaton, Warwickshire, England losest ICS interval: Cambrian Series 3 – Terreneuvian Epoch * ''A. hexacanthus'' Rasetti (1966, p. 13, pl. 7, figs 1–6) is part of a trilobite faunule that was collected from unnamed limestone beds which form several outcrops on a hill (Griswold farm) about 1 mile southeast of North Chatham, Columbia County, New York State, USA; the faunule is referred to as the ''Acimetopus bilohatus'' faunule from one of the most common and characteristic trilobites. The ''Acimetopus bilobatus'' faunule is notable for the number and variety of trilobites of the family Eodiscidae.

Ecology

''A. birdi'' occurs in association with other Weymouthiidae ('' Acimetopus'', '' Analox'', '' Bathydiscus'', '' Bolboparia'', '' Leptochilodiscus'', '' Serrodiscus''), ''Calodiscus'', several species of ''

Olenellus ''Olenellus'' is an extinct genus of redlichiid trilobites, with species of average size (about long). It lived during the Botomian and Toyonian stages (''Olenellus''-zone), , in what is currently North-America, part of the palaeocontinent Lau ...

'', and ''Bonnia'' (Dorypygidae).

Description

Like all Weymouthiidae, ''Acidiscus'' lacks eyes and facial sutures. The cephalic border carries one or two pairs of marginal spines. The glabella does not reach the border furrow and has two short pit-like pairs of lateral furrows. Occipital and genal spines are present. Thorax unknown, but all weymouthiids in which it is known have three segments. The pygidium is much like that in '' Serrodiscus'', with an axis composed of ten rings. Pleural fields unfurrowed.

References

{{Taxonbar, from=Q4674105 Weymouthiidae Agnostida genera Cambrian trilobites Animals described in 1966 Fossils of Canada Paleontology in Newfoundland and Labrador