''Serrodiscus'' Richter and Richter 1941. 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 late Lower Cambrian, with remains found in Canada (Newfoundland & Nova Scotia), China (Gansu), The United Kingdom (England), Germany (Silesia), Poland (Holy Cross Mountains), the Russian Federation (Tuva, Gorno-Altayskaya, Kuznetsk Alatau), and the United States (Massachusetts, New York State). It is named for the spines on the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

side of the

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

, which give it a serrated impression. Fletcher & Theokritoff (2008) designated Shaw’s (1950, pl. 79, fig. 24) specimen of “''Weymouthia nobilis'' (Ford, 1872)” as the holotype of a new species, ''Serrodiscus weymouthioides'', and considered ''Runcinodiscus'' Rushton (''in'' Bassett ''et al''., 1976) ?''Weymouthia nobilis'' (Ford, 1872)to be a junior synonym of ''Serrodiscus''. ''Weymouthia'' and ''Runcinodiscus'' had previously been viewed as closely allied with ''Serrodiscus'' (e.g. Rushton ''op. cit''., 1976).

Species list

* ''Serrodiscus serratus'' Richter & Richter (1941) - Type species 'Eodiscus (Serrodiscus) serratus'' * ''Serrodiscus silesius'' Richter & Richter (1941, pl. 1, figs. 11-14; Geyer & Elicki 1995, figs. 3.1-3.9, 5.1, 5.3). * ''Serrodiscus speciosus'' (Ford, 1872). * ''Serrodiscus bellimarginatus'' (Shaler & Foerste, 1888). * ''Serrodiscus weymouthioides'' Fletcher & Theokritoff 2008, = ''Weymouthia nobilis'' (Ford, 1872); Rushton (''in'' Bassett ''et al.'' 1976, p. 630) reasoned that ''Weymouthia nobilis'' (Ford, 1872) is a ''nomen dubium''. * ''Serrodiscus ctenoa'' Rushton, 1966. * ''Serrodiscus mackenziensis'' Fritz, 1973. * ''Serrodiscus daedatus'' Öpik, 1975. * ''Serrodiscus gravestocki'' Jell, (''in'' Bengston ''et al.'', 1990) '' * ''Serrodiscus areolosus'' Zhou in Zhou ''et al''., 1982. * ''Serrodiscus subclavatus'' Rasetti, 1966. * ''Serrodiscus spinulosus'' Rasetti, 1966. * ''Serrodiscus latus'' Rasetti, 1966. * ''Serrodiscus griswaldi'' Rasetti, 1967.

Distribution

* ''S. bellimarginatus'' (Shaler & Foerste, 1888) is known from the Lower Cambrian of Canada (Atdabanian, ''Callavia broeggeri'' zone, Branchian Series, St. Mary’s Member, Brigus Formation, Long Cove, Trinity Bay, and Redland Point, St. Mary’s Bay, Newfoundland. * ''S. speciosus'' (Ford, 1873) has been found in the Lower Cambrian of Poland (Atdabanian, Ocieseki Sandstone and Kamieniec Shale, Holy Cross Mountains). The species also occurs in the Brown’s Pond Formation (“Schodack Formation”), Troy, New York. Type locality for ''S. speciosus'' is Rasetti's (1966) locality cs-4 in limestone beds which form several outcrops on a hillside (Griswold Farm) about 1 mile southeast of North Chatham, Columbia County, New York State, USA; the faunule is referred to as the ''Acimetopus bilobatus'' faunule from one of the most common and characteristic trilobites. It also occurs in a continuously exposed section of about 250 feet of strata along the New York Central Railroad tracks on the east shore of the Hudson River at Judson Point. About 130 feet of exposed black shale overlie 120 feet of alternating sandstones, shales, sandy or relatively pure limestones, and limestone conglomerates. However, fossil evidence shows that the strata are overturned, with the black shale underlying the sandstone shale-limestone sequence. Fossils occur about 30 - 40 and 75 feet below the top of the shale, and indicate the Lower Cambrian ''Elliptocephala asaphoides'' fauna. * ''Serrodiscus ctenoa'' Rushton, 1966, was recovered from the Purley Shale Formation (c. 450' above base), ''Protolenus'' Biozone, of Camp Hill, St. Paul's Church, Stockingford, Nuneaton, Warwickshire, England losest ICS interval: Cambrian Series 3 – Terreneuvian Epoch Holotype is A 57067, held in the collections of the Sedgwick Museum of Earth Sciences, University of Cambridge, England. * ''Serrodiscus silesius'' Richter & Richter, 1941, ''Serrodiscus'' beds of ''Lusatiops'' Member, Niederludwigsdorf, near Görlitz, Saxonia, eastern Germany: quarry 1 (material of Schwarzbach 1934 and Richter, & Richter, 1941) and quarry 3. GEYER G. and ELICKI O. 1995. The Lower Cambrian trilobites from the Görlitz Synclinorium (Germany) — review and new results, ''Paläontologische Zeitschrift'' 69 (1) : 87-119. * ''Serrodiscus areolosus'' Zhou in Zhou ''et al''., 1982, was described rom the Shuangyingshan Formation, Lower Cambrian (Cambrian Series 2) of Dahuoluo, Subei County, northwestern Gansu, China. * ''Serrodiscus gravestocki'' Jell, (''in'' Bengston ''et al.'', 1990) was discovered in the Early Cambrian Hawker Group, Oraparinna Shale, Bunyeroo Gorge, Flinders Ranges, South Australia. * ''Serrodiscus subclavatus'' Rasetti, 1966a, collected from Rasetti's locality cs-4, Griswold Farm, North Chatham, New York State ee ''S. speciosus'' (q. v.) for detail * ''Serrodiscus spinulosus'' Rasetti, 1966a, collected from Rasetti's locality cs-4, Griswold Farm. * ''Serrodiscus latus'' Rasetti, 1966a, collected from Rasetti's locality cs-4, Griswold Farm. * ''Serrodiscus griswaldi'' Rasetti, 1967, collected from Rasetti's locality cs-4, Griswold Farm.

Description

Like all Weymouthiidae, ''Serrodiscus'' lacks eyes and facial sutures. The cephalon is semi-elliptical; glabella conical or parallel sided and usually with weak or effaced furrows. Front of glabella does not extend to the anterior furrow; preglabellar field short (sag.) and sometimes separating the genae by a shallow depression. Occipital ring may or may not carry a backward-directed spine. Cephalic border convex, with up to eight pairs of tubercles laterally. Thorax has three segments. The pygidium has a wide, subconical axis with more than eight rings. The pleural fields are extremely weakly furrowed (on internal mould only). Pygidial border becomes narrower towards posterior and usually carries about 8 ventral spines either side.

Behaviour

''Serrodiscus'' could protect its soft underside by enrollment and it has been demonstrated that the ventral spines on the pygidial doublure interlock the nodes on the cephalic border, probably improving defense.

References

{{Taxonbar, from=Q20720466 Weymouthiidae Agnostida genera Cambrian trilobites Cambrian trilobites of Europe Paleozoic life of Nova Scotia Paleozoic life of Yukon Cambrian genus extinctions