Serrodiscus Temporal range: | |
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Pygidia of Serrodiscus silesius | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Clade: | † Artiopoda |
Class: | † Trilobita (?) |
Order: | † Agnostida |
Family: | † Weymouthiidae |
Genus: | † Serrodiscus Richter & Richter, 1941 |
Species | |
See text | |
Synonyms | |
ParadiscusKobayashi, 1943 [type: Microdiscus speciosus Ford, 1872] Contents |
Serrodiscus Richter and Richter 1941. [1] is a genus of eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi T. (1943), [2] Order Agnostida (Salter 1864). [3] 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). [4] It is named for the spines on the ventral side of the pygidium, which give it a serrated impression.
Fletcher & Theokritoff (2008) [5] designated Shaw’s (1950, pl. 79, fig. 24) [6] specimen of “Weymouthia nobilis (Ford, 1872)” [7] as the holotype of a new species, Serrodiscus weymouthioides, and considered Runcinodiscus Rushton (in Bassett et al., 1976) [8] [= ?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).
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. [4]
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.