Weymouthia (trilobite)

Weymouthia is an extinct genus of eodiscinid agnostid trilobites, which lived at the end of the Lower Cambrian, in what are now the eastern United States, England, Siberia and China.

Weymouthia
Temporal range: Lower Cambrian
Llinedrawing of Weymouthia nobilis
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Trilobita
Order:
Agnostida
Family:
Weymouthiidae
Genus:
Weymouthia

Raymond, 1913
Type species
Agnostus nobilis
Ford, 1872
Species
  • Weymouthia nobilis (Ford, 1872) ( syn.Agnostus nobilis
  • Weymouthia caudata (Delgado, 1904) (syn. Delgadella souzai caudata)
  • Weymouthia emerici Czarnocki
  • Weymouthia minor Egorova, 1961
  • Weymouthia tchernyshevae Egorova, 1961

Description

Like all Agnostida, Weymouthia is diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. Like all Weymouthiidae, Weymouthia lacks eyes and rupture lines (or sutures). The headshield (or cephalon) is approximately as long as wide, lacks facial sutures and is eyeless. The tailshield (or pygidium) is about 1.2× as wide as long. Both are effaced except for a furrow close to their borders. The cephalic border bears lateral tubercles. The thorax consists of three segments.[1]

Etymology

Weymouthia is named after Weymouth, Massachusetts.[2]

Distribution
  • W. nobilis occurs in the Lower Cambrian of Massachusetts (Hoppin Slate, North Attleboro), and of the United Kingdom (Comley Quarry, Comley, 52.6° N, 2.8° W).[3]

Remarks

Fletcher & Theokritoff (2008) [4] designated Shaw’s (1950, pl. 79, fig. 24) [5] specimen of “ Weymouthia nobilis (Ford, 1872)” [6] as the holotype of a new species, Serrodiscus weymouthioides, and considered Runcinodiscus Rushton (in Bassett et al., 1976) [7] [= ?Weymouthia nobilis (Ford, 1872)] to be a junior synonym of Serrodiscus; Rushton (1976) had previously regarded Weymouthia and Runcinodiscus as closely allied with Serrodiscus. Weymouthia nobilis (Ford 1872), first described from the Taconic region of New York State, is also recorded from the Protolenus Limestone (Ac5) [Protolenid-Strenuellid Zone] at Comley, Shropshire, England (Cobbold 1931),[8] but Rushton (in Bassett et al., 1976, p. 637) showed that the English specimens are specifically distinct from W. nobilis as described by Ford (1872), and thus erected his new genus and species, Runcinodiscus index Rushton (in Bassett et al. 1976, p. 636-7).

References
  1. WHITTINGTON, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
  2. "Weymouth, MA, history". Retrieved 3 December 2012.
  3. HINZ, I. (1987). "The Lower Cambrian microfauna of Comley and Rushton, Shropshire, England". Palaeontographica Abteilung A. 198 (1–3): 41–100. cited in Paleobiology Database. "Weymouthia nobilis".
  4. FLETCHER, T. P. & THEOKRITOFF, G., 2008. The Early Cambrian of eastern Massachusetts. Northeastern Geology and Environmental Science, 30, 301-329.
  5. SHAW, A. B., 1950. A revision of several Early Cambrian trilobites from eastern Massachusetts. Journal of Paleontology, 24, 577-590.
  6. FORD, S. W., 1872. Descriptions of some new species of primordial fossils. American Journal of Science, Series 3, 3, pp. 419-422.
  7. BASSETT M. G., OWENS R. M., and RUSHTON A. W. A. 1976. Lower Cambrian fossils from the Hell’s Mouth Grits, Journal of the Geological Society, 132 (6): 623 – 644.
  8. COBBOLD, E. S. 1931: Additional fossils from the cambrian rocks of Comley, Shropshire. Q. J. Geo/. Soc. Lond. 87, pp. 459 - 511


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