Pleuroctenium

Pleuroctenium is a genus of very small agnostid trilobites whose fossils are found in Middle Cambrian-aged marine strata of Canada (Newfoundland and New Brunswick), Czech Republic, England and Wales, France, and Sweden. Species of Pleuroctenium can be easily distinguished from all other agnostids because the frontal lobe of the central raised area of the headshield (or glabella) is wider than and folds around the rear lobe.

Pleuroctenium
Temporal range: early Middle Cambrian (Amgaian to Mayaian)
↓
P. granulatum
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Trilobita
Order:
Agnostida
Suborder:
Agnostina
Superfamily:
Condylopygoidea
Family:
Condylopygidae
Genus:
Pleuroctenium

Hawle & Corda, 1847[1]
species
  • P. granulatum (Barrande, 1846) (type) synonyms Battus granulatus, Agnostus granulatus, Dichagnostus granulatus
    • P. granulatum granulatum
    • P. granulatum pileatum Rushton, 1966
    • P. granulatum scanense Westergård, 1946
  • P. bifurcatum (Illing, 1916)
  • P. magnificum Howell, 1936
  • P. tuberculatum (Illing, 1916)
Synonyms

Dichagnostus

Distribution
  • P. granulatum granulatum has been collected from the early Middle Cambrian of Canada (Paradoxides hicksi-zone Manuels River Formation, South-East Newfoundland), the Czech Republic (higher levels of the Skryje Shales, Jince Formation, Skryje-Týřovice area) and the United Kingdom (P. aurora-zone to upper part of the P. hicksi-zone, Abbey Shale Formation, Nuneaton).[1]

Description

Like all Agnostida, Pleuroctenium is diminutive, with the headshield (or cephalon) and tailshield (or pygidium) of approximately the same size (or isopygous) and outline, and only two thorax segments. The characteristic sidewise expansion of the frontal lobe of the glabella, occipital structures instead of basal lobes, and a rhachis with three pairs of side lobes and a rear lobe differentiate Condylopygidae from all other agnostids. Pleuroctenium can easily be distinguished from its sister taxon Condylopyge because the frontal glabellar lobe on both sides wraps around the rear lobe, giving it a crescent-like appearance. The frontal glabellar lobe is also generally weakly dissected lengthwise, unlike in Condylopyge. The glabella may carry spines.[2] The pygidium may carry a pair of stout, backwardly directed spines and in some exquisitely preserved specimen, the lateral side of the pygidium and the large spines carried up to 30 minute laterally directed secundairy spines.[1]

gollark: (carcinized)
gollark: I may need an "incdec-rs".
gollark: Yes, it seems like under heavy load people get dropped somehow?
gollark: Incdec is a cool fixpoint.
gollark: I have deployed apiobots to rectify its value.

References
  1. Fatka, O.; Herynck, J.; Najman, P. (2004). "New finds of agnostid trilobites in the Skryje-Týřovice area (Middle Cambrian, Barrandian Area, Czech Republic)" (PDF). Journal of the Czech Geological Society. 49 (1–2): 75–81.
  2. Whittington, H.B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997


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