Arthropoda Siebold, 1845

Skovsted, Christian B. & Peel, John S., 2007, Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of western Newfoundland, Acta Palaeontologica Polonica 52 (4), pp. 729-748 : 733

Phylum Arthropoda Siebold, 1845 Class Trilobita Walch, 1771

Discussion.—Trilobites are represented in the acid resistant residues from Newfoundland by a phosphatic mould of the cephalon of an unidentified Dorypygidae ( Fig. 3A ), silicified cephala of the eodiscid Calodiscus lobatus (Hall, 1847) ( Fig. 3B ), corynexochids ( Fig. 3C ), and protaspid olenellids ( Fig. 3D ). With the exception of C. lobatus , no specimen can be identified to species, although a number of polymeroid trilobites have been reported from the Forteau Formation of western Newfoundland (e.g., Wanneria logani [Walcott, 1910], Olenellus thompsoni [Hall, 1859], Bonnia parvulus Billings, 1861 , B. columbensis Resser, 1938 , “ Conocephalites ” miser Billings, 1861, Antagmus sp. , and other unidentified ptychoparioids; Schuchert and Dunbar [1934]; James and Kobluk [1978]; Knight and Boyce [2000]).

Morphologically diverse, flattened fossils with distinct tubercles and small spines ( Fig. 7J–N) clearly represent fragmented shells of a larger animal, presumably a trilobite. Most specimens appear to be internal moulds formed between the carapace and the doublure. In particular, large curved fragments with small marginal spines may represent the cephalic margins, occasionally with the genal spine preserved ( Fig. 7K). The trilobite(s) would have been covered externally with a multitude of small tubercles, preferentially along the margins of the sclerites. However, no trilobite with comparable tubercles is known from the Lower Cambrian of western Newfoundland, but the current remains are likely derived from meraspids.

Figures

Fig. 3. Trilobites, echinoderms, and sponges from the Lower Cambrian, Forteau Formation (Western Newfoundland). A. Dorypygidae indet., internal mould of fragmentary cephalon, NFM−671 from ICS 1421; in dorsal (A1) and left lateral (A2) views. B. Calodiscus lobatus (Hall, 1847), NFM−672, dorsal view of silicified cephalon. C. Ptychoparioid indet., NFM−673 from ICS 1421, silicified cephalon. D. Olenellid indet., NFM−674 from ICS 1421, dorsal view of silicified juvenile cephalon. E–J. Phosphatised echinoderm ossicles. E. Morphotype 1, NFM−675, dorsal view. F. Morphotype 1, NFM−676, dorsal view. G. Morphotype 1, NFM−677, ventral view. H. Morphotype 2, NFM−678, ventral view. I. Morphotype 2, NFM−679, dorsal view. J. Morphotype 2, NFM−680, oblique lateral view. K. Hexactinellid spicule, NFM−681, scale bar 100 ̊m. All specimens from JSP 1982−01 unless otherwise stated. All scale bars except K 500 ̊m.