Paradoxides davidis Salter 1863

Paradoxides davidis Salter, 1863

(Figs 11; 12)

Paradoxides davidis Salter, 1863: 276, unnamed text fig. p. 275;1864a: 234, 235, pl. 12, figs 1-3; 1864b: 1-4, pl. 10, figs 1-8. — Linnarsson 1882: 11-14, pl. 1, figs 14, 15; pl. 2, figs 1-9. — Grönwall 1902: 106-112, pl. 2, figs 3-7. — Cobbold 1911: 287, pl. 24, figs 17a, b, 18. — Illing 1915: 428, pl. 35, figs 9-11 (?). — Lake 1935: 203- 208, pl. 27, figs 1, 2; pl. 28, figs 1-3; pl. 29, figs 1-3. — Hutchinson 1952: 76, 77, pl. 2, figs 6-8; 1962: 115, pl. 19, fig. 10; pls. 20, 21; pl. 22, figs 1-5. — Hupé 1955: fig. 77.1. — Fletcher 1972b: 92, pl. 49, fig. 11; pl. 50, figs 1-6; pl. 51, figs 1, 2. — Bergström & Levi-Setti 1978: 6, 7.

Paradoxides davidis brevispinus Bergström & Levi-Setti, 1978: 11, fig. 7c; pl. 9, fig. 5; pl. 10, figs 1-7, n. syn.

Paradoxides davidis davidis Bergström & Levi-Setti, 1978: 7, 8, fig. 7a; pl. 2, figs 1-3; pl. 3, figs 1-5; pl. 4, figs 1-11; pl. 5, figs 1-11 (?). — Levi-Setti 2014: pls 150-154, n. syn.

Paradoxides davidis intermedius Bergström & Levi-Setti, 1978: 9, 11, pl. 6, figs 1-7. — Levi-Setti 2014: pl. 159, n. syn.

Paradoxides davidis trapezopyge Bergström & Levi-Setti, 1978: 8, 9, fig. 7b; pl. 6, fig. 8; pl. 7, figs 1-5; pl. 8, figs 1, 3, 4, 7, 8; pl. 9, figs 1-3. — Whittington 1992: 121, pl. 46. — Levi-Setti 2014: pls 155-158, n. syn.

Paradoxides (Paradoxides) davidis davidis – Morris & Fortey 1985: pl. 7, fig. 3, pl. 8, fig. 4 (?). — Martin & Dean 1988: 18, pl. 4, figs 11-17(partim). — Fletcher 2007: 47, figs 8G-I. — Fletcher & Greene 2013: 514, pl. 3, figs 7, 9-11, 14, 15.

Plutonides hicksi – Vaněk et al. 1999: 36, pl. 1, figs 1, 2, 5, 6.

Paradoxides (P.) davidis – Fletcher 2006: 34, figs 9, 10. — Rees et al. 2014: figs 1.10, 1.11b.

HOLOTYPE. — Specimens no. BM 45083 and BM 45084, British Museum, London, United Kingdom by original designation, from the Menevian Group of Port-y-rhaw, St. David’s, Wales, United Kingdom.

DIAGNOSIS. — Glabella with S1 curved backwards, S2 curved forward abaxially and backward axially, S3 and S4 absent; frontal lobe more than half of total glabellar length; occipital furrow curves slightly forward axially; librigenal spines and doublure lineated bifurcating and anastomosing, creating a narrow mashed net; thorax with 19 segments; posterior pleural spines extend far beyond pygidium; pygidium with concave posterior margin and axis with one ring (based on Lake 1935; Fletcher 1972b, with modifications).

MATERIAL EXAMINED. — 124 cephala, mostly cranidia, some doublures, and seven pygidia of Paradoxides davidis (for NFM numbers see Appendix 1). All specimens range between 9.56 and 17.89 m (Fig. 2) of the Manuels River Formation, type locality, Conception Bay South, Newfoundland, Canada.

OCCURRENCE. — Paradoxides davidis is an important regional biostratigraphical marker of the middle Cambrian (Howell 1925; Lake 1935; Hutchinson 1962), which has been documented from southeastern Canada, eastern Newfoundland, in the Paradoxides davidis and Ptychagnostus punctuosus zones (Hutchinson 1962; Fletcher 1972b; Martin & Dean 1988; Whittington 1992; Fletcher 2006, 2007; Fletcher & Greene 2013). It has also been reported from southeastern Canada in Nova Scotia (Hutchinson 1952), United Kingdom in Wales (Paradoxides davidis Zone; Salter 1863, 1864a; Lake 1935; Rees et al. 2014) and England (Cobbold 1911; Illing 1915), Denmark (Grönwall 1902), Sweden (Ptychagnostus punctuosus Zone; Linnarsson 1882; Westergård 1953) and the Czech Republic (Eccaparadoxides pusillus Zone; Vaněk et al. 1999).

DESCRIPTION

The cranidia range from 38.0 mm to 62.0 mm width and 31.0 mm to 55.0 mm length, while the pygidia range from 7.0 to 9.0 mm width and 10.0 mm to 12.0 mm length. The preservation of the cranidia is very good and the preservation of the pygidia is good, both preserved as internal casts and moulds. Some cranidial internal casts have a groove lining from the frontal margin across the glabella towards the middle to outer margin of the occipital ring. Some cranidia bear a small, macroscopically slightly visible node on the occipital ring. Several specimens are pyritized. The glabella is always the most well-preserved part of the cranidium. The pleural spines are usually broken. When preserved, the posterior pleural spines reach at least twice the pygidial length. Pygidia are shaped trapezoidally.

REMARKS

According toLake (1935) Paradoxides davidis is closely related to Paradoxides tessini Brongniart, 1822. Pa. tessini has a longer palpebral lobe, a blunter front margin of the glabella, a less backward-curved S1 furrow, 21 thoracic segments and a rounded posterior margin of the pygidium (Lake 1935). Illing (1915) described and figured one doublure and two thoracic fragments of Pa. davidis. The fragment illustrated on pl. 35, fig. 10, only consists of four to possibly five outer pleurae without the axis, whereas the specimen on pl. 35, fig. 11, is overexposed. An assignment of the two specimens to any species is therefore questionable.

Bergström & Levi-Setti (1978) divided Pa. davidis into four subspecies: Paradoxides davidis davidis, Paradoxides davidis trapezopyge, Paradoxides davidis intermedius and Paradoxides davidis brevispinus. They distinguish them (Pa. davidis davidis, Pa. davidis trapezopyge and Pa. davidis intermedius) by their mean pygidial width ratio, while the fourth, Paradoxides davidis brevispinus, is distinguished by the mean pygidial width ratio, a coarse ornamentation and notably short pleural spines. We here propose, that the identification of this latter subspecies is thus only applicable when the pygidium is attached to the thorax and cephalon. The articulated specimens of Pa. davidis davidis figured by Bergström & Levi-Setti (1978: pl. 3, figs 1, 2) have poorly preserved cephala and pygidia; their assignment to any species is here suggested questionable. Pygidial variations identified in Pa. davidis, as described by Bergström & Levi-Setti (1978), are herein interpreted as an intraspecific variation. The coarse ornamentation described byBergström & Levi-Setti (1978) is not identified in all specimens assigned to Pa. davidis brevispinus (e.g., Bergström & Levi-Setti 1978: pl. 10, fig. 6), while it is visible on the thorax on their pl. 8, fig. 8, assigned to Pa. davidis trapezopyge. The presence, or absence of ornamentation is therefore here interpreted as either an intraspecific variation or a matter of preservation. The short pleural spines are not as notable as mentioned by Bergström & Levi-Setti (1978) and are consequently not considered to be a reliable diagnostic characteristic. Based on the here described 123 cranidia and only seven pygidia, none of them attached to the cephalon, we suggest that a division of Pa. davidis into subspecies is not applicable.

Pa. davidis davidis figured by Morris & Fortey (1985: pl. 7, fig. 3) is a poorly preserved mould of a cephalon attached to the anterior portion of the thorax, crossed by several cracks. The S2 furrow apparently is aligned parallel to the S1 furrow, which does not match the diagnosis of Pa. davidis. Based on the preservation and the shape of S2 the assignment to this species is questionable. Martin & Dean (1988) assigned their specimens to the subspecies Pa. davidis davidis but included all subspecies introduced by Bergström & Levi-Setti (1978) in their list of synonyms. The juvenile cranidium illustrated by Martin & Dean (1988) on plate 4, figure 4, has four glabellar furrows and eye lobes reaching from S4 to L1. These characteristics do not agree with the diagnosis of Pa. davidis which is characterised by two characteristic glabellar furrows. The specimen is here excluded from the genus. The nearly articulated specimens documented byWhittington (1992) as Pa. davidis trapezopyge match the characteristics of Pa. davidis and are here assigned to the species. Vaněk et al. (1999) discussed and figured specimens assigned to Plutonides hicksi (Salter, 1866b). The illustrated cranidia on plate 1, figures 1, 2 and 6, only have S1 and S2 furrows with the typical shape of those of Pa. davidis; they are here assigned to Pa. davidis. Specimens illustrated by Fletcher (2007) and Fletcher & Greene (2013) assigned to Paradoxides (Paradoxides) davidis davidis show the characteristics of Pa. davidis and are hence assigned to this species.