Botsfordia caelata ( Hall, 1847 )

Skovsted, C. B., Knight, I., Balthasar, U. & Boyce, W. D., 2017, Depth related brachiopod faunas from the lower Cambrian Forteau Formation of southern Labrador and western Newfoundland, Canada, Palaeontologia Electronica (Oxford, England: 1990) 17 (15), pp. 1-52 : 33-37

Botsfordia caelata ( Hall, 1847)

Figure 18

* 1847 Orbicula caelata Hall , p. 290, plate 79, figure 9a–c.

1912 Botsfordia caelata (Hall) ; Walcott, p. 603, plate 59, figures 1a–q, 3a–b (see also for earlier synonymy).

v 1927 Botsfordia caelata (Hall) ; Poulsen, p. 249, plate 14, figures 1–2.

1929 Botsfordia caelata (Hall) ; Strand, p. 340, plate 1, figure 1.

1932 Botsfordia caelata (Hall) ; Poulsen, p. 15, plate 2, figures 1–2.

1956 Botsfordia caelata (Hall) ; Lochman, p. 1370, plate 4, figures 3–6.

?1977 Botsfordia caelata (Hall) ; Pelman, p. 30, plate 10, figures 1–7.

1983 Botsfordia caelata (Hall) ; Goryansky and Koneva, p. 135, plate 29, figures 11-13.

1996 Botsfordia caelata (Hall) ; Landing and Bartowski, figures 8.20, 23.

1996 Botsfordia caelata (Hall) ; Holmer, Popov, and Wrona, plate 10, figures 11, 13, possibly also figures 10, 12.

2001 Botsfordia caelata (Hall) ; Holmer, Popov, Koneva, and Bassett, p. 66, plate 17, figures 4-9.

2005 Botsfordia caelata (Hall) ; Skovsted and Holmer, p. 334, plate 3, figures 12-15, plate 4, figures 1-15.

?2010 Botsfordia caelata (Hall) ; Rozanov et al., p. 81, plate 48, figures 1-7.

?2016 Botsfordia caelata (Hall) ; Ushatinskaya and Korovnikov, p. 452, plate 3, figures 1-10.

Holotype. Not designated (see Walcott, 1912, p. 821).

Material. 49 ventral, 48 dorsal valves, and a single specimen with conjoined valves from the Middle shale of the Forteau Formation of southern Labrador ( FC 1-3, FC 1-4, FC1-5, FC1-7, FC2-5, FC2-6, FC2-7, FCX, ICS 1553, ICS 1562, ICS 1565, ICS 1575, ICS 1581) and the Devils Cove member of western Newfoundland (MSM-2, MSM-3, ECP- 1, ECP-3, ICS 1520).

Diagnosis. See Skovsted and Holmer (2005), p. 336.

Description. The material of Botsfordia caelata from the Forteau Formation is invariably fragmentary, but aspects of the external morphology are sometimes well preserved. The ventral valve is convex with catacline pseudointerarea with triangular pedicle groove and raised propareas ( Figure 18.5-6, 18.9 ). Dorsal valve gently convex with marginal umbo, a strongly ventrally deflected commissural plane along the posterior margin, curved pseudointerarea with a wide, triangular median groove ( Figure 18.11-13 ). Ventral larval shell sub-circular with a single central tubercle ( Figure 18.1- 2, 18.8 ) and ornamented by fine pits with a diameter of 0.7 to 1µm. Adult shell pustulose, with pustules of 8-14 µm in diameter, typically increasing in size anteriorly.

Ventral valve interior with a slightly thickened visceral area with elongate posterolateral and arcuate central muscle fields and divergent impressions of pedicle nerves ( Figure 18.5-6, 18.9-10 ). Dorsal valve interior with a low median ridge and deeply impressed posterolateral muscle fields ( Figure 18.11-13 ).

Remarks. The morphology of Botsfordia caelata is described in detail by Skovsted and Holmer (2005), but the Forteau Formation material adds new morphological information, in particular the morphology of the ventral larval shell and the finely pitted larval micro-ornament. The ventral valves of B. caelata differ from ventral valves of Pustulobolus triangulus by the smaller and non-orthogonal ventral pseudointerarea and from Eothele tubulus by the presence of a ventral pseudointerarea and the lack of a pedicle foramen throughout ontogeny. The dorsal valves of B. caelata are more similar to the dorsal valves of P. triangulus and E. tubulus but differ from P. triangulus by the shorter dorsal pseudointerarea and the ventrally deflected commissural plane, and from E. tubulus by the narrower pseudointerarea with propareas slightly wider than the median groove.

Botsfordia caelata is very common in eastern Laurentia ( Walcott, 1912; Lochman, 1956; Skovsted and Holmer, 2005) and is also known from Norway ( Strand, 1929) and Kazakhstan ( Gorjansky and Koneva, 1983; Holmer et al., 2001). The species has also been reported from the Siberian platform ( Pelman, 1977; Rozanov et al., 2010; Ushatinskaya and Korovnikov, 2016). The Siberian shells are very similar to the Laurentian specimens investigated by us but appear to differ in the more circular shape of the ventral valves and in the the smaller ventral and dorsal pseudointerareas as well as the less pronounced ventral flexing of the dorsal valve. For this reason we only include the Siberian material as questionably belonging to B. caelata .

In the Forteau Formation, Botsfordia caelata occurs exclusively in shallow water carbonates in the lower part of the formation deposited during the TST of the sequence and always in association with archaeocyathid buildups (i.e., Middle shale at Fox Cove in southern Labrador and scattered archaeocyathid clasts in the Devils Cove member at the Mount St. Margaret and ECP-sections in western Newfoundland). As with Pustulobolus triangulus and Eothele tubulus , the distributional pattern is based on identification of ventral valves only, as the dorsal valves of all three species are considered to be too similar to be clearly identifiable on their own unless perfectly preserved specimens are available. The occurrence in shallow water carbonates in the Forteau Formation may seem at odds with the presence of B. caelata in relatively deep water sediments elsewhere in eastern Laurentia (i.e., Taconic Allochthon [ Lochman, 1956] and the Bastion Formation of North-East Greenland [ Skovsted and Holmer, 2005]). However, in these cases the described specimens occur in event beds in distal shelf or continental slope settings and may have been derived from more near-shore environments. In Norway B. caelata occur in sandy limestone at TØmten ( Strand, 1929) that together with the occurrences in Kazakhstan in shallow water carbonates ( Holmer et al., 2001), seems to corroborate the distributional pattern of the species in the Forteau Formation. However the occurrence of possible specimens of B. caelata in the Sinsk biota of Siberia in an open marine setting with dysaerobic bottom waters ( Ivantzov et al., 2005) is clearly opposite to the pattern identified in the Forteau Formation and invites further study of both the taxonomy of the Siberian shells and the distributional pattern of B. caelata in other areas of east Laurentia.

Distribution. Assemblage 1, Devils Cove member and Middle shale, Forteau Formation of southern Labrador and western Newfoundland. Cambrian Series 2, Stage 4 of eastern Laurentia (New York State, Vermont, North-East Greenland), Norway, Kazakhstan, and possibly Siberia.

Figures

FIGURE 18. Botsfordia caelata (Hall, 1847) from the Forteau Formation of southern Labrador and western Newfoundland. 1, 8, Ventral valve NFM F-2536 from sample ICS1565; 1, exterior view; 8, detail of larval shell with pitted ornament. 2-4, Ventral valve NFM F-2537 from Devils Cove member, East Castor Pond, sample ECP-03; 2, external view; 3, oblique posterolateral view; 4, detail of pustulose adult shell ornament. 5-6, Ventral valve NFM F-2538 from Devils Cove member, East Castor Pond, sample ECP-03; 5, interior view; 6, oblique interior view. 7, Ventral valve exterior NFM F-2539 from Devils Cove member, East Castor Pond, sample ECP-03. 9-10, Ventral valve NFM F-2540 from Devils Cove member, East Castor Pond, sample ECP-03; 9, interior view; 10, detail interior surface in oblique view showing imprints of pedicle nerves. 11-13, Dorsal valve NFM F-2541 from Devils Cove member, East Castor Pond, sample ECP-03; 11, interior view; 12, oblique interior view; 13, detail of internal surface with dorsal pseudointerarea and posterolateral muscle scars. Scalebars equal 500 µm in figures 1-3, 5-7, 9 and 11-12; 100 µm in figures 4, 10 and 13; 10 µm in figure 8.