Eoobolus priscus ( Poulsen, 1932 )

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 : 28-29

Eoobolus priscus ( Poulsen, 1932)

Figure 15

v* 1932 Lingulella (Lingulepis) prisca Poulsen , p. 13, plate 1, figures 1–5.

2005 Eoobolus priscus (Poulsen) ; Skovsted and Holmer, p. 330, plate 2, figures 1-13, plate 3, figures 1-11. (includes synonymy).

2006 Eoobolus priscus (Poulsen) ; Jago, Zhang, Sun, Paterson, and Skovsted, p. 413, figure 4m, n.

2007 Eoobolus priscus (Poulsen) ; Skovsted and Peel, figure 2 a, b.

2007 Eoobolus priscus (Poulsen) ; Paterson, Skovsted, Brock, and Jago, p. 138, figure 3a-e.

2010 Eoobolus priscus (Poulsen) ; Rozanov et al., p. 81, plate 49, figures 8-12.

2010 Eoobolus priscus (Poulsen) ; Skovsted and Peel, figure 2.22.

2014 Eoobolus priscus (Poulsen) ; Ushatinskaya and Korovnikov, plate 5, figures 8-11.

2014 Eoobolus priscus (Poulsen) ; Devaere, Clausen, Monceret, Vizcaïno, Vachard, and Genge, figure 12a-l.

2016 Eoobolus priscus (Poulsen) ; Peel, Streng, Geyer, Kouchinsky, and Skovsted, figure 8ac, e, k, m.

Holotype. Ventral valve MGUH 3503 from the upper Bastion Formation at Hyolithus Creek, North-East Greenland ( Poulsen, 1932, plate 1, figure 3; Skovsted and Holmer, 2005, plate 2, figure 1).

Material. 42 ventral and 20 dorsal valves from the Forteau Formation of the Bonne Bay area, western Newfoundland (GM07-2.1, GM07-4.1, GM07-5.1, GM11-1-6, GM11-1-6A, GM11-1-6C, GM11-1-10 T, GM11-4-2, GM11-5-E, GM11-9A-9, GM11-9A-10, GM11-14A-5, GM11-14G-1, GM11-14 G-C, JSP 1982−01, ICS 1421; see appendices 1 and 2).

Diagnosis. See Skovsted and Holmer (2005), p. 332.

Description. This species is invariably represented in the Forteau Formation by fragmentary specimens, usually of the posterior part of the shell. Shell gently biconvex with sub-triangular outline. The ventral valve is elongated and posteriorly triangular with an apical angle of 75-90 degrees ( Figure 15.1, 15.4, 15.5, 15.7, 15.9 ); the dorsal valve has a more rounded posterior margin ( Figure 15.8, 15.10 ). Juvenile shell poorly preserved in available specimens and no juvenile ornament could be identified. Adult valve ornamented by closely set sub-circular pustules with a diameter of 5-8 µm ( Figure 15.3 ). Ventral pseudointerarea with narrow pedicle groove, somewhat expanding anteriorly, and raised propareas with well-defined flexure-lines ( Figure 15.5, 15.7, 15.9 ). Dorsal pseudointerarea slightly raised above valve floor with wide, triangular but poorly defined median groove; slightly flexed anteriorly in central part ( Figure 15.8, 15.10 ). Ventral valve interior with triangular impression of pedicle nerves ( Figure 15.5-7 ) bisecting small, circular umbonal muscle scars ( Figure 15.4 ) and larger scars in the posterior part of the anterior muscle field. Elongate posterolateral muscle scars inserted below propareas ( Figure 15.4, 15.6 ). Dorsal valve interior with elongate median tongue but otherwise poorly preserved ( Figure 15.10 ). Internally the shell is composed of thin laminae bisected by multiple acrotretid-like columnar structures ( Figure 15.12 ).

Remarks. Lingulella (Lingulepis) prisca was originally described from the Bastion Formation of North-East Greenland by Poulsen (1932). Skovsted and Holmer (2005) redescribed Poulsen’s type material together with large collections from new sections in North-East Greenland and referred the species to Eoobolus based on the combination of a finely pitted larval shell and a pustulose adult shell. Eoobolus priscus has also been reported from the Löndal Formation of North Greenland ( Peel et al., 2016). A columnar shell structure is described in Eoobolus for the first time by Peel et al. (2016), and this observation is corroborated by the find of a columnar shell structure in specimens from the Forteau Formation described here. Two specimens from the Forteau Formation identified as E. priscus were illustrated by Skovsted and Peel (2007), but new collections allow a more detailed comparison of the Newfoundland shells with the type material (in particular of the internal morphology) and confirms the identification.

Brachiopod shells from the lower Cambrian of Antarctica ( Holmer et al., 1996) and South Australia (Ushatinskaya and Holmer in Gravestock et al., 2001) described as Eoobolus aff. elatus were placed in synonymy of E. priscus by Skovsted and Holmer (2005). Later investigations of new collections from the Stansbury Basin of South Australia has confirmed that E. priscus is present in this region ( Jago et al., 2006; Paterson et al., 2007; Betts et al., 2017). Skovsted and Holmer (2005) also suggested that the poorly known Siberian species Eoobolus elatus Pelman in Pelman and Pereladov, 1986 is a junior synonym of E. priscus , an interpretation that was subsequently supported by Rozanov et al. (2010) and Ushatinskaya and Korovnikov (2014). Eoobolus priscus has also been described from the Pardailhan Formation, of the early Cambrian of Montagne Noire, France ( Devaere et al., 2014). However, as discussed by Streng et al. (2008), specimens referred to Eoobolus ? sp. aff. E. priscus ( Poulsen, 1932) from the Cambrian Series 3 Forsemölla Limestone of southern Sweden differ from E. priscus by the lack of a pitted larval shell and in minor details of internal morphology and is not included in the species by us.

Specimens described as Lingulella cf. prisca were reported from the Forteau Formation of Labrador by Spencer (1980) but the illustrated shells were excluded from E. priscus by Skovsted and Holmer (2005); here we assign these specimens to the new genus Pustulobolus (see below). In our collections E. priscus appears to be restricted to the Gros Morne district where the species occurs from the top of the Devils Cove member throughout the Mackenzie Mills members (sections GM1 to 14G). Throughout its range in the Forteau Formation, E. priscus is fairly common, although always in low numbers.

Distribution. Assemblage 3, upper part of Devils Cove member and Mackenzie Mill member, Forteau Formation of Gros Morne area, western Newfoundland. Dyeran Stage (Cambrian Series 2, Stage 3-4; approximately equivalent to the Adtabanian to Botoman stages of Siberia) of eastern Laurentia (North-East Greenland, Newfoundland, New York State, Pennsylvania), Botoman-Amgan Stages of Siberia ( Rozanov et al., 2010); Stage 3-4 of Antarctica (glacial erratics on King George Island; Holmer et al., 1996), and South Australia (Arrowie and Stansbury basins; Gravestock et al., 2001; Betts et al., 2017).

Figures

FIGURE 15. Eoobolus priscus (Poulsen, 1932) from the Forteau Formation of western Newfoundland. 1, Ventral valve exterior NFM 662 from Deer Arm Limestone, sample JSP 1982-01. 2-3, Ventral valve NFM F-2570 from Deer Arm Limestone, sample GM07-4-1; 2, external view; 3, detail of pustulose adult surface ornament. 4, Ventral valve interior NFM F-2571 from Deer Arm Limestone, sample GM07-4-1 showing arrangement of muscle scars. 5-6, Ventral valve NFM F-2574 from Deer Arm Limestone, sample GM07-5-1; 5, internal view; 6, oblique interal view showing imprints of pedicle nerves. 7, Ventral valve interior NFM F-2572 from Deer Arm Limestone, sample GM07-4-1. 8, Dorsal valve NFM F-2522 from Deer Arm Limestone, sample ICS 1421. 9, Ventral valve interior NFM F-2566 from Mackenzie Mills member, sample GM11-9A-10. 10-12, Dorsal valve NFM F-2567 from Mackenzie Mills member, sample GM11-9A-10; 10, internal view; 11, oblique internal view; 12, detail of columnar shell structure from naturally broken edge. Scalebars equal 250 µm in figures 1-2 and 4-11, 50 µm in figure 3 and 10 µm in figure 12.