Eoobolus sp.

Betts, Marissa J., Claybourn, Thomas M., Brock, Glenn A., Jago, James B., Skovsted, Christian B. & Paterson, John R., 2019, Shelly fossils from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia, Acta Palaeontologica Polonica 64 (3), pp. 489-522 : 498-500

Eoobolus sp.

Fig. 7A–C .

Material. —Fifteen ventral valves from Clast 5, three figured (SAM P57242–57244). From the Dailyatia odyssei Zone, WPC, Kangaroo Island, South Australia.

Description. —Material consists of relatively fragmentary ventral valves, making comprehensive description difficult. Valves sharply acuminate, apical angle ca. 80° ( Fig. 7A, B ). Elongate, apsacline pseudointerarea, propareas narrow, widening slightly anteriorly and separated by adpressed pedicle groove which widens anteriorly ( Fig. 7A, B ). Flexure lines parallel to posterolateral margins ( Fig. 7A, B ).

Remarks. —Assignment to the Eoobolidae relies on characters such as a pitted metamorphic shell and a pustulose adult shell that Balthasar (2009) showed was variably expressed, and hence not useful for family-level taxonomic designation. Balthasar (2009) placed Eoobolus in the Zhanatellidae , as material from the Mural Formation (Canadian Rocky Mountains) exhibited fine pits on both the metamorphic and adult shells in addition to other characters diagnostic of the Zhanatellidae . The diagnosis of Zhanatellidae Koneva, 1986 includes a flattened ventral valve pseudointerarea with variably developed flexure lines, with no information provided on the elevation of the dorsal pseudointerarea ( Popov and Holmer 1994: 70). Eoobolus is referred to the Eoobolidae herein, which can be distinguished from the Zhanatellidae in having a ventral pseudointerarea elevated above the valve floor with both a deep pedicle groove and well-developed flexure lines, and with a dorsal pseudointerarea always divided and raised above the valve floor ( Holmer et al. 1996: 41).

Distinguishing between species of Eoobolus is problematic since most exhibit high intraspecific variability Balthasar 2009; Ushatinskaya and Korovnikov 2014). The most stable character in Eoobolus for determining species appears to be the apical angle in adult ventral valves Balthasar 2009), along with the relative width and length of the ventral propareas ( Ushatinskaya and Korovnikov 2014). The few specimens recovered from the WPC have apical angles of approximately 80°, within the range of Eoobolus priscus ( Poulsen 1932) from the Bastion Formation of North-East Greenland (Cambrian Series 2) (70–90° according to Skovsted and Holmer 2005: 332) and E. aff. viridis from the Xihaoping Member of Shaanxi Province, China (Cambrian

Series 2, Stage 3) (80–90° according to Li and Holmer 2004: 197). The ventral propareas of Eoobolus sp. from the WPC are more slender than the broader triangular propareas of Eoobolus aff. viridis (compare Fig. 7A, B with Li and Holmer 2004: fig. 6K, 7G). The elongate, slender propareas and triangular pedicle groove of the WPC specimens are also similar to Eoobolus siniellus ( Pelman, 1983) from the Sinyaya Formation, Siberian Platform (Cambrian Series 2, Botoman Stage) (see Ushatinskaya and Korovnikov 2014: pl. 5: 1–7), although this species has a broader apical angle of 90–105° Ushatinskaya and Korovnikov 2014: 34).

Figures

Fig. 7. The lingulid brachiopods Eoobolus sp. (A–C) and Kyrshabaktella davidi Holmer and Ushatinskaya in Gravestock et al., 2001 (D–T) from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Ventral (A–H, N, Q–T) and dorsal (I–M, O, P) valves. A. SAM P57242 in internal view. B. SAM P57243 in internal view. C. SAM P57244, in external view (C1); C2, detail of post larval shell. D. SAM P57245 in internal view. E. SAM P57246 in oblique view. F. SAM P57247 in internal view. G. SAM P57248 in internal view. H. SAM P57249 in internal view (H1); H2, detail of the interarea. I. SAM P57250 in internal view. J. SAM P57251 in internal view. K. SAM P57252 in internal view. L. SAM P57253 in internal view. M. SAM P57254 in internal view. N. SAM P57255 in external view. O. SAM P57256 in external view (O1); O2, detail of external radial and concentric ornament. P. SAM P57257 in external view. Q. SAM P57258 in external view. R. SAM P57259 in external view. S. SAM P57260 in internal view. T. SAM P57261 in internal view.