Curdus pararaensis Holmer and Ushatinskaya

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 : 501-502

Curdus pararaensis Holmer and Ushatinskaya in Gravestock et al., 2001

Fig. 8 .

2001 Curdus pararaensis ; Holmer and Ushatinskaya in Gravestock et al. 2001: 130, pl. 22: 1–14.

2007 Curdus pararaensis ; Paterson et al. 2007b: 139, fig. 3L–N.

2017 Curdus pararaensis ; Betts et al. 2017b: 257, fig. 15V (non fig. 15P–U).

Material.—One dorsal valve from Clast 1 and 25 dorsal valves and 14 ventral valves from Clast 5; eight figured ( SAM P57262–57269). From the Dailyatia odyssei Zone, WPC, Kangaroo Island, South Australia.

Description.— Near-complete shells, oval to sub-pentagonal in outline, ventribiconvex. Largest near-complete valve Fig. 8B ) 2.7 mm in length, 2.7 mm in width, all near-complete valves slightly wider than long (mean 93%, N = 3, Fig. 8A, B, H ). Ornamentation with irregular filae ( Fig. 8A– C ) interrupted by drapes and nick-points ( Fig. 8A, C 1 , C 2 ). Metamorphic shells poorly preserved, undifferentiated from post-metamorphic shell ( Fig. 8C 2 , C 3 ).

Ventral valve pseuodinterarea broad, apsacline, forming shelf and gently curved posterior margin. Propareas are long, with flexure lines, and separated by deep triangular pedicle groove ( Fig. 8D, F ). Ventral valve interiors poorly preserved, valve floor with single, large, recessed scar, and no information retained of the viscera ( Fig. 8D, F ). Dorsal valve with more rounded posterior margin; pseudointerarea rudimentary, anacline, and with short propareas separated by a shallow pedicle groove ( Fig. 8E, G, H ). Well-preserved specimen interior ( Fig. 8E ) with raised slope immediately anterior of pedicle groove, developing into trilobate platform that extends for most of the valve floor.

Remarks. — This taxon was originally described from subsurface cores CurD1B and SYC-101 through the KLM (of the Parara Limestone) in the Stansbury Basin by Holmer and Ushatinskaya in Gravestock et al. (2001: 130, pl. 22: 1–14). This material was very fragmentary, consisting mostly of broken interareas and metamorphic shells ( Gravestock et al. 2001: pl. 22: 1–14). Additional examples of C. pararaensis are also fragmentary ( Paterson et al. 2007b; Betts et al. 2016, 2017b). Material from the WPC is also often abraded and damaged, though some shells retain outline morphology, revealing that the valves may have been in excess of 3 mm wide ( Fig. 8B ) and grossly sub-circular to sub-pentagonal in outline ( Fig. 8A, B, C 1 , D–H). External surfaces of the valves are also abraded, but some retain concentric growth lines, radial “drapes” and striae ( Fig. 8C ).

Curdus pararaensis bearssomesimilaritiesto Minlatonia tuckeri Holmer and Ushatinskaya in Gravestock et al., 2001. Major differences include ornamentation and the convexity of the valves. However, presentation of external ornament is controlled by preservation, and the shape of the valves in M. tuckeri was based on few intact (possibly juvenile) specimens. Hence, it is possible that C. pararaensis and M. tuckeri may be conspecific, though additional, well-preserved material is required to test this.

Curdus pararaensis was originally assigned to the Botsfordiidae based on general similarities witih Botsfordia asperella Koneva, 1979 , including some internal features Paterson et al. 2007b). However, Curdus does not have tubercles or pits on the metamorphic shell, and lacks a pustulose post-metamorphic shell ( Paterson et al. 2007b). Popov et al. (2015) assigned Curdus to the Neobolidae which was emended to include genera with a smooth metamorphic and postmetamorphic shell, strong, trilobate platform in the ventral valve, prominent dorsal median ridge and variously developed muscle platforms.

Stratigraphic and geographic range. — Lower Cambrian of South Australia, Arrowie Basin ( D. odyssei Zone ): Linns Springs Member of the Mernmerna Formation, Donkey Bore Syncline. Stansbury Basin ( D. odyssei Zone ): KLM (CurD1B and SYC-101 drillcores) and WPC clasts, Kangaroo Island.

Figures

Fig.8. The lingulid brachiopod Curdus pararaensis Holmer and Ushatinskaya in Gravestock et al., 2001 from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Dorsal (A, B, E, G, H) and ventral (C, D, F) valves. A. SAM P57262 in external view. B. SAM P57263 in external view. C. SAM P57264 in external (C1) and oblique (posterior) (C2) views; C3 shows external ornament of faint concentric growth lines. D. SAM P57265 in internal view. E. SAM P57266 in internal view. F. SAM P57267 in internal view. G. SAM P57268 in internal view. H. SAM P57269 in internal view.

Fig. 1. Map showing study area on northern Kangaroo Island, Australia. Dashed line indicates Stansbury Basin extent.

Fig. 2. Correlation chart showing shelly fossil biozones against the stratigraphic succession in the Flinders Ranges, Fleurieu Peninsula, and Kangaroo Island (adapted from Betts et al. 2018: fig. 27). Note: The succession in the NE Kangaroo Island is based on the Investigator-1 drill core in which the Mt. McDonnell Formation is not apparent (Gehling et al. 2011). Lower boundary of White Point Conglomerate (WPC) is likely faulted.Abundant and diverse shelly fauna (SSF) from the bioclastic limestone clasts in the WPC have an upper Dailyatia odyssei Zone age. Dashed lines indicate uncertain stratigraphic relationship. Abbreviations: K., Kulparina; P., Parabadiella; S., Sunnaginia.

Fig. 3. The solenopleurid trilobite Trachoparia? sp. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Latex cast of partial cranidium (SAM P57221) showing pustulose ornament and strongly tapered glabella in dorsal (A1), anterior (A3), and oblique anterolateral (A4) views; testate cranidium in dorsal view (A2).