Schizopholis yorkensis

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 : 502-503

Schizopholis yorkensis (Holmer and Ushatinskaya in Gravestock et al., 2001)

Fig. 9 .

2001 Karathele yorkensis ; Holmer and Ushatinskaya in Gravestock et al. 2001: 128–129, pl. 21: 1–11.

2016 Karathele (= Schizopholis ) yorkensis ; Betts et al. 2016: 195, fig. 17A–H.

Material. —Two dorsal valves and a single ventral valve from Clast 4 and seven dorsal valves and six ventral valves from Clast 5; six figured ( SAM P57270–57275). From the Dailyatia odyssei Zone, WPC, Kangaroo Island, South Australia.

Description.— Fragmentary dorsal and ventral valves lacking information on general morphology ( Fig. 9 ). Ventral valve with procline pseudointerarea ( Fig. 9D 1, E, F 1 ). Broad, open delthyrium in contact with, but not intruding into metamorphic shell, lateral margins widening postiorly ( Fig. 9F 2, D 2 ). Dorsal valve with rounded posterior margin ( Fig. 9A, B, C 1 ) and rudimentary apsacline pseudointarea ( Fig. 9E ). Interior with proportionally small propareas (0.91 mm wide on a broken dorsal valve which is at least 2.33 mm wide, Fig. 9E ) forming narrow shelf overhanging posterior margin of narrow cardinal muscle scars. Short median buttress, in single measured specimen extending 0.35 mm anteriorly along valve floor ( Fig. 9E ). Valve exteriors covered in irregularly spaced tubercles ( Fig. 9C 3 ) except along the ventral valve pseudointerarea and posterior margin of the dorsal valve, which are smooth ( Fig. 9A, B, C 1, D 1, F 1 ). Dorsal valve metamorphic shell mean length 0.23 mm and width 0.34 mm (N = 3) with two slightly elongate lobes and pitted microornamentation ( Fig. 9C 2 ). Ventral valve metamorphic shell mean length 0.33 mm and width 0.37 mm (N = 2) with single posterior lobe, two low anterior lobes and smooth, lacking microornament ( Fig. 9D 2, F 2 ). Metamorphic shells encircled by halo ( Fig. 9C 2, D 2, F 2 ).

Remarks.— This species was originally assigned to Karathele Koneva 1986 , which has since been synonymised with Schizopholis , a genus known from Cambrian Stage 4 of Australia, Antarctica and the Himalaya ( Popov et al. 2015). In their original description of material from the Stansbury Basin, Holmer and Ushatinskaya in Gravestock et al. (2001: 129) reported a maximum shell length of 1 mm and maximum width of 1.1 mm. The new material from the WPC includes shell fragments over 2 mm wide ( Fig. 9A, C 1 ). In addition, the width of the metamorphic shell was described as “ 150–160 mm across” in the original description Holmer and Ushatinskaya in Gravestock et al. (2001: 129), and despite the fact that the “mm” should have actually been in microns, the average size of the metamorphic shell is actually 360 μm in width ( Fig. 9C 2 ).

Schizopholis yorkensis from the WPC has a delthyrium that is broad and divergent throughout ontogeny ( Fig. 9D, F ), distinguishing it from Schizopholis napuru Kruse, 1990 , in which the delthryium converges later in ontogeny ( Kruse 1990: pl. 12: A, B, F). Schizopholis yorkensis can also be distinguished from other members of Schizopholis in having only two dorsal tubercles on the metamorphic shell ( Fig. 9B, C ), distinguishing it from Schizopholis quadrituberculum Percival and Kruse, 2014 and the type species Schizopholis coronata Koneva, 1986 , which have four (see Holmer et al. 2001: pl. 17; Percival and Kruse 2014: fig. 8).

Stratigraphic and geographic range. — Lower Cambrian of South Australia, D. odyssei Zone. Arrowie Basin ( Micrina etheridgei – D. odyssei zones): Ajax Limestone, Mt. Scott Range ; Winnitinny Creek Member of the Wilkawillina Limestone, Wirrapowie Limestone, Mernmerna Formation and Nepabunna Siltstone, Arrowie Syncline, northcentral-eastern Flinders Ranges; Winnitinny Creek Member of the Wilkawillina Limestone and Third Plain Creek Member of the Mernmerna Formation, Bunkers Range, central Flinders Ranges; Winnitinny Creek Member and Second Plain Creek Member of the Wilkawillina Limestone, Six Mile Bore, Linns Springs and Third Plain Creek members of the Mernmerna Formation, Upper Mernmerna Formation, Bunkers Graben; Wirrapowie Limestone and Mernmerna Formation, Elder Range, southern Flinders Ranges; Linns Springs and Third Plain Creek members of the Mernmerna Formation and Upper Mernmerna Formation, Donkey Bore Syncline, central Flinders Ranges; Mernmerna Formation, North Boundary Creek, Chambers Gorge area, eastern Flinders Ranges. Stansbury Basin ( D. odyssei Zone ): Parara Limestone, Yorke Penninsula; Curramulka and Minlaton-1 drillcore; WPC clasts, Kangaroo Island.

Figures

Fig. 9. The lingulid brachiopod Schizopholis yorkensis (Holmer and Ushatinskaya in Gravestock et al., 2001) from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Dorsal (A–C, E) and ventral (D, F) valves. A. SAM P57270 in external view. B. SAM P57271 in external view. C. SAM P57272 in external view (C1); C2, detail of the larval shell; C3, external pustulose ornament. D. SAM P57273 in external view (D1); D2, detail of the larval shell. E. SAM P57274 in internal view. F. SAM P57275 in external view (F1); F2, detail of the larval shell.

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).