Cordatia erinae Brock and Claybourn, 2019

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 : 504-507

Family? Paterinidae Schuchert, 1893 Genus Cordatia Brock and Claybourn nov.

ZooBank LSID: urn:lsid:zoobank.org:act:A3E82895-1D1D-4B3B-8B5C-F2D8A01C0841

Etymology: From Latin, cordatus, meaning heart-shaped; in reference to the large, heart-shaped muscle field in both valves.

Type species: Cordatia erinae Brock and Claybourn gen. et sp. nov., monotypic, see below.

Diagnosis.— The same as for the type species.

Remarks.— The weakly developed obtuse ( Fig. 11A 1 , D) to linear ( Fig. 11B, C 2 ) cardinal platform (lateral extremities broken away in some specimens, Fig. 11J–M ), orthocline ventral delthyrium and interarea, presence of a pair of very large muscle scars in both valves, and a smooth adult shell with drapes, wrinkling and concentric filae, suggest an affinity with the Order Paterinida . In addition, the stratiform organophosphatic ultrastructure in Cordatia Brock and Claybourn gen. nov. is closely comparable with the shell ultrastructure in cryptotretids, such as Cryptotreta undosa from the lower Cambrian of Sweden (e.g., Williams et al. 1998: pl. 5: 2). Better preserved shells of Cordatia Brock and Claybourn gen. nov., especially from the Ajax Limestone ( Fig. 11A–E ), are similar to Paterina Beecher, 1891 in general shape and outline, and both taxa lack a homeodeltidium and homeochilidium. Both taxa also have a smooth adult shell, ornamented by undulose concentric laminae/filae interrupted by nick points forming sets of drapes. However, the concentric filae/laminae of Cordatia Brock and Claybourn gen. nov. are relatively widespread and irregular in growth, whilst those in Paterina tend to be much more closely packed, often forming distinct wrinkles (compare Fig. 11E with Laurie 2000: 183, fig. 1a–d; Holmer et al. 2001: pl. 1: 8, 10–12). Internally, the ventral valve of Paterina has a well-developed delthyrium supported internally (and laterally) by a pair of strong delthyrial ridges (see Williams et al. 1998: pl. 11: 4, 5; Holmer et al. 2001: pl. 11: 9). Cordatia Brock and Claybourn gen. nov., on the other hand, lacks a distinct delthyrium (and the strong delthyrial ridges seen in Paterina ), instead having a variably developed, generally very shallow and orthocline cardinal platform in front of the beak. The interior of the dorsal valves of Paterina are generally poorly known, but none have the large, centrally-located cordate muscle field that characterises Cordatia Brock and Claybourn gen. nov.

The lack of a homeodeltidium and/or homeochilidium in Cordatia Brock and Claybourn gen. nov. distinguishes it from paterinate genera such as Pelmanotreta Skovsted, Ushatinskaya, Holmer, Popov, and Kouchinsky, 2015b (replacement name for the pre-occupied Cryptotreta Pelman, 1977 ), Tumulduria Missarzhevsky in Rozanov et al., 1969, Salanygolina Ushatinskaya, 1987 , Dzunarzina Ushatinskaya, 1993 , and Tallatella Topper and Skovsted, 2014 . The characteristic external undulose and irregular concentric ornament interrupted by surface wrinkling and nick points forming repeated sets of drapes, along with an obtuse to linear cardinal platform with orthocline ventral interarea in Cordatia Brock and Claybourn gen. nov. is more in keeping with Aldanotreta Pelman, 1977 and Askepasma Laurie, 1986 . However, Aldanotreta and Askepasma have much more clearly defined and strongly developed cardinalia. In addition, Askepasma has a distinctive reticulate shell surface ornament ( Topper et al. 2013: fig. 2C 2) that is also reflected in the ultrastructure of the shell ( Topper et al. 2013: fig. 7D), which is absent in Cordatia Brock and Claybourn gen. nov.

Stratigraphic and geographic range. —As for the type species, see below.

Figures

Fig. 11. The lingulid brachiopod Cordatia erinae Brock and Claybourn gen. et sp. nov. from the lower Cambrian of South Australia, Ajax Limestone, Flinders Ranges (AJX-M/415) (A–E) and White Point Conglomerate, Kangaroo Island (F–S). Ventral (A, D, G) and dorsal (B, C, E, F, H–S) valves. A. SAM P53644, holotype in internal (A1) and oblique (A2) views; A3, detail of the delthyrium, propareas, and muscle field. B. SAM P57290 in internal view. C. SAM P57291 in external view (C1); C1, detail of the metamorphic shell. D. SAM P57292 in external view. E. SAM P57293, detail of external ornament. F. SAM P57294 in oblique internal view. G. SAM P57295 in internal view. H. SAM P57296 in external oblique view. I. SAM P57297 in external view. J. SAM P57298 in internal view. K. SAM P57299 in internal view. L. SAM P57300 in internal view. M. SAM P57301 in internal view. N. SAM P57302 in internal view. O. SAM P57303 in external view. P. SAM P57304 in external view. Q. SAM P57305 in external view. R. SAM P57306 in external view. S. SAM P57307 in external 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.