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 : 507-508

publication ID	https://doi.org/ 10.4202/app.00586.2018
persistent identifier	https://treatment.plazi.org/id/03AB4756-FFCB-160E-BF20-BCB009542759
treatment provided by	Felipe
scientific name	Cordatia erinae Brock and Claybourn
status	sp. nov.

Treatment

Cordatia erinae Brock and Claybourn sp. nov.

Figs. 11 View Fig , 12 View Fig .

2007 Obolidae View in CoL gen. et sp. indet.; Paterson et al. 2007b: 138–139, fig. 3F–J.

2017 Curdus pararaensis ; Betts et al. 2017a: 257, fig. 15P–U.

ZooBank LSID: urn:lsid:zoobank.org:act:9E817F9D-1967-40BE-93F7-

1424571E3CB9

Etymology: In honour of Erin Fletcher (née Casey), who discovered the first specimens of this taxon in the Andamooka Limestone in 2005 during her Honours year.

Holotype: Ventral valve SAM P53644 View Materials ( Fig. 11A View Fig ).

Type locality: Ajax Limestone, Mt. Scott Range, NW Flinders Ranges , South Australia.

Type horizon: Stratigraphic section AJX-M/ 415 in the Mt Scott Range, northern Flinders Ranges, located 232.07 m above the base of the section ( Betts et al. 2016: fig. 2); early Cambrian, Dailyatia odyssei Zone ( Pararaia tatei Trilobite Zone ).

Material.— Thirty-two dorsal valves and two ventral valves from Clast 1, one dorsal valve and three ventral valves from Clast 4 and 28 dorsal valves and eight ventral valves from Clast 5; 22 figured including five specimens from the type locality AJX-M / 415 in the Mt Scott Range ( SAM P 53644 View Materials , 57290–57310 View Materials ) .

Diagnosis.— Small, uniformly convex ventral valve with transversely obtuse cardinal platform. Delthyrium incipient, little more than a weak, very shallow depression, set on a variably developed platform in front of a relatively small, flat orthocline beak. Ventral muscle field large, transverse with median ridge bounded postero-laterally by divergent low, but well-defined ridges. Interior of dorsal valve paratypes with distinctive rounded cardinal ridge forming the pseudointerea immediately in front of a small recurved beak. A low, narrow well-developed median ridge originates in umbonal chamber and widens and flattens anteriorly to approximately mid valve. A pair of large, elongately ovoid, weakly divergent, centrally located muscle scars straddle the median ridge forming a distinctly cordate muscle field.

Description. — Shell of variable size (length 0.53–3.82 mm, mean 1.6 mm; width 0.48–3.95 mm, mean 1.76 mm, N = 6), biconvex to ventribiconvex, outline ranging from transversely subrectangular to semi-circular in outline; fragmentary specimens often loose cardinal extremities and can appear subovoid in outline ( Fig. 11J, K View Fig ). Metamorphic shell relatively large, circular, seemingly smooth (though poorly preserved in most specimens) with diameter between 0.18–0.25 mm; metamorphic shell margin poorly delineated from adult shell ( Fig. 11C View Fig 1 View Fig ). Adult shell smooth, with relatively widely spaced, undulose and irregular imbricating lamellae ( Fig. 11E View Fig ), better developed towards shell margin; concentric laminae/filae interrupted by nick points and drapes, occasional wrinkles in well preserved specimens Fig. 11E View Fig ). Reticulate micro-ornament absent. Shell structure composed of densely packed stratiform apatitic laminae Fig. 12 View Fig ) occasionally with crustose or spherulitic interlaminae ( Fig. 12B View Fig 2, C 2 View Fig ). Columnar features lacking.

Ventral valve with transversely obtuse cardinal platform Fig. 11A View Fig 1 View Fig , D, G); propareas very narrow, tapering and becoming indistinct laterally ( Fig. 11A View Fig 1 View Fig ). Delthyrium is little more than a flattened or weakly concave platform ( Fig. 11A View Fig ) distinguished from propareas by presence of a slightly depressed platform located directly anterior of the weakly incurved beak ( Fig. 11A View Fig ). Homeodeltidium absent. Ventral valve interior with few morphological features. Ventral valve with large, indistinct visceral transverse muscle field bisected by very low, narrow short, incipient median ridge in umbo; postero-lateral margins of muscle field with well developed, narrow, gently curved bounding ridges ( Fig. 11A View Fig 3 View Fig ).

Dorsal valve weakly, but evenly convex, with straight posterior margin. Propareas anacline, narrow, forming a relatively flat continuous platform extending laterally across entire cardinal area ( Fig. 11B View Fig ); beak short, recurved. Homeochilidium absent. Interior of dorsal valve with well-developed, low narrow median ridge originating in umbo, extending, widening and flattening beyond anterior margin of muscle field. A pair of large, elongately ovoid, weakly divergent, centrally located muscle scars occur either side of the median ridge ( Fig. 11B, F View Fig ); muscle scars distinctly cordate in outline. Postero-lateral muscle bounding ridges of the central muscle scars poorly defined ( Fig. 11B, F, L View Fig ). Postero-lateral muscles present but weakly impressed and indistinct. Mantle canal system not preserved.

Remarks. — Paterson et al. (2007b: fig. 3F–K) originally had difficulty in providing a higher-level classification of this taxon, because the relatively few specimens from the KLM of the Parara Limestone tended to be small and the size and shape of the shells were affected by breakage of cardinal extremities, making the outline appear subcircular. The perceived subrounded outline, along with a smooth metamorphic and adult shell, suggested a relationship with the Obolidae . Fragmentary specimens of Cordatia erinae Brock and Claybourn gen. et sp. nov. were also incorrectly identified as Curdus pararaensis by Betts et al. (2017b: fig. 15P–U). Abundant new material from the WPC, along with well-preserved shells from the Ajax Limestone in the Mt Scott Range, preserves the full morphological details of the species, including the characteristic obtuse to linear cardinal platform ( Fig. 11 View Fig ), densely stratiform organophosphatic ultrastructure ( Fig. 12 View Fig ), weakly defined, orthocline delthyrium in the ventral valve, median ridge in the dorsal valve, and external, undulose, irregular, concentric laminae with nick points, drapes and wrinkling, and the large muscle field in both valves. These well-preserved features enable formal description of C. erinae gen. et sp. nov. as a new taxon within Paterinata ( Laurie 2000).

Stratigraphic and geographic range.— Lower Cambrian of South Australia: Stuart Shelf: SCYW-791A drill core, Andamooka Limestone ( D. odyssei Zone ); Arrowie Basin: AJX-M section, Ajax Limestone, Mt. Scott Range ( D. odyssei Zone / P. tatei Trilobite Zone ); MMF section, Third Plain Creek Member, Mernmerna Formation, Bunkers Range ( D. odyssei Zone / Pararaia bunyerooensis Trilobite Zone ); 10MS section, Linns Springs and Third Plain Creek members of the Mernmerna Formation, Bunkers Graben ( D. odyssei Zone ). Stansbury Basin: WPC clasts, Kangaroo Island ( D. odyssei Zone ).