Cyrtodonta carberryi Pojeta and Gilbert-Tomlinson, 1977

Jakobsen, Kristian G., Brock, Glenn A., Nielsen, Arne T. & Harper, David A. T., 2016, A Darriwilian (Middle Ordovician) bivalve-dominated molluscan fauna from the Stairway Sandstone, Amadeus Basin, central Australia, Acta Palaeontologica Polonica 61 (4), pp. 897-924 : 914

Cyrtodonta carberryi Pojeta and Gilbert-Tomlinson, 1977

Fig. 11G .

1977 Cyrtodonta carberryi sp. nov; Pojeta and Gilbert-Tomlinson 1977: 20, pl. 16: 3–5.

Type material: Holotype ( CPC 15549 ) figured by Pojeta and Gilbert-Tomlinson (1977: pl. 16: 5) . Paratypes ( CPC 15547 and CPC 15548 ) figured by Pojeta and Gilbert-Tomlinson (1977: pl. 16: 3, 4). All specimens are composite moulds .

Type locality: Gardiner Range , Amadeus Basin, southern Northern Territory, Australia .

Type horizon: Stairway Sandstone, Darriwilian (Middle Ordovician).

Material.― Five fragmentary specimens from the Areyonga Gorge section, Middle Ordovician of Australia. The best preserved composite mould ( CPC 41474 ) is figured ( Fig. 11G 1, G 2 ). The material was recovered from bed A + 4 in the Areyonga Gorge section. Pojeta and Gilbert-Tomlinson 1977: 20 and 53) reported additional eight specimens from a single locality in the Gardiner Range, about 30 km north west of the Areyonga Gorge section. All known material of C. carberryi is from the Stairway Sandstone (Pojeta and Gilbert-Tomlinson 1977; this study) .

Description.― Cyrtodonta with bulbous profile, oblique quadrate shape and prosogyral umbo. Dorsal margin straight and anterior margin straight to slightly oblique. Ventral margin rounded and posterior margin straight. Ornament of commarginal growth lines present. The illustrated adult specimen is 42 mm long and 25 mm high.

Remarks.―Many species have been assigned to Cyrtodonta . It is especially abundant in the Upper Ordovician of eastern North America, and the central Australian occurrences reported by Pojeta and Gilbert-Tomlinson (1977) were the first record of the genus from the Southern Hemisphere. Cyrtodonta carberryi differs from other Australian species of Cyrtodonta by its oblique quadrate shape and straight anterior margin. Cyrtodonta carberryi can be differentiated from C. staffordae by possessing a less symmetric shape as well as a slightly wider shell.

According to Pojeta and Gilbert-Tomlinson (1977: 20) the only known internal feature is two posterior lateral teeth in the left valve. However, the figured specimen ( Fig. 11G 1) is a right valve and at least one and possibly two impressions of posterior lateral teeth are indicated.

Stratigraphic and geographic range.― Cyrtodonta carberryi is endemic to central Australia. All known material of C. carberryi is from the Stairway Sandstone (Pojeta and Gilbert-Tomlinson 1977; this study) at localities in the Gardiner Range, Areyonga Gorge, and Petermann Creek, southern Northern Territory.

Figures

Fig. 11. Nucularcid and pteriomorphian bivalves from the Stairway Sandstone, Middle Ordovician, Australia. Internal moulds (B–K) and latex casts of external moulds (A, L, M). A. Sthenodonta sp. B (CPC 41468) from Petermann Creek, left-lateral view showing well marked growth lines. B. Johnmartinia cordata Pojeta and Gilbert-Tomlinson, 1977 (CPC 41469) from Areyonga Gorge; left-lateral view with dorsal border (B1), anterior view showing the pointy beak (B2). C–F. Nuculites wattii Tate, 1896 from Areyonga Gorge. C–E. Specimens in left (C, E) and right-lateral (D) dorsal views, showing well-defined anterior myophoric buttress, D additionally shows dorsal teeth (C, CPC 41470; D, CPC 41472; E, CPC 41472). F. Right-lateral view of fragmentary specimen with chevron shaped posterior teeth pointing anteriorly (CPC 41473). G. Cyrtodonta carberryi Pojeta and Gilbert-Tomlinson, 1977 (CPC 41474) from Areyonga Gorge; in right-lateral view with growth lines and at least one dorsal lateral tooth (G1), dorsal view illustrating the height of shell profile (G2). H–K. Cyrtodonta staffordae Pojeta and Gilbert-Tomlinson, 1977 from Petermann Creek (H–I, K) and Areyonga Gorge (J). H. Specimen in right-lateral view showing distinct growth lines (CPC 41475). I. Specimen in left-lateral view with three posterior lateral teeth (CPC 41476). J. Fragmentary posterior margin with duplivincular ligament and indications of three posterior lateral teeth (CPC 41478). K. Specimen in right-lateral view with a posterior lateral tooth (CPC 41477). L, M. Cyrtodonta sp. B. L. Anterior (L1) and left-lateral (L2) views of sub-ovate shell-profile (CPC 41479) from Petermann Creek. M. Sub-ovate shell-profile with growth lines (CPC 41480) from Areyonga Gorge. Scale bars 10 mm.

Fig. 2. Distribution of the Larapintine Sea in the Middle Ordovician. The extent of the Canning, Amadeus, and Georgina basins, all containing Middle Ordovician deposits, have been inferred together with the extent of continental landmass (marked with horizontal lines). Base map modified from Webby 1978. A. Webby’s interpretation (1978). B. New interpretation based on faunal correlation. Note the broken connection between the Amadeus–Georgina basins and the Canning Basin.