Technophorus walteri Pojeta, Gilbert-Tomlinson, and Shergold, 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 : 920-922

Technophorus walteri Pojeta, Gilbert-Tomlinson, and Shergold, 1977

Fig. 12M .

1977 Technophorus walteri ; Pojeta et al. 1977: 21, pl. 10: 14–16.

1977 Technophorus walteri ; Pojeta and Gilbert-Tomlinson 1977: 32, pl. 29: 13–16.

Type material: Holotype ( CPC 14775 ), internal mould figured by Pojeta et al. (1977: pl. 10: 16). They also described two additional internal moulds found at the same locality.

Type locality: Pacoota Sandstone , Waterhouse Range, Amadeus Basin, southern Northern Territory, Australia .

Type horizon: Probably of Early Ordovician age (see Pojeta et al. 1977: 22) .

Material.―One internal mould (CPC 41493) of a left valve from the Areyonga Gorge section, Middle Ordovician of Australia.

Description.―Small Technophorus , the specimen is 5.8 mm long and 3.3 mm high, with a single lateral radial rib intersecting the posteroventral angle of the shell. Anterior and ventral margins arcuate; posterior margin erect and strongly tapered. Umbo projecting slightly above the otherwise more or less straight dorsal margin. A prominent nearly erect pegma is clearly indicated.

Remarks.―The single lateral rib intersects the dorsal margin at an angle of about 45°, which is also in accordance with the description by Pojeta et al. (1977: 22), reporting that this angle is>40°. Pojeta and Gilbert-Tomlinson (1977: pl. 29: 13–16) also figured an articulated internal mould and left valve exterior from the Pacoota Sandstone but from different localities than the type material. The left valve illustrated on their pl. 29: 13 is very similar to the specimen at hand (compare to Fig. 12M ).

Stratigraphic and geographic range.―The discussed specimen was found in the silt dominated bed A +3 at Areyonga Gorge ( Fig. 4 ). All four rostroconchs found in this section were recovered from a few closely spaced beds in the upper part of the section. The range of Technophorus walteri is within the Stairway Sandstone Formation, Darriwilian (Middle Ordovician). The region is in the southern Northern Territory, corresponding to the central part of the Amadeus Basin ( Fig. 1).

Class Gastropoda Cuvier, 1797

Remarks.―Almost 300 fragmentary gastropod specimens (internal and external moulds) have been recovered from the two investigated sections and are about equally distributed between them. As most taxonomically important characters usually revolve around the shell morphology, generic discrimination of the gastropod species is very difficult and we have taken a cautious approach to leave all gastropod taxa in open nomenclature. Six different species are distinguished, tentatively referred to as Scalites ? sp., Raphistomina ? sp., Teiichispira ? sp., and Archinacelloid spp. A–C (the latter three are limpet-shaped archinacelloids).

Shergold (1986:10) listed the gastropods Clathrospira ? sp. and Helicotoma ? sp. as well as a Monoplacophora indet. from the Stairway Sandstone. These two gastropod species do not seem to be present in the studied material (Jan O. Ebbestad, personal communication 2013). The specimens initially identified as “monoplacophorans” consist of limpet-shaped patelliform gastropods, here placed tentatively within the superfamily Archinacelloidea , which is allied with Gastropoda according to Peel and Horný (1999). The Gastropoda are here treated as a monophyletic group, whereas Monoplacophora is split into Class Tergomya and Class Helcionellida (see Peel 1991; Wagner 2002). Distinction between tergomyans and gastropods is based on muscle scars which appear in pairs in the former and in a band in the latter. This character, however, is not preserved in any of the specimens in the current collection, precluding confident taxonomic determination.

Scalites ? sp. (CPC 41494, internal mould and latex cast of internal mould and CPC 41495, internal mould) is exclusively preserved as bases of large gastropods ( Fig. 12N, O ). The species occurs in the lower fossiliferous part of both investigated sections, but it is most abundant in the Petermann Creek section. The base contains 3.5 to 4 whorls. The aperture seems radial with the basal keel and reticulate ornamentation corresponding to what Wagner (2002) named Scalites . Tate (1896) listed Scalites ? eremos from the Stokes Siltstone. The genus is also described from the Ordovician of North America ( Raymond 1906), Korea ( Kobayashi 1934), and China ( Endo 1935).

Raphistomina ? sp. (CPC 41496) is a small gastropod and the most abundant in the material (36% of the gastropods). It has 4 whorls but no other characters are preserved ( Fig. 13A).

JAKOBSEN ET AL.—MIDDLE ORDOVICIAN MOLLUSCS FROM AUSTRALIA 921

A B C D1 E1 D2 E2 G F1 H1 F2 H 2

The species occurs in both investigated sections mainly in the upper fossiliferous part, but is most abundant in the Areyonga Gorge section.

Etheridge (1891) described the gastropod Raphistoma brownii from an unknown unit at Tempe Downs (close to the Petermann Creek section). Shergold (1986) listed this species from the Horn Valley Siltstone. The species Raphistoma tasmanica is reported from the Middle Ordovician of Tasmania by Pojeta and Gilbert-Tomlinson (1977: 55). Pojeta and Gilbert-Tomlinson (1977: 41) listed Raphistomina ? from the Nora Formation of the Georgina Basin. Additionally Raphistoma is also reported from the Darriwilian of North America ( Rohr et al. 1992) and North China ( Kobayashi 1934). Raphistomina and Raphistoma are distinct but closely related genera. The material at hand does not justify a closer affiliation due to the lack of diagnostic characters.

Teiichispira ? sp. (CPC 41497 and CPC 41498) is a large gastropod with a very flat base, perhaps five whorls and probably with an anisostrophic planispiral shape of the shell ( Fig. 13B, C). The aperture is tangential. Growth lines sweep back from the aperture, curving more strongly abaperturally near the periphery. The species is only known from a few loose samples of the Stairway Sandstone found at Petermann Creek. Teiichispira is also reported from the Lower Ordovician of the Georgina Basin (Pojeta et al. 1977: 43) and the Canning Basin ( Yu 1993: 437). Outside Australia it is a common Ordovician genus in North America ( Yochelson and Wise 1972) but it is also reported from Malaysia ( Kobayashi 1959).

Archinacelloid sp. A (CPC 41499 and CPC 41500) is the largest among the limpet-shaped patelliform gastropods in the Stairway Sandstone with ovate aperture shape, twice as long as high, with slightly curved apex towards the posterior margin. Subapical surface slightly concave and steeply inclined ( Fig. 13D, E). The species is the dominant archinacelloid in the Petermann Creek section; it has not been found in the Areyonga Gorge section. In the former section almost all archinacelloids were recovered from the lower part of the section, whereas archinacelloids are restricted to the upper part of the Areyonga Gorge section. About four times as many archinacelloids were found in the Petermann Creek section as compared to the Areyonga Gorge section. Archinacelloideans have also been reported from the Darriwilian of North America ( Raymond 1906), Czech Republic ( Horný 1997), and Norway ( Yochelson 1963) but the taxon has not previously been described from the Ordovician of Australia.

Archinacelloid sp. B (CPC 41501 and CPC 41502) is a relatively small species with ovate aperture, apex subcentral or slightly towards the posterior, apex sharply pointed. Anterior surface slightly convex, subapical surface nearly straight or slightly convex ( Fig. 13F, G). The species occurs in both investigated sections in about equal numbers. Archinacelloid sp. C (CPC 41503) resembles Archinacelloid sp. A, but the shell is lower, with a height corresponding to about one third of its length ( Fig. 13H). It may represent a variant of Archinacelloid sp. A, but is tentatively separated due to the lower shell profile (compare Fig. 13D 2 vs. Fig. 13H 2 ). The species occurs in both investigated sections with a few more representatives in the Petermann Creek section. In the Areyonga Gorge section specimens are only found in the upper part of the section, whereas the specimens found in the Petermann Creek section are ranging through most of the fossiliferous beds.

Figures

Fig. 12. Pteriomorphian and heteroconchian bivalves, rostroconchs and gastropods from the Stairway Sandstone, Middle Ordovician, Australia. Internal moulds (A, B, E–M, N1) and latex casts of internal (N2, O) and external (C, D) moulds. A, B. Modiolopsis pojetai sp. nov. from Petermann Creek. A. Holotype (CPC 41481) in left-lateral view showing discrete longitudinal dorsal slit-like mark. B. Paratype (CPC 41482) in right-lateral view with umbo steeply descending anteriorly. C, D. Colpantyx? sp. A from Areyonga Gorge; in right (C, CPC 41483) and left-lateral (D, CPC 41484) views with two umbonal radial ribs anteriorly and one posteriorly. E, F. Sphenosolen draperi Pojeta and Gilbert-Tomlinson, 1977 from Petermann Creek (E, CPC 41485; F, CPC 41486), specimens with flat shell and narrow elongated sub-rectangular shape. G–M. Rostroconchia. G–I. Ribeiria csiro Pojeta, Gilbert- Tomlinson, and Shergold, 1977 from Areyonga Gorge (G) and Petermann Creek (H–I); note the prominent triangular beak and curved ventral margin (G, CPC 41487; H, CPC 41488; I, CPC 41489). J. Ribeiria jonesi? from Petermann Creek, sub-rectangular profile and strong dorsally projecting umbo (CPC 41490). K, L. Pinnocaris sp. A from Petermann Creek with inflated pear-shaped profile (K, CPC 41491; L, CPC 41492). M. Technophorus walteri Pojeta, Gilbert-Tomlinson, and Shergold, 1977 from Areyonga Gorge (CPC 41493) with a single lateral radial rib and prominent nearly erect pegma indicated. N, O. Gastropoda, Scalites? sp. from Petermann Creek. N. CPC 41494 (N1), latex cast with clear growth lines (N2). O. CPC 41495, specimen with 3.5 to 4 whorls. Scale bars 10 mm, except C, D, M, 5 mm.

Fig. 4. Composite log of the Stairway Sandstone and abundance-charts showing distribution of bivalves and rostroconchs in the Areyonga Gorge section.

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.