Shetlandia Wrona, 2004

Claybourn, Thomas M., Skovsted, Christian B., Betts, Marissa J., Holmer, Lars E., Bassett-Butt, Lucy & Brock, Glenn A., 2021, Camenellan tommotiids from the Cambrian Series 2 of East Antarctica: Biostratigraphy, palaeobiogeography, and systematics, Acta Palaeontologica Polonica 66 (1), pp. 207-229 : 226-227

Shetlandia Wrona, 2004

Type species: Shetlandia multiplicata Wrona, 2004 ; Lower Cambrian clasts from the Miocene Cape Melville Formation , King George Island, South Shetland Islands, Antarctica .

Shetlandia multiplicata Wrona, 2004 Fig. 11 .

2004 Shetlandia multiplicata sp. nov.; Wrona 2004: 34, figs. 14, 15A– E, H–J, 16.

Material.—Exclusively fragmentary material, with 22 fragments recovered from samples HRA/24, HRA/25, and HRA/14 (NRM X10020–X10024, 5 figured), southern Holyoake Range ( Figs. 1 , 2 , Table 1). Cambrian Series 2, Stages 3, 4.

Description.—Fragments preserve flat to gently curved sclerite fields; no large plications or apexes are preserved. No micro-ornament is preserved. Two distinct arrangements of plicae occur on the fragments. Firstly, rows of closely stacked, overlapping arches delineate tall, prominent radial plicae which extend from the top of the plicae to the groove ( Fig. 11A ). The arches increase in size towards the base of the sclerite. These plicae are separated by grooves with concentrically oriented ribs at their base. These ribs do not contact the base of the arches ( Fig. 11A 2 ) but are part of the same growth series. The second type of ornament (found on only one sclerite fragment) is weakly developed pseudoplicae formed by a series of pustules in concentric rows ( Fig. 11D ). A markedly different type of ornament also occurs and consists not of plicae but of densely packed concentric, wall-like ribs which are also present on one fragment ( Fig. 11B 1 , C).

Remarks.— Shetlandia multiplicata was previously known only from glacial erratics recovered from the glaciomarine Miocene Cape Melville Formation, King George Island, South Shetland Islands of West Antarctica and is generally poorly understood (Wrona 1989, 2004). However, despite the fragmentary nature of the holotype, it has unique ornamentation and plication that is unknown from any other tommotiid genus.

The few fragments from the Shackleton Limestone in the Holyoake Range can be confidently assigned to Shetlandia multiplicata Wrona, 2004 , due the unique morphology of the dense plicae. The densely packed arches that make up these plicae are identical in morphology to those originally described from King George Island (Wrona 2004: fig. 14M–T). Pustules arranged into pseudoplicae are also found on some sclerite fragments from King George Island (Wrona 2004: fig. 15H, I). The third ornament of concentric wall-like ribs is also found on both sets of fragmentary material.

Stratigraphic and geographic range.—Cambrian Series 2, Stages 3, 4, of the Shackleton Limestone in southern Holyoake Range, Central Transantarctic Mountains, East Antarctica; carbonate clasts (Cambrian Series 2, Stage 4?) from the Miocene Cape Melville Formation, King George Island, West Antarctica (Wrona 2004).

Figures

Fig. 11. The tommotiid Shetlandia multiplicata Wrona, 2004, unknown type sclerite fragments from the Cambrian Series 2, Stages 3, 4, Shackleton Limestone, Holyoake Range, Transantarctic Mountains, East Antarctica. A. NRM X10020, general view (A1), detail showing arched growth series (A2). B. NRM X10021, general view (B1), detail of broken margin (B2). C. NRM X10022, general view (C1), detail of comarginal ribs and broken edge (C2). D. NRM X10023. E. NRM X10024. Scale bars 200 µm, except B2, 100 µm. A–C taken with backscattered electron detector.

Fig. 1. A. Topographic map of the Central Transantarctic Mountains (adapted from the USGS 2008) with the main geographic features and the sites visited by the Kansas University expeditions (study areas marked by section names GM, 87-L2, M, H, S). The locality GM is the type locality for Dailyatia braddocki, which is close to the location of the CM2 section. The locality M is the type locality of Dailyatia odyssei). B. The area of the Churchill Mountains visited by the Swedish-Australian expedition, showing the location of the CM2 section. C. The area of the Holyoake Range visited by the Swedish-Australian expedition, showing the location of the HRA section. D. Overview of Antarctica showing the extent of the Transantarctic Mountains, including the the location of the Argentina Range, and IC (location on sections unknown) in the Schneider Hills (sampled by the Kansas Expeditions).

Fig. 2. Stratigraphic columns of the sampled sections in the Holyoake Range (HRA) and Churchill Mountains (CM2). Grain size: B, boundstone; G, grainstone; M, mudstone; P, packstone; W, wackestone.