Hyolithelminthida Fischer, 1962
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publication ID |
https://doi.org/ 10.4202/app.00586.2018 |
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persistent identifier |
https://treatment.plazi.org/id/03AB4756-FFC4-1603-BC1C-BEBD0BCF215C |
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treatment provided by |
Felipe |
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scientific name |
Hyolithelminthida Fischer, 1962 |
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Order Hyolithelminthida Fischer, 1962 Family Hyolithellidae Walcott, 1886 Hyolithelminth tubes indet.
Fig. 19 View Fig .
Material.—Hundreds of specimens (all damaged or incomplete) from bioclastic Clasts 1, 4, and 5, 9 figured (SAM
P57368–57376). From the Dailyatia odyssei Zone, WPC, Kangaroo Island, South Australia.
Remarks.—Small, phosphatic tubes are extremely common in lower Cambrian shelly fossil assemblages and constitute a large proportion of the fauna from the WPC clasts. Rare instances of hyolithelminths preserved in life position (Aftenstjernesø Formation in North Greenland) confirmed that the tubular Hyolithellus at least, lived buried within the substrate with the aperture emerging at the sediment-water interface, probably with a filter-feeding lifestyle ( Skovsted and Peel 2011). Chang et al. (2018) described diverse early Cambrian tubular or conical fossils preserved as crack-outs with shells, and as carbonaceous compressions demonstrating that some taxa lived in gregarious communities clustered on the seafloor. Unfortunately, taxonomic identification of most early Cambrian tubes is complicated by their relatively simple morphologies and commonly fragmentary remains, particularly of those recovered via acid leaching methodologies.
The relative abundance of tubular forms in lower Cambrian shelly fossil assemblages is likely to be influenced by the suitability of available substrate. Betts (2012) noted that abundance of hyolithelminths increased in micritic and microbial limestone facies. These facies correspond with soft, muddy microbial substrates that may have been easier to penetrate in low energy conditions where smothering or accidental burial was less likely. Abundance of tubes in the limestone clasts in the WPC may be a result of hydrodynamic sorting or other biostratinomic processes concentrating these (and other) shelly fossils prior to burial.
Main morphologies of tubular fossils from the WPC include straight or very weakly curved specimens with circular cross-sections, similar to Hyolithellus ( Fig. 19C–F View Fig ). Diameter of these tubes can range from 150–1000 μm. Tubes may have thin walls or be thickened with multiple growth layers and have faint external concentric annulations, though external textures are likely to have been affected by abrasion. Others are compressed with an oval cross section, often split along the broadest side, bifurcating into two diverging halves/thecae as in Sphenothallus ( Fig. 19A, B View Fig ; Li et al. 2004). These tubes may display a basal disc, which has been inferred as a method of substrate attachment ( Bischoff 1989; Li et al. 2004). However, the holdfast or any other type of attachment structure is absent from all of the WPC specimens, which are consistently damaged or abraded, truncated at both ends, or split along the entire length of the tube.
A smaller proportion of the hyolithelminths from the WPC have distinctive, rapidly expanding, flattened tubes ( Fig. 19G–I View Fig ). Their cross section changes from circular at the narrow end to compressed and oval-shaped at the wider end. Similar tubes were reported by Paterson et al. (2007b: fig. 5A–C) from the KLM (Parara Limestone). Paterson et al. (2007b) noted that early Cambrian phosphatic tubes often exhibit a combination of characters belonging to a variety of taxa ( Paterson et al. 2007b). They exhibit similar growth patterns, and it is possible that differences in gross morphology are due to environmental influences, rather than having taxonomic significance. Hence, the material here is left under open nomenclature.
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