A large enigmatic fossil from the early Cambrian (Series 2, Stage 3) Heatherdale Shale of South Australia

ABSTRACT

A large enigmatic fossil is described from the early Cambrian (Series 2, Stage 3) Heatherdale Shale in the Fleurieu Peninsula, South Australia. It has an almost circular outline about 150 mm across, with an outer rim and 27–30 evenly-spaced rays that extend about two-thirds of the distance to the centre of the structure; it shows radial symmetry. There is a featureless central area with a width about one-third that of the entire specimen. The fossil is preserved as pale-coloured material that stands out slightly above the surrounding mudstone. XRF data indicate that there is little compositional difference between the fossil and the enclosing rock. The fossil may appear to be a transverse section of a larger organism, but it does not continue down into the surrounding rock. This suggests it is a non-mineralised compression fossil that retains the remnants of a three-dimensional structure. Possible affinities with radiodont oral cones, ctenophores, eldonioids, scyphozoa and archaeocyaths are discussed, but no definite assignment can be made.

KEYWORDS:

• Problematica
• oral cone
• Radiodonta
• ctenophores
• eldonioids
• scyphozoa
• archaeocyatha
• Heatherdale Shale
• early Cambrian

Acknowledgements

This paper is dedicated to the memory of Dr Roger Cooper, a leader of New Zealand palaeontology and geology for over fifty years. Students from the National Centre of Petroleum Geology and Geophysics found the specimen. Justin Payne (University of South Australia) is thanked for carrying out the XRF analyses and Pierre Kruse (South Australian Museum) for advice on archaeocyatha. Dr Mary-Anne Binnie (South Australian Museum Palaeontological Collection Manager) provided access to the specimen. This paper has been improved considerably by constructive comments from Greg Edgecombe and an anonymous reviewer.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article. 3D LiDAR of possible radiodont oral cone (SAMA P49419), early Cambrian (Series 2, Stage 3), Heatherdale Shale, South Australia is openly available in figshare at https://doi.org/10.6084/m9.figshare.21385593.v5