Abstract
A small assemblage of isolated Microdictyon plates is described from the lower Cambrian Ajax Limestone, Mt Scott Range (Flinders Ranges), South Australia. Microdictyon plates are primarily known from single, isolated, perforated phosphatic sclerites; only one species (M. sinicum) from the Chengjiang Lagerstätte is known from soft-bodied preservation of the complete organism. The isolated plates from South Australia display a wide range of morphologies potentially reflecting: 1, considerable diversification within the group at this time; 2, extensive intraspecific morphological variation; 3, different plate morphotypes along the trunk of the animal; or 4, significant ontogenetic variation in successive growth stages. The South Australian specimens are similar to several individual sclerites described from other Cambrian palaeocontinents, but appear closest to faunas described from South China. Problems associated with the taxonomy of isolated Microdictyon plates are discussed, including the lack of knowledge associated with intraspecific and/or ontogenetic variability and how individual plate morphology may relate to size or relative position along the length of the complete organism.
Acknowledgements
Financial support towards fieldwork and laboratory costs came from a Macquarie University Research Development Grant to GAB and CBS. Funding support for CBS was also provided by a postdoctoral grant from the Swedish Research Council (VR). We extend warm thanks to Graham Ragless of Beltana Station for access to the field area. We are indebted to P. Bell, B. Jonak, L. Strotz, P. Cockle, B. Morgan, B. Pyemont, N. Wilson and D. Smith for their assistance in the field. We are indebted to Dean Oliver (Dean Oliver Graphics) for drafting . Thanks to Richard Aldridge and Olaf Elicki for thoughtful and constructive reviews of the original manuscript.