POPULATIONS AND VARIATIONS IN THE EDIACARAN FOSSIL TAXA RUGOCONITES

The Ediacara Biota represents Earth’s first experiment in the development of multicellular animal life. Fossils of the soft-bodied organisms that make up this fauna can be found globally and are abundant where they occur. However, many aspects of this ecosystem remain enigmatic. Excavation of a succession of beds within the Ediacara Member cropping out west of the Flinders Ranges, South Australia, provides an opportunity for more detailed study of the population dynamics of these organisms, ultimately helping to clarify the ecology of these enigmatic fossils. A total of 28 beds have been excavated.

Rugoconites is a relatively common genus within the Ediacara Member of the Rawnsley Quartzite distinguished by its round, sometimes conical, shape and branching ridges radiating from its center with a well-defined outer rim. Although found in a variety of facies, Rugoconites is most commonly preserved on beds that are within the wave-base sands facies. Rugoconites occurs on ten of the excavated beds. Rugoconites dominates on one of these beds, but typically only a few individuals (usually less than five) occur on individual beds.

For this study, we made latex molds of 181 Rugoconites from Nilpena, South Ediacara, and those housed at the South Australia Museum, and used digital calipers to measure the diameter of the latex mold of each specimen. While in the literature Rugoconites have been described as ranging in diameter from 16-64mm, the Rugoconites measured in this study have an average diameter of about 28mm, but can vary greatly in size, with a range of nearly 100mm in diameter (3.93-100.39mm). This large range of sizes is not, however, observed in individual beds; the range of diameters on the only known Rugoconites-dominated bed is nearly an order of magnitude smaller (16.98-28.73mm). A similar range of sizes (9.00-21.58mm) exists on the bed with the second most Rugoconites. Furthermore, on each of these beds, about 2/3 of the Rugoconites fall within a 5mm range of one another.