BRANCHING OUT: ECOLOGY AND ONTOGENETIC PATTERNS OF THE EDIACARAN FOSSIL RUGOCONITES

The Ediacara Biota, Earth’s first experiment in complex, macroscopic life, is composed of more than forty morphologically diverse genera. Fossils of these soft-bodied organisms are preserved in the ~555 Ma Ediacara Member of the Rawnsley Quartzite outcropping in the Flinders Ranges area of South Australia. At the Nilpena National Heritage Ediacara Fossil Site, twenty-six beds multiple square meters in size have been excavated, revealing Ediacaran communities that have been preserved in-situ.

Rugoconites is a relatively common genus of the Ediacara Biota at South Australia. It occurs on ten of the twenty-six excavated beds at Nilpena and is found in four of the five described fossiliferous Ediacaran-aged facies in South Australia; though, it is most common in the wave-base sands facies. Although it is the dominant genus on one of these beds, it occurs in smaller numbers on the others. Rugoconites specimens on the same bed tend to be similar in size to one another.

Rugoconites is a round, sometimes conical, tri-radially symmetric fossil, primarily distinguished by the branching ridges that radiate from its center to a well-defined outer rim. At nearly 100 mm (from 4-100 mm in diameter), the size range of Rugoconites is larger than other superficially-similar (round, radially-symmetric) Ediacara taxa. The large size range of Rugoconites has also allowed for the opportunity to study growth patterns in this enigmatic organism. Preliminary results indicate that Rugoconites adds primary branches in sets of three, resulting in specimens with six, nine, twelve, and fifteen primary branches, with larger specimens having more primary branches than smaller ones. New primary branches may be the result of secondary branches becoming separate, primary branches as the organism grows, potentially providing new insight into the ontogenetic patterns of this enigmatic genus.