A new species of the iconic triradial Ediacaran genus Tribrachidium from Nilpena Ediacara National Park, Flinders Ranges (South Australia)

The Ediacara Biota is a suite of globally distributed, exceptionally-preserved, soft-bodied organisms appearing in the fossil record from 575 million years ago to the base of the Cambrian. Nilpena Ediacara National Park (NENP) in the Flinders Ranges of South Australia preserves one of the most morphologically and taxonomically diverse assemblages of this period. Tribrachidium heraldicum is one of the more abundant taxa at this site (> 200 specimens) and is described as a circular organism, ∼3–50 mm in diameter, showing triradial symmetry. Here we describe a new species from NENP within the Tribrachidium genus: Tribrachidium gehlingi new species. This new species has three main arm-like structures that are slightly curved and do not reach the outer margin. There are three secondary arm-like structures that are approximately half of the length of the main arms and it is, overall, lower in relief. The process of burial and deformation are unlikely to be the cause of these morphological differences because both species co-occur within the same bedding horizon. Tribrachidium heraldicum Glaessner in Glaessner and Daily, 1959 is a triradial Ediacaran organism found in abundance within the Ediacara Member of the Flinders Ranges, South Australia. Here we report and describe a new species within the genus Tribrachidium Glaessner in Glaessner and Daily, 1959: Tribrachidium gehlingi new species from Nilpena Ediacara National Park (NENP), South Australia. Tribrachidium gehlingi n. sp. has low relief and three slightly curved, main arm-like structures that leave a conspicuous gap between the end of the arm-like structures and rim. In place of the ‘bulla’ found on T. herladicum, there are three secondary arm-like structures approximately half of the length of the main arm-like structures. Key morphological differences between the two species are statistically significantly different. Additionally, the species occur together within the same fossiliferous event horizons, indicating that the observed morphological differences are unlikely a result of taphonomy.