Earliest evidence of behavioural handedness in the Ediacaran motile bilaterian Spriggina floundersi.

Fossils of the Ediacara Biota preserve the oldest macroscopic communities that include animals. Classification of many of these taxa has proved contentious. Instead, studies of ecological characters reveal key insights. Here we examine the Ediacaran fossil Spriggina floundersi from the Ediacara Member, Flinders Ranges and surrounding region. Specimens from Nilpena Ediacara National Park (NENP) and the South Australia Museum (SAM) present significant morphological variation. Fossils found in situ on discrete bedding planes at NENP reveal no systematic orientation of features, suggesting variable morphologies formed via biological processes, rather than external forces. Our results support motility in Spriggina, which involved bending about the long axis, propagation of pedal waves, vertical adjustment of the anterior region and horizontal manipulation of repeated body units. A significant number of fossil specimens are bent to the left (right in life). The nature of these bends does not match expectations of anatomical asymmetry and instead constitutes the oldest described evidence of behavioural handedness. Results are consistent with Spriggina as a bilaterally symmetrical, possibly segmented, benthic organism. These characters are unique compared with known Ediacaran ecologies but are common in various extant bilaterian groups, indicating major animal innovations prior to the Phanerozoic.