Emily Mitchell (University of Cambridge, UK)
Spatial analysis of Ediacaran ecosystems: a new approach to illuminate the origins of complex life
Ediacaran macro-organisms occupy a crucial position in the history of life on Earth, marking the transition between the microbially dominated Proterozoic and the Cambrian explosion of modern animals. The oldest Ediacaran macro-organisms exhibit unique morphologies, making it difficult to resolve their phylogenetic relationships or their basic ecology. However, the sessile nature of these Ediacaran macro-organisms, coupled with their in-situ preservation, means that their spatial positions reflect the biological and ecological processes that they were subject to in-life. As a result, detailed spatial analyses moves beyond descriptive statistics, enabling verifiable predictions to be made and ecological hypotheses to be tested.
Using a high-resolution tripod-mounted Laser Line Probe, we have comprehensively mapped 18 of the most diverse and abundant Ediacaran communities across Newfoundland, Canada and Charnwood Forest, UK, to a resolution of ~40 µm. By analysing the relationship of specimen height with spatial distributions, we found that competition for water-column resources did not structure these ecosystems, with the key advantage of large body-size limited to greater dispersal, contrary to previous suggestions. Furthermore, stemmed organisms do not exhibit any tiering, in contrast to non-stemmed organisms, illustrating that this morphological differentiation was also not driven by resource competition but by reproductive concerns. The relatively low-levels of direct inter-specific competition, likely results in less pressure for niche creation, thus speciation, which suggests it is longer-term abiotic processes that underlie Ediacaran speciation.