Evidence of sensory-driven behavior in the Ediacaran organism Parvancorina: Implications and autecological interpretations

Abstract

The ancient in situ fossil seafloor communities of the Ediacara biota present an unparalleled window into the assembly of the earliest complex macroscopic organisms, including early animals on Earth ca. 555 million years ago (mya). The unique preservation style of Ediacara fossil seafloors preserves whole communities virtually ‘frozen in time’, including both living and dead organisms at the time of burial. This phenomenon, where the fossilized organisms are arranged as they were in life offers an unparalleled opportunity to examine ecological patterns in some of the earliest examples of animal communities in deep time. The small, anchor-shaped fossil genus Parvancorina is common among the Ediacara biota; however, its morphology and ecology have received little attention. Here, we describe a population of juvenile Parvancorina preserved on a section of fossil seafloor recently excavated from the characteristic Ediacara Member from Ediacara Conservation Park in the Flinders Ranges, South Australia. We applied spatial methods to the sample population of Parvancorina (n = 202) and found that they demonstrated two size-clusters, distinguishing juveniles from adults, and further analyses showed that the smaller specimens tended to be spatially aggregated. For the first time among any Ediacara taxon, we found that this sample population of Parvancorina demonstrated a strong bimodal orientation, suggesting that orientation played an important behavioral role in its autecology. The aggregated spatial distribution and bimodal orientation of Parvancorina likely resulted from behavioral responses to the influence of benthic currents, suggesting that Parvancorina had a complex sensory network, and was capable of motility.