Calibrating the coevolution of Ediacaran life and environment

Abstract

<jats:p>The rise of animals occurred during an interval of Earth history that witnessed dynamic marine redox conditions, potentially rapid plate motions, and uniquely large perturbations to global biogeochemical cycles. The largest of these perturbations, the Shuram carbon isotope excursion, has been invoked as a driving mechanism for Ediacaran environmental change, possibly linked with evolutionary innovation or extinction. However, there are a number of controversies surrounding the Shuram, including its timing, duration, and role in the concomitant biological and biogeochemical upheavals. Here we present radioisotopic dates bracketing the Shuram on two separate paleocontinents; our results are consistent with a global and synchronous event between 574.0 ± 4.7 and 567.3 ± 3.0 Ma. These dates support the interpretation that the Shuram is a primary and synchronous event postdating the Gaskiers glaciation. In addition, our Re-Os ages suggest that the appearance of Ediacaran macrofossils in northwestern Canada is identical, within uncertainty, to similar macrofossils from the Conception Group of Newfoundland, highlighting the coeval appearance of macroscopic metazoans across two paleocontinents. Our temporal framework for the terminal Proterozoic is a critical step for testing hypotheses related to extreme carbon isotope excursions and their role in the evolution of complex life.</jats:p>

Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities

“…Arkarua thus joins a growing list of probable suspension feeders in the late Ediacaran White Sea assemblage, and suggests that a key pillar of the Phanerozoic marine carbon cycle – linkage between pelagic and benthic ecosystems – may have expanded from the Avalon to White Sea assemblages, ~ 571–550 Ma. In the absence of any obvious temporal correlation between putative environmental shifts (including the oxygenation state of global oceans) and the increases in both biological and ecological complexity in the late Ediacaran 67 , we propose that the expansion of benthic suspension feeding in the White Sea assemblage played an important role in shaping the waves of innovation that began in the late Ediacaran, and culminated with the Cambrian explosion 2 , 3 , 68 .…”

Local and global controls on carbon isotope chemostratigraphy

“…Re-Os ages confirm that the excursion is broadly synchronous, ranging between ∼574±4.7 to 567±3.0 Ma (Rooney et al 2020). These broad geochronological constraints, however, do not necessarily require that the excursion represent a global carbon cycle perturbation (sensu Fig.…”

“…5) and increasing geochronologic evidence for broadly synchronous perturbations (±5 Myr.) in shallow-water carbonate chemistry (Rooney et al 2020;Swanson-Hysell et al 2015).…”

Ediacaran macrofossils prior to the ~580 Ma Gaskiers glaciation in Newfoundland, Canada

“…Recent dating of the Shuram CIE to between ~574 and 567 Ma in NW Canada and Oman (Rooney et al . 2020; see also Canfield et al . 2020) would appear to confirm that, if the Wonoka–Shuram correlation is reliable, the taxonomically depauperate Palaeopascichnus assemblage in the Wonoka Fm.…”