Our present understanding of the origin of animals and Phanerozoic ecosystems depends critically on the ability to interpret impressions left behind by soft-bodied Ediacaran organisms, and to document their spatial and temporal distribution, which conceivably relate to strong environmental gradients in terminal Proterozoic seawater.
To our disadvantage, ever since their first discovery in South Australia, the terminal Proterozoic Ediacaran fossils have been recurrently found in clastic sediments that are unfavorable for the preservation of soft tissues. To enhance paleobiological resolution and track environmental perturbations, however, requires the discovery of new taphonomic windows (sets of conditions for preservation) for the Ediacaran biota in relatively continuous successions dominated by chemical sediments.
Yet, finding these fossils in alternative modes of preservation has been difficult. Grazhdankin et al. describe Ediacaran fossils uniquely preserved in fine-grained carbonate sediments, which promise a much-enhanced anatomical and paleoecological view of these enigmatic organisms and their taphonomic variants. Importantly, the appearance of Ediacaran fossils turned out to be not inferior or different to that seen in their counterparts found in clastic sediments, indicating that the celebrated weirdness of Ediacaran fossils is not due to unusual preservational circumstances.
On the other hand, the Ediacaran fossils are excluded from a taphonomic window that otherwise favors preservation of diverse organic tissues, suggesting that certain Ediacaran tissues, specifically of rangeomorph and frondomorph organisms, had unique properties.
Grazhdankin et al.’s results corroborate the hypothesis that the earliest macroscopic life forms were not ancestral to any Phanerozoic or modern organisms.
- Grazhdankin et al. Carbonate-hosted Avalon-type fossils in arctic Siberia. Geology, 2008; 36 (10): 803 DOI: 10.1130/G24946A.1
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