New Ediacaran fossils; environmental studies (Introduction)

by David Turell , Friday, November 05, 2021, 21:49 (905 days ago) @ David Turell

Changes in the Earth's changes do not develop Cambrian precursors:

https://www.science.org/doi/full/10.1126/sciadv.abi9643?et_rid=17445044&utm_campaig...

"Abstract
The rise of complex macroscopic life occurred during the Ediacaran Period, an interval that witnessed large-scale disturbances to biogeochemical systems. The current Ediacaran chronostratigraphic framework is of insufficient resolution to provide robust global correlation schemes or test hypotheses for the role of biogeochemical cycling in the evolution of complex life. Here, we present new radio-isotopic dates from Ediacaran strata that directly constrain key fossil assemblages and large-magnitude carbon cycle perturbations...These data calibrate the tempo of Ediacaran evolution characterized by intervals of tens of millions of years of increasing ecosystem complexity, interrupted by biological turnovers that coincide with large perturbations to the carbon cycle.

***

"The Ediacaran Period [635 to 539 million years (Ma) ago] is a pivotal period in Earth history, achiving the rise of complex macroscopic life. This evolutionary milestone occurred in the aftermath of extreme climate perturbations, the Cryogenian snowball Earth events, and amid several perturbations to the carbon cycle. These are recorded by large carbon-isotope excursions (CIEs) in marine carbonate records, defined as negative and positive deviations in the stratigraphic trend of carbonate-carbon isotope (δ13Ccarb) profiles. These perturbations have been documented worldwide and are commonly used to establish regional to global stratigraphic correlations. (my bold)

(From the discussion):

"Our new geochronological data provide the foundation for a refined global age model for the Ediacaran fossil record. Early Ediacaran fossils are dominated by acanthomorphic species alongside macroalgae and putative animal fossils from the Lantian biota. After 587.2 ± 3.6 Ma, there is an increase in the abundance and diversity of the acanthomorphic species, accompanied by the diverse embryos that exhibit complex development probably hosting total-group metazoan, and putative microscopic metazoans (e.g., sponges) in the Weng’an biota. Macroscopic complex Ediacaran organisms made their first appearance between 580 and 574 Ma ago, whereas rangeomorphs (including some stem-group eumetazoans) diversified between 574 and 564 Ma ago through the Shuram CIE, and the oldest known record of eumetazoan mobility appeared 564.8 Ma ago. Diversification of nonrangeomorphs and increased evidence for bilaterian mobility, as exemplified by the White Sea assemblage, are constrained by U-Pb dates of 557.3 ± 0.6 Ma and 553.0 ± 0.7 Ma. Following the 550-Ma CIE and postulated first pulse of extinction of Ediacaran taxa at the White Sea–Nama assemblage transition, skeletonized tubular fossils (cloudinids) and complex burrowing produced by bilaterian metazoans record the deep roots of the Cambrian explosion of metazoans alongside soft-bodied Ediacaran taxa. (my bold)

"Our age model presented for Ediacaran CIEs and fossil records provides the necessary chronometric context to test causal relationships, if any, between them. Independent of the drivers and global nature of the Ediacaran CIEs, the direct dates for Ediacaran fossil assemblages are a prerequisite for calibrating biostratigraphic records and improving the accuracy of molecular clock analysis to reconstruct the early evolutionary history of complex life. The emerging tempo of Ediacaran evolution is defined by assemblages of organisms with increasing ecosystem complexity that are relatively stable on tens of millions of year time scales, with new assemblages appearing across much shorter, discrete intervals. At the current resolution, these transitions in the fossil record coincide with CIEs, suggestive of a potential causal relationship between environmental perturbations recorded in the carbon cycle and biological turnovers."

Comment: note my bold. The Edicaran forms definitely advanced to macroscopic more complex forms and may have finally developed into early sponges, which represent first animal life. But that is it. What followed in the Cambrian were highly complex body forms with motility and complex organ systems and a crowning achievement, eyes! The gap remains despite this degree of research. Follow Bechly's advise and accept the collector's curve:

"The same approach is used by paleontologists for a statistical test of the completeness of the fossil record; it is called the collector’s curve. In most groups of fossils, we have reached this point of demonstrable saturation, where we can be pretty confident that the distinct discontinuities that we find are data to be explained and not just sampling artifacts. There is another reason why we know this: If the gaps and discontinuities in the fossil record were just artifacts, they should more and more dissolve with our greatly increasing knowledge of the fossil record. But the opposite is the case. The more we know, the more acute these problems have become. “Darwin’s doubt” did not get smaller over time but bigger, and if he were still alive, he would likely agree that the evidence simply does not add up, since he was much more prudent than many of his modern followers." (posted here)

You can wish for lost fossils, but it will remain a desperate wish.