New Ediacaran Fossils: Do They Ignite the Cambrian Explosion?
Well-preserved fossils of seaweed-like colonies have been reported from China. They are dated by the scientists at 600 million years old, from the Ediacaran period. Can these be missing links, lighting the fuse of biodiversity that culminated in the Cambrian explosion?
PhysOrg summarized the findings published in Nature.1 “In addition to perhaps ancient versions of algae and worms, the Lantian biota – named for its location – included macrofossils with complex and puzzling structures,” the article said. “In all, scientists identified about 15 different species at the site.” Pictures of the seaweed-like fossils show fronds with a distinctive holdfast, like modern seaweed use to cling to the seafloor.
The paper in Nature shows pictures of frond-like and tube-like organisms “with uncertain phylogenetic affinities,” but no clear Cambrian-like body plans. A couple of them, Guy Narbonne speculated in the same issue of Nature,2 are “probable ancestors of radial and bilaterian animals.” The discoverers mentioned a hopeful case: “The axial structure in Types D and E is puzzling and it could represent the digestive structure of worm-like animals,” they hinted; “In an animal model, the holdfast and stalk of Type D would be alternatively interpreted as the proboscis of an early worm-like organism.” The photos are not compelling.
Both papers spent much of their space discussing what effects varying levels of oxygen in the oceans might have had on the evolution of life. For instance, “To reconcile the conflicting geochemical and palaeontological indicators of palaeoredox conditions, we propose that the Lantian basin was largely anoxic but punctuated by brief oxic episodes,” the original paper said, harking back to the jargon of punctuated equilibrium, if that somehow helps evolution. “These oxic episodes were opportunistically capitalized on by benthic macroeukaryotes that were subsequently killed and preserved by frequent switch-backs to anoxic conditions.” Evolution did not seem to be going in any particular direction toward complex animal life.
The paper claims the Lantian biota is “probably older than and taxonomically distinct from the Avalon biota,” the previous record setter for “earliest-known fossil assemblage with macroscopic and morphologically complex life forms” at 579-560 million years old. That suggestion, however, does not create any evolutionary linkage between the two independent groups. Even so, neither fossil beds show any of the complex organs seen in Cambrian phyla. The paper calls them multicellular eukaryotes. The focus of the research was not so much on evolution upward and onward from these seaweed-like impressions, but “suggests that morphological diversification of macroscopic eukaryotes may have occurred in the early Ediacaran Period, perhaps shortly after the Marinoan glaciation, and that the redox history of Ediacaran oceans was more complex than previously thought.”
1. Yuan et al, “An early Ediacaran assemblage of macroscopic and morphologically differentiated eukaryotes,” Nature 470 (17 February 2011), pp. 390�393, doi:10.1038/nature09810.
2. Guy Narbonne, “Evolutionary biology: When life got big,” Nature 470 (17 February 2011), pp. 339�340, doi:10.1038/470339a.
Even with the most generous concessions to Mr. Darwin, these fossils do not help explain the Cambrian Explosion. They are simple frond-like colonies of eukaryotic algae, with no clear differentiation or body plans typical of Cambrian animals. No amount of acquiescence to the evolution-incestuous dating methods can link these imprints with trilobites and vertebrates by an evolutionary sequence.
That’s why they changed the subject to talking about rising and falling oxygen levels in the oceans. It’s a distraction and a red herring, intended to give a false impression that they are making some kind of progress solving this super-falsification of evolutionary predictions (01/07/2011).