Vendian biota
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The Vendian biota (also known as Vendian forms, Vendian fauna(s), Vendobionta or Vendazoa) are a group of ancient lifeforms that are found in rocks a bit older than the Cambrian faunas that represent the oldest fossils of classical paleontology.
The original descriptions came from the Ediacaran faunas of South Australia. It later turned out that similar faunas found in Namibia had been previously described, but their great age had not been appreciated. Subsequent discoveries have found similar fossils in Brazil, Antarctica, Newfoundland, the Canadian Maritimes, North Carolina, England, Canada's Northwest Territories, the western United States, Scandinavia, the White Sea, Siberia and Ural region of Russia, Poland, and other places.
These now extinct forms are generally flat, segmented, or frondlike with no visible organs other than holdfasts in some varieties. Many of these fossils are difficult to interpret, and trace fossils are common. They are probably entirely late Precambrian, although some possible Vendian forms have been identified in the Cambrian. Many believe that some or all of the Vendians are precursors to one or more modern phyla that arose in the Cambrian.
The Vendian "animals" (assuming that they were animals) are probably too large and complex to be single-celled. They universally lack mouths, any organs, or appendages. Symmetries may be two-, three-, four-, or even five-fold. No tracks are found that appear to be associated with the creatures. Some appear to be or have holdfasts. They include frond-like forms (e.g. the rangeomorphs), disks with various ornamentations, what appear to be air mattress-like forms, and other unlikely shapes. They were originally thought to be simple precursors of more modern forms, and a few elements of the fauna still look like possible precursors of such later forms as arthropods and mollusks. But most appear to belong to some evolutionary sidetrack. It has been proposed that they consitute an ancient phylum, the vendazoa, that largely died out just before the beginning of the Cambrian.
Other than a few dubious fossils from the Upper Cambrian in Ireland, there is no known overlap between the Vendazoa and modern lifeforms.
Well known Vendian forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Onegia, Yorgia and Pteridinium. The full list runs to 50 or more taxa. Some of those named are rare but interesting for one reason or another. Others are widely distributed.
External link
- Online exhibit at U. of California Museum of Paleontology (http://www.ucmp.berkeley.edu/vendian/vendian.html)
- The Ediacaran Biota page @ Paleos (http://www.palaeos.com/Ecology/Biota/Ediacara.html)