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What Types of Modern Phyla Were Found in the Ediacaran Period?

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  • Written By: Michael Anissimov
  • Edited By: Bronwyn Harris
  • Last Modified Date: 25 November 2016
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For many decades, scientists thought that multicellular life didn't exist before the dawn of the Cambrian period, 542 million years ago. Then, in 1967, a careful geological study of pre-Cambrian rock beds turned up frond-like organisms called Charnia. This was the first time that definitive pre-Cambrian metazoan fossils had been found, and it created a sensation. Since then, over 18 fossil beds from the Ediacaran period (before the Cambrian) have been found, with over 100 different types of organisms dating back to 600 million years ago. Scientists get into deep arguments over whether these ancient forms are related to modern-day animals, and the consensus is that some of them are.

Though common knowledge states that modern phyla have their origin in the Cambrian explosion about 520 million years ago, recent findings have confirmed representatives of modern phyla in the Ediacaran period. Some of these likely represent stem groups that bear little to no relation to living forms. The phyla that have representatives in the Ediacaran period are Porifera (sponges), Cnidaria (Inaria.), Ctenophora (comb jellies), probable Mollusca (Kimberella), probable Onychophora (Xenusion), probable Arthropoda (Parvancorina), probable Annelida (Cloudina), probable Echinodermata (Arkarua), and members of an extinct proposed phylum of bilateral animals, Proarticulata (Dickinsonia).

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Only three modern phyla (Porifera, Cnidaria, and Ctenophora) are mostly accepted by scientists as having existed in the Ediacaran period, and there is substantial reason to believe that Mollusca, Onychophora, Arthropoda, Annelida, and Echinodermata were represented as well. Early mollusks are among the oldest of the smally shelly fauna that mark the start of the Cambrian, and the Ediacaran fossil Kimberella has features like that of a mollusk, such as a univalve shell, and is found in conjunction with scrapings that strongly suggest a radula, the distinguishing feature of mollusks. Recent images of Xenusion strongly suggest that it is an early onychophoran (velvet worm), while Parvancorina clearly has a head, and despite the absence of fossilized limbs, looks like a stem group arthropod. Annelida and Echinodermata are more uncertain, but the numerous tube-shaped skeletons found from the Ediacaran period are suggestive of polychaete worms, and the five-fold symmetry of Arkarua makes it a probable echinoderm.

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serenesurface
Post 3

It's so interesting that even though many of the creatures existing today go far back in world's history, they look vastly different than they did now.

I'm sure if we saw the type of worm that existed during the Ediacaran period for example, it wouldn't exactly look like the worm we know today.

bluedolphin
Post 2

@ZipLine-- I'm not an expert on this topic but I don't think that multicellular organisms go father back than the Ediacaran period. And if they did, the chances of there being remaining fossils is rather slim. Shelled organisms leave the most fossils and those had not yet developed during the Ediacaran period. So I think that what we have found so far will be as far as it goes.

The other reason why I think that the first multicellular organisms appeared at this time is because there was significant climate change that occurred during this period. This probably encouraged the development of multicellular organisms.

ZipLine
Post 1

Science and technology are advancing. I think that with time, newer discoveries will be made about living things and how far back they go in history. I suspect that multicellular life existed even farther back than what we know now. Of course, time will show.

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