The Ediacaran Fauna
Up until 1947, it was believed that the Cambrian Explosion marked the first true abundance of multicellular life. However, this was discovered to be untrue after Sir Douglas Mawson and R.C. Sprigg mistakenly came across numerous "fossil jellyfish" in the Ediacara Hills while observing what was originally believed to be sandstones belonging to the lowest strata of the Cambrian. At first, these finding were dismissed as "fortuitous inorganic markings."(AAS Biographical Memoirs.) Several years later however, other discoveries of segmented worms, worm tracks, and impressions of two other assemblages that bear no resemblance to any known organism, living or extinct, prompted the South Australian Museum and the University of Adelaide to undertake a joint investigation of the region. Further studies by M. F. Glaessner, a paleontologist at Adelaide showed that the fossils were found well below the oldest Cambrian strata and that the strata actually dated from the Precambrian era. Several thousand specimens have since been collected in the Ediacara Hills. All the fossils collected were soft-bodied animals and their tissues were strengthened by spicules-needles of calcium carbonate that functioned as their support. The
The most abundantly distributed fossil at the South Australian site, the Dickinsonia, was represented by over one hundred specimens. These impressions may be related to some modern day flatworms and were covered with transverse ridges. The number of ridges varies with size-while smaller forms had 20 ridges, larger ones could have as many as 550. Another notable find was the Spriggina floundersi, which was named after R.C. Sprigg and Ben Flounder; the two geologists credited to their discovery. These small annelid worms ranged between one and three inches in length and had small horseshoe shaped heads. These worms resemble the modern Tomopteridae, which have heads similar to those of the Precambrian fauna, only wider. It now appears as though these marine worms are direct descendants from the ancient forms. Despite these controversial implications many paleontologists still believe the Ediacaran animals are in fact ancestors of the animals in the existing phyla. This controversy might not be resolved until the discovery of fossils providing more information.. (Levin 267) Charles Darwin found himself in this same situation some 150 years ago. Just as he was befuddled by the absence of the ancestors of the Cambrian animals, we are puzzled by the absence of direct ancestors of these Ediacaran fossils. The nature of these soft-bodied fossils justifies the characterization of the Precambrian as the "age of the jellyfish," however the term jellyfish only refers to a number of diverse forms, which belong to the Phylum Cnideria. (Glaessner 64) Six principle forms of animals have been discovered. The first are the rounded, discoidal impressions, resembling the modern day jellyfish. The second form is the stalk-like fronds with grooved branches that also belong to the Cni
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Approximate Word count = 1197
Approximate Pages = 5 (250 words per page double spaced)
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