The Ediacaran Fauna Essay -- essays research papers

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 Ediacaran organisms were marine animals, some crawled, some were attached to the sea floor and others would swim or just freely float. Their impressions were molded in the moving sands that washed over the mud flats and were preserved as casts in the sandstone. It is difficult to conceive how fossils of delicate soft-bodied animals could be preserved given the evidence of strong currents in the strata. However, extensive research has provided an explanation. Most of the animals settled on mud patches out of the water during calm currents. Some of these patches dried between tides and developed deep cracks. The next shifting current would then cover these cracks with a layer of sand and the lower surfaces preserved the mud in the form of perfect casts. (Glaessner 67)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 th... ...nimals. Gregory Retallack, a paleontologist from the University of Oregon, suggests that these fossils were lichens. Retallack's argument rests on the fact that the impressions were buried five kilometers under ground. He believes the fossils should have been crushed by the weight of the overlying sediment. But Retallack observed that the fossils "were as compaction resistant as some kinds of fossil tree trunks!" Because of this, Retallack concludes that these forms weren't animals, rather lichens made up of sturdy molecules such as chitin. Further evidence of this interpretation can be found in the Ediacaran organism's growth patterns and microscopic structure. (Woodmorappe 1) 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 anim als, we are puzzled by the absence of direct ancestors of these Ediacaran fossils.