Fossil assemblage lab[1] - Sam Lovely Fossil Assemblage...

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Sam Lovely Fossil Assemblage Study Lab 1. The Cambrian ocean assemblage is the earliest data point we were given but it is important to note that inarticulate brachiopods, blind trilobites (.1- .8 cm) and echinoderms dominate this assemblage. The first shell builders occur during this time period, and filter feeding brachiopods are abundant. The most important correlation from this time period is the observation that nearly all of these fossils are from animals that are sessile filter feeding organisms. This suggests very little predator-prey interaction, and is most likely caused due to the simplicity of the organisms themselves (eg. very simple). The Lower Paleozoic ocean assemblage is filled with coral, sponges, bivalves, but perhaps the most important observation is that of lobe fin fish and a much larger biodiversity compared to that of the Cambrian. This “explosion” of not only bio mass but bio diversity was the cause of rapidly evolving organisms as they began to gain mobility and spread across the earth’s oceans. The upper Paleozoic ocean assemblage contains Crinoids, Gastropods, Brachiopods, along with massive deposits of limestone. The massive deposits of limestone suggest a warm shallow sea climate where Crinoids dominated the ocean. The Crinoid’s Ca skeleton helped form the reef and large limestone layers. This time period is the time period of massive reef building. The Mesozoic contains perhaps the largest biodiversity in the history of the earth before the great extinction. The ocean assemblages of the Mesozoic contain Gastropods, Nautiloids, Clam-like shells, Ammonites, Sea urchins, Bivalves, and a large increase in Marine invertebrates. Brachiopods are absent from this assemblage as they nearly go extinct before the Mesozoic begins. There is a increase in mobility and complexity of nearly all organisms, and the first predators begin to evolve. The most likely cause for the drastic change in organisms and animals is from a change in the epi-continental seas at that time.
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