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Fossils appear very suddenly within about 30 my as

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Unformatted text preview: brian Earliest organism of bilaterian form Appears in strata that overlie last of several extreme glacial or proposed Snowball Earth episodes but these fossils are disputed cross section of body Idea that tiny animals evolved during Snowball period. Under this view, the global thaw resulted in the rapid evolution of animal forms, including larger size, hard body parts Metazoans Origins 2 hypotheses •  1) Syncy,al (mul,nucleate) ciliate hypothesis  ­ Metazoa evolved from mul,nucleated ciliate •  2) Colonial flagellate hypothesis – Hollow sphere of colonial flagellates Trichoplax adherens –  (BioEssays 2005 – 27:1294 ­1302) 7 4/9/13 Paleozoic Life – Cambrian Explosion ~543 MYA, Start of Paleozoic Era (Cambrian Period) Diversifi[email protected] of metazoans Oxygen approaches modern levels Cambrian Explosion – Almost all modern phyla & classes of skeletonized marine animals •  Also many groups of [email protected] phyla and classes •  Fossils  ­...
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