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Chapter Notes - Chapter 12(333-378 Life during Precambrian...

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Chapter 12 (333-378) Life during Precambrian – mostly of single celled microbes, with multicellular organisms (metazoans) appearing only in uppermost Proterozoic Hard shells – key improvement that produced good fossil records of Phanerozoic Almost every phylum of common shell-bearing invertebrates living today originated by Ordovician time Refer to table 12-1 page 34 Animals with backbones –vertebrates – appeared during the Paleozoic Earliest vertebrates were jawless fishes known from rocks in China as old as Cambrian In Devonian: an advanced lineage of fishes with stout fins and primitive lungs gave rise to four-legged animals called tetrapods Basal tetrapods: earliest of four-legged animals First tetrapods were amphibian because although capable of walking in land their eggs survived only in water Amniotic egg: freed tetrapods form their reproductive dependency on water bodies by Permian time, amniotes called therapsids
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