BLG 144 Chapter 27: Chapter 27
8 Mar 2017
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Chapter 27 |phylogenies and the history of life | biology. Cenozoic era: the paleozoic era begins with the appearance of most major animal lineages and ends with the obliteration of amost all multicellular life forms at the end of the permian period. In terrestrial environments of the mesozoic, gymnosperms were the most important plants and dinosaurs were the most important vertebrates: the cenozoic era is divided into the paleogene period and the meogene period. On land, angiospersms were the most important plants and mammals were the most important vertebrates. The cambrian explosion: the first animals were sponges, jellyfish, and perhaps simple worms appear n the fossil record. Its important to recognize that most or all of these hypotheses could be correct. Species die out from exposure to exceptionally harsh, short term conditions such as huge volcanic eruptions or catastrophic sea levels changes. In a general sense, background extinctions are thought to result primarily from natural selection.
