Lecture16_HistoryofLife - The History of Life I. A fossil...

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Unformatted text preview: The History of Life I. A fossil timeline: What happened and when? Evolution's "Greatest hits" origin of life ~3.4-3.8 billion years ago? first eukaryotes ~1.8 billion years ago first multicellular organisms ~1 billion years ago Cambrian explosion: bilaterians (the head), limbs in arthropods; chordates ~520 mya Silurian-Devonian explosion: origin of land plants ~400 mya: roots, vascular tissue, wood jaws ~410 the seed ~360 mya tetrapod limb ~355 mya the flower ~145 mya II. Innovations: the origin of tetrapods Tetrapods = the "four-footed" Where did limbs come from? Phylogeny of early tetrapod groups, estimated from similarities in differences in Lungfish-like Ray-finned Panderichthys fish Eusthanopteron Tiktaalik Tetrapods Acanthostega Tulerpeton Modern tetrapods map origin of map origin of map origin of appendage supported by bones arranged III. Adaptive radiations Adaptive radiation = the rapid diversification of a single lineage into an array of species that fill a wide variety of ecological niches Niche = the range of habitats or resources used by a species Examples: Why do adaptive radiations occur? 1) Ecological opportunity 2) Morphological innovation a new morphological trait that is an "adaptive NOTE: these hypotheses are very difficult to test V. Background extinctions and mass extinctions Background extinction = normal extinction rates, due to normal rates of environmental change Mass extinction = at least 60% of species present go extinct in less than 1 million years; due to extreme rates of environmental change The Big Five Note: At the Permian-Triassic event 250 million years ago, over Cause is not well understood 1. Impact hypothesis: an asteroid hit the Earth and initiated environmental changes that 2. "World Went to Hell" hypothesis Key observation: Siberian traps date to B. Evaluating the two hypotheses Impact hypothesis makes predictions: WWTH: we know that anoxia and high CO2 occurred, but what ...
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This note was uploaded on 04/10/2008 for the course BIOL 180 taught by Professor Freeman during the Fall '07 term at University of Washington.

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