HISTORYOFLIFE

HISTORYOFLIFE - 1 DIVERSITY THROUGH THE PHANEROZOIC AND A...

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1 DIVERSITY THROUGH THE PHANEROZOIC AND A BRIEF HISTORY OF THE VERTEBRATES I. GLOBAL DIVERSITY TRENDS OVER THE PALEOZOIC A. How has the diversification of life proceeded on the planet? B. John J. Sepkoski was perhaps the first person to try to answer this question in a serious, quantitative way was. Put together a graph of the number of families of marine organisms through time from the Cambrian to the present. Data derived from published data that represented over 200 years of fossil. C. Look at the graph – discuss a few of its most important features. Upper curve – all organisms; lower curve –organisms w/hard parts preserved. 1) Cambrian to Silurian rapid diversification up to 500 or so families. 2) Plateau at 500 families for about the next 380 ma – until the Permian/Triassic boundary. 3) Post Permian rapid rise that seems to be continuing and certainly exceeds the Paleozoic plateau of 500. 4) Several notable drops – 5 usually recognized and labeled Mass Extinction events (end Ordovician, end Devonian, end Permian, end Triassic, and end Cretaceous). What do we mean by a family of organisms? It is a category within the TAXONOMIC HIERARCHY: PHYLUM Vertebrata CLASS Mammalia ORDER Carnivora FAMILY Canidae GENUS Canis SPECIES familiaris Extinction occurs all the time so what distinguishes mass extinction events? They 1) are global in extent, 2) affect many organisms on land and sea, and 3) are of brief duration
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2 D. Basic causes of the trend of increasing diversity through time: 1) "Pull of the Recent" 2) Ecological diversification E. Pull of the Recent : as you go further back in time, the fossil record gets worse – that is, it is less likely to preserve all the species that existed at that time, so naturally species diversity will seem to increase as you approach the present. The apparent increase in the number of species over time due to preservation biases is known as the "pull of the recent." F. Ecological diversification . The number of ways to make a living has continued to increase over time – in part because organisms modify the environment - making it more heterogeneous – and thus creating new ways of life. Predation and competition encourage evolution (arms races are expected). Example: In the Paleozoic, initially there are just deposit-feeders
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HISTORYOFLIFE - 1 DIVERSITY THROUGH THE PHANEROZOIC AND A...

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