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That become extinct can evaluate the severity of the

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Unformatted text preview: tc. that become extinct — can evaluate the severity of the event Mass extinctions = geologically rapid (time), major reductions in global diversity (taxa) Background extinctions steady rate avging 2-4.6 families per million years declining over duration of the phanerozoic Five mass extinctions stand out from background: end Ordovician, end-Devonian, end-Permian, end-Triassic, end-Cretaceous Mass extinctions sit at the high end of a spectrum of extinction intensities —> different processes do not appear to operate at these two different scales. Bad genes? — failure to adapt to change Bad luck? — random accidents; no "fault" of organism Somewhat comparable to the intrinsic/extrinsic dichotomy we discussed for adaptive radiations. Quality of extinction: Which particular families, etc. become extinct? We can evaluate what features those families possessed. Do they give us clues? Selectivity of extinctions Taxonomic selectivity — different taxonomic levels affected differently Phylogenetic selectivity...
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