Bio1b Summer 2008 Evolution Lecture 7 Eric Harris Page 1 of 2 Updated on 06/17/08 EVOLUTION LECTURE 7: MACROEVOLUTION Reading: 7th ed., 481–490; 8th ed., 501–504, 525–531. A. Patterns of speciation in the fossil record i) Phyletic gradualism (anagenesis) – transformation of an unbranched lineage to a different state (species) ii) Cladogenesis – branching of new species from a parent species. Both Anagenesis and Cladogenesis may occur in the same evolutionary tree. iii) Punctuated equilibria – long periods of stasis punctuated with “sudden” episodes of speciation. B. Macroevolutionary mechanisms: Origin of evolutionary novelty i) Exaptations - structures that evolved in one context becomes co-opted for another function. ii) Morphology and development Allometric growth – slight changes in relative growth rates can have substantial changes in adult Heterochrony – evolutionary changes in the timing or rate of development Paedomorphosis – retention of ancestral juvenile structures in a sexually mature adult. Hypermorphosis Homeosis – alteration in the placement of different body parts iii) Species selection – “differential speciation success” Natural selection causes changes in each lineage. Species selection causes changes in the numbers of lineages with different properties.Bio1b Summer 2008 Evolution Lecture 7 Eric Harris Page 2 of 2 Updated on 06/17/08 C. Patterns in the fossil record: extinctions and radiations, diversification and decimation i) Conventional representation - cone of increasing diversity e.g., the Burgess shale ii) Adaptive radiations: e.g., origin of shells, origin of insect wings iii) Mass extinctions Permian extinction – extreme vulcanism and formation of Pangaea Cretaceous extinction – asteroid hypothesis and/or climate change Mass extinctions affect different groups very differently. Why do some groups
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