Bio1b Summer 2008 Evolution Lecture 7Eric Harris Page 1 of 2EVOLUTION LECTURE 7: MACROEVOLUTIONReading: 7th ed., 481–490; 8th ed., 501–504, 525–531.A. Patterns of speciation in the fossil recordi) 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 noveltyi) Exaptations - structures that evolved in one context becomes co-opted for another function.ii) Morphology and developmentAllometric growth – slight changes in relative growth rates can have substantial changes in adultHeterochrony – evolutionary changes in the timing or rate ofdevelopmentPaedomorphosis – retention of ancestral juvenile structures in a sexually mature adult.HypermorphosisHomeosis – alteration in the placement of different body partsiii) Species selection – “differential speciation success”Natural selection causes changes in each lineage. Species selection causes changes in the numbers of lineages with different properties.Updated on 06/17/08Bio1b Summer 2008 Evolution Lecture 7Eric Harris Page 2 of 2C. Patterns in the fossil record: extinctions and radiations, diversification and decimationi) Conventional representation - cone of increasing diversitye.g., the Burgess shaleii) Adaptive radiations: e.g., origin of shells, origin of insect wingsiii) Mass extinctionsPermian extinction – extreme vulcanism and formation of PangaeaCretaceous extinction – asteroid hypothesis and/or climate changeMass extinctions affect different groups very differently. Why do some groups survive?Updated on
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