1Bio1B Evolution 10Last lecture:Species & speciation• Hybridization - hybrid zones, reinforcement & hybrid-speciation• Macroevolution:– The fossil record, extinctions and major transitionsTodayFossil record (cont). [Text Pp. 521-524]Mass extinctions - the Cretaceous/Paleogene (“K/T”)boundary - cause & consequenceTransitional forms• Terrestrial vertebrates (tetrapods)• Birds & evolution of feathersEvolution of development programs [Text Pp. 525-530]• The eye, vertebrate limbs2The big 5massextinctions• Evidence from analyses of extinction (red) and blues(diversity) or families of marine invertebrates• Permian-Triassic - 96% species extinction, 8/27 orders ofinsects; Volcanism in Siberia?• Cretaceous-Paleogene (“K/T”), 65 Myr - demise ofdinosaurs & large terrestrial animals => mammalianradiation3The asteroid impacthypothesis - Luiz & WalterAlvarez, UC Berkeley(see Science, 5th March, p1214)Faunal turnover Carbon cyclechangeIridium spike4Understanding the transition of tetrapodvertebrates from water to landFig 34.20TiktaalikAcanthostega5Modification of existing structures for newpurposes: ears and feathersFig. 34.31. Bones of inner ear ofmodern mammals are derived fromjaw joint of ancestors (see also Fig.25.6LateJurassicfeathereddinosaurFeathers:for displayor warmthbeforeflight?Recent discovery:dinosaur featherswere colored -display?6Evolution ofdevelopmental genes=> phenotypic novelty• Molecular homology: geneswith common ancestrycontrolling development (topright)• Changes in timing andspatial pattern of expression=> change in phenotype• E.g Ubx suppresses legdevelopment in flies, but notshrimpFig. 25.227Origin of novelties:The vertebrate limb• Are the fish “fin” andvertebrate “limb”homologous?• Very different anatomy, yet…• Similar patterns of Hox geneexpression• Anatomic differences couldbe due to modification oftiming/duration ofexpression?Shubin etal. 2009Nature457:8188Origin of novelty:The eyeShubin et al.2009 Nature457:818Convergent evolution ordescent withmodification?Molecular homology ofkey genes - Pax-6 &opsin pathwaySubsequentmodification ofpathways andstructuresBoth
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