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Lecture 23: Mass Extinctions 5.) Cretaceous (144 - 65 mya)

Lecture 23: Mass Extinctions 5.) Cretaceous (144 - 65 mya). Mesozoic : (Permian → Cretaceous) huge ↑ in biodiversity End Cretaceous (65 mya): 85% of all spp. gone All non-avian dinosaurs & pterosaurs gone No terrestrial organisms >25 kg survive!

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Lecture 23: Mass Extinctions 5.) Cretaceous (144 - 65 mya)

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  1. Lecture 23: Mass Extinctions5.) Cretaceous (144 - 65 mya) • Mesozoic : (Permian → Cretaceous) huge ↑ in biodiversity • End Cretaceous (65 mya): 85% of all spp. gone • All non-avian dinosaurs & pterosaurs gone • No terrestrial organisms >25 kg survive! • Relatively unaffected: crocodiles, lizards, turtles, mammals, birds Cause:Iridium??

  2. Alvarez et al. (1980) • spike in levels of Iridium in sediments ~ 65 mya • Ir in core; rare in surface rock • common in space dust • 3 Ho for IR spike : • 1) volcanic activity? • 2) supernova? • 3) meteor impact?

  3. Evidence? • Vulcanism in India, Pakistan - enough to cause global devastation? • Supernova: no evidence of other materials (e.g. plutonium) common in space dust • Meteor: shocked quartz (impact pressure)

  4. Effects of a Meteor Impact • Shock Wave: fires, earthquakes • Debris Cloud: years of acid rain, dust, “nuclear winter” • Lowered solar radiation reaching earth: cold & dark →  1 productivity • Nickel Poisoning : effectively kills PSIS

  5. Yucatan Peninsula (Chicxulub) • “Smoking Gun” : impact crater • ~ 10 km meteor (crater ~ 150 km diam.) • cause or “coup de grace?”

  6. Cyclical Nature of Mass Extinctions Raup and Sepkoski (1984): 26 my cycle? Controversial : depends on time scale, taxa used in analysis

  7. Extra-terrestrial Cause? Suggested by periodicity: • Planet X (“Nemesis”): • Brown Dwarf (star that didn’t reach ignition mass) or Planet from another system • Passes through Oort comet cloud • Sends meteors to earth every 26 my • Controversial!!

  8. Background vs. Mass Extinctions Signor - Lipps effect: • Mass extinction may appear gradual: • Orgs. disappear from the fossil record at diff. times • Rare orgs less likely to be found in latest deposits even if they survived as long as common ones Converse: • Gradual extinction may appear mass • Pseudoextinctions etc.

  9. Characteristics of Survivors • characteristics of taxa affect speciation & extinction rate e.g. Marine Gastropods: • Planktonic larva: shallow, warm seas ↓ extinction rate (wide dist’n) b) Direct development: polar, deep seas ↑ speciation (isolated pop’ns) Direct forms predominate (sp. select’n)

  10. Surviving Mass Extinctions • Surviving spp. more likely to be generalists - can adjust to Δ’s in conditions • “Iterative Evolution”: forms “re-evolve” during Adaptive Radiations after mass extinctions • B/w mass extinctions: Spp.-Rich Clades survive background extinction better • “Bad Genes or Bad Luck?”

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