lecture 23 mass extinctions 5 cretaceous 144 65 mya n.
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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
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??

alvarez et al 1980
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?
evidence
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)

effects of a meteor impact
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
yucatan peninsula chicxulub
Yucatan Peninsula (Chicxulub)
  • “Smoking Gun” : impact crater
  • ~ 10 km meteor

(crater ~ 150 km diam.)

  • cause or “coup de grace?”
cyclical nature of mass extinctions
Cyclical Nature of Mass Extinctions

Raup and Sepkoski (1984): 26 my cycle?

Controversial : depends on time scale, taxa used in analysis

extra terrestrial cause
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!!
background vs mass extinctions
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.
characteristics of survivors
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)

surviving mass extinctions
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?”