BIOE 20C Lecture Notes - Lecture 10: Pelycosaur, Placodermi, Genetic Drift
12 Sep 2016
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Lecture 10 10/29/2015 7:57:00 PM
Major Events of the Cenozoic
• Radiation of flowering plants/insects
• Radiation of mammals
o Occupied niches originally taken up by large dinosaurs and
other dominant reptiles
• Appearance of hominids
Mass Extinctions
• Background extinctions
o Low rates of extinction
o Driven by
▪ Environmental change
▪ Associated natural selection
• Mass extinctions
o 60% spp in 1 million years
o Driven by random events
o More akin to genetic drift in effects
Permian Extinction
• Circa 248 mya
• 90-95% of marine taxa went extinct
• No good fossil record from this time period because of recycling of
rocks
• Big losers: Pelycosaurs, trilobites, placoderms
• 2 potential causes
o Rapid climate shift (cooler and drier)
o Massive volcanic eruptions
▪ Caused by formation of supercontinent Pangaea
Cretaceous Extinction
• 65 mya
• 85% species lost
• Big losers—dinosaurs (except for kind that eventually led to lineage
of modern day birds) and marine reptiles
• Unaffected--mammals, birds, amphibians, crocodiles, lizards/snakes
• Cause--massive meteor impact in Yucatan
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