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Mass Extinctions

Mass Extinctions. Tim Bradshaw December 7, 2005. Extinction. “ceasing of existence of a species or group of taxa” Classic cause: failure to adapt to changes in environment How do you define a species?. Defining species.

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Mass Extinctions

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  1. Mass Extinctions Tim Bradshaw December 7, 2005

  2. Extinction • “ceasing of existence of a species or group of taxa” • Classic cause: failure to adapt to changes in environment • How do you define a species?

  3. Defining species • Biological species concept – species are groups of actually/potentially interbreeding natural populations reproductively isolated from other such groups (Mayr 1942) • Evolutionary species concept – a species is a single lineage of populations that maintains an identity separate from other such lineages and has its own evolutionary tendencies (Wiley 1978) • Phylogenetic species concept – a species is an irreducible cluster of organisms that is diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent (Cracraft 1989)

  4. Species Lifespan • Mammals ~ 1million year lifespan • 5000 currently alive • Background rate ~ 1 species/200 years • 89 species extinct in last 400 years

  5. Geologic Time Scale • Era Time (mya) Period • 1.8 – 0.01 Quaternary • Cenozoic • 65 – 1.8 Tertiary • 144 – 65 Cretaceous • Mesozoic 206 – 144 Jurassic • 248 – 206 Triassic • 290 – 248 Permian • 354 – 290 Carboniferous • Paleozoic 417 – 354 Devonian • 443 – 417 Silurian • 490 – 443 Ordovician • 543 – 490 Cambrian

  6. OrdovicianEchinoderm Time • 490 – 443 mya great diversification of phyla, including 21 classes of echinoderms formation of reefs evolution of agnathans and trilobites plants invade land Gondwanaland centered in southern hemisphere

  7. Gondwanaland (~ 400 mya)

  8. End-Ordovician Extinction • 57% of marine genera wiped out • Trilobites take a dirt nap • Probable cause: Global cooling • Glaciation over Gondwanaland led to cooling and drop in sea levels • Time span: 2 my • Result: Paved the way for ostracoderms

  9. DevonianConquest of Land • 417 – 354 mya Osteichthyes develop (Sarcopterygii and Actinopterygii) Terrestrial arthropods evolve Land plants diversify (ferns, horsetails) Ichthyostegid amphibians evolve from rhipidistians

  10. Late-Devonian Extinction • 22% of marine families and 57% of marine genera • Loss of coral reefs and ostracoderms • Once again: global cooling from glaciation, • Time span: 4 million years

  11. Permian • First amniotes - captorhinomorphs • Fish/Insects/Reptiles continue to diversify • Amphibians decline • Formation of Pangea

  12. Permian-Triassic Extinction • Mother of Mass Extinctions • Say goodbye to 54% of all marine species • Lost 75% of all land vertebrate families • Estimated that 84% of all genera on Earth became extinct • Time span: 1 million years • Results: so long frogs, hello dinos

  13. Cause: Continental drift created a non-fatal but precariously balanced global environment, a supernova weakened the ozone layer, and then a large meteor impact triggered the eruption of the Siberian Traps. The resultant global warming eventually was enough to melt the methane hydrate deposits on continental shelves of the world-ocean.

  14. Causes • Plate Tectonics – Pangea formation • Supernova – destroy ozone layer • Asteroid impact – trigger volcanoes • Siberian traps – 200,000 cubic kilometers • Methane hydrate released from oceans • Oxygen depleted from oceans

  15. TriassicAge of the Reptiles • Pangea would soon break up into Laurasia and Gondwanaland • Marine groups diversified • Forams, modern corals, bony fish Gymnosperms dominate on land First dinosaurs and first mammals arrive

  16. End-Triassic Extinction • Loss of 25% of all families • Decimated sponges, marine reptiles and conodonts • Cause: largest volcanic event from Pangea rift • Results: Paved the way for more dinosaurs in more niches

  17. CretaceousAge of the Dinosaurs • Continents have fully separated • Angiosperms have developed and taken over • Birds evolve from theropod dinosaurs =

  18. Cretaceous-Tertiary Extinction • Death to the Dinosaurs • 50% of all genera • Pterosaurs, dinosaurs, sea reptiles • Cause: Celestial impact reduced photosynthesis • Results: Welcome bug eaters (aka mammals)

  19. Future Extinctions • Probable Cause: Us • Habitat destruction - estimated that 5-10% of species will be extinct in thirty years • Global warming – estimated that ~35% of species will become committed to extinction in the next fifty years

  20. Evolving past Extinction • Possible to become resistant to extinction?

  21. Probably not • Natural selection cannot plan ahead • Extinction causes are numerous, thus there is no carryover of extinction resistance • Just as likely for old taxa to go extinct as for new taxa

  22. Why do we see a decline in the background extinction rate during the Phanerozoic (Cambrian – today)?

  23. Two Theories • 1. average # of species per family has increased over time (Flessa and Jablonski 1985) 2. Taxa more likely to go extinct went extinct early in the Phanerozoic (Erwin et al. 1987)

  24. Importance of Mass Extinctions • Adaptive radiation • Release from competition, predation

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