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Paintings by Charles Knight

Explore key concepts, terms, and rates of extinction in Chapter 6 of Fossils & Evolution. Learn about mass extinctions, ecological limiting factors, and the Signor-Lipps effect. Discover the impact of environmental changes on species survival.

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Paintings by Charles Knight

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  1. Paintings by Charles Knight Fossils & Evolution—Chapter 6

  2. Fossils & Evolution—Chapter 6

  3. Fossils & Evolution—Chapter 6

  4. Fossils & Evolution—Chapter 6

  5. Fossils & Evolution—Chapter 6

  6. Fossils & Evolution—Chapter 6

  7. Fossils & Evolution—Chapter 6

  8. Fossils & Evolution—Chapter 6

  9. Fossils & Evolution—Chapter 6

  10. Late Cretaceous 85 million years ago Fossils & Evolution—Chapter 6

  11. Late Cretaceous 75 million years ago Fossils & Evolution—Chapter 6

  12. end-Cretaceous 65 million years ago Hell Creek Formation (coastal plain setting) Fossils & Evolution—Chapter 6

  13. Fossils & Evolution—Chapter 6

  14. Chicxulub crater Impact trajectory Earth History, Ch. 17

  15. Radar image of Chicxulub crater Fossils & Evolution—Chapter 6

  16. Chicxulub crater Gravity survey data Fossils & Evolution—Chapter 6

  17. Iridium layer at Gubbio, Italy Fossils & Evolution—Chapter 6

  18. Iridium layer near Drumheller (southern Alberta, Canada) Earth History, Ch. 17

  19. Chapter 6—Key concepts • 99.9% of all organisms that have ever lived are now extinct. “Background” extinction occurs when a species cannot adapt to a change in its environment. • Mass extinctions are episodes when the extinction rate far exceeds the normal background rate. Mass extinctions do not occur at predictable intervals, and each probably was caused by a unique set of circumstances. Fossils & Evolution—Chapter 6

  20. Ch. 6—Key terms • Ecologic limiting factors • Signor-Lipps effect • Pulse vs. Press extinction Fossils & Evolution—Chapter 6

  21. Extinction! Fossils & Evolution—Chapter 6

  22. Chapter 6—Extinction • Two categories of extinction: • Normal (or background) extinction • Mass extinction (dramatically accelerated) Fossils & Evolution—Chapter 6

  23. Rates of extinction • Agents of extinction are changes in ecologic limiting factors • Also, population size, number of populations, and geographic range of populations affect the probability of extinction Fossils & Evolution—Chapter 6

  24. Limiting factors • Ecologic limiting factors = physical, chemical and biologic properties of the environment that limit the distribution and abundance of a particular species • Temperature • Oxygen • Depth-related variables • Light, pressure, water chemistry, etc. • Salinity • Substratum (nature of the seafloor) • Food • Other biota (competitors, predators, infectious diseases) Fossils & Evolution—Chapter 6

  25. Rates of extinction • Probability of extinction vs. No. of populations • Suppose that, in a given interval of time, every population has a 50% chance of becoming extinct • Species with large numbers of populations are unlikely to suffer total extinction Fossils & Evolution—Chapter 6

  26. Fossils & Evolution—Chapter 6

  27. Probability of background extinction • Are species that have been around a long time more or less resistant to extinction than newly formed species? “overspecialization” model “resistence” model or probability of extinction probability of extinction duration of species existence duration of species existence Fossils & Evolution—Chapter 6

  28. Overspecialization model Resistence model Most genera do not survive very long. Importantly, though, the probability of survival does not increase or decrease with a taxon’s longevity. Fossils & Evolution—Chapter 6

  29. Mass extinctions background extinction levels Sepkoski (1982) Fossils & Evolution—Chapter 6

  30. Mass extinctions • Causes are poorly understood • Global climate change • Volcanism • Asteroid impact • Environmental deterioration • CO2 & methane poisoning • Anoxia Fossils & Evolution—Chapter 6

  31. Mass extinctions: 26 Ma periodicity suggests astronomical cause? Fossils & Evolution—Chapter 6

  32. Causes of mass extinctions • Causes are extremely difficult to determine • Timing is key to causal analysis • “Press” (gradual) vs. “pulse” (abrupt) extinction • Types of organisms affected is also key to causal analysis • Marine only vs. terrestrial and marine • Physiologic selectivity • e.g., filter feeders only, etc. Fossils & Evolution—Chapter 6

  33. Signor-Lipps effect • Consider two species, one rarely preserved (occurs in 10% of samples) and the other commonly preserved (occurs in 80% of samples) • Assume that both became extinct at “extinction level” • Where are we likely to find their highest observed occurrence? actual extinction level 2m Fossils & Evolution—Chapter 6

  34. Signor-Lipps effect • Mass extinctions appear gradual when last observed occurrences of taxa are plotted on stratigraphic sections suspected extinction level 2m Fossils & Evolution—Chapter 6

  35. False “gradualness” of mass extinctions • Probability of finding abundantly occurring taxa in a given sample is much greater than probability of finding rare taxa • Most taxa whose last observed occurrence is some distance below an extinction horizon are rare taxa Fossils & Evolution—Chapter 6

  36. False “gradualness” of mass extinctions Abundance (% of samples in which each species occurs) Highest occurrence of common species Likely will be at or near extinction level distance of highest observed occurrence below extinction level “hollow” distribution curve is consistent with Signor-Lipps effect Highest occurrence of rare species might be at extinction level or much lower Fossils & Evolution—Chapter 6

  37. JT-8 JT-6 JT-1 JT-18 JT-17 JT-16 JT-15 JT-14 JT-7 JT-13 JT-11 JT-2 JT-3 JT-10 JT-4 JT-5 JT-9 JT-12 Taskent Section, southern Turkey approx. 8.69m above base of section 7m 14 cm stromatolitic ls. P-T boundary 6m 7 cm oolitic ls. crinoidal grainstn possible intraclasts 5m 22 cm oolitic ls. 4m 3m 8 cm oolitic ls. algal wackestn 2m 16 cm oolitic ls. 1m 4 cm packstn dark grey to black wackestn (8 beds in 1 m) approx. 7.98m above base of section Fossils & Evolution—Chapter 6

  38. Fossils & Evolution—Chapter 6

  39. Fossils & Evolution—Chapter 6

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