Fossil lecture outline

1. Fossil lecture outline • Fossils, preservation, and bias • Establishing dates for fossils • How do these challenges affect our ability to address patterns of diversity and evolution? • Fossils and the history of life: diversity • Fossils and patterns of evolution: stasis and gradualism

2. Key questions to consider • How old is life on earth? How do we know? • How did the earliest life begin? What was it like? • How often do mass extinctions happen, and why? Why do some species survive and not others? • What are the major patterns in the history of life?

3. I. Fossil preservation • Fossil: any trace left by an organism from the past

4. Implications

5. Some geological basics: types of rock • Igneous: • Sedimentary: • Metamorphic:

6. Preservation of fossils: geologic cycle • Ocean sediments: • Continents:

7. Bias in fossils • Species? • Habitat? • Structures? • Rarity?

8. II. Dating fossils: methods • Relative dating: stratigraphic analysis • older layers below younger • layers start out horizontal • cross-cutting features are younger

9. Geologic time: Eons Paleozoic Mezozoic Cenozoic Proterozoic Archaean Hadean Origin of earth First life Oxygen in atmosphere Eukaryotes 543 mya macroscopic fossils 4.6 billion year history of earth

10. Geologic time: Periods Pre-Cambrian 495 439 408 354 323 251 543 290 206 144 65 1.8 Tertiary Silurian Miss. Permian Jurassic Cambrian Cretaceous Quaternary Ordovician Devonian Penn. Triassic Paleozoic Mezozoic Cenozoic Mnemonic: “Please, come over soon, dear,” Mary pleaded prettily. Tragically, John came too quickly. 0.543 billion year fossil history of earth (roughly)

11. Geologic time: Periods Pre-Cambrian Paleozoic Mezozoic Cenozoic 495 439 408 354 323 251 543 290 206 144 65 1.8 Tertiary Silurian Miss. Permian Jurassic Cambrian Cretaceous Quaternary Ordovician Devonian Penn. Triassic Burgess Shale, BC First insects First apes First mammals Cambrian “explosion” Mass extinction Mass exctinction First plants on land 0.534 billion year fossil history of earth

12. Dating methods: absolute • Radio-isotope dating (box 2.3) • potassium – argon (K-40 to Ar-40) • Carbon 14 (C-14  N-14 + ) Figure 2.19

13. Radioisotope dating • Radioactive decay does not depend on pressure or temperature X(t) = X(0)e-Lt Note: half life = 0.693 / L

14. Key assumptions

15. Key practices • Potassium – Argon • Carbon 14

16. Utility of radioisotope dating

17. Problem: C-14 levels vary

18. Carbon-14 calibration • Recent time: dendrochronology (10,000 years) • Ancient: calibrate using other isotopes,

19. Radioisotope verification • How do we know that the method works? • Early: • Coral clocks Annual rings in coral (bar is 0.5 mm) NOAA

20. Coral clocks • Length of earth orbit: 24 hours * 365.25 days = 8766 hours / yr • Change in speed of rotation due to friction: 20 seconds / million years • Day length = • Days per year =

21. What is the range of ages for the fish skeletons found in layer B? Decay constant for 40-K: 5.34 x 10 -10 A B C D E F A: Ash layer: crystals contain 99.85% 40K and 0.15% 40Ar B: Sandstone with fossil fish C: Limestone with fossil shells D: Mudstone containing pollen E: Mudstone layer F: Granitic intrusion: crystals contain 96% 40K AND 4% 40Ar

22. Origins of Life What is known about the common ancestor of all life? Is this true of the earliest life on earth?

23. Miller: prebiotic soup

24. Chicken and egg problem Proteins: DNA: So?

25. Life: the big picture

26. Organelles

27. History of Life: Before the Cambrian Explosion Anemones

28. Before the Cambrian Explosion Medusa

29. Rarely bilateral Kimberella

30. Cambrian Explosion: every known animal phylum (and more?) Pikaia Wiwaxia Burgess Shale, BC Anomalocaris

31. What caused the Cambrian Explosion? Halucigenia

32. When did animal diversity originate? Estimates of splits between arthropods and vertebrates (Agnatha): 833 – 953 mya

33. Factors in Cambrian explosion: gene duplication?

34. Hox gene evolution Protostomes Bilateria Deuterostomes

35. Diversity in time: number of genera of marine invertebrates Post-paleozoic diversity increase Paleozoic diversity plateau Number of genera Time (mya)

36. Correcting for bias: genera per fossil collected Number of genera Time (mya)

37. IV. What do fossils tell us about evolution?

38. 65 mya Oligo Eocene Pliocene present Case study: evolution of the horse Paleocene Pleistocene Oligocene Heiracotherium Eocene Miohippus Oligocene Merychippus Miocene Equus (horse) to present Florida Museum of Natural History

39. A more complete view Neohipparion: most common fossil

40. The pace of evolution How do traits change over time? gradualism stasis / puncuated equilibrium (“punc eq”):

41. Stasis vs. gradualism: which is the typical pattern? Challenges to testing:

42. Stasis vs. gradualism: evidence Bryozoans (colonial organisms, similar to coral)

43. Stasis vs. gradualism: evidence Bivalves (Mollusca) in Pliocene: 3 species, 24 characters

44. Trends in the history of life? • Complexity? • amount of DNA • number of cell types

45. *Haploid genome size. 1 pg = ~109 base pairs

46. Genome size: phylogenetic context

47. Complexity: cell types Number of cell types

48. Overall patterns of life on earth?

49. Fossils: summary

50. Fossils: references Caroll, S. B. 2005. Endless forms most beautiful: the new science of evo devo. Very readable description of insights into evolution from developmental genetics. Gould, S. J. 1990. Wonderful life: Burgess shale and the nature of history. Account of the discovery of the Burgess shale fossils and their early interpretation. Many of Gould’s ideas were shown to be incorrect soon after this book was published – in particular, it appears that most of the fossils can be assigned to contemporary phyla. Still an enjoyable and informative read. Lane, Nick. 2002. Oxygen: the molecule that made the world. Oxford University Press. Does a very nice job of recounting the evidence for oxygen levels on earth in the early history, and the interaction of the atmosphere with early life.