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Exploring Fossil Records: Tracing Evolutionary History

Dive into the world of fossils, from mineralized to organic matter, to understand the evolutionary past through phylogeny and mass extinctions. Learn about plate movements, geographical isolation, and the methods of fossil dating. Explore the fascinating field of systematics and taxonomy, unraveling the relationships between organisms and creating phylogenetic trees to reflect evolutionary affinities. Delve into the concepts of homology versus analogy and the intriguing phenomenon of convergent evolution. Discover the significance of molecular systematics and different schools of taxonomy.

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Exploring Fossil Records: Tracing Evolutionary History

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  1. Chapter 25Tracing Phylogeny

  2. Phylogeny • Phylon = tribe, geny = genesis or origin • The evolutionary history of a species or a group of related species.

  3. Phylogeny • Found in fossils and the fossil record.

  4. Fossils • Any preserved remnant or impression of a past organism.

  5. Types of Fossils 1. Mineralized 2. Organic Matter 3. Trace 4. Amber

  6. Mineralized Fossils • Found in sedimentary rock. • Minerals replace cell contents. • Ex: bone, teeth, shells

  7. Organic Matter Fossils • Retain the original organic matter. • Ex: plant leaves trapped in shale. • Comment – can sometimes extract DNA from these fossils.

  8. Trace Fossils • Footprints and other impressions. No organic matter present.

  9. Amber • Fossil tree resin. • Preserve whole specimen. • Usually small insects etc.

  10. Fossils - Limitations • Rare event. • Hard to find . • Fragmentary. • Dating.

  11. Fossil Dating Methods 1. Relative - by a fossil's position in the strata relative to index fossils. 2. Absolute - approximate age on a scale of absolute time.

  12. Absolute - Methods 1. Radioactive 2. Isomer Ratios

  13. Radioactive • Estimated from half-life products in the fossil. • Ex: Carbon - 14 Potassium - 40

  14. What do fossils tell us? • That the geographical distribution of organisms has changed over time. • Reason? – The land formations of the earth have changed.

  15. Continental Drift • The movement of the earth's crustal plates over time. • Drift is correlated with events of mass extinctions and adaptive radiations of life.

  16. Result of plate movement • Geographical Isolation. • New environments formed. • Old environments lost. • As the environments changed, so did Life.

  17. Example • Australian fauna and flora are unique. • Separated early and remained isolated for 50 million years.

  18. Homework • Read Chapter 25, 26 • Chapter 26 – today • Chapter 25 – Mon. 3/3 (XC) • Exam 2 – next week

  19. Mass Extinctions • The sudden loss of many species in geologic time. • May be caused by asteroid hits or other disasters.

  20. Examples • Permian Extinction • Cretaceous Extinction

  21. Permian Extinction • 250 million years ago. • 90% of species lost.

  22. Cretaceous Extinction • 65 million years ago. • Loss of the dinosaurs. • Good evidence that this event was caused by an asteroid that hit in the Yucatan, causing a “nuclear winter”.

  23. The crater

  24. Result of Mass Extinctions • Climate changes. • Areas are open for the surviving species to exploit. • Rapid period of speciation (adaptive radiation). • Many new species are formed in a very short period of time.

  25. Systematics • The study of biological diversity. • Uses evidence from the fossil record and other sources to reconstruct phylogeny.

  26. Systematics fuses: 1. Phylogeny- tracing of evolutionary relationships. 2. Taxonomy- the identification and classification of species.

  27. Taxonomy • Natural to humans. • Modern system developed by Linnaeus in the 18th century.

  28. Linnaeus Taxonomy 1. Binomial Nomenclature – two names for each organism. Ex - Homo sapiens 2. Hierarchical System – arranges life into groups. Ex - Kingdom  Species

  29. Goal of Systematics • To have Taxonomy reflect the evolutionary affinities or phylogeny of the organisms.

  30. Phylogenetic tree

  31. Question? • How to group taxa so that the phylogenetic relationships are correct ?

  32. Ideal Situation • Monophyletic Grouping - a single ancestor gave rise to all species in the taxon.

  33. Other Possibilities • Polyphyletic - grouping where members are derived from two or more ancestral forms. • Paraphyletic - grouping that does not include all members from an ancestral form.

  34. Problem • Not all “likeness” is inherited from a common ancestor. • Problem is of homology vs analogy.

  35. Homology and Analogy • Homology – likeness attributed to shared ancestry. • Ex: forelimbs of vertebrates • Analogy – likeness due to evolution solution for the same problem. • Ex: wings of insects and birds

  36. Convergent Evolution • When unrelated species have similar adaptations to a common environment. A specific example of Analogy. • Ex: Sharks and dolphins

  37. Only one is a cactus

  38. Need • Methods to group organisms by similarities and phylogenies. • One possible method is Molecular Systematics.

  39. Molecular Systematics • Compares similarities at the molecular level. • Ex: DNA, Proteins

  40. DNA Comparisons • A direct measure of common inheritance. • The more DNA in common, the more closely related.

  41. Schools of Taxonomy 1. Phenetics: Taxonomic affinities based on measurable similarities. 2. Cladistics: Branch points defined by novel characteristics.

  42. Cladistics

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