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Chapter 25 Tracing Phylogeny

Chapter 25 Tracing Phylogeny. Phylogeny. Phylon = tribe, geny = genesis or origin The evolutionary history of a species or a group of related species. Phylogeny. Found in fossils and the fossil record. Fossils. Any preserved remnant or impression of a past organism.

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Chapter 25 Tracing Phylogeny

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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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