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Exploring Evolutionary Relationships through Systematics

Learn about systematics, the comparative study of biological diversity to determine evolutionary relationships using cladistics and traditional methods. Discover how clades, sister taxa, and unique derived characters help in understanding the tree of life. Explore the concepts of convergent evolution and the different types of groups in the evolutionary context.

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Exploring Evolutionary Relationships through Systematics

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  1. Systematics BIOL 1407

  2. What is Systematics? • Comparative study of biological diversity • Intent: Determine evolutionary relationships • Photo Credit of 1st Tree of Life: Charles Darwin, 1837, courtesy of Wikimedia Commons

  3. Cladistics • Method used today by most biologists and paleontologists

  4. Clades • Groups based on shared ancestry • Clade= Ancestor + All Descendants

  5. Clade: Tetrapods • Common ancestor: Organism with four legs • Branch point circled in red • Clade = Ancestor + All Descendants

  6. Clade: Amniotes • Common ancestor: Organism with amniotic egg

  7. Classroom AssessmentClade: Reptiles Photo Credit: Drágo, 2008, Wikimedia Commons

  8. Traditional Systematics • Groups based on common characteristics  evolutionary relationships Crocodile Photo Credit: Marco Schmidt, 2007, Wikimedia Commons Tuatara Photo Credit: Michael Hamilton, 2006, Wikimedia Commons

  9. Cladistics • Descendants can have very different characteristics Green Tree Python Photo Credit: Keith Hooks @ Riverbanks Zoo, 2006, Wikimedia Commons Crimson Sunbird Photo Credit: Lip Kee Yap, 2008, Wikimedia Commons

  10. Traditional Reptiles & Birds • Traditional: Different-looking descendants placed in different groups

  11. Cladistics: Modern Reptiles • Molecular data + new fossils  Birds and reptiles share common ancestor • Clade Reptilia = Traditional Reptiles + Birds • Photo Credit of Red Lory Preening: Andrew Kraker, 2008, Wikimedia Commons

  12. Types of Groups • Monophyletic Group = Clade • Paraphyletic: Some descendants missing • Polyphyletic: Do not share same recent common ancestor

  13. Question? • What kind of group is the traditional reptiles?

  14. Convergent Evolution • Similar selection pressures  Similar traits evolve • Unrelated organisms look very similar Marsupial Mole Placental Mole

  15. Classroom Assessment Photo Credit for Marsupial Mole: Magnus Manske, 2007, Wikimedia Commons Photo Credit for Star-Nosed Mole: Kenneth C. Catania, 2006, Wikimedia Commons

  16. Cladograms • Shows evolutionary history of a group • Based on cladistics

  17. A Cladogram • Hypotheses about evolutionary relationships • Based on available data • May change with additional data

  18. Cladogram • Can be drawn differently • Same tree as previous slide

  19. Names of Clades • Clade names = Labels next to branching points • ≠ Names of the common ancestors

  20. Terminal Taxa • Located at ends of branches • No descendants on tree • Not always extant (living)

  21. Sister Taxa • More closely related to each other than to any other taxon • Share a more recent common ancestor

  22. Question? • What is the sister taxon of the birds?

  23. Question? • What is the sister taxon of the Bird and Saurischian Dinosaur Clade?

  24. Question? • What is the sister taxon of the Dinosaur Clade?

  25. Question? • What is the sister taxon of lizards and snakes?

  26. Question? • What is the sister taxon of the mammoth, Mammuthus?

  27. Question? • What is the sister taxon of the African elephants?

  28. Question? • What is the sister taxon to the dinosaur clade?

  29. Characters = Traits

  30. Loss of Trait = Character

  31. Types of Characters • Shared primitive: Found in all • Shared derived: Found in some but not all • Unique derived: Found in only one

  32. Shared Primitive Character

  33. Shared Derived Character

  34. Perspectives • Shared primitive? • Shared derived? • Matter of perspective

  35. Perspectives

  36. Hinged Jaws: Shared Primitive?Shared Derived? Chordates Vertebrates Gnathostomes

  37. Unique Derived Character Chordates Vertebrates Gnathostomes

  38. Question? • Which character is unique derived?

  39. Question? • Which character is shared primitive for tetrapods?

  40. Question? • Which character is shared derived for tetrapods?

  41. Classroom Assessment:The Mars Mission Photo Credit: Marty Wise, 2004

  42. The End Unless otherwise specified, all images in this presentation came from: Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.

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