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Systematics BIOL 1407
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What is Systematics? Comparative study of biological diversity Intent: Determine evolutionary relationships Photo Credit of 1 st Tree of Life: Charles Darwin, 1837, courtesy of Wikimedia Commons
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Cladistics Method used today by most biologists and paleontologists
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Clades Groups based on shared ancestry Clade = Ancestor + All Descendants
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Clade: Tetrapods Common ancestor: Organism with four legs Branch point circled in red Clade = Ancestor + All Descendants
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Clade: Amniotes Common ancestor: Organism with amniotic egg
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Classroom Assessment Clade: Reptiles Photo Credit: Drágo, 2008, Wikimedia Commons
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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
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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
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Traditional Reptiles & Birds Traditional: Different-looking descendants placed in different groups Class Reptilia Class Aves ScalesFeathers No FlightFlight “Cold- blooded” “Warm- blooded”
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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
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Types of Groups Monophyletic Group = Clade Paraphyletic: Some descendants missing Polyphyletic: Do not share same recent common ancestor
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Question? What kind of group is the traditional reptiles?
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Convergent Evolution Similar selection pressures Similar traits evolve Unrelated organisms look very similar Marsupial Mole Placental Mole
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Classroom Assessment Photo Credit for Marsupial Mole: Magnus Manske, 2007, Wikimedia Commons Photo Credit for Star-Nosed Mole: Kenneth C. Catania, 2006, Wikimedia Commons
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Cladograms Shows evolutionary history of a group Based on cladistics
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A Cladogram Hypotheses about evolutionary relationships Based on available data May change with additional data
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Cladogram Can be drawn differently Same tree as previous slide
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Names of Clades Clade names = Labels next to branching points ≠ Names of the common ancestors
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Terminal Taxa Located at ends of branches No descendants on tree Not always extant (living)
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Sister Taxa More closely related to each other than to any other taxon Share a more recent common ancestor
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Question? What is the sister taxon of the birds?
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Question? What is the sister taxon of the Bird and Saurischian Dinosaur Clade?
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Question? What is the sister taxon of the Dinosaur Clade?
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Question? What is the sister taxon of lizards and snakes?
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Question? What is the sister taxon of the mammoth, Mammuthus?
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Question? What is the sister taxon of the African elephants?
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Question? What is the sister taxon to the dinosaur clade?
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Characters = Traits
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Loss of Trait = Character
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Types of Characters Shared primitive: Found in all Shared derived: Found in some but not all Unique derived: Found in only one
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Shared Primitive Character
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Shared Derived Character
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Perspectives Shared primitive? Shared derived? Matter of perspective
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Perspectives
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Hinged Jaws: Shared Primitive? Shared Derived? Gnathostomes Vertebrates Chordates
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Unique Derived Character Gnathostomes Vertebrates Chordates
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Question? Which character is unique derived?
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Question? Which character is shared primitive for tetrapods?
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Question? Which character is shared derived for tetrapods?
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Classroom Assessment: The Mars Mission Photo Credit: Marty Wise, 2004
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The End Unless otherwise specified, all images in this presentation came from: Campbell, et al. 2008. Biology, 8 th ed. Pearson Benjamin Cummings.
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