Presentation on theme: "Systematics BIOL 1407. What is Systematics? Comparative study of biological diversity Intent: Determine evolutionary relationships Photo Credit of 1 st."— Presentation transcript:
Systematics BIOL 1407
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
Cladistics Method used today by most biologists and paleontologists
Clades Groups based on shared ancestry Clade = Ancestor + All Descendants
Clade: Tetrapods Common ancestor: Organism with four legs Branch point circled in red Clade = Ancestor + All Descendants
Clade: Amniotes Common ancestor: Organism with amniotic egg
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
Cladistics Descendants can have very different characteristics Green Tree Python Photo Credit: Keith Riverbanks Zoo, 2006, Wikimedia Commons Crimson Sunbird Photo Credit: Lip Kee Yap, 2008, Wikimedia Commons
Traditional Reptiles & Birds Traditional: Different-looking descendants placed in different groups Class Reptilia Class Aves ScalesFeathers No FlightFlight “Cold- blooded” “Warm- blooded”
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
Types of Groups Monophyletic Group = Clade Paraphyletic: Some descendants missing Polyphyletic: Do not share same recent common ancestor
Question? What kind of group is the traditional reptiles?
Convergent Evolution Similar selection pressures Similar traits evolve Unrelated organisms look very similar Marsupial Mole Placental Mole
Classroom Assessment Photo Credit for Marsupial Mole: Magnus Manske, 2007, Wikimedia Commons Photo Credit for Star-Nosed Mole: Kenneth C. Catania, 2006, Wikimedia Commons
Cladograms Shows evolutionary history of a group Based on cladistics
A Cladogram Hypotheses about evolutionary relationships Based on available data May change with additional data
Cladogram Can be drawn differently Same tree as previous slide
Names of Clades Clade names = Labels next to branching points ≠ Names of the common ancestors
Terminal Taxa Located at ends of branches No descendants on tree Not always extant (living)
Sister Taxa More closely related to each other than to any other taxon Share a more recent common ancestor
Question? What is the sister taxon of the birds?
Question? What is the sister taxon of the Bird and Saurischian Dinosaur Clade?
Question? What is the sister taxon of the Dinosaur Clade?
Question? What is the sister taxon of lizards and snakes?
Question? What is the sister taxon of the mammoth, Mammuthus?
Question? What is the sister taxon of the African elephants?
Question? What is the sister taxon to the dinosaur clade?
Characters = Traits
Loss of Trait = Character
Types of Characters Shared primitive: Found in all Shared derived: Found in some but not all Unique derived: Found in only one
Shared Primitive Character
Shared Derived Character
Perspectives Shared primitive? Shared derived? Matter of perspective