Systematics BIOL 1407 What is Systematics Comparative study

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

Classroom Assessment Clade: Reptiles Photo Credit: Drágo, 2008, Wikimedia Commons

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 Hooks @ 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 Scales Feathers No Flight “Coldblooded” “Warmblooded”

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

Perspectives

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

Unique Derived Character Chordates Vertebrates Gnathostomes

Question? • Which character is unique derived?

Question? • Which character is shared primitive for tetrapods?

Question? • Which character is shared derived for tetrapods?

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

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