 1) Linnaean system of groups  2) Cladistics Chapter 17.1, 17.2

 What kinds of objects do we put into groups?  Think of some classification systems you already know about  Taxonomy is the science of naming and classifying organisms

 A taxon is a group of organisms (taxa pl.) (least specific) domain  kingdom  phylum  class  order  family  genus  species (most specific)  Early classifying based on structural analysis  Example: illustration p. 520 chapter 18.1

 Organism’s scientific name: Genus epithet  Capitalize genus name, NOT species name  Italicize if typing, underline if handwriting  Humans: Homo sapiens

1) Misleading similarities result in mis-classifying (often due to convergent evolution)  Ex: birds AND mammals have 4-chamber hearts (but little else in common) 2) Transitional organisms strain the definitions of groups  Ex: Platypus – the egg-laying mammal (or should that be mammary-gland containing reptile?)

 Creates a system based on traits, not on group names  Organizes into clades – every organism and their common ancestor who has a certain trait chapter 18.2

common ancestor with a jaw common ancestor to all these animals lampreysalamandersharktunaturtledog connection to other organisms on tree evolution of jaws the jaw clade evolution of air sac (swim bladder) the lung / lung derivative clade common ancestor with an air sac evolution of tetrapody (4 legs) the tetrapod clade common ancestor with 4 legs evolution of amniotic egg the amniote clade common amniote ancestor evolution of mammary glands the mammal clade no jaws no air sac no 4 legs no swim bladder Goal: to understand the phylogeny = evolutionary history of species