1. Chapter 18: Classification
Section 18-2: Modern Evolutionary Classification
Chapter 18: Classification

2. Evolutionary Classification
Phylogeny – the study of how living and extinct organisms are related to one another
Phylogentic systematics, or evolutionary classification
Species grouped into larger categories reflecting lines of evolutionary descent
Organisms placed into higher taxa based on relationship – larger taxon, further common ancestor

3. Clades
Clade – a group of species tha includes a single common ancestor and all descendants of that ancestor, living and extinct
Must be a monophyletic group – all species from common ancestor
Cladistic analysis - how are clades related

4. Cladograms
Linked clades that illustrate how groups of organisms are related by showing how evolutionary lines (lineages) branched off from common ancestors
Speciation causes an ancestral lineage to branch into 2 new lineages at a node
Node is last point at which new lineages share common ancestor

5. Building Cladograms
“Root” represents common ancestor

6. Building Cladograms
Branching patterns shows degree of relatedness

7. Building CLadograms
Current hypotheses - evolutionary relationships among vertebrates

8. Derived Characteristics
Cladistics focuses on derived characteristics – a trait that arose in the most recent ancestor of a particular lineage and was passed along to its descendants
Depends on level of grouping
Four limbs is a DC for clade Tetrapoda
Hair is a DC for clade Mammalia – not four limbs

9. Derived Characteristics
Clade Carnivora: shearing teeth (both) Clade Felidae: retractable claws (only lion)

10. Losing Traits Absence of a trait is not a derived characteristic
Whales and snakes have lost tetrapod characteristic of four limbs, but are not closely related

11. Reading Cladograms Phylogeny of cat family
Each DC defines a clade – a DC “lower” than the branch point for a clade is not derived for that clade

12. Clades and Traditional Taxonomic Groups
Clade must be monophyletic
Many traditional taxonomic groups form valid clades – Linnaen class Mammalia = clade Mammalia
Birds and reptiles descend from common ancestor, but Linnaen class Reptilia does not include birds

13. Clades and Traditional Taxonomic Groups
According to cladistics a bird is a reptile

14. DNA in Classification
Homologies in genes used to determine evolutionary relationships
Changes in shared genes are derived characteristics
Using DNA makes evolutionary trees more accurate
Vultures, pandas