1. Modern Evolutionary Classification (Ch 18.2)
Unit 5: Evolution

2. Evolutionary Classification
Phylogeny: the evolutionary history of lineages
The goal of phylogenetic systematics, or evolutionary classification, is to group species into larger categories that reflect lines of evolutionary descent rather than overall similarities and differences.
Common Ancestors
Phylogenetic systems place organisms into higher taxa -- the larger a taxon the farther back the organisms shared a common ancestor
Clades: a group of species that include a single ancestor and all the descendents of that ancestor -- living and extinct
monophyletic group: a single common ancestor and ALL of its descendents
Clades are different than Linnaean taxa because clades are monophyletic instead of paraphyletic

3. Cladograms
Cladogram: links groups of organisms by showing how evolutionary lines or lineages branch off from common ancestors
Building Cladograms
Node -- the node represents the point where the organisms split off from a common ancestor
Root -- the bottom of the cladogram where there lies a common ancestor
Branching Patterns -- indicate degrees of relatedness among organisms

4. Building Cladograms

5. Derived Characters
Variation from Linnaean taxa -- derived characters: a trait that arose in the most recent common ancestor or a particular lineage and was passed along to its descendents
Example: Coyote vs. Lions
Tetrapoda: four limbs -- Carnivora: specialized teeth Mammalia: fur -- Felidae: retractable claws
Four limbs is not a derived character of Mammalia because then only Mammalia would have them. It had to come from an ancestor from before Mammalia.

6. Losing Traits
Although organisms could have derived characters from previous ancestors, not all organisms will inherit those derived characters.
Example: Snakes
Snakes are in the clade Tetrapoda, but they do not have four limbs
This specific trait was lost somewhere in the lineage -- systematists are cautious about not using the absence of a trait in their analysis of the organism
Example: Whales do not have four limbs either but snakes are more closely related to reptiles than whales

7. Interpreting Cladograms
The lowest node represents the last common ancestor (Tetrapoda)
The forks show where the organisms branched off due to evolution
The derived character listed among the main trunk defines a clade
Example: Amniota = amniotic egg
Derived characters that occur lower in the cladogram than the branch point for the clade are not derived for that particular clade
Example: Hair is not derived for Carnivora

8. Clades vs Taxonomic Groups
What is the difference between a clade and the Linnaean’s groupings?
Clades are monophyletic -- it contains all of the descendents of a common ancestor and does not leave any out
Clade -- Mammalia = Taxonomic -- Mammalia
They both include vertebrates with hair and other important characteristics
Traditional Groups do not always equal clades
Birds have not been associated with reptiles, but they all came from a common ancestor
Class Reptilia without Birds is NOT a clade

9. Clades vs Taxonomic Groups

10. DNA Classification Genes as Derived Characteristics
The more derived genetic characters two species share, the more recently they have shared a common ancestor and the more closely related they are in evolutionary terms
New Techniques Suggest New Trees
Molecular analysis shows that DNA from American vultures is more similar to the DNA of storks than the DNA of the African vultures
DNA evidence is also used when similar structures cannot provide a clear answer in terms of relation
Red panda vs. Giant panda