Modern Evolutionary Classification (Ch 18.2) Unit 5: Evolution

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

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

Building Cladograms

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.

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

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

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

Clades vs Taxonomic Groups

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