Lecture 9 Evolution Classification Because of how evolution

Lecture 9: Evolution & Classification Because of how evolution occurs: Hierarchical, nested classification is natural There is ONE TRUE PHYLOGENY • Based on interrelationships • Life started at one point & diverged Speciation Origin

Study of Evolutionary History • Taxonomy: classification (naming) • Systematics: describes evol’nry relationships Assume: similarity in heritable characters signifies closeness of relationship Use characters to deduce relationships & classify

Types of Taxonomy Phenetic: • Groups species by phenotypic similarity • May use physical, immunological, or genetic traits Phylogenetic: • Use evolutionary relationships • How recently shared common ancestor Phenetic & phylogenetic taxonomy often give similar results More on this next class

Terminology Evolution occurs in two ways: 1. Anagenesis: directional change in a lineage 2. Cladogenesis: branching by speciation Rate & pattern of anagenesis + branching pattern True Phylogeny

Reconstructing Phylogenies Use: 1. Ancestral Character (Plesiomorph): • • Primitive Inherited with little or no change from ancestor 2. Derived Character (Apomorph) • Recently changed Only CHARACTERS are PRIMITIVE, not SPECIES

Reconstructing Phylogenies Use Shared Characters: • Because of PARSIMONY (smallest number of changes in phylogeny) • Change takes time • Change is unlikely • Shared characters usually indicate close relationships

Shared Characters 1. Ancestral Homologies • • • Character found in both taxa Character found in common ancestor Character not in all descendants 2. Derived Homologies • • • Character found in both taxa Character found in common ancestor Character in all descendants of common ancestor

3. Analogies: • • • Characters have no common history Characters are not in common ancestor Characters developed independently CONVERGENCE May be evolutionary reversals to ancestral state - cause loss of info about relationships

A A A A A Derived Homology - character A A A Ancestral Homology Analogy - character A

More realistic example abcdef f e d c a= ancestral a= derived abcdef a b abcdef

Phylogenetic Groupings 1. Monophyletic 1. Shared derived homologies 2. Contains all the descendants of a common ancestor 3. e. g. all birds 2. Paraphyletic 1. 2. 3. 4. Shared ancestral homologies Species with derived characters not included Some but not all descendants of a common ancestor e. g. fish; reptiles – missing birds, mammals

3. Polyphyletic • • Analogies Common ancestor not in group Shared characters evolved independently e. g. vultures

Groupings A A A A Monophyletic A A A A A Paraphyletic A A A Polyphyletic

Phylogenetic Reconstruction: Whales • Sea-dwelling ~ 53. 5 mya • Descendants of Artiodactyla (even-toed ungulates) • Rudimentary & vestigial characters common to land mammals (pelvic girdle, diaphragm, sensory structures) • Intermediary fossils: Ambulocetus – the walking whale (47 mya)

Whale Phylogeny continued • Paraxonic foot symmetry: characteristic of artiodactyla (axis passes b/w 3 rd/4 th digits) • Molecular studies: closest to artiodactyla out of 48 mammals • Not just related to artiodactyls they ARE artiodactyls • Geochemical studies: move from FW to SW in tooth oxygen ratios

Previous viewpoint Recent viewpoint • Recent evidence: hippos more closely related to whales than other artiodactyla