PHYLOGENY evolution means organisms are related genealogy: family history phylogeny: taxon history phylogenetic tree = evolutionary tree branching diagram showing ancestor-descendant pathway over time either relative or absolute time Fig. 27.16

SYSTEMATICS systematics: biological science of reconstructing phylogeny; taxonomy history of organisms and their characters; "descent with modification" phylogeny converted into written classification groups within groups are reconstructed, then ranked at different levels of Linnaean hierarchy classification: grouping + ranking steps taxon (taxa): a group of organisms ranked at any level in Linnaean hierarchy

LINNAEAN HIERARCHY classification categories (levels) species, genus, family, order, class, phylum (division), kingdom, domain Linnaean hierarchy (Carolus Linnaeus); Fig. 1.14, 26.3

LINNAEAN HIERARCHY classification reflects hypothesized evolutionary history higher up Linnaean hierarchy, deeper in geologic time Table 25.1; Figs. 25.25, 26.4

PHYLOGENY cladistics: dominant systematics method for reconstructing phylogeny cladogram: phylogenetic tree reconstructed by cladistics method cladogram is a group of hypotheses how to read a phylogeny; Fig. 26.5 node: branch point line segments between nodes sister taxa at each resolved node fully reconstructed node has only 2 branches

PHYLOGENY common ancestor; descendants Fig. 26.4, 34.37

PHYLOGENY phylogenetic tree often converted to a written classification (gecko example) goal: name monophyletic groups, not non-monophyletic groups monophyletic group (clade): includes all branches after the reference node reference ancestral species + all descendants; Fig. 26.10

PHYLOGENY all named & ranked groups must be a clade, but not all clades must be named & ranked how do cladists reconstruct phylogeny? discover shared characters that uniquely define each monophyletic clade heritable characters: genetically based shared characters with 2 properties: 1) homologous 2) derived concept of homology a shared character (similarity) is either a homology or a homoplasy (= analogy)

HOMOLOGY descent with modification: species, characters homologous character: shared similarity due to descent from common ancestor modified or unmodified; forelimb of land vertebrates (tetrapods); Fig. 22.17 descended with modification from tetrapods; Fig. 34.2

HOMOPLASY homoplasous (= analogous) character: shared similarity due to convergent evolution, not common ancestry marsupial/eutherian mammal example; Fig. 34.34

PHYLOGENY first challenge to systematist which shared similar characters are due to homology vs. homoplasy? homologies have evolutionary information; homoplasies have misinformation second challenge which shared homologies are ancestral vs. derived? two types: shared ancestral, shared derived; not primitive, advanced outgroup comparison

PHYLOGENY ancestral, derived are relative concepts can be derived at one level in tree, ancestral at another level in tree Fig. 34.2

PHYLOGENY outgroup comparison if same character in ingroup and outgroup, it is ancestral; origin deeper in time if unique to ingroup, it is derived; origin more recent in time character-taxon matrix; Fig. 26.11

SYNTHESIS reconstruct phylogeny using shared derived homologous characters define clades by their unique shared derived homologous characters rank clades into Linnaean hierarchy (categories) name key clades (monophyletic groups) Domain Eukarya Kingdom Animalia Phylum Chordata Class Mammalia Order Carnivora Family Felidae Panthera pardus