Taxonomy & Phylogeny
Classification of Organisms
Classification
• What characters are
suitable for
classification
• Systematics
– Combination of
taxonomy &
phylogeny
– Systematic approach to
understanding
evolutionary
relationships among
organisms
Hierarchical Classification System
• Taxa
– Major groupings or categories
– Nested set of increasing inclusiveness
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Cladistic Tree of Life
Wittiker’s 5 Kingdom Classification Scheme
Taxonomic Rules
• Binomial nomeclature
–
–
–
–
Genus species
Genus name is noun
species name is adjective
Higher taxonomic levels (families, orders, etc..) are
also nouns
Taxonomy Relates to Phylogeny
• Taxonomic characters allow phylogenetic
grouping
• Useful taxonomic characters
– Morphological
– Molecular (biochemical)
• Chromosomal
• Proteins
• DNA
• Homologies
– Character similarities attributed to common ancestry
Using Taxonomic Characters to Construct Phylogenies
• Ancestral character state
– The form of the trait present in the most recent
common ancestor of the groups being considered
• Derived character state
– The variant forms of the trait present in the members
of the groups being considered
• Polarity
– Relationship of character trait state to ancestral state
Example of Polarity Determination
• Study group
– Amniotes – animals with amniotic membrane around
developing embryo
– Birds, Reptiles, Mammals
• Character being studied
– Dentition – teeth
• Character states
– Present
– Absent
• Question: Is dentition a derived or ancestral trait for
amniotes?
• Outgroup comparison
– Phylogenetically close group, but non-amniote
Example of Polarity Determination
Amphibians
&Fish
Reptiles
Birds
Mammals
no teeth
teeth
teeth
teeth
Non-Amniote
Amniote
Common Ancestor
teeth
• Outgroup has teeth
– therefore teeth are considered ancestral & be presumed to occur in most recent
common ancestor of amniotes and non-amniotes
• Teeth in amniotes is an ancestral character state
• Loss of teeth in birds is a derived state
Cladograms
• Clade
– Groups of organisms that share derived character
states
• Synapomorphy
– Shared, derived character
• Cladogram
– Nested, hierarchical assembly and representation of
clades
Phylogenetic Relationships Established by
Comparison of Multiple Characters
Cladograms vs Phylogenetic Trees
• Cladogram
– Lacks information
• duration of lineages
• Amounts of evolutionary change
• Phylogenetic tree
– Establishes extinct vs extant lineages
– Indicates evolutionary timescale & degrees of
change
• Length of lines or numerical indications
Molecular Phylogeny
• Comparison of
cytochrome c
mutations
Human
Phylogenetic Groupings
• Monophyletic
– All descendents and most recent common ancestor
• Paraphyletic
– Leaves out some descendents from a recent common ancestor
• Polyphyletic
– Arbitrary groupings which do not include common ancestors
Cladistics & Cladograms vs Traditional Taxonomy
• Cladistics
– Taxonomic groupings based solely on establishing
monophyletic relationships
– Cladograms establish monophyletic taxonomic levels
• Traditional taxonomy
– Common descent – phyletic relationship
– Adaptive evolutionary change – ecological zones
Fig. 32.7