Systematics, Cladistics And Phylogeny

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Taxon

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Refers to a single taxonomic rank. Can refer to species, genus, family, etc.

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Monophyletic Group

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A taxon with a common ancestor for all descendants; a grouping of organisms with a single evolutionary origin for all. Ex: Mammals, reptiles and birds are monophyletic as Amniota

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Synapomorphy

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Derived characters shared by multiple taxa; comparing like characters among related taxa. (e.g. use of placenta and milk in placental mammals)

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Paraphyletic group

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A taxon that includes some but not all organisms descended from the most common ancestor. Ex: Reptilia is a paraphyletic grouping because it excludes birds from the group though the most recent common ancestor of reptiles is also that of birds

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Symplesiomorphy

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A trait shared by a common ancestor and some but not all of its descendents, unites a parphyletic group (e.g. scales and ectothermy in Reptilia)

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Polyphyletic Group

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A taxon whose members do not share a most recent common ancestor. Ex: "invertebrates" includes numerous taxa with no recent common ancestor.

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Convergent Evolution

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The independent evolution of similar characters in species with widely different evolutionary lineages (e.g. bats and birds)

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Homoplasy

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A character/trait shared by a taxon due to convergent evolution or evolutionary reversal and not common ancestry

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Ancestral Trait

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Character state that a taxon retains from its ancestors (sometimes called "primitive")

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Derived trait

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An innovated character state in a taxon that distinguishes it from related taxa (apomorphy)

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Taxonomy

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The science of naming and classifying the diversity of life

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Evolution

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Descent with modification

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Systematics

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Sorting organisms by identifiable characteristics, i.e. similarity and common descent

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Systematics "schools of thought" (3)

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1)Traditional evolution ("Neo-Darwinian")

2) Phenetic or numerical

3) Cladistic or Phylogenetic

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Neoteny

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Retention of larval or embryonic traits beyond the time of reproductive maturity

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Homology

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Common traits across taxa that imply shared ancestry

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Polytomy

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"Pitchfork" or "trident" representation of divergence among sister taxa; node with two or more immediate descendants but not a "resolved" node

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Analogy

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Similarities that do not necessarily imply common ancestry

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Parsimony

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The simplest answer is the best answer: the hypothesis that requires the fewest intermediate taxa from ancestral to derived character states assumed most likely

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Phenetics

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Classifying organisms purely on total number of similarities in characteristics

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Cladistics

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Classifying organisms on the proportional number of similarities in characteristics but with respect to their implied common ancestry

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Cladogram

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Branching diagram depicting the accepted genealogy of a taxonomic group

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Morphology

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Study of the form of creatures and the relationships between their varied structures

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Taxonomic Ranks (neo-Linnean system, Hint: there are 8)

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Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

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Apomorphy

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A character that has changed from its ancestral condition; contrasting between traits of related taxa

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Autapomorphy

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An attribute unique to one evolutionary lineage of organisms

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Binomial Nomenclature

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The Linnean system that assigns generic names to organisms (Genus, species)

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Character/Character State

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Any identifiable characteristic of an organism. Characters can be anatomical, behavioral, ecological or physiological. Character = trait

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Reversal

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Return to an ancestral character (sometimes called "devolution"; e.g. whales and ichthyosaurs reverting their physiology back to tails similar in function to ancient Sarcopterygii, a common ancestor to both)

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Out-groups vs. In-group

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A way of thinking about related taxa that narrows down synapomorphies in taxa of interest (in-group) with respect to a closely related taxon's (out-group)ancestral apomorphies

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Phylogenetic

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Pertaining to the development of an evolutionary lineage

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Plesiomorphy

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An ancestral character, unchanged among related taxa

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Sister group(s)

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Group(s) of organisms most closely related to the study taxa, excluding their direct descendants. Ex: Dromaeosauridae (e.g. velociraptors) and Avialae (e.g. birds) are sister groups