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Phylogeny Terms

Phylogeny Terms
Plesiomorphy - plesio: “near,” “close” An ancestral character, i.e. limbs
Symplesiomorphy – sym: “united” Shared ancestral characters, i.e. limbs for Tetrapoda
Apomorphy – apo: “away from” A derived character, i.e. mammory glands
Synapomorphy – syn: “united” Shared derived characters, i.e. mammory glands for mammals. Synapomorphies allow
biologists to recognize clades or lineages.
The presence of mammary glands is a synapomorphy for mammals in relation to tetrapods but is a symplesiomorphy for
mammals in relation to one another: rodents and primates.
Homoplasy – homo: “same” A shared character that has not been inherited from a common ancestor, i.e. wings. Similar
due to reasons other than common ancestry.
Polytomy – poly: “many” The relationships cannot be fully resolved, so there are more than two branches from the
same node.
Monophyletic – mono: “one” A single
group that consists of a common ancestor
and all its descendants, i.e. a clade. All the
descendants, but no others are included.
Plants make up a monophyletic group
within the Eukaryote domain.
Paraphyletic – para: “side by side” A group
that contains some, but not all of the
descendants of a common ancestor.
Eukaryotes are a paraphyletic group,
because plants, fungi, and animals are
three branches among many that make up
Polyphyletic – poly: “many” A group that
does not contain an ancestor common to
all descendants. An unnatural group that
does not include the most recent common
ancestor. Convergent evolution is an
example. Bats and birds do not share a
recent common ancestor, yet they both
have wings. The wings are a homoplasy;
bats & birds are a polyphyletic group.