Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun An evolved character or trait that is shared by some or all members of a phylogenetic group and their common ancestor but is not unique to that group. A segmented spinal column is a plesiomorphy of mammals, being present as well in other groups such as fishes, reptiles, amphibians, and birds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun cladistics A character state that is present in both outgroups and in the ancestors

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[Greek plēsios, near to; see pel- in Indo-European roots + –morphy.]

Examples

  • A characteristic present in both the outgroups and the ancestors is called a plesiomorphy (meaning "close form," as in close to the root ancestor; also called an ancestral state).

    A Disclaimer for Behe?

  • I believe the "third eye" is a plesiomorphy for amniotes, so, yes, it makes sense to include that.

    Life's Time Capsule: The Synapsid Gallery

  • Any character or taxon that is prior in the evolutionary tree is considered “primitive”, or more technically, a plesiomorphy, the English of which is “underived”.

    The words of the world - The Panda's Thumb

  • The first Old World higher primates would be a plesiomorphy; German edition of his book entitled (in English) 'Phylo - it has no valency for sorting taxa within that group.

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  • like to an extinct lognecked short-taield reptile with paddles for locomotion

    February 17, 2009