Symplesiomorphy vs. Plesiomorphy: What's the Difference?
Symplesiomorphy and Plesiomorphy Definitions
Symplesiomorphy
(cladistics) An ancestral trait shared by two or more taxa.
Plesiomorphy
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.
Plesiomorphy
(cladistics) A character state that is present in both outgroups and in the ancestors
