Derived

In phylogenetics, a trait is derived if it is present in an organism, but was absent in the last common ancestor of the group being considered.

For the sake of precision, the term "derived" is preferred to "advanced," a term which may inaccurately imply superiority. Simplicity is often secondarily derived - for example, the absence of leaves in the whisk fern "Psilotum" is a result of their secondary loss, and when considered in the context of ferns as a whole, is a derived trait. Likewise, the primitive character state for birds (i.e. the state possessed by their last common ancestor) is flight, which was secondarily lost by penguins and dodos.

Whether or not a trait is considered derived depends on the group in question. For example, among the tetrapods, having five fingers is the primitive trait - as their last common ancestor bore a five-digit hand. However, amongst the vertebrates, five fingers is a derived trait, as the last common ancestor to the vertebrates did not even bear fingers.Verify source|date=June 2008

References