The terms ‘transitional’ and ‘intermediate’ are for the most part used as synonyms; however, a distinction between the two can be made:
- “Transitional” can be used for those forms that do not have a significant number of unique derived traits that the derived relative does not possess as well. In other words, a transitional organism is morphologically close to the actual common ancestor it shares with its more derived relative.
- “Intermediate” can be used for those forms that do have a large number of uniquely derived traits not connected to its derived relative.
Following this definition, all living organisms are in fact to be regarded as intermediate forms when they are compared to some other related life-form. Indeed there are many species alive today that can be considered to be transitional between two or more groups.