Archaeopteryx + modern birds, just variation within kind?
It has been suggested that the differences between Archaeopteryx and modern birds represents simple within-group variation. However, this is not correct. Modern birds show a large number of derived morphological characters not possessed by Archaeopteryx. Morphologically, Archaeopteryx clearly appears more closely related to theropod dinosaurs that any other group and is grouped with birds over theropod dinosaurs due to the possession of only two main characters, presence of feathers, and presence of a fully reverted hallux (toe). The relevant morphological variation can be represented graphically (if crudely) in the following figure: | ^ | A = Archaeopteryx | | | ___________________ T | | | i | | MODERN BIRDS | m | __ __ __ __ __| | e | | |___________________| | | FOSSIL | | __| BIRDS | | | A|__ __ __ __ __ __| | |___| |______________________________________________ “reptile” “bird” <--- Morphology --> As can be seen, the variation within birds shows a distinct trend. The more “reptile
