 However, with no ontogenical (developmental) basis to definitively state which digits are which on a theropod hand (because no non-avian theropods can be observed growing and developing today), the labelling of the theropod hand is not absolutely conclusive.Paleontologists have traditionally identified avian digits as I-II-III.They argue that the digits of birds number I-II-III, just as those of theropod dinosaurs do, by the conserved phalangeal formula.