 This is an important and fiercely debated area of research because its results may challenge the consensus that birds are (descendants of) dinosaurs.Embryologists and some paleontologists who oppose the bird-dinosaur link have long numbered the digits of birds II-III-IV on the basis of multiple studies of the development in the egg.This is based on the fact that in most amniotes, the first digit to form in a 5-fingered hand is digit IV, which develops a primary axis.