 However, such frame shifts are rare in amniotes and—to be consistent with the theropod origin of birds—would have had to occur solely in the bird-theropod lineage forelimbs and not the hindlimbs (a condition unknown in any animal).This is called "Lateral Digit Reduction" (LDR) versus "Bilateral Digit Reduction" (BDR) (see also "Limusaurus"

A small minority, known by the acronym BAND (Birds Are Not Dinosaurs) including ornithologists Alan Feduccia and Larry Martin, continues to assert that birds are more closely related to earlier reptiles, such as "Longisquama" or "Euparkeria", than to dinosaurs.Embryological studies of bird developmental biology have raised questions about digit homology in bird and dinosaur forelimbs.