DEVELOPMENTAL PATTERNS AND THE IDENTIFICATION OF HOMOLOGIES IN THE AVIAN HAND

Homologies of digits in the avian hand have been debated for 150 years . Cladistic analysis nests birds with theropod dinosaurs. Theropod han ds retain only digits I-II-III, so digits of the modern bird hand are often identified as I-II-III, Study of the developing manus and pes in amniote embryos, including a variety of avian species, shows stereoty ped patterns of cartilage condensations. A primary axis of cartilage c ondensation is visible in all species that runs through the humerus in to digit IV. Comparison to serially homologous elements of the hindlim b indicates that the retained digits of the avian hand are II-III-IV.