the first specifically anatomical investigation separate from a surgical or medical procedure is associated by early commentators with alcmaeon of croton. leonardo da vinci made notes for a planned anatomical treatise in which he intended to compare the hands of various animals including bears. pierre belon, a french naturalist born in 1517, conducted research and held discussions on dolphin embryos as well as the comparisons between the skeletons of birds to the skeletons of humans. his research led to modern comparative anatomy.