Foot characteristics has been an important feature for classifying birds into different taxonomic orders. Early in the 19th century ornithologist Hans Gadow created a list of 40 morphological characteristics including foot scale arrangement and number of toes (along with many other features) to help define the orders of existing birds.
Oftentimes, students learning ornithology are taught the 34 orders by studying the feet of various bird species. The variation from webbed to unwebbed feet, color and scale arrangement is amazing. Who knew you could identify a bird by its feet!