All species of birds belong to the phylum Chordata. Animals in the Chordata phylum share many traits as embryos; however, these traits can disappear by birth, allowing for great diversity in the phylum.
Chordata embryos all contain a notochord, some form of a hollow nerve cord, pharangeal slits and a postanal tail. Mammals, bony and cartilaginous fish, reptiles and amphibians are all considered Chordata.
Birds are distinguishable from other Chordata by the presence of feathers; however, most bird species also have scaly feet, light bones for flying, and particularly good vision. Experts believe birds, rather than reptiles, are the descendants of dinosaurs.