Aves are a class in the phylum Chordata. Animals in this phylum include humans, sharks, frogs, bats, cows, lizards, and birds. These animals all share four traits: a dorsal hollow nerve cord, notochord, pharyngeal gill slits, and a post-anal tail. However, not all of these features remain present in the animal all of its life, and for many species in phylum Chordata, these characteristics can be found in the embryonic stages of life. The dorsal hollow nerve cord runs along the back of the animal and has many nerves branching off of it, while the notochord acts as a support structure for the nerve chord. In vertebrae, Aves included, these two body parts eventually develop into the backbone and spinal cord. The pharyngeal gill slits were used for feeding and the intake of gases in early chordates, but this trait lost its advantageous nature in aves, and is now only present in the embryonic stage. The last trait, a tail, is important to aves. Originally used to help amphibious chordates move, members of the class Aves have many different types of tails that are each tailored to the environment a particular species inhabits. The two main functions of tails are to increase stability and efficiency while flying, and to attract mates. These natural pressures have allowed the tails in class Aves to develop into tails of all shapes, sizes, and colors.
Further Reading: Chordates
Further Reading: Chordates