The main characteristics of hummingbirds and other members of the class Aves are a horny beak and lack of teeth, feathers, large stomach and embryonic development in hard-shelled eggs. Birds are also endothermic, which means they are warm blooded. All bird species evolved from the Archaeopteryx, a primitive flying animal that lived 150 million ago.
The order Apodiformes contains all swifts (family Apodidae), tree swifts or crested swifts (family Hemiprocnidae) and hummingbirds (family Trochilidae). These birds are small, have long wings and diminutive feet covered with skin instead of scutes, which are hard scales present in other orders. Apodiformes comes from the Latin for "footless," as members of the order have short legs and perch instead of settling on the ground.
The family Trochilidae contains two subfamilies: Phaethornithinae, which include six genera of hermit hummingbirds, which have beaks curved downward and live on the nectar of tropical flowers called heliconias; and the largest Trochilinae, which contains more than 100 genera and includes the typical iridescent hummingbirds. Members of the family Trochilidae are the only birds able to fly backward and flap their wings up to 80 times per second; their flying speed can reach up to 34 mph.
The largest genus of hummingbirds are found in South and Central America and include Amazilia; Agyrtria; Chlorostilbon, featuring vibrant green to blue feathers; and Coeligena, which has dark colors and white patterns. Hummingbirds found in North America include the rufous hummingbird (Selasphorus rufus), the ruby-throated hummingbird (Archilochus colubris), the magnificent hummingbird (Eugenes fulgens), the blue-throated hummingbird (Lampornis clemenciae) and the green violet ear (Colibri thalassinus). Endemic to Cuba, the bee hummingbird (Mellisuga helenae) is the smallest living bird, weighing about 0.063 oz. and measuring 2 inches.