Interclavicle
An interclavicle is a bone which, in most tetrapods, is located between the clavicles. Therian mammals are the only tetrapods which never have an interclavicle, although some members of other groups also lack one. In therians, it is replaced by the sternum which is similar in shape and function but forms via endochondral ossification. The interclavicle, on the other hand, develops through intramembranous ossification of the skin. Monotremes, although part of the mammalian class, do have interclavicles. Dinosaurs also lack an interclavicle, allowing the development of sternal plates eventually culminating in the evolution of the bird sternum, a crucial step in the evolution of bird flight.
