Monotremata may be separated from the inheritance to other mammals during the Mesozoic. They are often placed in separate subklas from other mammals, Prototheria. They still have many ancestral traits therapsidnya (for example, complex pectoral girdles, lay eggs instead of giving birth, the hand with the humerus and femur terorietasi holding laterally on the body, and cloaca). Skull monotremata almost like a bird in appearance, with long rostrum and smooth appearance. Modern Monotremata not toothed at the adult; sutura difficult to see; rostrum rises, like beak, and covered with leather, and no lacrimal bone. Monotremata have the same essential characteristics of mammals, such as hair (but without the vibrissae), the heart of four rooms, single dentari bone, not bone middle ear and the ability to produce milk.