All modern mammals (platypus, opossum and human) have a middle ear separated from the lower jaw (see example from living opossum). This jaw-ear separation is an important evolutionary innovation. It becomes possible for mammals to have a delicate and highly sensitive ear structure for better hearing, and to have a more robust lower jaw and jaw hinge for better feeding. Also, the jaw and ear are not interfering with each other. By comparison, the middle ear bones are a part of the lower jaw and form the jaw hinge in pre-mammalian relatives (see the example of Morganucodon).
The ear bones in Maotherium are partly separated from the jaw, and more similar to those in modern mammals than to mammaliaforms, but still retain the pre-mammalian condition in which the jaw and the ear are connected to each other. Moreover, the connected jaw-ear structure of Maotherium is similar to the ear structure of modern mammals at embryonic and fetal growth stages. This phenomenon is known as "paedomorphosis" ("paedo:" child-like; "morphosis:" similarity) and is caused by timing change in growth. The analysis of the new fossil suggests that the evolutionary pattern of the mammalian ear is directly related to timing changes in growth, as well as in changes in genes for mammalian development.