the totality of imperfect adaptations that arises in certain groups of animals in the course of evolution and subsequently causes the extinction of those groups. The term “inadaptation” was introduced by the Russian paleontologist V. O. Kovalevskii in 1873. A classic example of inadaptation in the evolution of ungulate mammals is the imperfect changes in the skeleton and joints of the extremities in most groups of ungulates when they changed their mode of locomotion from digitigrade to unguligrade. Inadaptive forms appeared earlier than adaptive ones but were later supplanted by the latter. Thus, placental mammals supplanted marsupials, which were at one time widely distributed but are now preserved only in Australia and America.