Past studies of mammalian posture and locomotion have been made principally on cursorial species and current concepts are stereotyped accordingly. Mammalian limbs are usually characterized in terms of vertical orientation and parasagittal excursion; the assumption prevails that this type of stance and limb movement is typical of the class.
In the present study, walking movements in eight mammalian species (Tachyglossus aculeatus, Didelphis marsupialis, Tupaia glis. Mesocricetus auratus, Rattus norvegicus, Mustela putorius, Heterohyrax brucei, and Felis domestica) were studied cineradiographically with particular attention given to limb posture and excursion relative to the parasagittal and horizontal planes. Only the cat and, to a lesser degree, the hyrax conform to the postural and locomotory pattern that has been regarded as characteristic of most terrestrial, quadrupedal mammals. In the other six species, the humeri and femora usually function in positions more horizontal than vertical and at angles oblique to the parasagittal plane. Furthermore, the excursion pattern of these species have interspecific differences; some patterns are more variable than others. The classical conception of “mammalian posture” and “mammalian locomotion” is inaccurate both as a description of the features possessed in common by living terrestrial mammals and as a hypothetical approximation of the condition in ancestral mammals. At present, non-cursorial mammals such as the opossum and tree shrew are more realistic models on which to base deductions concerning posture and locomotion in eatly mammals.