A dynamic similarity hypothesis for the gaits of quadrupedal mammals

TLDR

The dynamic similarity hypothesis states that mammals move similarly when traveling at speeds yielding equal Froude numbers, a condition common to most mammals over 5 kg. The authors tested the hypothesis using data from a diverse sample of mammals. The hypothesis predicts relationships among size, speed, and gait features, and is supported for many cursorial quadrupeds, remaining a reasonable approximation across cursorial, non‑cursorial, bipedal, and avian species.

Abstract

The dynamic similarity hypothesis postulates that different mammals move in a dynamically similar fashion whenever they travel at speeds that give them equal values of a dimensionless parameter, the Froude number. Thus, given information about one species, it could be possible to predict for others relationships between size, speed and features of gait such as stride length, duty factor, the phase relationships of the feet and the patterns of force exerted on the ground. Data for a diverse sample of mammals have been used to test the hypothesis. It is found to be tenable in many cases when comparisons are confined to quadrupedal mammals of the type described by Jenkins (1971) as “cursorial”. Most mammals of mass greater than 5 kg are of this type. Although the hypothesis applies less successfully to comparisons between cursorial and non‐cursorial mammals it is shown to be a reasonable approximation even for such comparisons and for comparisons between quadrupedal mammals and bipedal mammals and birds.