Biomechanical determinants of transverse and rotary gallop in mammals

In transverse gallop, the placement of the second hind foot is followed by that of the contralateral forefoot, while in rotary gallop it is followed by the ipsilateral forefoot, and the sequence of footfalls appears to rotate around the body. Three-hundred-and-fifty-one filmed sequences have been analysed to assess the gallop type of 89 investigated mammal species belonging to the Carnivora, Artiodactyla and Perissodactyla orders. Twenty-three biometrical, ecological and physiological parameters have been collected for each species, both from literature data and from experimental measures. Most of the species showed only one kind of gallop: transverse (40%) or rotary (39%). Some species performed rotary gallop only at high speed (17%), while a small number showed both kinds of gallop at any speed (4%). Two main principal components extracted by PCA accounted for size (PC1) and velocity (PC2), with the latter associated with the rotary galloper group. A canonical correlation analysis showed a significant separation of the two groups on the second canonical function (F = 14.2; d.f. = 1; p < 0.001), mainly based on the metacarpus/humerus and metatarsus/femur length ratio. The gait pattern analysis provided significant differences between transverse and rotary gallop in fore and hind duty factor (t-test; p < 0.001), and in duration of the fore contact (t-test; p < 0.001). Our results assessed the typical gallop gait in the investigated species and confirmed the correlation between cursoriality and rotary gallop and identified some morphological characters correlated with the gallop type