Data from: The crouching of the shrew: mechanical consequences of limb posture in small mammals

An important trend in the early evolution of mammals was the shift from a
sprawling stance, whereby the legs are held in a more abducted position,
to a parasagittal one, in which the legs extend more downward. After that
transition, many mammals shifted from a crouching stance to a more upright
one. It is hypothesized that one consequence of these transitions was a
decrease in the total mechanical power required for locomotion, because
side-to-side accelerations of the body have become smaller, and thus less
costly with changes in limb orientation. To test this hypothesis we
compared the kinetics of locomotion in two mammals of body size close to
those of early mammals (< 40 g), both with parasagittally oriented
limbs: a crouching shrew (Blarina brevicauda; 5 animals, 17 trials) and a
more upright vole (Microtus pennsylvanicus; 4 animals, 22 trials). As
predicted, voles used less mechanical power per unit body mass to perform
steady locomotion than shrews did (P = 0.03). However, while lateral
forces were indeed smaller in voles (15.6 ± 2.0% body weight) than in
shrews (26.4 ± 10.9%; P = 0.046), the power used to move the body from
side-to-side was negligible, making up less than 5% of total power in both
shrews and voles. The most power consumed for both species was that used
to accelerate the body in the direction of travel, and this was much
larger for shrews than for voles (P = 0.01). We conclude that side-to-side
accelerations are negligible for small mammals–whether crouching or more
upright–compared to their sprawling ancestors, and that a more upright
posture further decreases the cost of locomotion compared to crouching by
helping to maintain the body’s momentum in the direction of travel.