Walking on five legs: investigating tail use during slow gait in kangaroos and wallabies

Abstract

Pentapedal locomotion is the use of the tail as a fifth leg during the slow gait of kangaroos. Although previous studies have informally noted that some smaller species of macropodines do not engage in pentapedal locomotion, a systematic comparative analysis of tail use during slow gait across a wide range of species in this group has not been done. Analysis of relative movement of the pelvis, tail, and joint angles of the lower limbs during slow gait, using 2D landmark techniques on video recordings, was carried out on 16 species of Macropodinae. We also compared the relative lengthening of the tibia using crural index (CI) to test whether hindlimb morphology was associated with pentapedal locomotion. Pentapedal locomotion was characterised by three features: the presence of the ‘tail repositioning phase’, the constant height of the pelvis and the stationary placement of the distal tail on the ground during the hindlimb swing phase. The mean CI of pentapedal species was significantly greater than that of non-pentapedal species (1.71 versus 1.36; P < 0.001). This lends support to the hypothesis that the use of pentapedal locomotion is associated with the relative lengthening of the hindlimb, which in turn is associated with body size and habitat preference within the Macropodinae.

The extraordinary osteology and functional morphology of the limbs in Palorchestidae, a family of strange extinct marsupial giants

“…It is also possible that the relative gracility of the palorchestid hindlimb is evidence not of them being facultatively bipedal, but tripodal– that is, providing additional support for the rearing body with a muscular tail, behaviour well-known in macropodids [88, 97] and recently reasoned in the extinct vombatiform Thylacoleo [98]. Palorchestes has previously been noted to possess a ‘kangaroo-like tail’ [47, 99] larger than that of their diprotodontid kin, potentially as an adaptation to tripodal posture [6], though this has never been fully investigated.…”

Proximal Humerus Morphology Indicates Divergent Patterns of Locomotion in Extinct Giant Kangaroos

“…At speeds below around 6 km/h all extant kangaroos perform some sort of gait that involves bearing weight on both forelimbs and hind limbs, either walking or bounding (Windsor and Dagg 1971). The specialized slow gait of extant large kangaroos is a pentapedal walk, with the tail acting as a "fifth limb" to aid in propulsion (O'Connor et al 2014;Dawson et al 2015). In contrast with hopping locomotion, the energetic costs of quadrupedal bounding increase with speed, and scale in a similar fashion to the costs of quadrupedal locomotion in other mammals.…”

Climbing adaptations, locomotory disparity and ecological convergence in ancient stem ‘kangaroos’

“…In addition, various smaller-bodied macropodids displayed very similar astragalar morphologies (figures 2 a , c and 3 b ), especially those that tend to use quadrupedal bounding and/or hopping to manoeuvre through spatially complex habitats, such as dense vegetation and rocky uneven terrain (e.g. Setonix , Petrogale [7,10,11,48]).…”

“…In addition, many larger-bodied kangaroos (as well as the atypical forest-dwelling Dorcopsis wallabies [7]) use pentapedal progression, integrating the muscular tail for stabilization and propulsion [9]. Pentapedal locomotion is specifically correlated with increased hind limb length and the preferential occupation of open habitats [10]. On the other hand, smaller-bodied wallabies and rat-kangaroos living in dense vegetation or on rocky outcrops tend to use bounding gaits at slower speeds [10,11].…”

“…Pentapedal locomotion is specifically correlated with increased hind limb length and the preferential occupation of open habitats [10]. On the other hand, smaller-bodied wallabies and rat-kangaroos living in dense vegetation or on rocky outcrops tend to use bounding gaits at slower speeds [10,11].…”