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Did giant kangaroos walk more like dinosaurs?
New in PLoS ONE. The illustration looks a bit like a bipedal dinosaur
except for the pronated forelimbs...
Christine M. Janis, Karalyn Buttrill & Borja Figueirido (2014)
Locomotion in Extinct Giant Kangaroos: Were Sthenurines Hop-Less Monsters?
PLoS ONE 9(10): e109888.
Sthenurine kangaroos (Marsupialia, Diprotodontia, Macropodoidea) were
an extinct subfamily within the family Macropodidae (kangaroos and
rat-kangaroos). These “short-faced browsers” first appeared in the
middle Miocene, and radiated in the Plio-Pleistocene into a diversity
of mostly large-bodied forms, more robust than extant forms in their
build. The largest (Procoptodon goliah) had an estimated body mass of
240 kg, almost three times the size of the largest living kangaroos,
and there is speculation whether a kangaroo of this size would be
biomechanically capable of hopping locomotion. Previously described
aspects of sthenurine anatomy (specialized forelimbs, rigid lumbar
spine) would limit their ability to perform the characteristic
kangaroo pentapedal walking (using the tail as a fifth limb), an
essential gait at slower speeds as slow hopping is energetically
unfeasible. Analysis of limb bone measurements of sthenurines in
comparison with extant macropodoids shows a number of anatomical
differences, especially in the large species. The scaling of long bone
robusticity indicates that sthenurines are following the “normal”
allometric trend for macropodoids, while the large extant kangaroos
are relatively gracile. Other morphological differences are indicative
of adaptations for a novel type of locomotor behavior in sthenurines:
they lacked many specialized features for rapid hopping, and they also
had anatomy indicative of supporting their body with an upright trunk
(e.g., dorsally tipped ischiae), and of supporting their weight on one
leg at a time (e.g., larger hips and knees, stabilized ankle joint).
We propose that sthenurines adopted a bipedal striding gait (a gait
occasionally observed in extant tree-kangaroos): in the smaller and
earlier forms, this gait may have been employed as an alternative to
pentapedal locomotion at slower speeds, while in the larger
Pleistocene forms this gait may have enabled them to evolve to body
sizes where hopping was no longer a feasible form of more rapid