Stiff backs and strong joints show that giant kangaroos may have walked instead of hopped.
These, now extinct, giant kangaroos were most likely unable to hop and used a more rigid body posture to move their hindlimbs one at a time, says a study published October 15th, 2014 in the open-access journal PLOS ONE by Christine Janis from Brown University and colleagues.
The “short-faced”, large bodied sthenurine kangaroos- a now extinct relative to modern-day kangaroos- first appeared in the middle Miocene and became extinct in the late Pleistocene. The largest of these kangaroos had an estimated body mass of 240 kg, almost three times larger than that of the biggest currently living kangaroos. Scientists think that kangaroos of this size may not have had the physical ability to hop. Analysis of different sthenurine species limb bone when compared to other kangaroos indicates various anatomical differences, especially in the larger species.
The physical differences the authors of this study discovered suggest that the large kangaroo species lacked various specialised features for rapid hopping, but had anatomy suggesting they supported their body weight with an upright posture and were able to support their weight on one leg at a time using their larger hips, knees, and stabilised ankle joints. Previous studies described that sthenurines’ specialised forelimbs and rigid lumbar spine would limit their ability to move slowly, using the tail as a fifth limb, as is typical in smaller kangaroos.
Instead, the authors propose that sthenurines adopted a walking gait on two hind legs, in the smaller and earlier forms, this gait may have been used as an alternative gait to using the tails as fifth limb at slower speeds. Larger Pleistocene kangaroos may have used this gait exclusively as they evolved larger body sizes, where hopping quickly was no longer possible.
“People often interpret the behavior of extinct animals as resembling that of the ones known today, but how would we interpret a giraffe or an elephant known only from the fossil record? We need to consider that extinct animals may have been doing something different from any of the living forms, and the bony anatomy provides great clues,” said Christine Janis.
If you would like to read the full paper, free access is available: http://dx.plos.org/10.1371/journal.pone.0109888
Contributing Source: PLOS
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