According to a study carried out by scientists from Spain and the United States, members of Sthenurinae – an ancient family of kangaroos that lived until 30,000 years ago – likely preferred walking to hopping.
Procoptodon goliah, a giant short-faced kangaroo that lived during the Pleistocene in Australia; pencil drawing, digital coloring. Image credit: © Nobu Tamura.
Sthenurinae (sthenurine kangaroos) was an extinct subfamily within the family Macropodidae (kangaroos and rat-kangaroos).
These short-faced, large-bodied ‘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 of these animals, 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 gait.
Previous studies suggested that sthenurine kangaroos’ specialized forelimbs and rigid lumbar spine would limit their ability to move slowly, using the tail as a fifth limb, as is typical of smaller kangaroos.
Instead, Dr Borja Figueirido of the University of Malaga in Spain and his colleagues posit 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 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 rapidly was no longer a possible option.
Skeletons of the extinct sthenurine kangaroo Sthenurus stirlingi and the extant Eastern grey kangaroo (Macropus giganteus). Image credit: Lorraine Meeker / American Museum of Natural History.
The researchers make their case based on statistical and biomechanical analyses of the bones of sthenurine and other kangaroos past and present.
In all, they made nearly 100 measurements on each of more than 140 individual kangaroo and wallaby skeletons from many genera and species.
“Extant kangaroos hop at fast speeds and move about on all fours for slow speed travel. This requires a flexible backbone, sturdy tail, and hands that can support their body weight. Sthenurines don’t appear to have had any of those attributes,” said Prof Christine Janis of Brown University, who is the first author of the paper published in the journal PLoS ONE.
“Whether any of the sthenurines still hopped to attain fast speeds, bipedal walking was much more likely to be at least their mode of slow speed locomotion.”
The hypothesis that sthenurines were walkers would still benefit from other lines of evidence such the discovery of preserved tracks.
“But until that is found, the balance of the anatomy shows that these roos were specialized – and sometimes sized – for walking, not for hopping,” Prof Janis said.
Source: sci.news
