THEY had faces like rabbits and some were 2 metres tall. But now it seems that an extinct giant kangaroo didn't hop – it walked.
Known as "short-faced giant kangaroos",
sthenurines roamed Australia for 12.5 million years before being wiped
out 30,000 years ago. No one knows what killed off these relatives of
modern kangaroos, although they may have struggled as Australia's
climate grew more arid.
Unlike kangaroos today, these ancient
giants walked just like us. "All our evidence fits with these animals
leaning on one leg at a time, like humans," says Christine Janis of Brown University in Providence, Rhode Island.
She and her team took hundreds of
measurements of the bones of 66 living species of the kangaroo family
and 78 extinct species, including 71 from sthenurines, to calculate the
likely size and function of each animal's bones and muscles.
They found that the ill-fated sthenurines
had bone structures resembling those of animals that move by shifting
weight from one foot to the other, like humans and apes (PLOS One, DOI: 10.1371/journal.pone.0109888).
A flange at the base of their shin bones, similar to those found in
horses and humans, would have prevented their feet from collapsing
sideways under the weight of their body.
Like walking primates, their pelvises fanned out
at the rear. "They had big bums, and much more room for these large
gluteal muscles than today's kangaroos," says Janis. These muscles would
have supported each leg during walking.
Sthenurines had stiffer spines and shorter
tails than modern kangaroos, which use their tails like a fifth leg.
"It's reasonable that the ancestors of modern-day kangaroos moved
differently," says Max Donelan of Simon Fraser University in Burnaby,
Canada. "If pentapedal walking did not make biomechanical sense to these
large, extinct kangaroos, they would have likely found a different
solution."
Janis suggests they were browsers, taking
advantage of their height and bipedalism to browse trees and shrubs for
berries or other food, without having to waste energy hopping between
them.
This article appeared in print under the headline "Extinct giant kangaroos didn't hop – they walked"
