Extinct giant kangaroos tiptoed one leg at a time

Fossil clues suggest refrigerator-sized sthenurines did not hop

illustration of extinct kangaroo walking

NOT A HOPPER  The extinct supersized kangaroo Sthenurus stirlingi probably tiptoed one hind leg at a time instead of hopping, says a new study.

Brian Regal, C.M. Janis et al/PLOS ONE 2014

The real hulks among extinct kangaroos probably didn’t hop. They tiptoed on one rear leg at a time, a new study says.

As recently as 30,000 years ago, the kangaroo genealogical tree had a now-extinct branch called Sthenurinae. Members of this subfamily ranged from small to whopper, with the largest weighing up to 240 kilograms. That’s a bit more than a typical full-sized fridge and far heavier than today’s biggest kangaroos, red males that bulk up to 90 kilograms.

An analysis of bones from 78 sthenurines of various sizes suggests the prehistoric big guys were bipedal walkers, says functional anatomist and paleontologist Christine Janis of Brown University in Providence, R.I. Among the clues: The giant roos’ bones suggest a body too heavy for frequent hopping, and their hips flared with plenty of room for attaching big gluteal muscles similar to those that help humans balance on one leg while stepping forward with the other.

When not hopping, today’s kangaroos walk on all fours and use their tails to help them swing their hind legs forward (SN Online: 7/3/14). The spines of the biggest sthenurines, however, look too stiff for that motion, Janis and colleagues say October 15 in PLOS ONE.

THEN AND NOW A skeleton of the extinct kangaroo Sthenurus stirlingi (top) suggests its body was heavier and its spine less flexible than that of the modern eastern gray kangaroo (bottom). C.M. Janis et al/PLOS ONE 2014

The sthenurines’ gait would not have been a Godzilla-like lumber though. Modern kangaroos hop on the end of their feet. Janis expects that the giant kangaroos likewise walked on tiptoe.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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