Mainland Australia’s biggest kangaroos went extinct 40,000 years ago, but scientists are still figuring out how these big beasts moved.(ABC TV: Catalyst)

ABC News in Australia has an article about extinct giant kangaroos.  Giant kangaroos like Procoptodon goliah lived in Australia until about 40,000 years ago.  It weighed about 240 kilograms (> 500 lbs).  Did they hop or did they walk?  Scientists still aren’t sure, but fossils suggest they walked on they hind legs.

To understand how long-dead kangaroos got around, it’s worth examining why today’s ground-dwelling roos, such as eastern greys (Macropus giganteus), are such remarkable jumpers.

Crucial to their bounciness is their Achilles tendon, a thick, tough cord of connective tissue that connects lower leg muscles to the heel bone.

When a hopping kangaroo’s foot strikes the ground, their Achilles tendon lengthens and stores energy, like a stretched elastic band.

Then as they push their foot off the ground, the Achilles recoils, helping propel their leg up and forwards into the next hop.

By storing and releasing energy in their Achilles with each bound, kangaroos can bolt long distances with relatively little effort.

But it also means a kangaroo’s Achilles, which is almost as thick as a human finger, must deal with huge forces passing through it.