15 October 2014 Last updated at 20:26
By Jonathan WebbScience reporter, BBC News
They roamed Australia while mammoths and Neanderthals lived in Europe - and it now seems they did so by putting one heavy foot in front of the other.
According to new research, the extinct "sthenurine" family of giant kangaroos, up to three times larger than living roos, was able to walk on two feet.
Today's kangaroos can only hop or use all fours, but their extinct cousins' bones suggest a two-legged gait.
The biggest members of the family may not have been able to hop at all.
The study, published in the journal Plos One, is a detailed comparison between the size and shape of the bones found in living kangaroo species and those of the sthenurines, which died out some 30,000 years ago.
Something completely different
This extinct family ranged in size from quite small animals, around 1m tall, to the mighty Procoptodon goliah, which stood at a towering 2m and weighed 240kg - heavier than an adult male lion.
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