Kangaroos did not always hop around, as an extinct, huge species of the animal would not have been able to, leaving them to walk places.

According to Reuters, authors of a study published in the journal PLOS One made the observation through a biomechanical examination of fossils. Called sthenurines, these extinct kangaroos had shorter faces, bigger bodies and lived between 13 million and 30,000 years ago.

The largest species, known as Procoptodon goliah, were estimated to weight some 530 pounds, measure 10 feet in length and stood as tall as six-feet, two-inches. Among several anatomical differences with modern kangaroos was their head, which more resembled a rabbit's.

"Today's kangaroos mostly use hopping as their fast gait - although tree kangaroos rarely hop," study lead author Christine Janis, a paleontologist at Brown University, told Reuters. "But for slow speeds they use a type of 'pentapedal' walk, using all four legs and the tail.

"Something the size of Procoptodon would have had a hard time hopping, if it hopped at all," he said. "Research on living kangaroos shows that they are close to the limit in terms of tendon strength while hopping."

Modern kangaroos are able to increase their speed through hopping, but can slow themselves to more of a stroll if they want. They also use their tales as a third leg.

"At best, they'd have been really clumsy hoppers," Janis told the Washington Post of the larger extinct kangaroos. "All of the differences we found were suggestive of putting weight on one foot at a time.

"Hopping is a tricky gait, and modern kangaroos are near the limit, in terms of size."