Kangaroos are descended from animals that walked, and did not hop across the ground as they traveled. Analysis of the bones and body structures of extinct kangaroos reveal members of the largest group of the animals were unable to hop like their modern counterparts.

Sthenurines evolved in Australia roughly 13 million years ago, going extinct 30,000 years before the modern era. These animals disappeared not long after human beings first appeared on the massive island.

Procoptodon goliahs, the largest species of the sthenurines, stood over six feet tall, were 10 feet long, and weighed up to 530 pounds. Faces of the animals resembled those of modern rabbits.

Researchers found the animals likely walked upright, placing one foot in front of another, similar to humans. Modern kangaroos are unable to carry out those motions.

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

Researchers carefully examined skeletons of more than 140 kangaroos, as well as other related species, such as wallabies. Investigators found evidence around the body structure of these kangaroo ancestors that suggest they walked, rather than hopped. Teeth in the animals were shown to be better-suited for eating leaves from trees than grass, suggesting members of the species stood upright.

Janis and her team believe smaller sthenurines may have walked most of the time, although they could have hopped at higher speeds. Larger individuals likely walked under nearly all conditions, the researchers theorize.

Procoptodon was the largest kangaroo known to paleontologists. These animals first lived 125,000 years ago, becoming extinct around 300 centuries ago, along with their cousins, the sthenurines.

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

Sthenurines were first discovered by paleontologists in the 19th Century, but were not seriously studied, in part due to their humorous physical characteristics.

"They were short faced, not long-faced like modern kangaroos, and the smallest of them were as big as the largest modern kangaroos. It wasn't clear how they could hop at that size," Janis said.

The Musky Rat-kangaroo, a tiny version of the animal, is one of the few modern kangaroos that does not hop.

Study of kangaroo ancestors, and their mode of transportation was published in the online journal PLOS One.