Scientists believe that the kangaroo's giant ancestors may have parachuted up to 250kg. For the first time, a study has shown that heavier tendons and bones in ancient animals allowed them to jump.
Researchers say giant 250kg kangaroos that once lived in what is now Australia were capable of jumping despite their enormous size, The Guardian writes.
While modern kangaroos are known for their ability to travel long distances by hopping with both hind legs at once, there has long been debate about whether their extinct relatives had a similar bouncing ability.
Dr Megan Jones from the University of Manchester, who led the research, said: “When modern kangaroos jump, the Achilles tendon is actually stretched. That's great because it stores a lot of energy, so when they move to the next jump, it's quite energy efficient. But that means if the kangaroos were larger and didn't change anything else, you would have to cut that tendon.”
Unlike many previous studies that looked at whether giant kangaroos could jump based on the anatomy of modern species, Megan Jones and her colleagues took a different approach. In a paper published in the journal Scientific Reports, the team describes how they studied fossils of multiple species of giant kangaroos, including a species of sthenurine – short-nosed wandering kangaroos that lived between 13 and 30,000 years ago.
“They weigh up to 250kg, while the heaviest red kangaroo today is 90kg,” Dr. Jones said.
The team also studied fossils of protemnodon, a long-faced animal that lived from 5 to 40,000 years ago, and giant macropus – an animal that resembles a larger version of kangaroos living today.
For each giant kangaroo species, the researchers assessed the strength of the Achilles tendon in the ankle, part of the tissue needed for jumping, as well as the strength of the fourth metatarsal, the weakest bone in the hind limb.
“It wouldn't be good if their tendons were fine, but their bones would start to break if they jumped,” said Megan Jones.
The results showed that in all giant kangaroos studied, the fourth metatarsal bone was strong enough to support jumping, as well as the heel bone with enough space to accommodate a tendon thick enough for that movement.
While some researchers previously suggested that thicker tendons might make jumping more difficult, the researchers say this is unlikely, noting that some jumping creatures alive today, including kangaroo rats, have relatively thick tendons but use jumping to navigate difficult terrain and escape predators.
Jones emphasized that it is possible that giant kangaroos used jumping for similar purposes, adding that they were unlikely to jump over long distances or for long periods of time.
“It is possible that giant kangaroos not only jump less frequently or travel shorter distances, but also reduce stress by jumping more slowly,” the authors added.
However, Jones notes that the new study only suggests that giant kangaroos are capable of jumping, not necessarily do so, so other modes of locomotion are not ruled out.
“Any given kangaroo will use a combination of gaits: some will move slowly, some will move quickly,” Dr. Jones explains.
Dr. Gilbert Price, a paleontologist at the University of Queensland in Australia who was not involved in the study, said the big difference from previous studies is that the new study is based on fossils of giant kangaroos themselves.
“This shows that giant kangaroos changed their proportions in such a way that mechanical jumping was possible, even if it was less efficient than modern species,” he said.
However, he added: “The study does not suggest that these animals jumped across the landscape like modern red kangaroos, just that jumping was not ruled out and that is an important difference.”
Price believes this research could also help shed light on the fate of giant kangaroos.
“If you want to understand why these animals went extinct, you first need to understand what they actually were like,” he said. “Drawing attention back to their biology and ecology is not only more detailed but also key to understanding what happened.”
