Kangaroo’s tail serves as fifth leg for walking
The signature gait of kangaroos is a marvel. As they hop, they seem to float along almost effortlessly on their large, springy hind feet, tail stretched out behind for balance.
A classic study showed that the faster they went, up to a point, the less energy they used.
But they also have a slower, walking motion that they use when they are feeding, moving only a few feet at a time to the next patch of grass. And for that, they depend on the tail not for balance or as a kind of crutch to lean on, but as a muscular, very important fifth leg.
J. Maxwell Donelan and Shawn M. O’Connor, both of Simon Fraser University in British Columbia, and colleagues studied kangaroo walking in the lab of Terence J. Dawson at the University of New South Wales in Australia, where they trained five red kangaroos to walk on a force-measuring device and made videos of them.
Donelan, who has focused much of his work on humans and how they expend energy, said that “anybody who has ever seen a kangaroo walk knows that it uses its tail.” But what interested him was how the animal used it.
It turned out, as he and his colleagues reported in the journal Biology Letters in June, that the tail exerted as much force as the four other legs combined. It is as important in kangaroo walking as one of our two legs is in human walking. If a leg is defined by its function and contribution to movement, Donelan said, the kangaroo has five legs when it is walking.
The Trail of Tears and of damaged skulls
Evicted from their Southeastern homeland by the federal government in the 1830s, Native Americans were sent on forced marches to eastern Oklahoma that became known as the Trail of Tears, an ordeal of disease, starvation and death. Now a study of Cherokee remains suggests that the stress interfered with the normal growth of their skulls.
“It is a sign that something was going on in the environment that was hindering growth,” said Ann H. Ross, an anthropologist at North Carolina State University and an author of the study, which appears in Annals of Human Biology.
Previous studies have shown that cranial length is affected by stress. For the new research, the authors looked at the skull measurements of adult Cherokees born between 1783 and 1874, data collected in the late 19th century by anthropologist Franz Boas and his students. The skulls of those born later in the period were significantly shorter than those born earlier.
– New York Times