Bipedalism left its mark on human skull: Kangaroos and upright rodents show same signs

by Mary Caperton Morton
Monday, June 19, 2017

The transition to bipedal walking in our ancestors changed the hominin skeleton in many ways. New research looking at how upright walking affected the structures at the base of the skull in both early humans and other bipedal mammals, like kangaroos, is shedding light on a once-controversial marker for bipedalism.

The foramen magnum is the opening at the base of the skull where the spinal cord passes through, connecting the brain to the rest of the body. Compared to quadrupedal primates, the foramen magnum in humans is shifted forward with the head balanced directly atop the spine. But some anthropologists have questioned the association between a forward-shifted foramen magnum and bipedal walking, saying it should not be interpreted as a hallmark of bipedalism in early hominin specimens.

To study the possible link, Gabrielle Russo of Stony Brook University in New York and Chris Kirk at the University of Texas, Austin, compared the position and orientation of the foramen magnum in 77 mammal species, including marsupials, rodents and primates. They found that humans, kangaroos and bipedal rodents, such as springhares and jerboas, all possess a foramen magnum located farther forward compared to quadrupedal animals.

“We’ve now shown that the foramen magnum is forward-shifted across multiple bipedal mammalian clades using multiple metrics from the skull, which I think is convincing evidence that we’re capturing a real phenomenon,” Russo said in a statement. The study, published in the Journal of Human Evolution, also identified specific measurements that may help anthropologists map out the evolution of bipedalism in the first hominins.

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