Anthropologists confirm link between cranial anatomy and two-legged walking

Sep 27, 2013
Anthropologists confirm link between cranial anatomy and two-legged walking
Comparison of the skeletons of three bipedal mammals: an Egyptian jerboa, an eastern gray kangaroo and a human.

Anthropology researchers from The University of Texas at Austin have confirmed a direct link between upright two-legged (bipedal) walking and the position of the foramen magnum, a hole in the base of the skull that transmits the spinal cord.

The study, published in a forthcoming issue of the Journal of Human Evolution, confirms a controversial finding made by anatomist Raymond Dart, who discovered the first known two-legged walking (bipedal) human ancestor, Australopithecus africanus. Since Dart's discovery in 1925, physical anthropologists have continued to debate whether this feature of the cranial base can serve as a direct link to bipedal .

Chris Kirk, associate professor of anthropology and co-author of the study, says the findings validate foramen magnum position as a for fossil research and sheds further insight into human evolution.

"Now that we know that a forward-shifted foramen magnum is characteristic of bipedal mammals generally, we can be more confident that fossil species showing this feature were also habitual bipeds," Kirk says. "Our methods can be applied to fossil material belonging to some of the earliest potential ."

The foramen magnum in humans is centrally positioned under the braincase because the head sits atop the upright spine in bipedal postures. In contrast, the foramen magnum is located further toward the back of the skull in and most other mammals, as the spine is positioned more behind the head in four-legged postures.

As part of the study, the researchers measured the position of the foramen magnum in 71 species from three mammalian groups: marsupials, rodents and . By comparing foramen magnum position broadly across mammals, the researchers were able to rule out other potential explanations for a forward-shifted foramen magnum, such as differences in .

According to the findings, a foramen magnum positioned toward the base of the skull is found not only in humans, but in other habitually bipedal mammals as well. Kangaroos, kangaroo rats and jerboas all have a more forward-shifted foramen magnum compared with their quadrupedal (four-legged walking) close relatives.

These particular mammals evolved locomotion and anteriorly positioned foramina magna independently, or as a result of convergent evolution, says Gabrielle Russo, who is a postdoctoral research fellow at Northeast Ohio Medical University and lead researcher of the study.

"As one of the few cranial features directly linked to locomotion, the position of the foramen magnum is an important feature for the study of human evolution," Russo says. "This is the case for early hominin species such as Sahelanthropus tchadensis, which shows a forward shift of the foramen magnum but has aroused some controversy as to whether it is more closely related to humans or African apes."

Explore further: Digging up the 'Spanish Vikings'

More information: www.sciencedirect.com/science/… ii/S0047248413001681

Related Stories

Human skull study causes evolutionary headache

Dec 20, 2011

Scientists studying a unique collection of human skulls have shown that changes to the skull shape thought to have occurred independently through separate evolutionary events may have actually precipitated each other.

Holes in fossil bones reveal dinosaur activity

Jul 08, 2011

(PhysOrg.com) -- New research from the University of Adelaide has added to the debate about whether dinosaurs were cold-blooded and sluggish or warm-blooded and active.

It's all in the way we move

Mar 13, 2013

When, how and why modern humans first stood up and walked on two legs is considered to be one of the greatest missing links in our evolutionary history. Scientists have gone to the far ends of the earth – and the wonderful ...

Recommended for you

Digging up the 'Spanish Vikings'

17 hours ago

The fearsome reputation of the Vikings has made them the subject of countless exhibitions, books and films - however, surprisingly little is known about their more southerly exploits in Spain.

Short-necked Triassic marine reptile discovered in China

Dec 17, 2014

A new species of short-necked marine reptile from the Triassic period has been discovered in China, according to a study published December 17, 2014 in the open-access journal PLOS ONE by Xiao-hong Chen f ...

Gothic cathedrals blend iron and stone

Dec 17, 2014

Using radiocarbon dating on metal found in Gothic cathedrals, an interdisciplinary team has shown, for the first time through absolute dating, that iron was used to reinforce stone from the construction phase. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.