Nav: Home

New findings shed light on origin of upright walking in human ancestors

February 28, 2019

The oldest distinguishing feature between humans and our ape cousins is our ability to walk on two legs - a trait known as bipedalism. Among mammals, only humans and our ancestors perform this atypical balancing act. New research led by a Case Western Reserve University School of Medicine professor of anatomy provides evidence for greater reliance on terrestrial bipedalism by a human ancestor than previously suggested in the ancient fossil record.

Scott W. Simpson, PhD, led an analysis of a 4.5 million-year-old fragmentary female skeleton of the human ancestor Ardipithecus ramidus that was discovered in the Gona Project study area in the Afar Regional State of Ethiopia.

The newly analyzed fossils document a greater, but far from perfect, adaptation to bipedalism in the Ar. ramidus ankle and hallux (big toe) than previously recognized. "Our research shows that while Ardipithecus was a lousy biped, she was somewhat better than we thought before," said Simpson.

Fossils of this age are rare and represent a poorly known period of human evolution. By documenting more fully the function of the hip, ankle, and foot in Ardipithecus locomotion, Simpson's analysis helps illuminate current understanding of the timing, context, and anatomical details of ancient upright walking.

Previous studies of other Ardipithecus fossils showed that it was capable of terrestrial bipedalism as well as being able to clamber in trees, but lacked the anatomical specializations seen in the Gona fossil examined by Simpson. The new analysis, published in the Journal of Human Evolution, thus points to a diversity of adaptations during the transition to how modern humans walk today. "The fact that Ardipithecus could both walk upright, albeit imperfectly, and scurry in trees marks it out as a pivotal transitional figure in our human lineage," said Simpson.

Key to the adaptation of bipedality are changes in the lower limbs. For example, unlike monkeys and apes, the human big toe is parallel with the other toes, allowing the foot to function as a propulsive lever when walking. While Ardipithecus had an offset grasping big toe useful for climbing in trees, Simpson's analysis shows that it also used its big toe to help propel it forward, demonstrating a mixed, transitional adaptation to terrestrial bipedalism.

Specifically, Simpson looked at the area of the joints between the arch of the foot and the big toe, enabling him to reconstruct the range of motion of the foot. While joint cartilage no longer remains for the Ardipithecus fossil, the surface of the bone has a characteristic texture which shows that it had once been covered by cartilage. "This evidence for cartilage shows that the big toe was used in a more human-like manner to push off," said Simpson. "It is a foot in transition, one that shows primitive, tree-climbing physical characteristics but one that also features a more human-like use of the foot for upright walking." Additionally, when chimpanzees stand, their knees are "outside" the ankle, i.e., they are bow-legged. When humans stand, the knees are directly above the ankle - which Simpson found was also true for the Ardipithecus fossil.

The Gona Project has conducted continuous field research since 1999. The study area is located in the Afar Depression portion of the eastern Africa rift and its fossil-rich deposits span the last 6.3 million years. Gona is best known as documenting the earliest evidence of the Oldowan stone tool technology. The first Ardipithecus ramidus fossils at Gona were discovered in 1999 and described in the journal Nature in 2005. Gona has also documented one of the earliest known human fossil ancestors - dated to 6.3 million years ago. The Gona Project is co-directed by Sileshi Semaw, PhD, a research scientist with the CENIEH research center in Burgos, Spain, and Michael Rogers, PhD, of Southern Connecticut State University. The geological and contextual research for the current research was led by Naomi Levin, PhD, of the University of Michigan, and Jay Quade, PhD, of the University of Arizona.
-end-
This research was made possible by use of the human and ape skeletal collections housed at the Laboratory of Physical Anthropology, Cleveland Museum of Natural History. Major financial support was provided by the L.S.B. Leakey Foundation, Spain's Ministerio de Economia, Industria y Competitividad, Marie Curie EU Integration Grant, U.S. National Science Foundation, Case Western Reserve University, the National Geographic Society, and the Wenner-Gren Foundation.

Simpson, S., et al. "Ardipithecus ramidus postcrania from the Gona Project area, Afar Regional State, Ethiopia." Journal of Human Evolution. DOI: 10.1016/j.jhevol.2018.12.005

For more information about Case Western Reserve University School of Medicine, please visit case.edu/medicine.

Case Western Reserve University

Related Fossil Articles:

Fossil fish gives new insights into the evolution
An international research team led by Giuseppe Marramà from the Institute of Paleontology of the University of Vienna discovered a new and well-preserved fossil stingray with an exceptional anatomy, which greatly differs from living species.
What color were fossil animals?
Dr. Michael Pittman of the Vertebrate Palaeontology Laboratory, Department of Earth Sciences, The University of Hong Kong led an international study with his PhD student Mr.
New Cretaceous fossil sheds light on avian reproduction
A team of scientists led by Alida Bailleul and Jingmai O'Connor from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences reported the first fossil bird ever found with an egg preserved inside its body.
Fossil deposit is much richer than expected
Near the Dutch town of Winterswijk is an Eldorado for fossil lovers.
Researchers add surprising finds to the fossil record
A newly discovered fossil suggests that large, flowering trees grew in North America by the Turonian age, showing that these large trees were part of the forest canopies there nearly 15 million years earlier than previously thought.
Chinese Cretaceous fossil highlights avian evolution
A newly identified extinct bird species from a 127-million-year-old fossil deposit in northeastern China provides new information about avian development during the early evolution of flight.
Parasites discovered in fossil fly pupae
Parasitic wasps existed as early as several million years ago.
Cracking open the formation of fossil concretions
Researchers developed a unified model of the formation mechanism of spherical carbonate concretions, which often contain exceptionally well-preserved fossils.
First an alga, then a squid, enigmatic fossil is actually a fish
A fossil slab discovered in Kansas 70 years ago and twice misidentified -- first as a green alga and then as a cephalopod -- has been reinterpreted as the preserved remains of a large cartilaginous fish, the group that includes sharks and rays.
Actual fossil fuel emissions checked with new technique
Researchers have measured CO2 emissions from fossil fuel use in California and compared them to reported emissions.
More Fossil News and Fossil Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.