Spine Shows Ancient Human Kin Climbed Like Apes, Walked Like Men

A two-million-year-old fossil could change what we thought we knew about one of our ancient human relatives.

Photo Insert: Australopithecus sediba

A few vertebrae from the lower back of an Australopithecus sediba reveal that the hominin was surprisingly well adapted to walking upright like a human, in addition to climbing like an ape, Michael Irving reported for New Atlas.

Whether or not A. sediba was a direct ancestor of modern humans remains up for debate, but either way it’s a fascinating creature. It lived about two million years ago, stood around 1.5 m (5 ft) tall, and had a strange mix of modern and ancient facial features. The report was published in the journal e-Life.

The species was described from two specimens, a juvenile male and an adult female, uncovered in Malapa, South Africa. And now, scientists have discovered and described extra bones belonging to the female specimen, designated MH2 and nicknamed Issa.

These new bones are lumbar vertebrae from the animal’s lower back, a part of the body that can reveal much about how a creature got around.

“The lumbar region is critical to understanding the nature of bipedalism in our earliest ancestors and to understanding how well adapted they were to walking on two legs,” says Professor Scott Williams, lead author of the study.

“Associated series of lumbar vertebrae are extraordinarily rare in the hominin fossil record, with really only three comparable lower spines being known from the whole of the early African record.”

Previous research had assumed that A. sediba would have had a relatively straight spine, as seen in modern apes and more ancient hominins, like other australopithecines.

It’s usually an indicator of powerful trunk muscles, perfect for climbing. But surprisingly, the newly discovered vertebrae showed an inward curve, a feature known as lordosis. That makes it rather human-like and suggests an adaptation for walking upright as we do.

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