Fossil spine suggests ancient human relative walked like us, but climbed like an ape

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About two million years ago, an ancient human relative, Australopithecus sediba, lived in what is today southern Africa, near a cave called Malaba that is part of the Cradle of Humankind. Until recently, it was not clear how much the species spends climbing trees and walking on two feet on the ground.

The discovery of a lumbar vertebra in the lower back of a single female Australopithecus sediba – along with other parts of the vertebrae of the same sample – changed this. Scientists from New York University in the US, the University of the Witwatersrand in South Africa and 15 other institutions have published a journal article showing that Australopithecus sediba walks like a human but climbs like a monkey. I asked Natasha Joseph of The Conversation Africa lead author Scott A. Williams about the research and its implications.

What was known about Australopithecus sediba before this search?

Quite a lot. This species was first discovered in 2008 (and announced in 2010); The recovery of new fossil material from Malaba has continued since then. This is partly because excavations have been carried out at the site since 2008, and also because large blocks removed from the site have been examined using medical computerized tomography (CT) to see if there are fossils inside. If so, the blocks are prepared down to reveal the fossils.

New lumbar vertebrae fossils came from one of these blocks, removed from a temporary road made by miners many years ago. They blew up the site and used some big blocks to build the mining route – and they were blowing up hominin fossils, too.

Fragments of two partial skeletons (a juvenile male ‘Karabo’ and an adult female ‘Isa’) were found in and outside the remains of Malaba Cave. So, we learned that there were at least two people in Malaba, dating back less than two million years, who were two distinct species – one that retained many of the primitive features of Australopithecus However, it also contained skull, teeth, and skeletal features that were more like members of our own species. It was a very controversial species for this reason.

What prompted you to examine this particular group of fossils?

I wrote my dissertation on the evolution of the spine in hominins, a group that included our closest and closest relatives, apes (chimpanzees, gorillas, orangutans, and gibbons). Announcement a. Sediba It was published during that time and I wrote to Professor Lee Berger, who discovered the first fossil remains with his nine-year-old son, asking which vertebrae I could see in the published figures. He kindly invited me to work on it and I’ve been doing so ever since.

We have already described the vertebrae recovered up to about 2013, and in 2018 published full and detailed descriptions and comparative analyzes of the skeletons.

Initially, what we knew about Issa’s spine came from the lower thoracic vertebrae, lower lumbar vertebrae, and partial pelvis. A significant portion of the lumbar spine was missing.

But all the while, new fossils were discovered – and in 2016, new lumbar vertebrae were being prepared. This allowed us to study Jesus’ almost complete lower back.

What did the new lumbar vertebrae reveal?

We were able to say a lot more about Jesus’ lower back and his adaptations to bipedalism than we could before. In 2013, we only had the two inferior lumbar vertebrae. Of these, we found the bony wedge to indicate that Issa likely had a very lordotic – curved forward – lower back.

The new fossils allow us to include more lumbar vertebrae, which really balances our appreciation for curvature into something quite similar to the degree of lordosis that we modern humans have; In fact, the bony wedge of Jesus was very similar to the average modern human female. So we were able to reject our previous hypothesis that Isa is characterized by “hyperdysplasia” (at the extreme end of modern human diversity, or hyperlordosis)

Australopithecus sediba Silhouette showing newly discovered vertebrae (colour) along with other skeletal remains of the species.
©: New York University

They illustrate other obvious adaptations to walking on two legs, such as the expansion of the interarticular aspects of the lumbar vertebrae, which form a “pyramidal configuration” and allow weight of the upper body to be transferred down through the lower back.

However, Issa also has features that suggest she was a tree climber. She had a strong lower back to lift herself up in trees and hang under branches. This mosaic of features is typical of other parts of the body a. Sediba He asserts that the species walked on two feet on the ground, but climbed trees like monkeys.

Does this help us locate the species on our human family tree?

get close a. SedibaEvolutionary relationship with other hominins, personality-based analyzes of the whole body are needed, and we are getting more and more a. Sediba every year. Given what this research and others have shown, I think it’s a candidate for a close relative of the genus to turn down. Hopefully Isa’s skull will not be destroyed by miners: recovering that and other parts of her body and from Karabu would go a long way to resolving the controversy.

Is there a way for others to study fossils?

3D models of the new fossils and all of our previously published fossils and reconstructions are available online. We welcome anyone to download and study them to replicate our analyzes, make their own analysis, or 3D-print them for teaching or other purposes.

The fossils themselves, sponsored by Wits University in South Africa, are also available for study by qualified researchers. The more open access, the better the science because individuals from diverse backgrounds and backgrounds will undoubtedly provide new observations and strides toward a better understanding of human evolution.

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