“Australopithecus sediba”, Walks like a Human, Climbs like a Monkey

JAKARTA, KOMPAS — An international team of scientists has found a two million year old spinal fossil of an extinct species of ancient human relative. This finding completes the “missing link” and proves that early hominins used their upper limbs to climb like apes and their lower limbs to walk like humans.

An international team of scientists from New York University, the University of the Witwatersrand and 15 other institutions announced the findings Wednesday (11/24/2021) in an open access journal. e-Life, as released by New York University.

The find is a fossil of a lumbar vertebra from the lower back which is part of an individual human relative, Australopithecus sediba. This find, together with other vertebral fossils found in Malapa, South Africa, and previous finds, form one of the most complete lower back vertebrae ever found in the early hominid record. The findings provide insight into how these early human relatives walked and climbed.

The fossils were discovered in 2015 during excavations of a mining track located next to the Malapa site in the Cradle of Humankind World Heritage Site, just northwest of Johannesburg, South Africa.

Malapa was the locus of discovery by Professor Lee Berger of the University of the Witwatersrand and his then nine-year-old son, Matthew. The research team found the first remains of a new species of ancient human relative named Australopithecus sediba in 2008.

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Fossils from the site have been dated to about two million years ago. The vertebrae described in this study are found in consolidated cement-like rocks known as breccias.

Instead of risking damaging the fossils, they were prepared virtually after scanning with Micro-CT at the University of the Witwatersrand. Once ready, the bones were reassembled with fossils found during previous work on the site and found to be in perfect junction with the fossil skeleton spine, as part of the original type specimen. Australopithecus sediba which was first described in 2010.

The skeleton’s catalog number is MH 2, but researchers have dubbed the female skeleton “Issa”, which means protector in Swahili. This discovery also establishes that, like humans, sediba has only five lumbar vertebrae.

“The lumbar region is critical for understanding the nature of bipedalism in our earliest ancestors and for understanding how well they adapted to walking on two legs,” said Scott Williams of New York University and Wits University and lead author of the paper.

“A related series of lumbar vertebrae is extremely rare in the hominin fossil record, with really only three comparable lower spines known from across the early African record,” he says.

The discovery of the new specimen means that Issa is now one of two early hominin skeletons that retain the relatively complete vertebrae and lower teeth of the same individual. That gives certainty about the spine species.

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“Issa is one of the most complete skeletons of an ancient hominin ever found. This spine complements the lower back and makes Issa’s lumbar region a contender for not only the best hominin lower back ever discovered, but also perhaps the best preserved,” said Berger, study author and leader of the Malapa project.

Mark transition

He added that this combination of completeness and preservation gave the team an unprecedented look at the anatomy of the species’ lower back.

With a more complete spine and excellent fossil preservation, this research found that Lordosis sediba more extreme than any other Australopithecus ever found. The amount of spinal curvature observed only exceeds that seen in the spine of a 1.6 million year old Turkana boy (Standing man) from Kenya and some modern humans.

“The presence of Lordosis and other features of the spine represent a clear adaptation to walking on two legs. There are other features, such as a large, upward-oriented transverse process, suggesting strong trunk muscles, for arboreal behavior,” said Professor Gabrielle Russo of Stony Brook University and author of the study.

Strong transverse bones pointing upwards usually indicate strong trunk muscles, as observed in apes. Shahed Nalla of the University of Johannesburg and Wits, a rib expert and researcher on the study, says: “When combined with other parts of the trunk anatomy, it shows Sediba maintain a clear adaptation to climbing.”

When combined with other parts of the torso anatomy, this shows Sediba retains a distinct adaptation to climbing.

Previous studies of this ancient species highlight mixed adaptations across skeletons in the Sediba showing the transitional nature between human-like walking and climbing adaptations. This includes features studied in the upper limbs, pelvis, and lower limbs.

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“The spine holds all of this together,” says Cody Prang of Texas A&M, who studies how early hominins walked and climbed.

“In what ways these combinations of traits persisted in our ancestors, including potential adaptations for walking on the ground on two legs and climbing trees effectively, are big questions that stand out about human origins,” he said.

This study concludes, Sediba became a transitional form of an early human relative and the backbone was clearly intermediate between modern humans (and Neanderthals) and great apes. “Issa walks like a human, but can climb like an ape,” says Berger.

To view the virtual fossils published in the new study, download it for free at Morphosource.org.

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