Ancient human relative, Australopithecus sediba, ’walked like a human, but climbed like an ape’

NEW lower back fossils are the “missing link” that settles a decades old debate proving 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 Johannesburg (UJ), the University of the Witwatersrand and 14 other institutions revealed the discovery of two-million-year-old fossil vertebrae from an extinct species of ancient human relative, in research published in the open access journal e-Life on Tuesday.

The recovery of new lumbar vertebrae from the lower back of a single individual of the human relative, Australopithecus sediba, and portions of other vertebrae of the same female from Malapa, South Africa, together with previously discovered vertebrae, form one of the most complete lower backs ever discovered in the early hominid record and give insight into how this ancient human relative walked and climbed.

“These fossil discoveries form the largest collections of hominin fossils and have pegged the importance of the Cradle of Humankind in the story of human evolution.

“I believe this breakthrough has also opened up the field of palaeontology for greater involvement by specifically South African students and scientists,” says Prof Shahed Nalla an associate professor in the Department of Human Anatomy and Physiology at UJ.

He contributed to the taxonomy of Homo Naledi as well as the analysis of the thoracic elements associated with the fossil find.

The fossils were discovered in 2015 during excavations of a mining trackway running next to the site of Malapa in the Cradle of Humankind World Heritage Site, just north-west of Joburg .

Malapa is the site where, in 2008 Professor Lee Berger from the University of the Witwatersrand and his then nine-year old son, Matthew, discovered the first remains of what would be a new species of ancient human relative named Australopithecus sediba.

Fossils from the site have been dated to approximately two million years before present.

The vertebrae described in the present study were recovered in a consolidated cement-like rock, known as breccia, in near articulation.

Rather than risking damaging the fossils, they were prepared virtually after scanning with a Micro-CT scanner at the University of the Witwatersrand, thus removing the risk of damaging the closely positioned, delicate bones during manual preparation.

Once virtually prepared, the vertebrae were reunited with fossils recovered during earlier work at the site and found to articulate perfectly with the spine of the fossil skeleton, part of the original type specimens of Australopithecus sediba first described in 2010.

The skeleton’s catalogue number is MH 2, but the researchers have nicknamed the female skeleton “Issa,” meaning protector in Swahili. The discovery also established that like humans, sediba had only five lumbar vertebrae.

“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,” said Professor Scott Williams of New York University and Wits University, and lead author on the paper.

The discovery of the new specimens means that Issa now becomes one of only two early hominin skeletons to preserve both a relatively complete lower spine and dentition from the same individual, allowing certainty as to what species the spine belongs to.

“While Issa was already one of the most complete skeletons of an ancient hominin ever discovered, these vertebrae practically complete the lower back and make Issa’s lumbar region a contender for not only the best-preserved hominin lower back ever discovered, but also probably the best preserved,” said Berger, who is an author on the study and leader of the Malapa project.

Previous studies of the incomplete lower spine by authors not involved in the present research hypothesised that sediba would have had a relatively straight spine, without the curvature, or lordosis, typically seen in modern humans.

They further hypothesised Issa’s spine was more like that of the extinct species Neandertals and other more primitive species of ancient hominins older than two million years.

The present study found the lordosis of sediba was in fact more extreme than any other australopithecines yet discovered, and the amount of curvature of the spine observed was only exceeded by that seen in the spine of the 1.6-million-year-old Turkana boy (Homo erectus) from Kenya, and some modern humans.

“Issa walked somewhat like a human but could climb like an ape,” Berger said.

Professor Cody Prang of Texas A&M, who studies how ancient hominins walked and climbed added that the spine tied this all together.

Cape Times