3.3 mln year old fossil from Ethiopia shows origin of human spine
(EBC; May 23, 2017) - The 3.3million-year-old fossilised remains of a baby girl have revealed the human spine evolved much earlier than previously believed.
New analysis of baby ape-girl Selam's fossilised remains found she had only 12 pairs of ribs - fewer than in most apes - and the most complete spinal column of any early human relative - including vertebrae, neck and rib cage.
The new information revealed that portions of the human skeletal structure, which enable efficient walking, were established millions of years before it was thought.
Selam was discovered in Dikika in Ethiopia in 2000 by Professor Zeresenay Alemseged and found to be from the species Australopithecus afarensis.
This is the same as the famous Lucy skeleton found in 1974 and believed to be a forebear of the human genus, Homo.
The earliest humans climbed trees and walked on the ground, which helped them get around in diverse habitats and cope with changing climates.
Prof Zeresenay said: "Continued and painstaking research on Selam shows the general structure of the human spinal column emerged over 3.3 million years ago - shedding light on one of the hallmarks of human evolution.
"This type of preservation is unprecedented, particularly in a young individual whose vertebrae are not yet fully fused."
Many features of the human spinal column and rib cage are shared among primates.
But the human spine also reflects our distinctive mode of walking upright on two feet.
For instance, humans have fewer rib-bearing vertebrae - bones of the back - than those of our closest primate relatives.
Humans also have more vertebrae in the lower back, which allows us to walk effectively.
When and how this pattern evolved has been unknown until now because complete sets of vertebrae are rarely preserved in the fossil record.
Prof Carol Ward, of Missouri University, said: "For many years we have known of fragmentary remains of early fossil species that suggest that the shift from rib-bearing, or thoracic, vertebrae to lumbar, or lower back, vertebrae was positioned higher in the spinal column than in living humans.
"But we have not been able to determine how many vertebrae our early ancestors had.
"Selam has provided us the first glimpse into how our early ancestors' spines were organised."
These latest findings are published in Proceedings of the National Academy of Sciences.