Fossil Reveals Origins Of Human Spine

A 2-and-a-half-year-old early human ancestor was recently revealed to have spines similar to modern humans -- but extremely different as well. New research revealed that the Australopithecus afarensis, a human ancestor that lived 3.3 million years ago, already had the same number of lumbar and throracic vertebrae as humans.

The young hominin called "Selam," however, showed a different transition between her upper and lower back, which scientists took to mean to have given her a boost for walking on two limbs. The author of the study published in the National Academy of Sciences, Carol Ward, said that researchers never knew before whether or not early human ancestors have the same pattern and the same number of vertebrae as modern humans.

Knowing for sure is important because the structure of the spine is a key to walking upright. Chimpanzees and gorillas, for instance, have 13 pairs of ribs as opposed to the 12 pairs of humans. Their backs are also longer than those of other great ape counterparts.

While early hominins or human ancestors are more or less known for their personification in transition from scuttling on all fours to bipedalism, spines remained a mystery. This is because vertebrae and ribs are usually small. These delicate bones do not usually preserve well in the fossil record.

Finding Selam changed that. The female A. Aferensis was discovered in Dikika, Ethiopia, in 2000, and researchers have been chipping her bones out of hard sandstone in an attempt to keep them free from damages. They learned that while the ancestor was bipedal, it also climbed trees.

Selam's vertebrae are each about half an inch across and so tiny that it could not be removed from the surrounding sandstone. However, Selam still had a spine with 12 ribs and 12 throracic vertebrae, much like the spine of modern humans.

Yet Selam's spine was very different -- its thoracolumbar transition. The changes occur at the facet joints. In modern humans, the joints change subtly in shape and orientation at the 12th thoracic vertebrae. But in Selam, the change happened at the 11th throracic vertebrae.

While this does not explain everything about human ancestors, Scott Williams said, as per Live Science, "How many vertebrae they had is the starting point for a lot of our other questions, speculations, hypotheses and models."