The fossilized shoulder joint of an early hominin called “Little Foot” suggests that the upright species was also adept at swing by trees, with a skill that modern man has long since forgotten.
Some 3.7 million years ago, in what is now South Africa, a human relative straddled two evolutionary moments: our tendency to spend time in trees and our emerging preference to walk on the ground. That copy, called StW 573 or Little Foot, was a Australopithecus prometheus. The fossil was finally fully excavated in 2018, more than 20 years after its discovery, when paleontologists finished loosening the fossil from the breccia in which it was encapsulated. Little Foot immediately offered a remarkable look at human origins.
Research describing shoulder joint morphology was published this week in the Journal of Human Evolution. The research team inspected Little Foot’s chest girdle: literally the specimen’s shoulder blade and collarbone. By comparing the belt’s formation to that of other human relatives, including some of the great apes, the team explored how Little Foot and others of its kind got around.
“By understanding how the shoulder joints of early hominins are structured, and more generally how their shoulder blades are able to move on their torso, we can understand how they used their upper limbs in interaction with the environment,” says Kristian Carlson. , a biological anthropologist at the University of Southern California and lead author of the new paper, in an email. “This is a critical question at this time in our evolutionary history.”
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In its subtle form, Little Foot’s chest girdle indicated to the researchers that the humanoid was exploiting trees for survival, perhaps to buy a meal or to avoid becoming one. That corresponds to Research last year on the specimen’s vertebrae, suggesting that Little Foot was capable of head movements (useful for climbing) beyond modern human capabilities. That said, Little Foot was still bipedal, with the upright gait that comes with humans. The new finding provides an interesting comparison with Ardi (a copy of Ardipithecus ramidus), a lesser-known ancient relative from 4.4 million years ago. Paleoanthropologists recently suggested that Ardi’s hands were built to swing in trees, although some experts disagreed, saying that Ardi was more human-like than ape-like. While the fossil record is as petrified as it gets, the conclusions drawn from the bones we pull from the ground remain fickle. It will take a while to see if the interpretations of Little Foot’s lifestyle, taken from these shoulder bones, are correct.
Little Foot’s chest girdle is the earliest evidence of such a skeletal structure so close to when hominids split off from ape and bonobo ancestors. That upper limb is a crucial piece of the puzzle, although Carlson said it can only tell us so much.
“As special as Little Foot is, it is only one individual,” he explained. “While we are still intensively exploring other anatomical regions of the Little Foot skeleton, we must also continue to appreciate the growing morphological variability that appears to exist within the early hominin fossil record, for example in Australopithecus.”
Based on their comparisons, Carlson’s team determined that Little Foot’s shoulder structure could be a good indicator of what that structure looked like in even older human relatives, in the 7 to 8 million year time frame. Such a discovery would make Little Foot look like a spring chicken. But until that happens, it looks like we’re stuck with one of the most complete Australopithecian fossils ever found, the ongoing analysis of which reveals new details and theories with each passage. Woe to us!
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