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A re-analysis of a fossil three million years ago suggests Australopithecus afarensis a former hominid, had equally capable children on two feet as they were in the trees – an important discovery that sheds new light on this critical step in the evolution of hominids.
A tiny fossilized foot, no larger than a human thumb, reveals some of the physical abilities of A. afarensis and their possible behaviors, according to new research published today in Science Advances .
Scientists have known for a long time, or at least suspect, that A. afarensis an early hominid similar to a monkey that exists somewhere within our family tree, either directly or through of closely related species, walked on two feet. In fact, some scientists have gone so far as to suggest that these ancient great apes were exclusively bipedal, completely abandoning their arboreal ancestry in favor of the heel-toe expression. The new document, directed by Jeremy DeSilva of Dartmouth College, shows that infants A. afarensis children were able to stand up and walk upright. But it's important to note that these young hominids still had the ability to climb – an important physical attribute that may have helped them hook onto their mothers, climb trees and escape predators.
In 2002, Zeresenay Alemseged, professor of biology and anatomy of the body at the University from Chicago and co-author of the new paper, found the partial fossilized remains of an infant, about two years old. -half a year at his death, in the Dikika region of Ethiopia. The child Dikika, also known as "Selam", consists of a skull, an almost complete spine with ribs, shoulders, part of the arms and legs, and the foot, considered the most complete foot of a child discovered.
"Most fossil records are composed of adults – it is unusual to find fossilized remains of children, and these give us a wonderful insight into the growth and development of our ancestors" said DeSilva to Gizmodo.
The fossil was identified as belonging to A. afarensis (the same species as the famous Lucy fossil), and dating back to 3.32 million years ago. The study published today improves the initial analysis of 2006 because many parts of the skeleton, including the partial foot, were buried in sediments. Many of these bones have now been exposed, allowing for a more in-depth analysis of the young specimen.
The foot analysis of the child Dikika suggests that the infant already had the bone structure required to stand and walk – consistent conclusion with what anthropologists have already learned footprints found in Laetoli , Tanzania, and Lucy's fossil, an adult A. afarensis found in Hadar, Ethiopia. But the foot also has characteristics very similar to those of the monkey, characteristics that would have allowed the young man to hang on to his mother while she was climbing the trees herself or her mother was saved.
"This foot is very human and indicates that the child Dikika was walking on two legs," DeSilva told Gizmodo. "However, the bone at the base of our big toe – called medial cuneiform – has a link to the big toe that is more curved and slightly sloping than what is found in humans today. Such a curved surface would allow the movement of this big toe – which modern monkeys use to grasp.We conclude, and from past studies on the shoulders of the child Dikika, that she could have climbed, and also grabbed her mother during the trip. "
As the researchers point out, Dikika's child's physique features suggest that she was probably a better climber than adults, and that she, like the others A. afarensis spent more time in the trees than her parents.
"They were smaller, probably more mischievous, and also had to rush into the trees to get away from predators more often than adults" DeSilva. "We think it helps to explain the differences we see between the child's bones Dikika and the more human bones of adults."
Or as the authors write in the study:
The child Dikika was similar in size to a comparably aged chimpanzee and was probably still dependent and perhaps often actively engaged in adults. Given the energy costs of carrying infants, adults and juveniles may have benefited from the presence of [climbing traits] in the juvenile foot of A. afarensis .
As A. afarensis evolved the ability to walk upright on earth, this species, and especially its children, still retained the ability to climb trees. These two abilities were probably a very good adaptation in an African ecosystem rich in dangerous predators.
The deduction of fossil behaviors is a precarious exercise, so they are, at best, enlightened assumptions. More fossils are needed, but this turns out to be a rare commodity for this period. As it was noted, the child Dikika lived about 3.32 million years ago and his fossil was compared to Lucy, who is about 3.2 million years old, and to footprints from Laetoli, which are about 3.6 million years old.
"For your readers, these dates may seem to be pretty much in the same state of mind, but in reality, the Dikika child lived 120,000 years before Lucy, and Lucy lived more than 400,000 years after these footprints were made, "said DeSilva. "Fossils are rare, and these time scales are so vast, we probably miss a lot of things happening at that time! But, you work with what you have, and make adjustments when new fossils are inevitably discovered. "
[Science Advances]
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