The dikika foot is a part of a partial skeleton of a 3.32-million-year-old skeleton of an Australopithecus afarensis child. Credit: Zeresenay Alemseged
More than 3 million years ago, our adult human ancestors were walking on two feet and not have the option of a fashionable baby sling to carry their children in. Instead, the Australopithecus afarensis toddlers had a special grab teen who helped them on their mothers, and escape into the trees, reports a study published 4 July in the Science Progress.
The evidence comes from THICK-1-1 — a relatively complete 3.3 million-year-old skeleton of a 2.5 – to 3-year-old female Australopithecus afarensisdiscovered in the dikika, Ethiopia. The skeleton, nicknamed Selam — after the word for peace in Ethiopia’s official language of Amharic, contains the oldest and most complete foot bones of this species ever found. [Image Gallery: 3-Year-Old Human Ancestor ‘Selam’ Revealed]
“It is a very exciting discovery,” said Will Harcourt-Smith, a paleontologist at the American Museum of Natural History in New York, who was not involved in the study, and was a reviewer of the paper. “It is really special and really allows us to learn something more about this creature.”
Man-like, with a chimpanzee-like toe
Zeresenay Alemseged, a paleoanthropologist at the University of Chicago, discovered Selam’s preserved skeleton in 2000. The skeleton was initially given the name “Lucy’s baby” because of its close proximity to the adult female A. afarensis fossil dubbed Lucy, found in 1974. But Selam is actually dead is more than 100,000 years before Lucy was still alive.
Selam foot was later discovered in 2002 and is approximately 2 cm (5.5 inches) long — that is a bit shorter than a sticky note. The structure of the ankle, and the general anatomy of the foot is the same as that of the modern man, with a clear difference: The big toe is curved, similar to a chimpanzee. But in contrast to the chimpanzee’s big toe, Selam is in line with her other toes, similar to the toes on a human foot.
“So, it is a man-as in not sticking out to the side, but it had a lot more mobility, and would be likely to move and grab on to stuff. Not [as] a chimpanzee, but certainly more than a man could,” said Jeremy DeSilva, a paleoanthropologist at Dartmouth College in New Hamphshire and lead author of the study.
The anatomy of Selam heel was also surprising, he said. Lucy and other adult A. afarensis fossils had robust heel bone, which are similar to those in the human being is born with, and they are suitable for walking upright. But Selam heel was relatively small and delicate. “So that suggests that [A. afarensis] grew their heels quite differently than we do,” DeSilva told Live Science. “Even though we have the same anatomy they had, we were different.”
Climb, but walk more
Selam’s curved toe suggests that A. afarensis babies and toddlers were grabbing their mother’s body is worn and were also in climbing trees for food or protection, especially in the night. That is an inference on the basis of the fact there is no evidence of a fire or a construction for a million years in Africa, said DeSilva. “We also have fossils of very large predators,” he said. “I can’t image how they would have survived if they were not in the trees at night.”
But they were still not great climbers, explained to Carol Ward, an anatomist and paleoanthropologist at the University of Missouri, who was not involved in this research, but the analysis of Selam’s spine and ribs. “Even if a baby could have more things between the first and the second toe, it would not have had the seizing of opportunities, such as a monkey,” Ward told Live Science in an e-mail. She said Selam’s foot is clearly adapted for walking on two feet and demonstrates “how important the life on the ground was for these animals, and that effective climbing was much less important.”
Although Selam’s foot is relatively complete, there are missing pieces of cartilage that rotted over time. “That makes it a little difficult to say what you want about how the joints work,” Harcourt-Smith Live Science. For example, the researchers “claim that the bow is low and maybe flat in this person, and I think they are probably correct, but it should be taken with a little salt,” he said.
Nonetheless, this discovery is unprecedented and “let us go on to the study of the growth and development of our ancestors in a way that we haven’t,” said DeSilva. “It opens up this window into what the life of a child of 3 million years ago.”
Original article on Live Science.