Old World monkeys, a group including baboons and macaques, and apes such as gorillas and chimpanzees, evolved a way of moving that was different from that of their common ancestral species, according to a study.
The researchers, from the American Museum of Natural History in the US, analysed the first well-preserved femur of Aegyptopithecus zeuxis -- a common ancestor of Old World monkeys and apes.
The results of the study, published in the journal Nature Communications, suggested that apes and old world monkeys each evolved a way of moving that was different from the ancestral species as they adapted to different niches in their environments.
"Our study shows that Aegyptopithecus preserves an ancient hip morphology not present in living anthropoid primates," said Sergio Almecija, first author of the study from the American Museum of Natural History.
The fossil analysed by the researchers was discovered in 2009 and is the most complete femur of the common ancestor Aegyptopithecus -- likely a tree-dwelling species weighing about 7 kilogrammes that lived in what is now Egypt about 30 million years ago.
The researchers said this was close to the time when hominoids -- the group that includes apes and humans -- split from the larger group that includes Old World monkeys.
The femur was well preserved, the researchers said, allowing them to infer details about the hip joint -- a major anatomical region for inferring locomotion.
Using a combination of 3D shape analysis, and modeling of the evolutionary connection between related species. the researchers compared the fossil femur to other extinct and modern species like humans, chimpanzees, and Victoriapithecus and Homunculus.
"As far as the hip is concerned, it seems that apes, humans, and Old World monkeys have all parted ways long ago -- which would explain why they move around so differently today," Almecija said.
The ancestral hip joint, the researchers said, is as far from those of modern Old World monkeys as from those of the great apes.
This dissimilarity, the researchers said, meant each group evolved a distinct way of moving as they specialized for success in different environmental niches.
The researchers also suggested that living great apes such as orangutans, chimpanzees, and gorillas may have independently developed similar hip joints that allow them to have wide-ranging, flexible movement through their arboreal habitats.
"What I find really exciting about the modeling approach is that we can develop better hypotheses about what drove the divergence of apes and monkeys, and the emerging picture is that navigating the environment is one of the key factors," said Ashley Hammond, co-author of the study from the American Museum of Natural History.
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