Washington: A new study has revealed that early human ancestors stopped swinging in trees and started walking on the ground sometime between 4.2 and 3.5 million years ago.
Lead author Gabriele Macho, a paleoanthropologist at the Catalan Institute of Paleontology in Barcelona, and his colleagues made the determinations after analyzing wrist bones from two early hominid relatives: Australopithecus anamensis and Australopithecus afarensis (also known as the "Lucy" fossil). The former species is 600,000 years older than the latter and is believed to be its ancestor.
The researchers performed high-resolution CT scans of the central wrist bones, called capitates, of a modern orangutan, gorilla, chimpanzee and person to see how these bones differ between arboreal animals and more terrestrial ones, reports Discovery News.
They found that full-time tree swingers and dwellers load more force on the little finger side of their hands while terrestrial individuals load the thumb side more.
The researchers observed that the Australopithecus anamensis wrist bones exhibited pressure loads associated with modern arboreal animals.
The analyzed Australopithecus afarensis bones conversely showed stress loads comparable to those of more terrestrial species, including modern humans.
The researchers concluded that the important shift in early hominid lifestyle happened around the time when A afarensis first emerged.
It`s likely that Australopithecus anamensis walked on the ground at times too, but Macho points out that "form follows function."
Other evidence from the early human fossil record supports that major changes took place at about 4.2 million years ago.
Macho explained, "We know from cranio-dental remains that they also broadened their dietary niches and were no longer soft fruit eaters, as the last common ancestor is assumed to have been."
The study was published in the latest issue of Folia Primatologica.