Researchers determined how the ancient African species Ardipithecus ramidus is related to humans.
The species, nicknamed "Ardi," was a primate with a small brain and humanlike teeth; it also had feet designed for climbing trees and a pelvis made for walking on the ground, an Arizona State University news release reported.
These strange features have left researchers scratching their heads over where "Ardi" sits on the "tree of human and ape relationships," the news release reported. Scientists wanted to know if the species was an ape that had acquired some humanlike features in its past or if it was a real human ancestor.
In order to gain insight into the mysterious species researchers looked at the base of a "partially-persevered" Ardi skull. The team found patterns that linked the species with Australopithecus and modern humans, but not apes.
"Given the very tiny size of the Ardi skull, the similarity of its cranial base to a human's is astonishing," ASU paleoanthropologist William Kimbel said in the news release.
The cranial base is extremely helpful in gaining insight into the evolution of a species because it can reveal information such as the brain position, posture and chewing system. The human cranial base is unique, and differs greatly from that of apes.
"[The] base is shorter from front to back and the openings on each side for passage of blood vessels and nerves are more widely separated," the news release reported.
Ardi's cranial base had characteristics that are found in humans but not apes. These characteristics were present in Australopithecus skulls 3.4 million years ago.
Researchers are not sure if walking upright changed human ancestor's cranial position or if the changes were influenced by brain shape.
"The Ardi cranial base fills some important gaps in our understanding of human evolution above the neck," Kimbel said. "But it also opens up a host of new questions ... just as it should!"
