If so, then Ardi and her compatriots, who were close in size to chimps, most likely split their time between walking on all fours and moving through trees, he argued April 2019 in eLife. ramidus had a foot that most closely resembles those of present-day chimps and gorillas. Using the same statistical approach, Prang has previously argued that Ar. The researchers then compared those measurements with comparable ones from other fossil hominids and from living primates. To assess which species possessed especially similar hands, Prang’s team analyzed the sizes and dimensions of four fossils from Ardi’s hands. Still, Prang cautions, chimps have evolved over the past several million years and don’t represent “living fossils” that can be used as stand-ins for the ancient ancestor of humans and chimps. That makes the older chimp lineage a closer relative of early hominids. Not until after Lucy’s kind had died out did bonobos diverge into a species apart from chimps, between 1.6 million and 2 million years ago ( SN: 10/27/16). That fossil species, best known for Lucy’s partial skeleton, inhabited East Africa from around 3.9 million to 3 million years ago. Hand fossils showing a more humanlike design and grip first appeared in a later hominid, Australopithecus afarensis, Prang’s group reports. That hand design was retained by early hominids such as Ardi’s East African species, Ardipithecus ramidus, the team reports February 24 in Science Advances. That ancestor, who lived roughly 7 million years ago, had hands designed much like those of tree-adept, knuckle-walking chimps and bonobos, he and his colleagues say.

“The last common ancestor of humans and chimpanzees was more similar to chimps than to any other living primate,” says paleoanthropologist Thomas Prang of Texas A&M University in College Station. These results, based on statistical comparisons of hand bones from fossil hominids and present-day primates, stoke an ongoing debate not only about how Ardi moved ( SN: 2/22/19) but also what the last common ancestor of humans and chimps looked like ( SN: 12/31/09). One of the earliest known hominids, a 4.4-million-year-old partial skeleton of a female dubbed Ardi, had hands suited for climbing trees and swinging from branches, a new investigation suggests.

Chimpanzee hand fossil