Featured Research

from universities, journals, and other organizations

'Ardi' skull reveals links to human lineage

Date:
January 6, 2014
Source:
Arizona State University
Summary:
One of the most hotly debated issues in current human origins research focuses on how the 4.4 million-year-old African species Ardipithecus ramidus is related to the human lineage. New research confirms "Ardi's" close evolutionary relationship to humans. Researchers turned to the base of a beautifully preserved partial cranium of Ardi, which reveals a pattern of similarity that links Ardi to Australopithecus and modern humans and but not to apes.

The 4.4 million-year-old cranial base of Ardipithecus ramidus from Aramis, Middle Awash research area, Ethiopia.
Credit: Image courtesy of Tim White

One of the most hotly debated issues in current human origins research focuses on how the 4.4 million-year-old African species Ardipithecus ramidus is related to the human lineage. "Ardi" was an unusual primate. Though it possessed a tiny brain and a grasping big toe used for clambering in the trees, it had small, humanlike canine teeth and an upper pelvis modified for bipedal walking on the ground.

Scientists disagree about where this mixture of features positions Ardipithecus ramidus on the tree of human and ape relationships. Was Ardi an ape with a few humanlike features retained from an ancestor near in time (between 6 and 8 million years ago, according to DNA evidence) to the split between the chimpanzee and human lines? Or was it a true relative of the human line that had yet to shed many signs of its remote tree-dwelling ancestry?

New research led by Arizona State University paleoanthropologist William Kimbel confirms Ardi's close evolutionary relationship to humans. Kimbel and his collaborators turned to the underside (or base) of a beautifully preserved partial cranium of Ardi. Their study revealed a pattern of similarity that links Ardi to Australopithecus and modern humans, but not to apes.

The research appears in the Jan. 6-10 online edition of Proceedings of the National Academy of Sciences. Kimbel is director of the ASU Institute of Human Origins, a research center of the College of Liberal Arts and Sciences in the School of Human Evolution and Social Change. Joining ASU's Kimbel as co-authors are Gen Suwa (University of Tokyo Museum), Berhane Asfaw (Rift Valley Research Service, Addis Ababa), Yoel Rak (Tel Aviv University) and Tim White (University of California at Berkeley).

White's field-research team has been recovering fossil remains of Ardipithecus ramidus in the Middle Awash research area, Ethiopia since the 1990s. The most recent study of the Ardi skull, led by Suwa, was published in Science in 2009, whose work (with the Middle Awash team) first revealed humanlike aspects of its base. Kimbel co-leads the team that recovered the earliest known Australopithecus skulls from the Hadar site, home of the "Lucy" skeleton, in Ethiopia.

"Given the very tiny size of the Ardi skull, the similarity of its cranial base to a human's is astonishing," says Kimbel.

The cranial base is a valuable resource for studying phylogenetic, or natural evolutionary relationships, because its anatomical complexity and association with the brain, posture and chewing system have provided numerous opportunities for adaptive evolution over time. The human cranial base, accordingly, differs profoundly from that of apes and other primates.

In humans, the structures marking the articulation of the spine with the skull are more forwardly located than in apes, where 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.

These shape differences affect the way the bones are arranged on the skull base, such that it is fairly easy to tell apart even isolated fragments of ape and human basicrania.

Ardi's cranial base shows the distinguishing features that separate humans and Australopithecus from the apes. Kimbel's earlier research (with collaborator Rak) had shown that these human peculiarities were present in the earliest known Australopithecus skulls by 3.4 million years ago.

The new work expands the catalogue of anatomical similarities linking humans, Australopithecus and Ardipithecus on the tree of life, and shows that the human cranial base pattern is at least a million years older than Lucy's species, A. afarensis.

Paleoanthropologists generally fall into one of two camps on the cause of evolutionary changes in the human cranial base. Was it the adoption of upright posture and bipedality that caused a shift in the poise of the head on the vertebral column? If so, does the humanlike cranial base of Ar. ramidus confirm postcranial evidence for partial bipedality in this species? Or, do the changes tell us about the shape of the brain (and of the base on which it sits), perhaps an early sign of brain reorganization in the human lineage? Both alternatives will need to be re-evaluated in light of the finding that Ardi does indeed appear to be more closely related to humans than to chimpanzees.

"The Ardi cranial base fills some important gaps in our understanding of human evolution above the neck," adds Kimbel. "But it also opens up a host of new questions . . . just as it should!"


Story Source:

The above story is based on materials provided by Arizona State University. The original article was written by Julie Russ, Institute Of Human Origins. Note: Materials may be edited for content and length.


Journal Reference:

  1. William H. Kimbel, Gen Suwa, Berhane Asfaw, Yoel Rak, and Tim D. White. Ardipithecus ramidus and the evolution of the human cranial base. Proceedings of the National Academy of Sciences, 2014 DOI: 10.1073/pnas.1322639111

Cite This Page:

Arizona State University. "'Ardi' skull reveals links to human lineage." ScienceDaily. ScienceDaily, 6 January 2014. <www.sciencedaily.com/releases/2014/01/140106160041.htm>.
Arizona State University. (2014, January 6). 'Ardi' skull reveals links to human lineage. ScienceDaily. Retrieved August 21, 2014 from www.sciencedaily.com/releases/2014/01/140106160041.htm
Arizona State University. "'Ardi' skull reveals links to human lineage." ScienceDaily. www.sciencedaily.com/releases/2014/01/140106160041.htm (accessed August 21, 2014).

Share This




More Fossils & Ruins News

Thursday, August 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Disquieting Times for Malaysia's 'fish Listeners'

Disquieting Times for Malaysia's 'fish Listeners'

AFP (Aug. 19, 2014) Malaysia's last "fish listeners" -- practitioners of a dying local art of listening underwater to locate their quarry -- try to keep the ancient technique alive in the face of industrial trawling and the depletion of stocks. Duration: 02:29 Video provided by AFP
Powered by NewsLook.com
Mother And Son Find Woolly Mammoth Tusks 22 Years Apart

Mother And Son Find Woolly Mammoth Tusks 22 Years Apart

Newsy (Aug. 15, 2014) A mother and son in Alaska uncovered woolly mammoth tusks in the same river more than two decades apart. Video provided by Newsy
Powered by NewsLook.com
Fossils Reveal Ancient Flying Reptile With 'Butterfly Head'

Fossils Reveal Ancient Flying Reptile With 'Butterfly Head'

Newsy (Aug. 14, 2014) Newly found fossils reveal a previously unknown species of flying reptile with a really weird head, which some say looks like a butterfly. Video provided by Newsy
Powered by NewsLook.com
Clearing WWII's Explosive Legacy in the Pacific

Clearing WWII's Explosive Legacy in the Pacific

AFP (Aug. 11, 2014) The hulks of tanks can still be found rusting in the jungles of Palau, but the fierce fighting that scarred the Pacific island nation in WWII has left a more dangerous legacy - unexploded bombs that pose a constant risk to locals. Duration: 00:47 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins