'Ardi' skull reveals links to human lineage

January 6, 2014

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. Ardipithecus ramidus bones Download Full Image

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 ASU 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!"

Julie Russ

Assistant director, Institute of Human Origins


Knowledge of anatomy advances via crowdfunding project

January 6, 2014

Furthering our understanding of the workings of muscles, joints and other body parts without harming the subjects being studied is the goal of an Arizona State University professor and her students. The research team is turning to the public for help through crowdfunding for its “Imaging the Future” project.

In the laboratory of Lara Ferry of ASU’s New College of Interdisciplinary Arts and Sciences, undergraduate students conduct their own independent research projects using cutting-edge visualization tools to identify novel or abnormal bones, muscles or other tissue complexes, without harm to the specimen. Ferry, Lara Download Full Image

“This means we can study live specimens, or fragile museum specimens that are hundreds of years old in some cases, without harm to the specimen,” said Ferry, who teaches courses in New College’s bachelor’s degree program in life sciences. New College is the core college on ASU’s West campus.

Imaging the Future is among the first of several ASU research projects currently kicking off crowdfunding campaigns. The campaigns are part of ASU’s new, official crowdfunding program, managed by the ASU Foundation for a New American University. Several student ventures have already launched campaigns through the program.

Now, the Office of Knowledge Enterprise Development (OKED) is managing a new effort for faculty research, kicking off a rolling pilot period that began in December and continues through 2014.

Crowdfunding is a means of securing financial support by helping individuals tap into their networks through the Internet. While a lot of research funding relies on receiving large amounts of money from a single donor, crowdfunding campaigns usually succeed through small donations from many individuals.

Support for Imaging the Future helps undergraduate students make substantive contributions to the project. Ferry is typical of New College faculty members in that she strongly supports undergraduate research opportunities.

“Besides being a leading researcher in the field of functional morphology, Dr. Ferry has a strong reputation for being an incredible mentor to graduate and undergraduate students alike,” said Misty Paig-Tran, who recently completed her doctorate at the University of Washington, and now works with Ferry as a post-doctoral research assistant.

“I was really impressed by how successful her lab is at incorporating undergraduates into cutting-edge research, and how often these students go on to graduate degrees,” Paig-Tran said. “Dr. Ferry not only mentors students at ASU, but has provided mentoring to a much larger group of students while she served as the president of the American Elasmobranch Society.”

Undergrads working with Ferry make use of sophisticated imaging tools, including microMRI (magnetic resonance imaging) and microCT (computed tomagraphy). Much of the work focuses on fish no bigger than a person’s finger.

“Fishes are the oldest of the vertebrates, and the most diverse,” Ferry explained. “We are making incredible advances in our ability to understand and diagnose function in these organisms. Key questions we are asking in our research are: How do joints work? How are muscles powering a moving system? Ultimately, we are gaining new and exciting information, and taking our understanding deeper than ever before.”

Working with Ferry is enabling Paig-Tran to conduct research and to emulate Ferry’s success as a student mentor.

“I am learning how to mentor students from a variety of backgrounds, an incredibly valuable skill that I will take with me as I transition from post-doctoral scholar to junior faculty,” Paig-Tran said. “This is perhaps the most exciting aspect of the project. Undergraduates tend to address questions in a very different way than doctoral-level personnel. Sometimes this new eye on old problems leads to great ideas and discovery. For many students the opportunity to work with cutting-edge techniques isn’t available until they enroll in graduate school, so being part of a lab that jump-starts this process is really special.”

You can see all of ASU’s crowdfunding campaigns, powered by the USEED platform, at asu.useed.net. Because contributions are made through the ASU Foundation, a nonprofit organization that supports ASU, donations may be considered charitable contributions.

Jan. 18 is the deadline to make a contribution to the Imaging the Future project.

If you are an ASU researcher interested in raising money through crowdfunding, contact Kathryn Scheckel, assistant director of special projects for OKED, at 480-965-9293. If you are an ASU student or staff member interested in crowdfunding, please contact Shad Hanselman, senior director of the Office of Annual Giving at the ASU Foundation, at 480-965-0516.