by Dan Jenk

The discovery of a nearly intact 3.3 million year-old juvenile skeleton has scientists talking. The find will fill an important gap in understanding the evolution of a species thought to be among the earliest direct ancestors to humans.

William Kimbel is a paleoanthropologist with ASU’s Institute of Human Origins. He is part of the team that studied the skeleton. The bones belong to an approximately 3-year-old female Australopithecus afarensis. She was found in Dikika, Ethiopia more than five years ago. The skeleton belongs to the same species as Lucy, one of the most well known fossils ever found.

Kimbel says that the infant Dikika skeleton is expected to provide an important reference point for scientists. It will help them explain how changes in growth and development contributed to the evolution of humans.

“It’s extraordinarily rare to have such a complete skeleton,” says Kimbel, science director at IHO. “It’s unprecedented to have such a complete skeleton of a young child.”

The researchers described their discovery and initial analysis in a paper published in the Sept. 21, 2006 issue of the journal Nature. The skeleton was discovered by lead author Zeresenay Alemseged, director of the Dikika Research Project and a former IHO postdoctoral researcher.

The skeletal remains include the skull and jaws with teeth, and parts of the shoulders, spinal column, ribs, right arm, fingers, legs and left foot. Alemseged has been preparing the skeleton for the last five years. He must carefully chip away sandstone from the fragile bone fragments. It will be several more years before the preparation is complete.

Kimbel says the findings are expected to provide insights into the growth and development cycle of Australopithecus afarensis. The infant remains will be compared to Lucy. That remarkably complete adult female skeleton was among the first Australopithecus afarensis to be discovered. Lucy dates back 3.18 million years. She was discovered in 1974 in the Hadar region of Ethiopia by Donald Johanson, who directs ASU’s Institute of Human Origins.

“Most differences between humans and their ancestors can be associated with developmental changes,” Kimbel explains.

The genetic makeup of humans is very similar to that of our close relatives, like the chimpanzee. As a result, most anatomical differences are explained by changes in the pattern of growth from infant to adult.

Understanding growth and development and how it has changed in human ancestry is central to the study of human evolution, Kimbel says. Information about growth and development can help scientists to answer questions about the mechanisms that drove changes in body form that we see in the fossil record.