WASHINGTON–The most complete ancient infant has been discovered by an Ethiopian paleoanthropologist in the sandstone of the Dikika region of northern Ethiopia.
The bundle of bones, no bigger than a cantaloupe, is dated to 3.3 million years ago and is arguably the best fossil of its species, Australopithecus afarensis, ever found. That is the same species as the superstar fossil called Lucy, a 3.2 million-year-old adult female discovered nearby in 1974.
“This is something you find once in a lifetime,” says Zeresenay Alemseged of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the team that discovered the baby. Unlike Lucy, the baby has fingers, a foot and a torso. “But the most impressive difference between them is that this baby has a face,” said Zeresenay. (Ethiopians’ first names are their formal names.) The face’s anatomy was key to identifying the fossil as A. afarensis.
The find will be reported in the November issue of National Geographic magazine and is published in the Sept. 21 issue of the journal Nature. A special Web site featuring the entire National Geographic article, unpublished photographs and a podcast interview with the author are live at www.nationalgeographic.com/ngm.
The world’s oldest baby, a three-year-old female who died while still of nursing age, offers new clues about how this early human ancestor blurred the line between ape and human. For example, according to Zeresenay, the shape of the baby’s shoulder blades resembles a young gorilla’s, suggesting she could climb trees. But the angle of the femur from knee to hip is close to that of a modern human, implying she walked efficiently on two legs.
“I see A. afarensis as foraging bipeds (walking on two feet), but climbing trees when necessary, especially when they were little,” Zeresenay said.
Zeresenay, one of the new generation of Ethiopian paleoanthropologists and a 2004 National Geographic Emerging Explorer, first led a band of fossil hunters into the badlands of the Afar depression in 1999. Extreme heat, flash floods, malaria, wild beasts and occasional shootouts between rival ethnic groups plague the harsh region. There was no shade on Dec. 10, 2000, when team members searched under a scorching sun for the prize that had eluded them so far — fossils of hominins.
Expedition member Tilahun Gebreselassie was the first to see the baby’s tiny face peering out from a dusty slope, as Zeresenay worked nearby. It was no bigger than a monkey’s, but a smooth brow and short canine teeth told Zeresenay right away that it was a small hominin. Not only was the baby’s skull in perfect shape, but tucked beneath the head in a hard ball of sandstone were many bones of the upper body.
The cause of the baby’s death was not evident. It appeared that the ancient Awash River had rapidly buried the body in pebbles and sand in a flood event, which was possibly the cause of death. The remains were thus protected from the elements and gradually became fossilized. Etching away sandstone with a dentist’s drill, Zeresenay navigated between tiny vertebrae and ribs so that anatomical details could be seen. The task has taken five years so far.
The payoff: details rarely seen in a fossil australopith, such as a full set of both milk teeth and unerupted adult teeth. Most of her tiny ribs were positioned, as in life, along a sinuous spinal column. One finger was still curled in a tiny grasp. Where her throat once was, Zeresenay found a rare example of a hyoid bone, a bone that was to become crucial to human speech, offering an early glimpse of the evolution of the voice box.
“Outside of its completeness, the major importance of this find is the light it will shed on how this species lived and grew,” said Bill Kimbel of the Institute of Human Origins at Arizona State University, a coauthor of the Nature paper.
“With the entire brain cast we can now examine whether our earliest ancestors grew their brains in the uniquely human way,” said another coauthor, Fred Spoor of UCL (University College London).
From the waist down, the Dikika baby looked like us. One of her humanlike knees was complete with a kneecap no bigger than a dried pea. But her upper body, like Lucy’s, had many apelike features. Her brain was small, her nose flat like a chimpanzee’s, and her face long and projecting. Her finger bones were curved and almost as long as a chimp’s. Her two complete shoulder blades are the first ever found from an australopith individual.
“Analyzing the functional significance of these bones in more detail will be among the exciting challenges that we will face in the coming years,” Zeresenay said.
Zeresenay’s research at Dikika was funded by the National Geographic Society, the Institute of Human Origins, the Leakey Foundation and, since 2004, the Max Planck Institute for Evolutionary Anthropology. About 40 individuals, including seven researchers, have worked to uncover the remains of the baby and interpret the many aspects of the find, including geology and environment (see Nature papers).