Geologists Help Find And Explain Earliest Known Human Ancestor Child

The fossil bones were found in an area not far from where the landmark "Lucy" remains were discovered in 1974. Lucy was an unusually complete adult specimen of the up-right walking genus Australopithecine given the new species name "afarensis" because it was found in Afar in the Hadar region of Ethiopia. Because the new fossil was also found in Hadar, the popular press has dubbed the new 3.3 million year-old child fossil bones "Lucy's child."

"Not only is this fossil the oldest juvenile hominid discovered to date, the fossil is remarkably well preserved for a specimen of such antiquity," said Wynn. "Juvenile specimens in such a pristine state of preservation are known from much later species, such as the Neanderthals, while most of the early pre-humans are known from a few teeth and isolated and disarticulated bones."

By contrast, "Lucy's child" preserves a nearly complete upper body, with the complete face and features of the brain preserved in detail. Scientists found the three-year-old child's almost complete skull associated with scapulae (shoulder bones) and clavicles, some vertebrae, some rib bones and fingers, parts of leg bones and metatarsals, all buried, most likely by a flood, soon after the child died. The more non-human-like nature of the shoulder, leg and fingers bones have lead scientists to speculate that this Australopithecine may have spent considerable time in arboreal as well as terrestrial locomotion; climbing in trees as well as walking the earth. More delicate bones, such as the hyoid bone (important for human speech) and scapula, are preserved in anatomical precision.

"This unique preservation will provide anthropologists with many clues as to early human adaptations such as upright walking and the potential for - or lack of - the capacity for speech," noted Wynn. Wynn provided geological expertise to help explain the geological context of the find and co-authored a number of the papers and said the unique state of preservation of this fossil is a direct result of the geological environment in which it lived 3.3 Million years ago.

"In this part of Ethiopia's developing rift valley, the floor of the rift was dropping down very rapidly due to the spreading of Earth's crustal plates that define the rift zones of East Africa," explained Wynn. "Rapid rates of tectonic activity provided the setting for rapid accumulation of sediments which buried the fossil shortly after death."

The fossil was buried in sediments of a delta which accumulated during a flooding event. The child may have died in the flood, or at least only a few days prior. Because the fossil was buried shortly after death, it was encapsulated in sediment as a corpse, leaving the anthropologists to later extract the bones preserved in exquisite detail.

"Our approach also provided answers about the paleoenvironment and the complex geological history of the site," said Wynn. "We were also able, through an examination of the local geology, and especially the active volcanic history of the region, to provide a solid geological date for the fossil."

Diana Roman, a volcanology professor at the University of South Florida and a co-author on the Nature paper, used chemical "fingerprints" preserved in volcanic glass to identify unique eruptions of known geological age that were used to "bracket" the age of the fossil.

"Volcanoes thought to have been active during the time that "Lucy's child" lived, and which are preserved in the geological record, may have influenced the local environments and influenced the habitats that the she lived in," suggested Roman.

Wynn and coauthors reported that other fossils found at the site provide evidence of a range of habitats in the local environment. Fossils of hippo, crocodile and freshwater snails show that permanent water was present in the delta at the intersection of a river and a lake. Other fossils of antelopes are similar to modern East African antelopes that live in closed woodlands, while species such as the white Rhino, elephants, and relatives of the wildebeest, show that savanna grasslands were also present.

"Our analysis indicates that a mosaic of habitats were present, and all of these environments were close enough that "Lucy's child" and her immediate family would have been able to find refuge and food resources in some of the more densely wooded habitats like the forests, but also would have been able to exploit food resources in the grasslands nearby," concluded Wynn.