‘Little Foot’ older than ‘Lucy’, analysis finds

Chuck Bednar for redOrbit.com – @BednarChuck
Using advanced dating techniques, a team of researchers from Purdue University and colleagues from France, Canada and South Africa have discovered that the rare and nearly complete “Little Foot” Australopithecus skeleton is among the oldest hominid remains ever discovered.
In a study published online Wednesday by the journal Nature, a team led by Dr. Ryan Gibbon of the University of New Brunswick’s Department of Anthropology revealed that a radioisotopic dating method known as isochron burial dating concluded that Little Foot was 3.67 million years old, making it an older relative of the 3.2 million-year-old Australopithecus skeleton “Lucy.”

Little Foot is kind of a big deal
Little Foot was discovered by Ronald Clarke, a professor in the Evolutionary Studies Institute at the University of the Witwatersrand, 21 years ago in a cave at Sterkfontein, South Africa. Stone tools found at the same location have been dated at 2.18 million years old, making them some of the oldest known stone tools in South Africa, the researchers said in a statement.
Clarke explained that the fossil represents a species known as Australopithecus prometheus, a vastly different creature from its contemporary Australopithecus afarensis that is more similar to the Paranthropus lineage of hominid. He added that the study serves as a reminder that there may have been many Australopithecus species in Africa, each with different backgrounds.
“It is important to remember that we base our understanding of evolutionary scenarios on a small number of sites with only a few fossils from those sites. This new date is a reminder that there could well have been many species of Australopithecus extending over a much wider area of Africa,” Dr. Gibbon told redOrbit via email on Thursday. “We are far from having a complete picture, but this just makes this type of science so exciting.”
“What we are showing is that australopithecines diverged early in their evolution and covered a large geographic area in Africa,” added Dr. Darryl Granger, a professor of earth, atmospheric and planetary sciences at Purdue who co-led the research team. “New discoveries and new dates remind us that human evolution is not necessarily a simple line drawn from one species to another. Later species such as Australopithecus africanus and Paranthropus did not have to evolve from A. afarensis, Lucy’s species.”
Using radioisotopes to accurately date tools and fossils
The method used to date Little Foot and the stone tools, isochron burial dating, determines when a fossil and the rocks surrounding it were first buried underground by measuring the radioactive isotopes aluminum-26 and beryllium-10 in quartz contained within rock samples. Those isotopes build up when the rock is on the surface and decay when it becomes buried or deposited.
The ratio of the remaining aluminum-26 and beryllium-10 (the stuff which hasn’t already decayed) can be used to determine how long the rock has been underground, the research team noted. An isochron (a graph of isotope ratios) is created to gauge the accuracy of the dating. Using this technique, the study authors said that they came up with a relatively small margin of error of just 160,000 years for Little Foot and 210,000 years for the stone tools.
“Earlier dating with cosmogenic nuclides was criticized because material could have washed in separately from the fossil,” Dr. Granger told redOrbit. “In this work we date a variety of different rocks, ranging from fist-sized to fine sand, and from soil to freshly broken bedrock. “
“We show that they all came in at once, and that the sediment around the fossil accumulated rather quickly,” he added. “This effectively rules out the earlier criticism, allowing a much greater confidence in the reliability of the age. We can be certain that the sediment and the fossil within it came into the cave through the same entrance and at the same period in time.”
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