November 18 () –
The teeth of an extinct monkey species are a clue to correct downward the ages of fossils of human ancestors throughout South Africa.
A study by University of Oregon anthropologist Stephen Frost and a team of colleagues updates the proposed ages of key fossil sites in South Africa, sites that hold important clues to human evolution.
The results suggest that the oldest hominin fossils in South Africa are no more than 2.8 million years old. That number contradicts other recent studies that use different methods to propose dates as old as 4 million years ago.
Frost and his colleagues report the findings in a paper published Oct. 24 in Proceedings of the National Academy of Sciences. Frost collaborated closely with Hunter College’s Chris Gilbert, as well as UO anthropologist Frances White and graduate student Hailay Reda. “The ages of these things matter a lot”, Frost said.
Changing the age of a fossil also changes the context around it, and therefore the explanations scientists propose. to weave disparate fossils into a cohesive evolutionary story. The ages of the South African fossil beds have been controversial for years, and paleoanthropologists have proposed a wide range of possible dates.
“South Africa was the first place where these really early human fossils were discovered,” Frost said. it’s a statement. But because of the way they were collected, sometimes dynamite was involved, “much of the evidence for the antiquity of these deposits has been destroyed.”
To estimate the dates at the fossil sites, the team used the teeth of Theropithecus oswaldi, a species of monkey that went extinct about half a million years ago. Over time, monkey teeth have gotten bigger and bigger, in a way that can be captured in a mathematical equation. So by looking at the size of the teeth found at a particular site, scientists can estimate when they and other nearby fossils formed.
T. oswaldi is a good candidate for this type of comparative analysis, Frost said. The teeth of the species are abundant; they are found at all the key sites where hominin fossils have also been discovered. And they are usually plentiful, which reduces the risk of a few outliers removing the data.
In fact, more than 30 years ago, scientists used fossil monkeys to estimate the ages of fossil beds in South Africa. But with many more samples and better technology now available, Frost and his colleagues thought it was time to reevaluate.
“The techniques we’ve used have been around for a long time and have proven to be very powerful,” Frost said. “Due to time constraints, the estimates were broader 30 years ago.”
The researchers combined the monkey tooth data with other dating methods, such as measuring magnetic signatures and radioactive isotopes in rocks.
Some recently published papers have used newer dating methods suggesting much older ages for some South African fossil beds. When that research came to light this summer, Frost and his team had already been working on their reassessment of the same areas. And his method returned different results for certain key sites.
The disparity in dates affects how scientists interpret the fossils found at those sites. A particularly prominent example is Little Foot, one of the most complete early human skeletons ever discovered.
Some studies have suggested that the fossil is 3.67 million years old, but Frost’s data suggests it’s about a million years younger than that. (His team’s finding lines up with other estimates made using uranium-lead radiometric dating.)
Frost hopes the results will spark further conversation and research on the ages of hominid fossils found in South Africa. Other researchers could make similar updates to age estimates made by comparing between sites of other species.
“Ultimately getting good age estimates for these South African sites has been a search for the Grail for 75 years or moreFrost said. “I hope other experts on different animal groups will make similar updates. This would be much stronger if it were in all fossils.”
