A multinational team of researchers has uncovered fossil proteins dating back 3.8 million years — a discovery that will enhance future understanding of ancient organisms.
The team has identified fossil proteins in 3.8 million year-old ostrich eggshells. Image credit: Matthew Collins.
Fragments of ancient ostrich eggshells are abundant in Africa, and often found at archaeological and paleontological sites.
They were exploited by the earliest modern humans as raw materials to make art, and jewelry and, or for carrying water. The shell is very thick and hardwearing and therefore survives under many different environmental conditions.
A new study published in the journal eLife suggests that survival of protein fragments in the ancient eggshell could provide genetic information almost 50 times older than any DNA record.
The study’s authors analyzed and tracked egg fossils from archaeological sites in Tanzania and South Africa, where it is expected DNA and proteins would not survive the extreme environmental conditions.
“Twenty-four eggshell samples were sourced from well-dated sites in South Africa and Tanzania: Elands Bay Cave (300-16,000 years), Pinnacle Point Caves (50,000-150,000 years), Wonderwerk Cave (one million years), Olduvai Gorge (1.34 million years) and Laetoli (2.6-4.3 million years),” they said.
The team speculated that proteins might survive better if they were stuck onto solid surfaces.
“Evidence suggested that it was the more fluid, unstable, region of the protein that promoted and regulated mineral growth in the shell, but it was also less likely to survive over time and the intense heat of the African climate,” said study lead author Dr. Beatrice Demarchi, from the University of York, UK.
“As we examined older and older eggshells, we could see that this assumption was surprisingly wrong, as it was in fact the unstable regions that survived the best. They were able to bind more strongly to the eggshell, allowing it be preserved in time.”
“To date, DNA analysis from frozen sediments has been able to reach back to about 700,000 years ago, but human evolution left most of its traces in Africa and the higher temperature there takes its toll on DNA preservation,” said senior author Prof. Matthew Collins, also from the University of York.
“We had known for many years that proteins could give more clues into the past, but when we looked at protein decay in eggshells, it gave us unusual results when compared to other fossil materials and, until now, we have not really known why.”
3.8-million-year-old ostrich eggshell fragments from Laetoli, Tanzania. Image credit: Terry Harrison.
“Ancient proteins derived from the enamel of fossil teeth have the potential to yield important clues to the evolutionary relationships, species identity, sex, and migration patterns of early human ancestors,” said co-author Prof. Terry Harrison, of New York University.
“Remarkably, the oldest eggshell in the study – from the famous 3.8 million year-old site of Laetoli in Tanzania – a region of the protein was still there, giving us a unique insight into what to look for when analyzing fossils of this kind,” said co-author Dr. Colin Freeman, from the University of Sheffield, UK.
“Now that we know minerals can trap and preserve proteins in this way, we can be much more targeted in our study of ancient remains.”
A separate discovery from the team yielded ancient proteins from 1.7-million-year-old tooth enamel of extinct mammals — deer, horses, and rhinoceroses — from the Dmanisi site in Georgia, which is the oldest site outside of Africa bearing the remains of human ancestors.
“These findings open up the possibility of recovering remnants of ancient proteins from the earliest human fossils,” Prof. Harrison said.
_____
Beatrice Demarchi et al. 2016. Protein sequences bound to mineral surfaces persist into deep time. eLife 5: e17092; doi: 10.7554/eLife.17092
