Researchers say they have identified fossil proteins in a 3.8 million-year-old ostrich eggshell, suggesting that proteins could offer valuable new insights into the evolutionary tree, much further back in time than was previously thought.
The study (“Protein Sequences Bound to Mineral Surfaces Persist into Deep Time”), published in the journal eLife, demonstrates that survival of protein fragments in the ancient eggshell may provide genetic information almost 50 times older than any DNA record.
The findings shed new light on how animals and humans lived and interacted in the past, how some species became extinct, and why some evolved and continue to thrive today. Crucially, the research provides archaeologists with the ability to be more targeted in which fossils they submit for deeper analysis.
The team at the Universities of York, Sheffield, and Copenhagen analyzed and tracked egg fossils from well-dated sites in Tanzania and South Africa, where it is expected that DNA and proteins would not survive the extreme environmental conditions.
“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 Matthew Collins, Ph.D., from the University of York's Department of Archaeology, who led the team. “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.”
The researchers speculated that proteins might survive better if they were stuck onto solid surfaces, and so they tested the theory with the support of computational scientists at the University of Sheffield, who modeled the binding of proteins in ostrich eggshells.
According to Beatrice Demarchi, Ph.D., from the University of York's Department of Archaeology, “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.
“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.”
Fragments of ancient ostrich eggshells are abundant in Africa and often found at archaeological and palaeontological sites. They were exploited by the earliest modern humans as raw materials to make art and jewelery or for carrying water. The shell is very thick and hardwearing and therefore survives under many different environmental conditions.
Colin Freeman, Ph.D., from the University of Sheffield, noted that “Remarkably, the oldest eggshell in the study—from the 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.”
“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.”