Study shows proteins in eggshells can survive much longer than previously thought.
Ancient ostrich shells are a common find at paleontological sites in Africa. Being thick and tough, these shells are able to withstand harsh environmental conditions over time.
The proteins in these eggshells are also hardy, according to a new study published in eLife, and can survive as long as 3.8 million years. These ancient proteins could yield genetic information roughly 50 times older than any ancient DNA on record.
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A team of researchers was tracking egg fossils across Tanzania and South Africa — places so hot that DNA and proteins in ancient shells are expected to have become degraded long ago.
“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,” says lead researcher Matthew Collins, from the University of York, in a press release.
Compared to other fossil materials, the protein in ostrich eggshells was able to survive over a much longer period. Through modeling, the researchers determined the key to the proteins’ longevity was their strong binding to mineral surfaces in the shell, which kept the proteins from decaying.
"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 analysing fossils of this kind,” said study co-author Colin Freeman, from the University of Sheffield.
They were surprised to find that it was the most unstable regions of the proteins that tended to preserve the best, as they were” able to bind more strongly to the eggshell,” according to first author Beatrice Demarchi, from the University of York.
Fragments of proteins have been found in even older fossils, but the researchers note that being able to extract entire protein sequences will offer new insights. For example, it will open up new avenues for inferring evolutionary relationships, which often rely on comparisons of bone shapes.
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