Scientists from Denmark and the UK say they have extracted genetic information from a 1.7-million-year-old rhino tooth, making it the largest and oldest genetic data ever recorded.
Members of the same team set the previous record in 2013 when they revealed they had sequenced the bone remnants of a horse frozen for 700,000 years in the permafrost of Yukon, Canada.
In the new work, described in a paper in the journal Nature, the researchers identified an almost complete set of proteins – a proteome – in the dental enamel of a fossil discovered in Dmanisi, Georgia.
The project brought together scientists from the University of Copenhagen, Denmark, and St John's College, University of Cambridge, London. Their subject was a Stephanorhinus, an extinct rhinoceros which lived in Eurasia during the Pleistocene (1.6 million to 10,000 years ago).
"For 20 years ancient DNA has been used to address questions about the evolution of extinct species, adaptation and human migration but it has limitations,” says first author Enrico Cappellini, from Copenhagen’s Globe Institute.
“Now for the first time we have retrieved ancient genetic information which allows us to reconstruct molecular evolution way beyond the usual time limit of DNA preservation.
"This new analysis of ancient proteins from dental enamel will start an exciting new chapter in the study of molecular evolution."
DNA data that genetically tracks human evolution only covers the last 400,000 years, the researchers say, but the lineages that led to modern humans branched apart around six to seven million years ago, meaning there is no genetic information for more than 90% of the evolutionary path.
In this study, they discovered that the proteins in the rhino’s tooth enamel – the hardest material present in mammals – had lasted longer than DNA and was more genetically informative than collagen, the only other protein so far retrieved from fossils older than one million years.
"Dental enamel is extremely abundant and it is incredibly durable, which is why a high proportion of fossil records are teeth,” Cappellini says.
"We have been able to find a way to retrieve genetic information that is more informative and older than any other source before, and it's from a source that is abundant in the fossil records so the potential of the application of this approach is extensive."
This rearranging of the evolutionary lineage of a single species may seem like a small adjustment, the researchers say, but they believe identifying changes in numerous extinct mammals and humans could lead to massive shifts in our understanding of the way the world has evolved.
"This research is a game-changer that opens up a lot of options for further evolutionary study in terms of humans as well as mammals,” says lead author Eske Willerslev, who also was a lead author of the 2013 study.
“It will revolutionise the methods of investigating evolution based on molecular markers and it will open a complete new field of ancient biomolecular studies."