Although researchers have been able to sequence DNA teased out from long-dead samples — the sequencing of a 700,000-year-old horse was reported in 2013 — there's a point at which DNA becomes too degraded to analyze. But proteins persist longer and examining them, Smithsonian.com says, is enabling researchers to glimpse the even more distant past.
A University of Copenhagen-led team of researchers used such a protein-focused approach to examine a 1.77-million-year-old Stephanorhinus tooth. As they report in Nature, the researchers used mass spectrometry to determine what proteins were present in their ancient rhinoceros' dental sample. Based on this, they performed a molecular phylogenetic analysis that indicated Stephanorhinus was a sister group to the clade containing the wooly rhinoceros and Merck's rhinoceros, and not its direct ancestor, as Smithsonian.com notes.
"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," first author Enrico Cappellini from the University of Copenhagen says in a statement. "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."