WASHINGTON, DC.- A new study co-led by the Smithsonian’s Museum Conservation Institute and Harvard University reveals that 1.5–18 million-year-old mammalian fossils from Kenya contain proteins in their enamel that could be used to interpret their biology and evolution. These findings, published in Nature today, July 9, push the availability of proteins for analysis back over 15 million years, opening the door to a greater understanding of evolution during the Earth’s current geological era, the Cenozoic Era.

Ancient proteins extracted from fossils contribute to a comprehensive picture of how extinct species lived and evolved. Paleontologists have used ancient proteins to reveal unexpected relationships between species on the tree of life, aspect of species’ population structure over large geographic regions and even behavioral adaptations that one cannot observe by solely examining fossilized bone. However, proteins degrade over time, limiting how far back in time they can be used to understand ancient life. They degrade even faster in warm conditions, making it especially difficult to understand the ancient history of tropical ecosystems.

“The ability to use proteins to study ancient life in the Cenozoic has generally been limited to the last few million years,” said Timothy Cleland, a physical scientist at the Museum Conservation Institute and the senior investigator on this study. “The natural degradation of proteins severely limits our ability to gain a full understanding of how these animals lived and evolved. Our findings, however, reveal that protein trapped within dense enamel can persist longer, even in tropical environments where temperature accelerates protein loss, and can reveal details about life much farther back in the fossil record.”

The study demonstrates that protein fragments found in enamel, such as enamelin, ameloblastin and dentin matrix acidic phosphoprotein 1, are present and intact at sufficient concentrations in fossils going back possibly to 29 million years—18 million years with high confidence—meaning these protein fragments can be used to study the biology of extinct species back to the early Miocene, a period when the modern community of African mammals was first taking shape.

The research team analyzed specimens from multiple geological timepoints in the Turkana Basin, Kenya, which has produced the richest record of Cenozoic mammal evolution in eastern Africa and is also one of the hottest regions in the world. They examined protein fragments ranging from 1.5 million-year-old elephant fossils to 29 million-year-old fossils from Arsinoitheriidae, a family of extinct, rhinoceros-like ungulates. The team found that the youngest fossils contained the highest count of intact peptide fragments, and that despite the hot, arid environment in which these proteins sat for millions of years, the team could be confident in the protein record stretching through roughly a third of the Cenozoic Era.

“Ancient DNA has produced a revolution in our understanding of recent human origins,” said Daniel Green, field program director at Harvard University and the study’s lead author. “We hope that paleoproteomics may lead to a similar revolution in the study of evolutionary processes that occurred many millions of years earlier.”

For Green, one of the study’s most important findings is just how much information can be safely stored inside tooth mineral over tens of millions of years. “These are the hardest structures in our bodies, and we already know they contain a detailed chemical record of ancient climate, environment and behavior. These findings show that they also preserve molecular records of evolutionary processes.”

“We were thrilled to discover that these protein fragments persist for millions of years longer than expected and are excited to pursue new and long-standing macroevolutionary questions using ancient proteins in fossil teeth,” said Kevin Uno, an associate professor of human evolutionary biology at Harvard University and one of the leaders of the American, European and African consortium conducting the research.

The presence of these protein sequences within enamel tissues in one of the most reliably warm regions in the world indicates that in the future, paleontologists may discover proteins in even older fossils that will support the study of prehistoric evolution and biology among species around the globe.