Proteins from rhino fossil found in Nunavut crater dated to 20 million years

Scientists studying a 21-to 24-million-year-old rhino fossil found in the Haughton Crater on Nunavut's Devon Island say the high Arctic environment preserved the oldest recoverable ancient proteins found so far.

The proteins recovered from the rhino tooth, found decades ago, are 10 times older than any previously recoverable sample of ancient DNA, said Danielle Fraser, the Canadian Museum of Nature's head of paleobiology and one of the research scientists involved in the study. 

The researchers, whose findings were published Wednesday in the journal Nature, say their ability to time stamp the proteins well into "deep time" was made possible with newer technologies, and they say that should encourage future paleontological work in the world's coldest places to gather similarly preserved fossils.

Reconstructing evolution was previously limited to four-million-year-old samples and the ancient proteins identified so far reached only into the middle-late miocene, roughly 10 million years ago. 

Ancient DNA does not typically survive beyond one million years, but the high Arctic's dry, cold environment, and the hardiness of tooth enamel, kept the proteins in the rhino fossil intact. In a lab in Copenhagen, scientists successfully extracted and sequenced data from the proteins inside the tooth, Fraser said.

"It's very clear that the Arctic is creating a freezer allowing these proteins in these animals to be preserved over much longer time periods than we would expect. This really extends our ability to understand evolution back much farther than we previously thought," said Fraser. 

To understand deep time, Fraser says, imagine a clock representing the entire history of the evolution of life on earth.

"Humans are the last few milliseconds on that clock right before you hit the 12," she said. "And that 23 million years is going to be about five minutes ago."

This scientific study analyzed highly-preserved fossils by looking at their ancient proteins, rather than morphology — what the bones look like compared to each other — to determine an extinct species' evolutionary path. 

Rhinos once lived across the world, with some debate about whether the species originated in Asia or North America. Ancient DNA science can provide better insight into how and when they evolved, said Fraser.

Rhino evolution 

Modern rhinos are thought to have diverged from other rhinocerotids during the Middle Eocene-Oligocene, between 25 and 41 million years ago. 

The study's authors say their research supports the divergence of two main subfamilies of rhinos (Elasmotheriinae and Rhinocerotinae), and a bone analysis suggests a more recent split, roughly 22 to 34 million years ago.

The unique environment of the Haughton Crater on Devon Island is promising for future studies on preserved proteins, said Fraser.

The rhino fossil was collected decades ago by the late Mary Dawson, a vertebrate paleontologist from Philadelphia's Carnegie Museum of Natural History. Dawson collected it in 1986 at a time when protein extraction and ancient DNA technology "effectively didn't exist," according to Fraser.

Fraser said in recent years, teams working on Devon Island or Ellesmere Island have worked with local community members like Jarloo Kiguktak of Grise Fiord, Nunavut. Kiguktak, an experienced fossil collector, said he joins the researchers on their search for specimens.

How did they do it?

The study's authors say they sequenced enamel proteins from the rhino fossil and more than 1,000 amino acid chains (peptides), which are the building blocks of proteins.

They confirmed the proteins were ancient by matching the signs of age-related damage to expected burial conditions more than 20 million years ago in the Arctic environment, the researchers said. 

Dental enamel is the hardest material of vertebrates and it protects the proteins from breaking down over time, the research states.

Fraser said while paleontology may sometimes be seen as "nerds studying their dinosaurs," these findings allow for reconstruction of molecular patterns.

"We are nerds, and we love studying our fossils," she said.

The fossil record is the "only record of the ancient world," and of animal species' long-term response to changes in climate, she said.