Almost four decades ago, researchers discovered a collection of perfectly preserved fossils inside an impact crater in the Canadian High Arctic. Now, those remains have finally yielded their secrets, revealing they belong to an extinct species of hornless rhinoceros that lived 23 million years ago.
Scientists have named the animal *Epiatheracerium itjilik*, with the species name meaning “frost” or “frosty” in Inuktitut. These creatures were similar in size to modern Indian rhinos (*Rhinoceros unicornis*), according to a statement from the Canadian Museum of Nature (CMN).
The newly identified fossils are the only specimen found to date and show that the animal died as a young adult, though the exact cause of death remains unknown.
“What’s remarkable about the Arctic rhino is that the fossil bones are in excellent condition,” said Marisa Gilbert, a CMN paleobiologist and co-author of a new analysis of the remains. “They are three-dimensionally preserved and have only been partially replaced by minerals. About 75% of the skeleton was discovered, which is incredibly complete for a fossil.”
The bones were preserved inside the 14-mile-wide (23 kilometers) impact crater thanks to it rapidly filling with water. This crater formed from an asteroid or comet impact around the same time the Arctic rhino lived, suggesting the rhino died inside the crater before it became a lake.
At that time, the climate in this region was far warmer than it is today. Plant remains indicate that the Canadian High Arctic—specifically Devon Island in Nunavut, where the crater is located—hosted a temperate forest.
As the Miocene epoch (23 million to 5.3 million years ago) transitioned into the Pliocene epoch (5.3 million to 2.6 million years ago), and eventually gave way to the last ice age, the fossils were broken up by freeze-thaw cycles and gradually pushed to the surface of the crater. Researchers discovered the fossils in 1986.
Subsequent field trips to the crater uncovered more bones belonging to the Arctic rhino specimen. These expeditions also unearthed another species that lived 23 million years ago, the walking seal (*Puijila darwini*), which likely lived alongside the Arctic rhinos.
Gilbert and her colleagues described *E. itjilik* based on the characteristics of its teeth, lower jawbone, and cranium, comparing them with those of other rhino species. They then determined the Arctic rhino’s place in the rhinoceros evolutionary tree by analyzing its ties to 57 extinct and living rhino groups.
Their findings were published on October 28 in the journal *Nature Ecology and Evolution*.
The study suggests that *E. itjilik* was most closely related to rhinos that lived in what is now Europe earlier than 23 million years ago. True modern rhinos (*Rhinocerotidae*) evolved about 40 million years ago in North America and Southeast Asia. Their descendants subsequently spread to every continent except South America and Antarctica.
“Today, there are only five species of rhinos in Africa and Asia,” said Danielle Fraser, the study’s lead author and head of paleobiology at CMN. “But in the past, they were found in Europe and North America, with more than 50 species known from the fossil record.”
The newfound Arctic rhino is the most northerly rhinoceros ever discovered.
The North Atlantic Land Bridge, which emerged in the latter stages of the Cretaceous period (145 million to 66 million years ago), played a key role in rhino migration. However, when this land bridge disappeared is still debated. Some studies indicate it collapsed 56 million years ago, while others suggest it remained more or less continuous until about 2.7 million years ago.
The new findings support the latter hypothesis. Since Rhinocerotidae arrived in Europe 33.9 million years ago during an extinction and dispersal event known as the Grande Coupure, or “great cut,” and the study suggests these rhinos had reached North America by 23 million years ago, the land bridge likely persisted at least until the beginning of the Miocene epoch.
“It’s always exciting and informative to describe a new species,” Fraser said. “Our reconstructions of rhino evolution show that the North Atlantic played a much more important role in their evolution than previously thought.”
https://www.livescience.com/animals/extinct-species/ancient-frosty-rhino-from-canadas-high-arctic-rewrites-what-scientists-thought-they-knew-about-the-north-atlantic-land-bridge