Paleontologists at the Canadian Museum of Nature have recently been studying the skeletal remains of a rhinoceros. This might not sound remarkable at first, but what makes these remains fascinating is that they were found Devon Island in the Canadian Arctic.
Today, mammals inhabit nearly every corner of the Earth. In Asia, Europe and North America, mammals arrived via three routes, one over the Bering Strait and two over the North Atlantic.
The Bering Land Bridge is the best known, having enabled the arrival of humans in North America approximately 20,000 years ago and shaped the population genetics of animals such as bears, lions and horses.
Less well known are the two routes that traversed the North Atlantic, one from the Scandinavian Peninsula over Svalbard and Greenland, and another from Scotland over Iceland to Greenland and the Canadian Arctic.
However, it has typically been thought that land animals could not have crossed the North Atlantic by the Early Eocene, a period around 50 million years ago when the Earth’s climate was warmer.
However, the Arctic rhino’s remains provide tantalizing evidence that land mammals were able to traverse the North Atlantic using frozen land bridges much more recently than the Early Eocene.
A rhinoceros in the Arctic
The new species of rhinoceros was discovered from a nearly complete specimen collected from the Haughton Formation of Devon Island in Nunavut — lake sediments formed in an asteroid impact crater that likely date to the Early Miocene, around 23 million years ago.
The sediments of the Haughton Formation preserve plants, mammals and birds, among others. The majority of the rhinoceros was collected in the 1980s by paleontologist Mary Dawson and her team, with additional collections by paleontologists Natalia Rybczynski, Marisa Gilbert and their team in the 2010s.
The rhinoceros lacked a horn, which is common among extinct rhinos. It is remarkable, however, in possessing features of much more ancient forms, like teeth of forms many millions of years older. It also has a fifth toe on the forefoot, which is rare among rhinoceroses.
Anatomical comparison and evolutionary analysis suggest the specimen belongs to an existing genus, Epiaceratherium, found only in Europe and western Asia. In naming the new species, the team consulted with Jarloo Kiguktak, an elder from the nearest Indigenous community to the Haughton Crater, Aujuittuq (Grise Fiord). Together, they named it Epiaceratherium itjilik. Itjilik is an Inuktitut word meaning frost or frosty, an homage to the Arctic setting where the specimen was found.
Most surprisingly, the team’s evolutionary analysis placed E. itjilik closest to the European species of Epiaceratherium. This indicates that its ancestors likely crossed from Europe to North America via the North Atlantic at some point during the late Eocene period around 33-38 million years ago.
Bio-geographic analyses further revealed a surprisingly high number of rhinoceros crossings over the North Atlantic directly between Europe and North America, some in the last 20 million years. While a finding of such a recent crossing via the North Atlantic has often been considered unlikely, emerging geological evidence tells a different story.
How did rhinos get to the Arctic?
Today, land animals are impeded from crossing between Europe and North America by several deep, wide waterways. The Faroe Islands, Iceland and Greenland are separated by the Faroe-Bank Channel, Faroe Shetland Channel and the Denmark Strait. Between the Scandinavian Peninsula, Svalbard and Greenland are the Barents Sea and Fram Strait. It is believed that land animals could traverse at least one of these areas only up until the Early Eocene about 50 million years ago.
Recent studies, however, are starting to paint a more complex picture of North Atlantic geological change. Estimates for the timing of formation of the various channels that now break up North Atlantic land masses are highly variable.
Mathematical modelling suggests a highland connected Svalbard to northern Europe as recently as the 2.7 million years ago. An array of new data also suggest the Fram Strait was shallow and narrow until the Early Miocene, around 23 million years ago. The Faroe-Shetland channel may have opened between 50 and 34 million years ago, while the Iceland-Faroe Channel and Denmark Strait were submerged later, 34 to 10 million years ago.
This suggests that rhinoceroses could have walked on land for at least part of their journey across the North Atlantic. They could possibly have swum the relatively short distances between land masses but the team hypothesized that seasonal sea ice may also have facilitated their movement.
Seasonal ice
More than 47 million years ago, the Arctic Ocean and surrounding regions were ice-free all year. Ocean cores collected from the Arctic Ocean — samples of mud, sand and organic material drilled from the seafloor — contain evidence of ice-rafted debris during the Middle Eocene, approximately 47 to 38 million years ago. This indicates the presence of seasonal ice.
Another ocean core collected between Greenland and Svalbard also contains ice-rafted debris originating from across the Arctic dating from between 48 to 26 million years ago. What is emerging, therefore, is the possibility that land animals crossed the North Atlantic by a combination of routes formed over land and seasonal ice.
Vertebrate fossils from the islands that once comprised the North Atlantic land bridges are extremely rare. Given that much of the land bridges are now submerged, direct evidence for how animals spread across the North Atlantic may be lost.
Bio-geographic studies like the one conducted by the team at the Canadian Museum of Nature highlight how discoveries in the Arctic are reshaping what we know about mammal evolution. These insights further our understanding of how animals moved across our planet.
Danielle Fraser received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC RGPIN-2018-05305). Natalia Rybczynski, who co-authored the study mentioned in this article, received funding from the W. Garfield Weston Foundation. Mary Dawson, a co-author on the study, received funding for field work from National Geographic.
This article was originally published on The Conversation. Read the original article.
