Fossil primate relatives from 52-million-years ago have been found north of the Arctic circle for the first time. Two early primates have been identified from fragments of jaws and teeth.
Today, primates almost exclusively live in warm, tropical environments, so it may come as a surprise that their ancestors lived so far north.
But, 50 million years ago during the geological epoch called the Eocene, substantial global warming effects made the Earth much warmer. In fact, the Eocene (which lasted from around 56 million to 34 million years ago) was the warmest period during the Cenozoic era – the era which spans the last 66 million years since the Age of Dinosaurs.
The Eocene is, therefore, a crucial case study of how ecosystems react to climate change.
“Global warming is transforming Arctic ecosystems in ways that are difficult to predict, but ancient episodes of global warming show how future changes in the Arctic might unfold. The first primate-like fossils ever recovered north of Arctic Circle show that these tropically adapted mammals were able to colonize the Arctic during an ancient episode of global warming approximately 52 million years ago, by adopting a new diet of nuts and seeds that enabled them to survive six months of winter darkness,” the authors write in a paper published in PLOS ONE.
Both the ancient primate relatives, named Ignacius mckennai and Ignacius dawsonae, were found on Ellesmere Island in Canada.
Sitting well above the Arctic circle, average temperatures on the island today average 3.3°C in the warmest month, July, plummeting to an average of -38°C in February.
But during the Eocene, global mean annual surface temperatures are estimated to have been 13°C higher than in the late 20th century. There were no permanent ice caps. And the polar regions were very different.
Ellesmere Island 52 million years ago would have been home to a swamp-like environment.
But even with the warmer temperatures, fossils of early primate relatives in North America have been restricted to much lower latitudes, prompting palaeontologists to suggest that the two newly discovered species were descended from a common ancestor who possessed a spirit “to boldly go where no primate has gone before.”
“No primate relative has ever been found at such extreme latitudes,” says lead author Kristen Miller, a PhD student at the University of Kansas. “They’re more usually found around the equator in tropical regions. I was able to do a phylogenetic analysis, which helped me understand how the fossils from Ellesmere Island are related to species found in midlatitudes of North America – places like New Mexico, Colorado, Wyoming and Montana. Even down in Texas we have some fossils that belong to this family as well.
”None of these species are related to squirrels, but I think that’s the closest critter that we have that helps us visualize what they might have been like. They were most likely very arboreal – so, living in the trees most of the time.”
The pair also have teeth and jaws which suggest they ate hard food items, likely for feeding on tougher foods during long, dark Arctic winters where softer meals were hard to come by.
“A lot of what we do in paleontology is look at teeth – they preserve the best,” Miller explains. “Their teeth are just super weird compared to their closest relatives. So, what I’ve been doing the past couple of years is trying to understand what they were eating, and if they were eating different materials than their middle-latitude counterparts.”
The team think the early primate relatives were forced to survive on nuts and seeds during the relatively harsh polar winter.
“That, we think, is probably the biggest physical challenge of the ancient environment for these animals,” adds corresponding author Dr Chris Beard, also at the University of Kansas. “How do you make it through six months of winter darkness, even if it’s reasonably warm? The teeth, and even the jaw muscles of these animals, changed compared to their close relatives from midlatitudes. To survive those long Arctic winters, when preferred foods like fruits were not available, they had to rely on ‘fallback foods’ like nuts and seeds.”
The researchers suggest that, while warmer temperatures prompted some organisms to move north, long periods of Arctic darkness may still have been a limiting factor in which animals and plants survived.
“It does show how something like a primate, or a primate relative that’s specialized to one environment, can change based off of climate change,” Miller says. “I think probably what it says is primates’ range could expand with climate change or move at least towards the poles rather than the equator. Life starts to get too hot there, perhaps we’ll have a lot of taxa moving north and south, rather than the intense biodiversity we see at the equator today.”