Primate-Like Critters Survived in the Arctic When It Was a Lush, Warm Swamp | Science

Fifty-two million years ago, the now frigid islands of northern Canada featured lush cypress swamps where alligators splashed. Now, for the first time, scientists have revealed that this ancient Arctic ecosystem was also home to primate-like animals.

A new study published Wednesday in PLOS One describes two species of lemur-like creatures, the first primate-like animals known to have inhabited the Arctic in the Eocene Epoch. “Finding a close relative of primates up north of the Arctic Circle is unique,” says co-author Chris Beard, a vertebrate paleontologist at the University of Kansas. “That hasn’t existed in the fossil record up till now.”

During the warm days of the Eocene, Canada’s Ellesmere Island would have been almost unrecognizable to us—Beard likens it to a Georgia cypress swamp that’s been transported north of the Arctic Circle. “This ecosystem that existed on Ellesmere Island 52 million years ago simply doesn’t exist on Earth today,” he says. But across millennia, the far-northern island has been marked by darkness that lasts for months at a time. Like other plants and animals that thrived at such high latitudes during Earth’s last greenhouse era, these two lemur-like species developed special adaptations to survive in a warm, swampy forest that was cloaked in darkness for half the year.

Detailed analysis of the animals’ fossilized teeth and jaw fragments, which indicate their jaw muscles were optimized for bite force, led scientists to surmise that the lemur-like animals survived because they were able to regularly eat hard nuts and seeds. Unlike many other primates of their era, these features allowed them to munch on such “fallback foods” during the Arctic winter, when typical fare like fruits would not have been available, the authors of the new study suggest.

Beard and colleagues describe two different species, Ignacius mckennai and Ignacius dawsonae, that were closely related to primates and were the size of a small cat or rabbit. The latter is named for the noted paleontologist Mary Dawson, who pioneered fossil hunting work on Ellesmere Island in the 1970s.

The team studied eight tooth and jaw fragment specimens found near Bay Fiord, in central Ellesmere Island. The fossils have been housed at the Canadian Museum of Nature in Ottawa, and experts at the National Museum of Natural Sciences in Madrid were able to create detailed 3D models of the teeth. Those models were compared to 95 other fossil primates, including Ignacius who lived south of Ellesmere Island, and living species, like South America’s titi, saki and uakari monkeys, adapted to eating harder fare. The comparative results show that Ellesmere’s primates had distinctive dental features, like low-crowned molars, adapted for biting and chewing hard foods. Muscle markings showed the Ellesmere Island species also had lower jawbones adapted for higher bite forces.

More recent conditions on the once-swampy island, where extreme cold and dryness now produce a polar desert, have preserved an extensive fossil record. Other animals known to have lived on Ellesmere include giant tortoises and pig-like animals similar to the modern tapir. Plant records show redwood and cypress species were found in the diverse wet forests the primates called home. Deciduous forests of elms, alders, birches and sycamores also thrived in the area. “The light regime would have been a challenge, not just for the animals but also for the plants, since photosynthesis requires light,” says Christopher West, a paleobotanist at the Royal Tyrrell Museum of Paleontology in Alberta, Canada, who was not involved with the study.

But so far only two species of primate-like animals are known to have survived under these unusual conditions, though elsewhere their numbers were large and diverse during the Eocene Era. Wyoming’s fossil record, for example, shows a huge diversity of primates and close relatives lived in an area that wasn’t dramatically colder than the High Arctic. However, Wyoming did have light-filled days year-round.

“It’s interesting that not every primate or relative that was around at this time was able to colonize Ellesmere Island,” Beard says. “So there was apparently something special about this particular lineage that enabled them to do it.”

Hibernating, or at least entering an extended state of torpor, was one possible solution. It’s rare among primates, but the fat-tailed dwarf lemur uses the strategy to ride out Madagascar’s seven-month dry season. But on Ellesmere Island, the animals’ teeth and jaws suggest a different story, with 3D models showing they could grind up very hard food.

Jaelyn Eberle, a vertebrate paleontologist specializing in fossil mammals at the University of Colorado Boulder, previously showed that some large Arctic mammals shifted their diets to survive winter. Pulling carbon and oxygen isotopes from fossil teeth of the hippo-like Coryphodon, her team found that the animals switched from summer plants and leaves to winter fare like twigs, leaf litter and fungi. “I suspect with these primates it makes a lot of sense that they would eat something quite different in the winter to hold them over,” she says.

West notes that paleobotanists aren’t entirely sure what types of winter fare would have been available on the Eocene Ellesmere Island. “As for botanical evidence, fossil plants, there are few things that align with the types of fruit or seeds they would be talking about, but we just don’t really have a lot of fossil fruits or seeds,” he says. “So there’s a little more work to be done.”

Based on extensive morphological analysis, scientists think that both Ignacius dawsonae and Ignacius mckennai were likely descended from a single ancestral species that first colonized the High Arctic. “If that’s true, then the Arctic itself becomes a little laboratory of evolution for the few lucky animals that are able to get there,” Beard explains.

Eberle says scientists don’t always know why some animals, like the tapir-like creatures, apparently thrived in the warm Arctic but are rarely found at middle latitudes. Equally puzzling is why others, like the horses commonly seen at Eocene sites farther south, didn’t inhabit the Arctic. “People have been up there working for over four decades, and nobody has recovered a horse tooth,” she says. “The fauna in the Arctic is quirky. The things that occur in the Arctic are unusual, and the absence of things, like the lack of a single horse in the Arctic, is just as intriguing.”

The million-dollar question of why some species survived there and others didn’t is “what this paper is also trying to get at,” Eberle suggests.

Studies of Ellesmere Island’s ancient ecosystem and how animals adapted to survive there are quite timely, because scientists are pondering what future Arctic ecosystems will look like as the region warms. Though ice will melt and temperatures will rise, the future Arctic will still experience the same kind of feast or famine annual light cycle that it did 50 million years ago. And potential new arrivals to the area will face the same challenges that ancient primates did.

“It’s true that some kinds of animals that you don’t expect in the Arctic are able to colonize it, tapirs, crocodiles, primate-like animals—they can come,” Beard says. “But it’s not like the floodgates completely open so that every subtropical animal of earth is in the Arctic.”

Any new species that do move into a warming Arctic, like the ancient ones, will need to develop their own ways of living in the dark.

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