We have been discovering dinosaur fossils in the Arctic for 70 years. However, most palaeontologists assumed that these came from dinosaurs that ventured north during summers and migrated south to avoid the harsh winters. Now, the discovery of infant dinosaur fossils suggests that some species might have thrived year-round in the frigid tundra.
“We knew dinosaurs had been there, but we didn’t know if they could deal with the cold or even the darkness of winter,” says Patrick Druckenmiller at the University of Alaska Museum of the North.
Although migration has long been assumed as the answer to this question, it has its problems. “In order to migrate from our field site [to below the Arctic circle], you’re looking at a minimum 3000-kilometre round trip on foot,” says Druckenmiller.
He and his colleagues found an assemblage of hundreds of bones and teeth of between 1 and 2 millimetres long at a site in the Prince Creek Formation in northern Alaska. This included the remains of seven species of dinosaur that had either died within the egg or soon after hatching, suggesting that the dinosaurs weren’t visitors but year-round residents able to weather the dark night of the Arctic winter. The species were from eight families, including Ornithopoda, Hadrosauridae, Tyrannosauridae and Deinonychosauria.
“There’s good evidence that these dinosaurs had incubation periods of over five months,” says Druckenmiller. He argues that if they laid their eggs in spring when most vegetation appears, their eggs would hatch with winter on the horizon. Migration at that time is something a newborn is unlikely to survive.
The Prince Creek fossil site is the furthest north that dinosaurs have been confirmed to have lived. Accessing the site today involves landing a small aeroplane on a gravel bar along the creek and then assembling rafts to float through a series of sheer cliffs held together by permafrost.
It is a frozen tundra now, but the climate was very different 70 million years ago. Petrified logs at the site suggest the area was at least partially forested then. “It’s all the more amazing that, thanks to plate tectonics, Alaska was actually 10 degrees farther north than it is today,” says Druckenmiller.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2021.05.041
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