Life in the Arctic is tough: brutal winds, freezing temperatures and months of utter darkness. For a long time, palaeontologists believed no dinosaurs could have lived in such icy extremes, until researchers in the 1950s discovered the first fossils in the polar region.
Now, thanks to a decade of painstaking research in Alaska, scientists from the University of Alaska and Florida State University have uncovered a trove of baby dinosaur bones and teeth, proving that not only did dinosaurs live and thrive in the frigid north – which, though milder than today, still averaged 6°C across the year – they reproduced there, too.
“These represent the northernmost dinosaurs known to have existed,” says author Patrick Druckenmiller of the University of Alaska Museum of the North. “We didn’t just demonstrate the presence of perinatal remains – in the egg, or just hatched – of one or two species; rather we documented at least seven species of dinosaurs reproducing in the Arctic.”
“We unexpectedly found remains of perinates representing almost every kind of dinosaur in the formation,” adds co-author Gregory Erickson, from Florida State University. “It was like a prehistoric maternity ward.”
The findings build on the discovery in Alaska in June 2020 of the first baby dinosaur fossil north of the Arctic Circle.
The new nursery of bones, detailed in a paper in Current Biology, suggests Arctic dinosaurs weren’t seasonal wanderers that migrated south when the colder months set in, but hardy, year-round residents. It suggests, above all, that dinosaurs were warm-blooded.
“Year-round residency in the Arctic provides a natural test of dinosaurian physiology,” says Erickson. “Cold-blooded terrestrial vertebrates like amphibians, lizards, and crocodilians have yet to be found, only warm-blooded birds and mammals and dinosaurs. I think that this is some of the most compelling evidence that dinosaurs were in fact warm-blooded.”
Recovering the tiny fossils, some no larger than the head of a pin, was a meticulous job.
“The field season is short in the Arctic and access is very difficult – aircraft and small boats are required,” says Druckenmiller. “To make matters more challenging, the only way to see the rocks is in river-cut steep bluffs along the largest river in northern Alaska, the Colville. These bluffs are prone to catastrophic collapses, making it hard to safely find and extract fossils.
“As such, we have focused on finding discrete bonebed horizons where we can more efficiently excavate many bones. In the process, we’ve also discovered numerous new microfossil deposits that have provided for a wealth of new knowledge about the whole ecosystem that lived in the Arctic over 70 million years ago.”
Once they recovered the sediment, the researchers hauled the soil down to the river’s edge, where they washed the material through screens to remove large rocks and soil. The material was screened further in the lab, with the sediment examined under a microscope to find bones and teeth.
“Recovering these tiny fossils is like panning for gold,” says Druckenmiller. “It requires a great amount of time and effort to sort through tons of sediment grain-by-grain under a microscope.”
According to the researchers, the new discovery solves several dinosaur mysteries, but opens up another: how did the animals survive Arctic winters?
“Perhaps the smaller ones hibernated through the winter,” says Druckenmiller. “Perhaps others lived off poor-quality forage, much like today’s moose, until the spring.”