MOST ARTISTIC impressions of dinosaurs picture them in lush forests or on vast temperate savannahs. That is fair enough. Such landscapes were common during the beasts’ heydays, the Jurassic and Cretaceous periods. These pictures do, though, ignore the fact that dinosaur fossils have, for decades, been dug up in places which were at that time polar. Whether these are the remains of migrants which came for the summer, or of permanent residents, is debated. But a discovery of bone fragments and teeth from dinosaur hatchlings (see picture), just published in Current Biology by Patrick Druckenmiller of University of Alaska, Fairbanks, and his colleagues, suggests some dinosaurs did indeed make their full-time homes in the Arctic.
Modern animals that migrate to polar climes, notably birds, do often breed there. But their eggs hatch quickly and their young develop fast enough to fledge and fly to warmer places before winter arrives. Growth lines in fossilised dinosaur embryos found elsewhere suggest they needed as much as six or seven months of incubation before they were ready to hatch. Palaeontologists therefore reckon any discovery of fossilised eggs or hatchlings near the palaeo-poles would mean the species concerned must have been year-round residents rather than migrants.
Until now, no such hatchlings had been found, and the only known polar dinosaur eggs were from the Kakanaut formation of north-eastern Russia, which was only just within the Arctic Circle when its rocks were laid down. Dr Druckenmiller’s discoveries are from the Prince Creek Formation of northern Alaska, which may have been as close as 5° of latitude from the North Pole when its rocks formed 70m years ago.
The fossils themselves come from a range of dinosaur groups, including ceratopsians (related to the likes of Triceratops), duck-billed hadrosaurs, large carnivores related to Tyrannosaurus and smaller velociraptor-like predators. This suggests a diverse and flourishing ecosystem, despite the fact that Prince Creek was continuously dark for 120 days a year and had an average annual temperature of 6°C—meaning snow would have been common in winter.
How all these creatures survived those conditions was, Dr Druckenmiller suggests, a consequence of dinosaurs’ warmbloodedness and the downy feathers many of them are now known to have sported. No direct evidence of feathers has yet been found among the Alaskan fossils, but their ubiquity elsewhere makes it likely they had them.
This article appeared in the Science & technology section of the print edition under the headline “Arctic dinosaurs”