Did Dinosaurs Live in the Arctic? Fossils From Months of Darkness
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On the Colville River in northern Alaska, five hundred kilometres above the Arctic Circle, a bluff of frozen mudstone contains thousands of dinosaur bones, including the remains of hatchlings small enough to fit in a hand. Similar sites exist in Australia, which sat inside the Antarctic Circle at the time, and on the Antarctic Peninsula itself. These animals lived through four months of continuous winter darkness at latitudes where the Cretaceous world was cool, and the fossils raise a set of questions about how they survived that are still being worked out.
Where the fossils are
Three regions dominate. The Prince Creek Formation of northern Alaska, about 70 million years old, has produced the richest polar dinosaur assemblage known, worked since the 1980s from a riverbank that thaws for a few weeks a year. Southeastern Australia, particularly the sea cliffs at Dinosaur Cove and Flat Rocks in Victoria, was at roughly 75 degrees south in the early Cretaceous and has produced small ornithopods and other material dug out by volunteers through tunnels blasted into the rock. Antarctica itself has yielded material from James Ross Island and the Transantarctic Mountains, including the crested theropod Cryolophosaurus. In all three the fossils were found long after the idea of polar dinosaurs had been dismissed, since the animals were assumed to be tropical reptiles that could not have tolerated cold or darkness.
What the polar world was like
The late Cretaceous was much warmer than the present, with no permanent ice at either pole, and the Alaskan sites are estimated from plant fossils and geochemistry to have averaged around six degrees Celsius annually, comparable to modern Scotland, with winter temperatures dipping below freezing and snow likely. That removes extreme cold as the main problem and leaves a harder one, which no amount of warming changes: the astronomy. At those latitudes the sun does not rise for months, and a continuous winter night stops photosynthesis, so the plant growth on which the whole food chain depends shuts down regardless of temperature. The environment was a conifer and fern forest with a brief, intensely productive summer and a long dead season, and any animal living there year-round had to solve the winter food problem.
How they might have coped
Four strategies have been proposed, and the evidence has narrowed the list:
- •Migration, the original assumption: herds moving south each autumn and back in spring. It has lost ground, since bone histology indicates that the Alaskan hadrosaurs grew year-round and juveniles too small to travel thousands of kilometres are present in quantity
- •Hibernation or torpor, plausible for small animals and difficult for a multi-tonne one, with some evidence from burrow structures associated with small ornithopods in Australia
- •Year-round residence with a changed diet, browsing on evergreen conifers, bark, fungi, rotting wood and litter through the dark months, which is what modern boreal herbivores do
- •Physiology: a high metabolic rate, insulating feathers or fuzz, and large body size that retains heat, all of which the evidence increasingly supports
The nesting discovery
The strongest single result came in 2021, when a team working the Alaskan site reported hundreds of bones and teeth from perinatal dinosaurs, meaning animals either about to hatch or newly hatched, across at least seven different families including hadrosaurs, ceratopsians, tyrannosaurs and small theropods. Because incubation in these groups took three to six months, laying in spring means hatching in late summer, leaving newborns facing the polar winter within weeks. Animals that small cannot migrate, which makes year-round residence close to certain and turns the Arctic from a summer feeding ground into a permanent habitat with its own breeding population. The finding also strengthens the case for warm-bloodedness, since raising young through a sunless winter at near-freezing temperatures is not something a reptile dependent on external heat can do.
Why it matters beyond the poles
Polar sites are unusually informative because they set the hardest test. An animal that bred and overwintered at 80 degrees north must have had insulation, a high and self-generated metabolic rate, adaptations for feeding in darkness and probably parental care, and each of those is a claim about dinosaurs generally that is difficult to test in a temperate quarry. Enlarged optic lobes and large eye sockets in some polar species point to vision adapted for low light. The assemblages are also distinct from those at lower latitudes, with their own species rather than northern visitors, which tells us the group could specialise for extreme environments rather than merely tolerating them. And the sites bear on the extinction, since a population already adapted to months without sunlight is exactly the kind that might have been expected to survive an impact winter, and did not, which is a point in favour of the event having been severe rather than marginal.
How we know where the rocks were
Finding a fossil at a high latitude today does not by itself prove the animal lived at a high latitude, since continents move. Geologists work out where rocks were when they formed using palaeomagnetism. As fine sediment settles or lava cools, tiny grains of magnetic minerals such as magnetite line up with the Earth's magnetic field and are locked in place. The field lines run nearly horizontal near the equator and dip steeply near the poles, so the angle recorded in the grains reveals the latitude of formation, and for northern Alaska it shows that the Prince Creek dinosaurs lived even closer to the pole than the site lies today.
The Australian sites show plate movement working in the other direction. In the early Cretaceous, Australia was still joined to Antarctica as part of the southern supercontinent Gondwana, and the coast of Victoria lay deep inside the Antarctic Circle. The two landmasses separated gradually and Australia has since drifted thousands of kilometres north, so fossils now dug from cliffs a short drive from Melbourne come from animals that lived through polar winters. The same reasoning is applied to every fossil forest or coal seam found near the poles, since each case has to be checked: some grew far from where they now lie, and others really did grow in polar light.
The bones that waited twenty years
The first dinosaur bones from Arctic Alaska sat unrecognised for more than two decades. In 1961 a geologist working for Shell, Robert Liscomb, collected bones along the Colville River while mapping rocks for oil, but at the time nobody expected dinosaurs in the far north, and the bones were assumed to belong to Ice Age mammals. Liscomb died in a rock fall the following year, and his finds went into storage. Only in the 1980s did palaeontologists look at them again and realise they were hadrosaur bones, which sent field teams back to the river and opened up the site described above.
The episode is a lesson in how expectation shapes what scientists see. Bones are interpreted against what is thought possible, and a fragment that fits no expected category is easily filed under the nearest familiar one. Since the Alaskan bones were recognised, the same rocks have produced named species of their own, including a horned dinosaur, Pachyrhinosaurus perotorum, and a small tyrannosaur called Nanuqsaurus, whose name comes from the Inupiaq word for polar bear. Each was found because people finally went looking in a place where the textbooks had said there was nothing to find.
Dinosaurs in Antarctica too
Polar dinosaurs lived at the other end of the world as well. In 1990 and 1991 geologists working on Mount Kirkpatrick in Antarctica, high in the Transantarctic Mountains, found the bones of a large meat-eating dinosaur with a strange crest running sideways across its head. Named Cryolophosaurus, the frozen-crested lizard, it lived in the Early Jurassic, around 190 million years ago.
At that time Antarctica was part of the supercontinent Gondwana, far warmer than today, though still at high latitude with long winters of darkness. Since then dinosaur fossils have been found on the Antarctic Peninsula and elsewhere on the continent. Digging is extremely difficult, carried out in brief summer seasons in harsh conditions, so every find from Antarctica is hard won.
The takeaway
Dinosaur fossils are abundant well inside both polar circles, in northern Alaska, southeastern Australia and Antarctica, from a world with no permanent ice but with four months of continuous winter darkness that halted plant growth. The 2021 discovery of newly hatched animals from at least seven families in Alaska shows they bred there rather than visiting in summer, since hatchlings cannot migrate, which makes year-round residence and a high self-generated metabolic rate close to certain and adds weight to the case that dinosaurs generally were warm-blooded.