Not in need of warmth – dinosaurs even roamed through the Arctic and not only that: They also reproduced there and apparently survived the dark and cold winter. This comes from fossil finds of baby dinosaurs in Alaska, which came from different species – from sometimes large herbivores to a relative of Tyrannosaurus rex. The results refute earlier assumptions that the dinosaurs of the far north migrated to the south to hibernate and also laid their eggs there. It is also another piece of evidence that dinosaurs were warm-blooded, say the paleontologists.
For a long time they were thought to be lizard-like beings that needed high ambient temperatures to get going. But the assumption that the dinosaurs’ habitats were restricted to the warm regions of the world was disproved as early as the 1950s: Researchers discovered dinosaur fossils for the first time in regions that were in polar latitudes during the lifetimes of the animals. In the age of the dinosaurs it was warmer there than it is today, but the arctic winter was also characterized by frost and darkness. Meanwhile, many fossil finds show that a diverse dinosaur society once existed in these harsh habitats. However, it remained unclear whether the animals lived there all year round. It seemed possible that they only spent the summer there and hibernated south to give birth to their young there.
“We are now presenting, for the first time, clear evidence that the northern dinosaur species were able to reproduce in high latitudes,” says Patrick Druckermiller from the University of Alaska at Fairbanks. The results are based on fossil finds from the Prince Creek Formation in northern Alaska, where the remains of various types of dinosaurs have previously been discovered. As the paleontologists report, they now encountered many astonishingly small bits of bone and teeth in deposits that date back to around 70 million years ago. They collected the fossils, some of which were the size of a pinhead, by washing the sediment through ever finer sieves. “This work is like panning for gold,” says Druckermiller. “The fossils that we found through this painstaking work are a scientific treasure,” says the paleontologist.
Arctic baby dinosaur fossils
More detailed investigations of the remains and comparisons with known dinosaur fossils then showed that they were the remains of teeth and bones of so-called perinatal dinosaurs – babies that were either still in the egg or had just hatched. It wasn’t just about the young of one species – the scientists were able to identify representatives from different groups. They included large herbivores such as hadrosaurs and ceratopsians as well as carnivores such as dromaeosaurs and also a relative of Tyrannosaurus rex: the comparatively small Nanuqsaurus hoglundi. “We found remains of perinates that include almost every type of dinosaur known from the formation,” says co-author Gregory Erickson of Florida State University in Tallahassee.
As the researchers explain, the findings also indicate that the arctic dinosaur species stayed in the north all year round. It can be assumed that the incubation times of the eggs in these dinosaur species were between three and six months. Since the arctic summers are short, even if the dinosaurs had laid their eggs in spring, the offspring would have been too young to migrate south in autumn, the scientists explain. Apparently, the animals were able to cope with the challenges in the habitat far north of the Arctic Circle. Although the global temperatures during the Cretaceous Period were significantly higher and, as a result, the conditions in the Arctic were milder than today, the winters there were harsh, the researchers emphasize: There was four months of darkness, there was snow and ice, and there was little fresh vegetation for food .
Cleverly adapted and warm-blooded?
“As dark and bleak as the winters may have been, in return there was 24 hours of daylight in the summers – great conditions for young dinosaurs to develop – if they could grow fast enough before winter set in,” says co-author Caleb Brown of the Royal Tyrrell Museum of Palaeontology, Drumheller, Canada. A year-round stay in the Arctic raises further questions, say the scientists: How did these dinosaur species survive the harsh winter? “Maybe some went into hibernation,” says Druckermiller. “Perhaps others survived until spring because they were able to get by with the still scarce food supply, similar to today’s moose,” says the paleontologist.
As he and his colleagues emphasize, no fossils of clearly cold-blooded creatures such as amphibians, snakes or turtles, which were often found in the lower latitudes in the era, have so far been found in the region. This suggests that these animals could not cope with the temperature conditions that prevailed in the arctic areas at the time. Conversely, this means: Warm-bloodedness (endothermia), as possessed by today’s birds and mammals, probably enabled the dinosaurs to live in the cold. “The study thus throws light on the question of the extent to which the dinosaurs already possessed this characteristic,” says Druckermiller. “We think that endothermic was probably an important part of their adaptability,” says the paleontologist.
Source: University of Alaska, Cell Press, technical article: Current Biology, doi: 10.1016 / j.cub.2021.05.041