Because dinosaurs were already adapted to polar environments, they may have survived cold winters during the end-Triassic extinction event, when most other animals died out.
During the Late Triassic and early Jurassic periods, some dinosaurs may have evolved traits that allowed them to survive freezing winters. It could explain how they came to rule the world for the next 135 million years.
Analysis of rock sediment in the Junggar Basin in northwest China, where dinosaur footprints have previously been discovered, adds to growing evidence that dinosaurs lived in frigid, icy forests as well as lush green, tropical landscapes.
Paul Olsen of Columbia University in New York and his colleagues discovered evidence that the region frequently froze over while it was inhabited by prehistoric reptiles. The sediment contains unusually large particles, which are typical of frozen lakes.
Dinosaur fossils have been discovered near the poles, but models claiming that temperatures fell below freezing between 237 million and 174.1 million years ago have been challenged, so no one knows if the reptiles actually lived in cold conditions.
Olsen's team's findings could explain how dinosaurs came to dominate Earth after nearly all large land and sea creatures in the tropics were wiped out.
Most medium and large continental reptiles vanished abruptly at the end of the Triassic when temperatures plummeted and decade-long eruptions clouded the air with sulfur. According to Olsen, the adaptation of polar dinosaurs to cold probably explains why medium-large dinosaurs reappeared almost everywhere after the extinction event.
According to Olsen, when temperatures dropped during the end-Triassic period, these dinosaurs were ready, having survived by feeding on polar vegetation and braving the cold with feathers that served as insulation. These dinosaurs then spread throughout the world during the Jurassic period, replacing large non-insulated reptiles that had been wiped out.
According to Olsen, the evidence is the latest to suggest that our understanding of dinosaurs needs to be revised. "What our paper shows is that our understanding of the dinosaurian world is fundamentally incorrect," he says. "Polar dinosaurs are not on the outskirts." They are common. Dinosaurs, in fact, are fundamentally cold-adapted animals."
Reference: DOI: 10.1126/sciadv.abo6342