Dinosaurs lived in an endless summer, surrounded by steaming jungles and lush swamps—at least if movies such as Fantasia and Jurassic World are to be believed. But that classic image is changing. Paleontologists now know some dinosaurs lived in comparatively chilly habitats with months of darkness and occasional snow on the ground. Frigid conditions like these, a controversial new study argues, may have helped them survive one of Earth’s worst extinctions.
“There are several interesting ideas thrown in the mix of the new paper,” says Alfio Alessandro Chiarenza, a paleontologist at the University of Vigo who was not involved with the work. But more evidence is needed to bear out some of the study’s broad claims, he and others say.
Scientists led by Columbia University paleontologist Paul Olsen zeroed in on the events of approximately 201 million years ago. Around this time, at the end of the Triassic period and just prior to the following Jurassic period, many geologists think massive volcanic eruptions cooled Earth, triggering a mass extinction on land and in the seas. Some kinds of organisms fared better than others. Although all existing groups of dinosaurs walked through the disaster virtually unscathed and went on to wildly proliferate through the Jurassic, many other forms of reptiles and amphibians perished. Adaptations to life in colder habitats, the new paper proposes, is what separated the survivors from those that went extinct.
Olsen and his colleagues ground their claim on geological and fossil discoveries in China’s Junggar Basin. Rocks here from the end of the Triassic and the earliest Jurassic include dinosaur tracks. The new study reports that the rocks also contain pebbles and other debris carried along by rafts of ice, suggesting cold temperatures. The team concludes the dinosaurs must have been thriving in the cold.
Plumage might have been their key adaptation, Olsen argues. Fossils show that many dinosaurs and flying pterosaurs sported feather and featherlike body coverings. Most of these rarely preserved feathers are found in later dinosaurs, but other researchers have suggested the last common ancestor of dinosaurs and pterosaurs had some form of feathery coat more than 243 million years ago. If so, the late Triassic dinosaurs in the Junggar Basin had warm winter coats made of plumage, Olsen and his colleagues contend today in Scientific Reports. Covered in feathe-like warmth, the dinosaurs managed to survive the chill of the end-Triassic extinction, the researchers speculate.
It’s a provocative idea, but paleontologists have yet to find direct evidence of feathers or their precursors among Triassic dinosaurs, Chiarenza points out. If feathery fossils turn up in Triassic rocks, says Sara Varela of the University of Vigo, then researchers can compare their age and location to models of the Triassic climate to see whether dinosaur plumage really did allow them to brave the cold.
Olsen notes that fossils from near the Triassic Arctic and Antarctic are rare and little-known so far. And even among rocks that preserve warmer Triassic regions, Chiarenza says, the known fossil record is fragmentary. Future discoveries of Triassic creatures and their habitats will certainly test this paper’s hypothesis, he says. “We all want to understand why some lineages disappear and others don’t,” Varela says. But for now, she says, the answers await discovery in the rock.