BEIJING, July 15 (Xinhua) -- An international research team found that dinosaurs were born with feathers, helping them insulate from the cold and survive the mass extinction about 200 million years ago.

The insulated dinosaurs were well adapted to the period of volcanic activities and plummeting temperatures, and rapidly took over the regions formerly dominated by large non-insulated reptiles, said the study paper published in the journal, Science Advances.

Previous studies have shown that no glaciers existed on Earth from the late Triassic (about 230 million to 200 million years ago) to the early Jurassic period, and forests covered the continent then.

The joint team of Chinese and American scientists from the Nanjing Institute of Geology and Palaeontology (NIGP) under the Chinese Academy of Sciences and Columbia University found abundant lake ice-rafted debris in the Junggar Basin in northwest China's Xinjiang Uygur Autonomous Region.

The debris derived from the late Triassic and early Jurassic strata indicated that seasonal freezing occurred at the poles despite no glaciers.

They also found well-preserved dinosaur footprint fossils in the basin, which suggested that dinosaurs lived in the polar regions from the late Triassic to the early Jurassic period and had adapted to the seasonal frigid temperatures.

"We infer through phylogenetic bracket analysis that dinosaurs were primitively born with feathers, not for flying, but most likely for insulation," said Sha Jingeng, a researcher at the NIGP.

The paper showed that the feathers, or protofeathers, were filamentous integumentary coverings, which enabled the dinosaurs to access rich deciduous and evergreen Arctic vegetation, even under freezing winter conditions.

The research team believed that the volcanic winters led to the mass extinction at the end of the Triassic. Volcanic ash and aerosols caused by massive volcanic eruptions obscured the sun and increased the reflection of solar radiation, leading to a reduction in global temperatures on land.

The volcanic winters that lasted for years decimated all medium to large-sized non-insulated continental reptiles, leaving feathered dinosaurs to survive, said the paper.

"Dinosaurs saw a rapid expansion in size and distribution range, nearly doubling their total population, in the Jurassic period. From then on, the creature began its domination on land lasting about 130 million years," Sha said.