Dinosaurs took over in ice, not warmth, new study on ancient mass extinction suggests
Thrive amid a series of sudden global chills that kill rivals
Many of us know the traditional theory of how the dinosaurs died 66 million years ago: a violent collision of Earth with a meteorite, and the ensuing global winter, when dust and debris clogged the atmosphere. But there’s been an extinction before, more mysterious, and less discussed: the one 202 million years ago that killed the large reptiles that ruled Earth before that, apparently clearing the way for dinosaurs to take over. What caused the so-called Triassic-Jurassic extinction, and why did dinosaurs thrive while other creatures died?
We know that the Triassic period before extinction and the subsequent Jurassic period began the age of dinosaurs, and the world was generally hot and humid. However, a new study has turned the idea of thermophilic dinosaurs upside down: It provides the first physical evidence that Triassic dinosaur species — then a small group largely relegated to the polar regions — often endured there Freezing conditions. Obvious indicators: dinosaur footprints and strange rock fragments that only ice can deposit. During the extinction, the cold snaps that had occurred at the poles spread to lower latitudes, killing the cold-blooded reptiles, the study’s authors said. Adapted dinosaurs survived the evolutionary bottleneck and spread. The rest is ancient history.
“Dinosaurs have been under the radar during the Triassic,” says Paul OlsonColumbia University geologist Lamont-Doherty Earth Observatory, and the lead author of the study. “The key to their ultimate dominance is pretty simple. They’re basically cold-adapted animals. When it’s cold everywhere, they’re ready, and other animals aren’t.”
Lava flows in the distance, and a primitive feathered theropod took away a mammal victim during the snowy volcanic winter caused by a massive eruption during the Triassic-Jurassic extinction. Dinosaurs survived because they had adapted to freezing conditions at high latitudes, a new study suggests. (painting by Larry Feld)
The research, based on recent excavations in a remote desert in northwestern China’s Junggar Basin, has just been published in the journal scientific progress.
Dinosaurs are thought to have first appeared in temperate southern latitudes during the Triassic period about 231 million years ago, when most of the earth’s land was connected together to form a giant continent that geologists call Pangea mainland.them to the far north About 214 million years ago. Before the 202-million-year mass extinction, the wider tropical and subtropical regions in between were dominated by reptiles, including relatives of crocodiles and other terrifying creatures.
During most of the Triassic and Jurassic, atmospheric carbon dioxide concentrations were at or above 2,000 parts per million—five times higher than today—so temperatures must have been high. There was no evidence of polar ice caps at that time, and excavations showed that deciduous forests grew in the polar regions. However, some climate models suggests that high latitudes are sometimes cold; even with this much carbon dioxide, they receive little sunlight most of the year, and temperatures drop at least seasonally. But until now, no one has produced any physical evidence that they are frozen.
The Pangaea supercontinent 202 million years ago, shortly before the Triassic-Jurassic extinction. Evidence of early dinosaurs has been found in designated areas; most species are restricted to high latitudes, and a few species closer to the tropics tend to be smaller. The red area at the top is what is now the Junggar Basin in northwestern China. (Olsen et al., Science Advances, 2022)
At the end of the Triassic, a short geological period of about one million years saw the extinction of more than three-quarters of all terrestrial and marine species on Earth, including shells, corals and all large reptiles. Some cave-dwelling animals, such as turtles, survived just as well as some early mammals.It’s not clear what exactly happened, but many scientists associate it with a series of massive volcanic eruption This could go on for hundreds of years. At this time, Pangaea began to split, opening up what is now the Atlantic Ocean and separating what is now America from Europe, Africa and Asia. Among other things, volcanic eruptions can cause carbon dioxide in the atmosphere to soar beyond its already high levels, causing deadly temperature spikes on land and making ocean water too acidic for many organisms to survive.
The authors of the new study cite a third factor: During the most intense stages of eruptions, they spew sulfuric aerosols that deflect large amounts of sunlight, causing recurring volcanic winters across the globe that overwhelm high greenhouse gas levels. These winters may last a decade or more. Even tropical regions may experience persistent freezing conditions. Scientists say this killed the uninsulated reptiles, but the cold-adapted, insulated dinosaurs were able to persevere.
Evidence from researchers: fine-grained sandstone and siltstone formations left by shallow paleo-lacustrine sediments in the Junggar Basin. These sediments formed 206 million years ago in the Late Triassic, which experienced the mass extinction and beyond. At that time, before the continents rearranged, the basin was located at about 71 degrees north latitude, well above the Arctic Circle. Footprints discovered by the authors and others suggest that dinosaurs existed on the coastline. Meanwhile, in the lake itself, researchers found massive pebbles up to about 1.5 centimeters wide in the usually fine sediment. Away from any obvious shoreline, pebbles are useless there. The only plausible explanation for their existence: they are ice drift debris (IRD).
A shale cliff in northwest China’s Junggar Basin, where scientists found ice-drifted pebbles in fine-grained sediment. (Paul Olson)
Simply put, IRDs are created when ice forms on coastal land and contains some underlying rock. At some point, the ice becomes unmoored and drifts into the adjoining body of water. When it melts, the rock falls to the bottom, where it mixes with ordinary fine sediment. Geologists have extensively studied ancient IRDs in the ocean, fed by glacial icebergs, but rarely on lake beds. The discovery of the Junggar Basin adds to the scarce record. The authors said the pebbles were likely picked up during the winter, when lake water froze along the pebbled shoreline. When the warmer weather returned, chunks of ice floated away with the pebble samples and later fell back down.
“This suggests that these areas were often icy and dinosaurs were doing well,” said study co-authors. Dennis KentGeologist at Lamont-Doherty.
How do they do it? Since the 1990s, there has been increasing evidence that many, if not all, non-avian dinosaurs, including tyrannosaurs, had primitive feathers.If not for flight, some of the covering may be used for mating display purposes, but researchers say The main purpose is insulation. There is also ample evidence that, unlike cold-blooded reptiles, many dinosaurs had Warm blood hypermetabolism system. Both qualities will help the dinosaur in cold conditions.
“Severe winter events during volcanic eruptions may have brought icy temperatures to the tropics, where extinction events of many large, naked, featherless vertebrates appear to have occurred,” Kent said. “And those of us in high latitudes adapted to the cold. The excellent feathered friend of temperature did a great job.”
The discoveries challenge conventional images of dinosaurs, but some prominent experts say they are convinced. “There is a stereotype that dinosaurs always lived in dense tropical jungles, but this new study shows that during parts of the year, high latitudes were frozen or even covered in ice,” said professor of paleontology and evolution. Stephen Brusatte said. University of Edinburgh. “Dinosaurs living in high latitudes happened to already have winter coats [while] Many of their Triassic rivals disappeared. “
Randall Irmis, curator of paleontology at the Utah Museum of Natural History and an expert on early dinosaurs, agrees. “This is the first detailed evidence from high paleolatitudes, the first evidence for the last 10 million years of the Triassic, and the first evidence for true icing conditions,” he said. “People are used to thinking that this is a hot and humid period for the entire planet, but it’s not.”
To better understand this period, Olsen said, the next step is for more researchers to hunt for fossils in pre-polar regions such as the Junggar Basin. “The fossil record is so bad that nobody is exploring,” he said. “These rocks are grey and black and difficult to explore [for fossils] in these layers. Most paleontologists are drawn to the late Jurassic period, where many large skeletons are known to exist. The ancient North Pole was largely ignored. “
Co-authors of the study are Sha Jingeng and Fang Yanan of the Nanjing Institute of Geology and Palaeontology; Clara Chang and Sean Kinney of the Lamont-Doherty Earth Observatory; Jessica Whiteside of the University of Southampton; and Hans-Dieter of the Smithsonian Institution Indictment; Morgan Schaller of Rensselaer Polytechnic Institute; and Vivi Vajda of the Swedish Museum of Natural History.
