How a Mass Extinction Driven by Ancient Volcanoes Led to the Age of the Dinosaurs

Everyone knows about the mass extinction that ended the Age of Dinosaurs. About 66 million years ago, a seven-mile-wide asteroid slammed into our planet and began a mass extinction that wiped out all the dinosaurs except for beaked birds, not to mention about 75 percent of known species. But a different mass extinction was responsible for the success of the dinosaurs. Around 201 million years ago, incredible volcanic outpourings in the supercontinent Pangaea shook up life on Earth and gave early dinosaurs a chance to thrive.

Paleontologists have known something strange happened between the end of the Triassic Period and the beginning of the Jurassic for the better part of a century. In the latest days of the Triassic, early dinosaurs lived alongside giant amphibians, gharial-like phytosaurs and an array of crocodile relatives that took forms ranging from armadillo-like to apex predators. In the earliest Jurassic rocks, however, some of these groups entirely vanished and others were severely reduced in diversity as dinosaurs began to proliferate. The seas, too, saw changes in reef composition, precipitous drops in plankton and the disappearance of whale-sized ichthyosaurs while their smaller relatives lived on during the same time. The shifts in Earth’s biodiversity are the ripples of one of the most catastrophic events in our planet’s history.

The Triassic-Jurassic extinction was not as rapid or violent in its consequences as the asteroid impact of 66 million years ago. So far as paleontologists have been able to reconstruct the ancient Earth at the time, the extinction was a protracted grind of climate and environmental change. The most likely trigger is incredible outpours of greenhouse gases in what experts call the Central Atlantic Magmatic Province (CAMP). The ancient volcanoes in that area, situated around the center of Pangaea, oozed and belched greenhouse gases in pulses over 600,000 years, covering roughly three million square miles in volcanic rock and causing sharp climate swings between hot and cold. “With such rapid release of carbon dioxide, sulfur dioxide, soot and other thermogenic gases, there is a cascade of effects,” says geologist Victoria Petryshyn of the University of Southern California. Acid rain, increased UV radiation from ozone depletion and other environmental effects would have flowed from the sudden changes.

“It’s hard to say that any debate in science is ever finalized, because new evidence could always emerge, but in terms of ultimate causes the Triassic-Jurassic extinction is quite strongly linked to the CAMP eruptions,” says Western Carolina University geologist Shane Schoepfer. The eruptions were occurring when the extinction took place, and even extinctions in the deep sea appear to be linked with the volcanic activity.

Much like other periods of intense volcanic activity, such as the eruptions that caused Earth’s third mass extinction 251 million years ago, the incredible volumes of carbon dioxide, methane and other gases spewed into the atmosphere caused oceans to become more acidic and prompted periods of climate warming as well as volcanic winters. The changes also had many downstream effects geologists are still working to understand. “One of the largest effects of warming on the ocean is the slowing of ocean circulation,” Schoepfer says. The change often causes the deep ocean to become oxygen-depleted, as well as changing how nutrients that plankton rely on circulate. Such fundamental changes to the foundations of ecosystems have reverberating effects. The disaster wasn’t a single event, but actually a period of intense pressure that many forms of life had not evolved to cope with.

As with all mass extinctions, of course, paleontologists have long been puzzled by why some groups of living things went extinct and others survived. “There are winners and losers in every mass extinction,” Petryshyn says. Some groups disappear, while others, which might have seemed rare or in the background, seem to become more abundant after an extinction. “Groups of life that may have been struggling or flying under the radar since the Paleozoic suddenly make a comeback because the board has been reset,” she says, noting that microbe-made ocean rocks from the Early Jurassic show a spike at a scale not seen in hundreds of millions of years. Sponges, too, had a resurgence in the disrupted seas that followed the Triassic-Jurassic extinction until ocean ecosystems built themselves up again.

Among the most significant mysteries of the end-Triassic extinction, however, is why dinosaurs and pterosaurs fared so much better than so many of their reptilian neighbors. At the end of the Triassic, the crocodile-like phytosaurs entirely disappeared, as did many forms of crocodile relatives that were diverse and widespread in the Triassic. Large, flat-headed amphibians called metoposaurs entirely vanished, as well, not to mention various reptile groups that had emerged early in the Triassic only to disappear by the end. Dinosaurs and their flying pterosaur relatives, however, seemed unbothered by the changes and did not suffer the same losses.

In a sense, having to live shoulder to shoulder with a broader array of larger and more diverse reptile groups might have molded dinosaurs and pterosaurs into creatures capable of surviving the volcanic effects. Dinosaurs and pterosaurs shared a common ancestor in the Triassic, an animal that likely was small, was covered in fur and fed on insects to fuel a warm, constant body temperature. The tiny Kongonaphon, named in 2020 from fossils found in Madagascar, is one such creature. From such ancestors, a study published earlier this year in Nature proposed, the earliest dinosaurs evolved into omnivores that fed on insects, plants and whatever other morsels they could catch, generally living at small size among the other reptiles of their time.

Some dinosaurs were getting bigger by the end of the Triassic. Climate changes during the period underwrote a vegetation boom that provided some previously omnivorous dinosaur lineages with enough green food to begin specializing on eating plants. The early ancestors of long-necked giants like Apatosaurus began this way. As prey grew bigger, more carnivorous dinosaurs followed the trend and became larger—roughly the size of polar bears. At this moment, the intense volcanic activity changed the world.

The dinosaurs and early pterosaurs that thrived during the Triassic likely retained the warm-running metabolisms and fuzzy coats of their ancestors. Even though direct fossil evidence of fuzzy Triassic dinosaurs has yet to be found, paleontologists expect they were fluffy reptiles given that both dinosaurs and pterosaurs of the Jurassic and Cretaceous had feathers and likely inherited them from a common ancestor. Paired together, warm body temperatures and insulating coats allowed dinosaurs to better survive the swings between warm and cold climates at the end of the Triassic. Other reptiles that lacked such insulation, such as the many crocodile relatives, were more vulnerable to the shifts and the environmental changes that came with them. “Any species needing to survive a mass extinction like this would have to deal with multiple stressors,” Petryshyn says, and the combination of changes might have been too much for many Triassic reptiles.

The traits that dinosaurs and pterosaurs evolved at small size, when the animals were squeaking by in a world filled with more imposing reptiles, may have allowed them to survive the end-Triassic upheavals and walk into a relatively open Jurassic world where there was more ecological opportunity to evolve into new forms—at the beginning of the true Age of Dinosaurs.