How a Mass Extinction Driven by Ancient Volcanoes Led to the Age of the Dinosaurs #fossils #dinosaurs #massextinction #extinction

Crocodile relatives, like the predatory Saurosuchus, were hit hard by the Triassic-Jurassic extinction. Kentaro Ohno CC BY 2.0

Smithsonian Magazine features a story on the Triassic-Jurassic mass extinction, a pivotal event that reshaped life on Earth. The late Triassic was vastly different from the Jurassic and Cretaceous periods that followed. During this time, early dinosaurs played only minor roles, while the landscape was dominated by giant amphibians, a diverse array of crocodilian relatives—ranging from agile, dog-like runners to fearsome, dinosaur-like apex predators—and the gharial-like phytosaurs.  What triggered the mass extinction that ultimately paved the way for dinosaur dominance? The most likely culprit was the breakup of Pangaea, which set off environmental changes that led to widespread extinction.

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.