The End-Triassic Extinction is one of Earth’s “Big Five” mass extinction events. Occurring around 201 million years ago, this event profoundly reshaped life on Earth, clearing the way for new forms to flourish and influencing the trajectory of evolution for millions of years.
Defining the Extinction Event
The End-Triassic extinction, also known as the Triassic-Jurassic extinction, transpired around 201 million years ago, marking the transition between the Triassic and Jurassic periods. This event led to a substantial loss of biodiversity, with estimates suggesting that as much as 76% of all marine and terrestrial species, and roughly 20% of all taxonomic families, perished. This rapid disappearance of life forms occurred in less than 10,000 years.
Marine ecosystems experienced considerable devastation, with several groups facing severe reductions or complete extinction. Conodonts, a group of eel-like vertebrates, were entirely wiped out, and many Triassic ceratitid ammonoids also vanished. Other marine invertebrates, including many families of brachiopods, gastropods, and bivalves, suffered significant losses, along with certain marine reptiles like phytosaurs. On land, a considerable portion of vertebrate fauna disappeared, though some groups, such as dinosaurs, pterosaurs, crocodiles, turtles, mammals, and fishes, were less affected.
Leading Theories for the Extinction
The most widely accepted explanation for the End-Triassic extinction points to massive volcanic activity associated with the Central Atlantic Magmatic Province (CAMP). This immense igneous province, one of Earth’s largest, formed during the initial stages of the supercontinent Pangea’s breakup. It released vast quantities of lava and gases across areas that now span southwestern Europe, northwestern Africa, northeastern South America, and southeastern North America. The timing of these eruptions aligns with the extinction’s onset, providing strong evidence for their causal role.
The volcanic outpouring from CAMP released substantial amounts of greenhouse gases, primarily carbon dioxide (CO2) and sulfur dioxide (SO2), into the atmosphere. This rapid influx of gases led to significant global warming, with atmospheric CO2 levels in the Late Triassic already estimated to be three times higher than present-day levels. This warming caused widespread climate change, altering terrestrial and marine environments.
Beyond global warming, increased atmospheric CO2 dissolving into the oceans likely resulted in widespread ocean acidification. This acidification made it challenging for marine organisms, particularly those that build shells or skeletons from calcium carbonate, to survive. Additionally, environmental disruptions may have led to widespread anoxia, or a lack of oxygen, in marine environments. Some research suggests a substantial increase in anoxic bottom waters following the extinction, potentially increasing hydrogen sulfide levels, which are toxic to many forms of life.
The release of methane hydrates from the seafloor is another factor that could have exacerbated warming. Methane is a far more potent greenhouse gas than carbon dioxide, and a sudden release of these frozen methane reserves could have triggered a more rapid and intense warming event. While volcanic emissions are thought to be the primary driver, the interplay of these factors—volcanic gases, climate change, ocean acidification, and potential methane release—created a complex environmental cascade.
Ecological Aftermath and Recovery
The End-Triassic extinction reshaped Earth’s ecosystems, creating a world different from the one that preceded it. The widespread demise of numerous dominant species left many ecological niches vacant. This ecological restructuring provided an opportunity for surviving groups to diversify and fill these newly available roles.
Dinosaurs, already present during the Triassic, were among the groups that survived the extinction relatively unscathed. Their ability to adapt to changing environmental conditions allowed them to take advantage of the cleared ecological landscape. With many competitors, such as large crurotarsans (ancestors of crocodiles), eliminated, dinosaurs underwent rapid diversification. This event directly paved the way for dinosaurs to become the dominant terrestrial vertebrates throughout the ensuing Jurassic and Cretaceous periods, a reign lasting approximately 135 million years.
Other groups also survived and diversified in the aftermath. Pterosaurs, the first flying reptiles, continued to evolve and became prominent aerial predators. Early mammals, small and less diverse during the Triassic, also endured the extinction event and began to diversify, laying the groundwork for their eventual success in later geological periods. The recovery of ecosystems was a gradual process, but the End-Triassic extinction is a clear example of how sudden environmental shifts can alter the course of life’s evolution, leading to the rise of new dominant forms.