The End-Triassic mass extinction represents a pivotal moment in Earth’s history. Often overlooked, this event fundamentally reshaped life on our planet by clearing the way for dinosaurs’ rise.
It was significant as it would be the last mass extinction until the end of the Mesozoic. So what caused the End-Triassic mass extinction?
The End-Triassic mass extinction was triggered by extensive volcanic eruptions in the Central Atlantic Magmatic Province (CAMP). These eruptions released massive quantities of carbon dioxide, causing rapid global warming and severe ocean acidification. Combined with the breakup of Pangaea, these volcanic events disrupted global ecosystems, ultimately driving the extinction of approximately 76% of species.
If you’ve been following this series, you know that extinction events are not that simple. If you’re ready, let’s press on and explore the causes of this extinction.
Recapping the End-Permian Mass Extinction
The Triassic was a small window of time between two mass extinctions. First, let’s look at where we’ve been to understand where we’re going.
Our previous article on mass extinctions discussed the End-Permian Mass Extinction, also known as the “Great Dying.” This was the most catastrophic of the “Big Five” mass extinctions.
Scientists hypothesize that continent-sized volcanism and methane seeps produced sudden, dramatic climate change. This drove 90-98% of all life on Earth extinct.
The damage to Earth’s ecosystems during the End-Permian event was so severe that many major taxa vanished Notable groups were the trilobites, rugose corals, and various terrestrial taxa.
The extinction event was devastating. It marked the end of the Paleozoic Era and the start of the Mesozoic Era, known as the “Age of the Dinosaurs.”
Life did not quickly recover after this massive change. Several million years passed before ecosystems bounced back.
Only then did the number of species return to levels like those before the great extinction. Now for their story.
The Triassic Recovery
Following the Great Dying, the beginning of the Triassic Period, 252 to 201 million years ago, was marked by very low biodiversity. Those organisms that managed to survive the Great Dying were paleozoic holdovers. As such, Early Triassic taxa resembled Late Permian taxa.
As the Triassic period progressed, these survivors underwent evolutionary “adaptive radiations.” This process describes how organisms rapidly evolve and diversify, filling ecological niches.
Check out the video below if you have a few minutes. It does a great job explaining this concept in the Triassic.
By the Late Triassic, these paleozoic survivors had transformed into the distinctive taxa of the Mesozoic Era. Let’s discuss a few.
Cephalopods
The ceratitids were a remarkable cephalopod group from the Triassic period. They belonged to the larger ammonoid family.
During the Middle and Late Triassic, they underwent explosive evolutionary diversification. Their population and variety exploded.
Their success was brief. By the end of the Triassic, the ceratitids had vanished from marine ecosystems.
Here is a ceratitid cephalopod, Ceratites nodosus, from Triassic rocks found in Germany.
The ceratitid cephalopods were not the only new marine life in the Triassic. Another group emerged during this period: the first true ammonites.
These marine creatures would become significant predators in prehistoric oceans. During the Jurassic and Cretaceous Periods, ammonites dominated marine ecosystems. Their fossil record provides key insights into ancient sea life.
Stony Corals
Another taxon to rise to prominence in the Triassic Period was the Scleractinians. Known as stony corals, these animals first appeared in the Mid-Triassic. Scleractinians became the dominant reef-building organisms, a position that they still enjoy today.
Above is a modern scleractinian coral, Diploria labyrinthiformis. Also known as the Brain Coral, this animal stems from an evolutionary heritage stretching back at least 240 million years.
Fish, Fish, and More Fish
Yet another taxon to experience adaptive radiation was the Actinopterygians. These are known as ray-finned fishes.
Almost all modern fishes belong to this clade. These animals thrived for at least 150 million years since they appeared in the Devonian Period. They exploded in diversity during the Triassic. Like the stony corals mentioned above, they would endure to the present day.
Pictured above is a modern ray-finned fish: a Scorpionfish (Scorpaena sp.). His ancestors had been on Earth for at least 400 million years. They experienced adaptive radiation during the Triassic.
Terrestrial Vertebrates
As these various taxa evolved to dominate the oceans, terrestrial taxa evolved to conquer land. The first lizards, turtles, pterosaurs, and crocodilians appeared and diversified in the Triassic. We also saw the very first dinosaurs and mammals arise.
Dinosaurs Enter Center Stage
The first definitive dinosaurs, such as Eoraptor and Herrerasaurus, appear in Late Triassic rocks. This indicates that dinosaurs evolved at least 230 million years ago.
Dinosaurs may have appeared earlier, but scientists still debate this. Were these fossils “true” dinosaurs or only dinosaur-like ancestors?
Gaps in the fossil record make identifying the first dinosaur harder. Still, experts agree that dinosaur ancestors spread throughout the Triassic Period. By the end of the Triassic, true dinosaurs began their reign, dominating the Mesozoic Era.
The above picture is an Eoraptor on display in a museum in Japan. Meaning “dawn thief,” it’s the oldest confirmed dinosaur ever found.
If you’ve ever wondered where dinosaurs came from, it’s complicated. The UK’s Natural History Museum site has a great article on just that.
Mammals Enter… Stage Left
While dinosaurs evolved and diversified, mammals also emerged. They descended from therapsids, a group of mammal-like reptiles. Like dinosaurs, there’s debate about what defines a true mammal versus a mammal-like ancestor. Scientists agree true mammals had evolved by the Late Triassic.
The earliest mammals were small, about the size of mice. They likely fed on insects, plants, and lizards.
These mammals probably lived in burrows or tree canopies and were mostly nocturnal. Scientists believe this lifestyle helped them survive, as dinosaurs had already grown larger and dominated, limiting mammals’ ability to evolve into bigger forms.
Ironically, the mammal’s small sizes would also block dinosaurs from evolving into smaller forms. Perhaps while dinosaurs kept mammals small, mammals also kept dinosaurs large.
Above is a museum exhibit showing a model of what one of the first mammals, Morganocudon, may have looked like.
The End-Triassic Extinction
The good times of the Triassic recovery would not last. 51 million years after the Great Dying, disaster struck again with the End-Triassic Extinction. In this fourth mass extinction, roughly 76 percent of all taxa went extinct, and about 20 percent of all families went extinct too.
Compared to the other four mass extinctions, the End-Triassic was among the least severe. Let’s not kid ourselves: a mass extinction is a mass extinction.
Two of the hardest-hit groups in the extinction were the ammonoids, a group of cephalopods, and the conodonts. Only one group of ammonoids survived, and the conodonts, which managed to survive the previous three mass extinctions, went extinct.
Mammal-like reptiles and amphibians were also affected by the event. Other victims were various families of marine organisms.
Conodonts are important for studying ancient rocks. Their tooth-like fossils are common in the Paleozoic and Triassic layers.
This makes them excellent index fossils, which we covered in another article. They survived several extinctions but disappeared during the End-Triassic event.
The MIT website provides a good overview on the source of this event including Central Atlantic Magmatic Province (CAMP). We’ll touch on that in a bit in the section on Pangea.
Many taxa still managed to survive the extinction. Dinosaurs, pterosaurs, turtles, crocodilians, mammals, and many fishes survived the event, as did most plants. These organisms would evolve into the life commonly associated with the rest of the Mesozoic Era.
Was There a Silver Lining to the End-Triassic Mass Extinction?
Interestingly, many scientists argue that the End-Triassic event opened up new ecological niches for the dinosaurs by eliminating animals that competed with them.
As such, an event that could have driven the dinosaurs to extinction actually may have rocketed them into dominating terrestrial ecosystems throughout the rest of the Mesozoic Era. Go figure.
If this hypothesis is correct, then it’s ironically, a mass extinction that saved the dinosaurs from being just a footnote in Earth’s history. So, what happened?
Like the other mass extinctions, scientists still don’t know exactly what caused the End-Triassic extinction. They do have some strong hypotheses. If you’ve arrived at this article after reading the articles on previous mass extinctions, you may notice some common trends.
For more on the End-Triassic extinction’s winners and losers, check out this article from Sam Noble Museum. There is a pretty neat graphic.
The End of Pangaea
Throughout the Triassic Period, most of Earth’s land was combined into a supercontinent. This continent was called Pangaea. Towards the end of the Triassic, however, Pangaea began to rift apart, and Earth’s continents began their slow drift into the positions that we find today.
Accompanying this rifting was the eruption of massive volcanoes over several hundred thousand years. As these volcanoes erupted, they released massive amounts of greenhouse gases into the atmosphere. This triggered ocean acidification and global warming.
The Earth may have warmed enough that it even triggered a release of methane reserves from the ocean. This would have exacerbated global warming further. Methane is an even more potent greenhouse gas than carbon dioxide.
This image shows the extent of the end-Triassic volcanic eruptions (shown in red) that likely triggered the End-Triassic Event.
Astute readers may recall similar events that occurred at the end of the Permian Period, triggering the End-Permian Event. While the End-Triassic volcanic eruptions were similar, they were likely less severe.
This difference explains why the End-Triassic event caused fewer extinctions. Notably, life on land was much harder hit than aquatic life.
Other Explanations of the End-Triassic Extinction
Not all scientists agree with the volcanic eruption hypothesis for the End-Triassic Mass Extinction. Some argue that the End-Triassic was caused by an extraterrestrial impact like the asteroid that killed the dinosaurs. Others argue that the End-Triassic wasn’t a mass extinction at all but rather a slower, more drawn-out turnover of taxa.
| Potential Cause | Explanation |
|---|---|
| CAMP Volcanism | Eruptions from the Central Atlantic Magmatic Province (CAMP) released CO₂ and other gases, triggering global warming. |
| Ocean Acidification | CO₂ from volcanic activity lowered ocean pH, depleting calcium carbonate needed by marine species like ammonoids. |
| Pangaea Splits | The breakup of Pangaea altered habitats and ocean currents, amplifying climatic and environmental stresses. |
| Methane Release | Warming from volcanic activity may have released trapped oceanic methane, worsening the greenhouse effect significantly. |
| Extraterrestrial Impact | Some suggest an asteroid impact contributed, but evidence supporting this theory is limited. |
This version balances brevity with enough detail to clarify each cause. Let me know if you’d like further tweaks!
While there these ideas are interesting, they lack evidence. The timeline for the eruptions coincides perfectly with the decline in life, making a much stronger case.
Jurassic Rebirth
Following the End-Triassic Mass Extinction, life on Earth quickly rebounded, and the survivors of the mass extinction found new evolutionary opportunities awaiting them. Dinosaurs found vacant ecological niches ready for the taking, which they quickly exploited.
As a result, the dinosaurs rose to prominence and would dominate the Earth for the next 140 million years. That’s until an asteroid suddenly struck the Earth and changed everything once again.
That’s yet another story for another day. It’s the topic of the next article in this series.
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