Dinosaur evolution
The Survivors Who Shouldn't Have Won
Dinosaurs didn't rise to dominance because they were superior — they inherited the Earth after a stroke of geological luck that nearly erased them too.
The Idea
The standard story of dinosaurs is one of triumph: powerful creatures who ruled the Mesozoic for 165 million years. What that story glosses over is how precarious their ascent actually was. Dinosaurs first appeared around 230 million years ago during the Triassic period, but for their first 30 million years they were bit players — occupying ecological niches at the margins while other reptile groups, particularly the crurotarsans (the lineage that eventually gave us crocodilians), dominated the landscape. Then, around 201 million years ago, the End-Triassic mass extinction hit. Volcanic eruptions on a scale almost incomprehensible to us — the opening of the Central Atlantic Magmatic Province — flooded the atmosphere with carbon dioxide, acidified the oceans, and collapsed ecosystems globally. The crurotarsans were devastated. Dinosaurs, for reasons palaeontologists are still working to understand, were not. They survived, and into the ecological vacuum they expanded explosively. What followed was an adaptive radiation — the rapid diversification of a lineage into newly available niches — that produced everything from the long-necked sauropods to the feathered theropods that eventually became birds. The lesson buried here is subtle but important: evolutionary dominance is not always a story of the best design winning. Sometimes it is a story of who happened to be standing when the music stopped.
In the World
The clearest window into this contingent triumph comes from the Ghost Ranch quarry in New Mexico, where thousands of fossils from the late Triassic and early Jurassic boundary have been excavated since the 1940s. Palaeontologist Paul Olsen and his colleagues studied the rock layers there with unusual precision, correlating them to known dates of the End-Triassic eruptions. What they found was striking: in the layers just below the extinction boundary, dinosaur fossils are relatively rare and small. In the layers just above it — geologically speaking, almost immediately after the catastrophe — dinosaur footprints multiply dramatically, and the animals themselves are larger. The crurotarsans, meanwhile, essentially vanish. Olsen's team described this as a near-instantaneous ecological takeover, unfolding over perhaps tens of thousands of years rather than millions. That sounds slow by human standards, but in geological time it is a blink. Perhaps even more telling: some of the early post-extinction dinosaurs, like Anchisaurus, were anatomically quite similar to their Triassic predecessors. They didn't suddenly become more sophisticated. They simply survived into a world where their main competitors no longer existed. The quarry at Ghost Ranch, made famous in a different context by the painter Georgia O'Keeffe who lived nearby and was transfixed by its landscape, turns out to be one of the best places on Earth to watch an accidental dynasty begin.
Why It Matters
There is a cognitive bias — sometimes called survivorship bias — that leads us to reverse-engineer success. We look at whoever won and assume their traits explain the victory. Dinosaurs were magnificent, yes. But their magnificence came after the opportunity, not before it. The same pattern appears throughout evolutionary history, and arguably in human history too: the dominant form is often not the one that was always best suited, but the one that happened to be present and viable when a gap opened up. Sitting with this idea changes how you read stories of dominance and success. It doesn't make achievement meaningless — once dinosaurs had the stage, what they did with it was genuinely extraordinary, lasting longer than any mammals have managed so far. But it does suggest that separating talent from timing is harder than it looks, and that the losers of history were not necessarily the less worthy contenders. They may simply have been standing in the wrong place when the volcano erupted.
A Question to Ponder
If the End-Triassic extinction had never happened and the crurotarsans had continued to dominate, what kind of intelligence — if any — might have eventually evolved on Earth?
Get a new one of these every morning.
Start learning with Thinkable