Imagine you are handed a photograph of an animal and asked to guess whether it inherited the Earth.
The animal in the photograph is about the size of a large pig. Its body is squat and barrel-shaped, its legs short and slightly splayed, its feet broad. Its head is oddly reptilian, ending in a wide, blunt turtle-like beak. Two small tusks protrude from its upper jaw. It has no other teeth. Its eyes are small, its expression difficult to read, its overall appearance somewhere between a boar and a snapping turtle.
You would almost certainly say no. There is nothing about this creature that suggests dominance. Nothing to suggest speed, strength, cleverness, or apex-predator power. Nothing to suggest that it will one day out-compete every other land vertebrate on the planet, walk unchallenged across every continent, and leave behind more fossils than any other animal that has ever lived on solid ground.
But it did. The animal in the photograph is Lystrosaurus. And for a brief and extraordinary span of the Early Triassic, approximately 251 million years ago, it did what no other terrestrial vertebrate has ever done before or since.
It became almost everything.
What “almost everything” actually means
In the Early Triassic fossil record, in specific well-studied beds in South Africa, Antarctica, India, and China, Lystrosaurus remains account for approximately 90 to 95 percent of all terrestrial vertebrate fossils recovered.
Not 90 percent of one family. Not 90 percent of the herbivores. Ninety to ninety-five percent of every vertebrate species that lived on land at the time. In an entire ecosystem, spanning multiple continents of a still-unified Pangaea, this one squat pig-turtle-shaped animal made up nearly the entire fauna of large land vertebrates.
No other land animal in the 500-million-year history of complex life on Earth has ever come close to that level of dominance. Not dinosaurs. Not mammoths. Not humans in aggregate, in terms of raw numerical dominance across all land ecosystems simultaneously. During certain windows of the Early Triassic, essentially every four-legged animal you would have encountered anywhere on Earth would have been a Lystrosaurus.
The paper documenting the recovery from the end-Permian extinction, published by Michael Benton and colleagues, is the source of the widely cited figure. The Benton 1983 estimate of ~90 percent dicynodont dominance has held up under subsequent palaeontological scrutiny and remains, four decades later, the accepted characterisation of Early Triassic terrestrial ecosystems.
How this happened
The reason Lystrosaurus achieved this level of dominance is not that it was an evolutionary marvel. It was, in most respects, a fairly unremarkable herbivore.
What it was, uniquely, was still there.
Around 252 million years ago, at the boundary between the Permian and Triassic periods, Earth experienced the largest mass extinction event in its history. The End-Permian extinction — sometimes called the “Great Dying” — killed approximately 96 percent of marine species and 70 to 75 percent of terrestrial vertebrate families. The cause was a combination of massive volcanic activity from the Siberian Traps, catastrophic release of greenhouse gases, ocean acidification, oxygen depletion, and cascading ecological collapse. It was the closest complex life on Earth has ever come to disappearing entirely.
Most terrestrial vertebrates did not survive. The gorgonopsians — the top predators of the late Permian, sabre-toothed and imposing — disappeared entirely. Most therapsid herbivores went extinct. Most reptile lineages did. The land was essentially emptied.
Lystrosaurus, and specifically one particular species called Lystrosaurus curvatus, was one of the few land vertebrates that made it through.
The reasons why are still debated. Some palaeontologists have proposed that its burrowing lifestyle allowed it to survive the atmospheric changes that killed surface-dwelling species. Others have pointed to specific anatomical features — a barrel chest that accommodated large lungs, high neural spines for efficient breathing muscles, short internal nostrils — that may have been adaptations for coping with low-oxygen air. Still others have concluded that its survival was, more than anything else, a matter of luck.
Whatever the specific cause, when the extinction was over, Lystrosaurus found itself alive on a planet that had lost almost everyone it used to share space with.
There was nothing left to eat it. There was almost nothing left to compete with it for the plants it fed on. Every ecological niche that had previously been occupied by other herbivores was now vacant.
Lystrosaurus expanded to fill essentially all of them.
What sheer dominance actually looks like
Within a few million years of the extinction event, Lystrosaurus populations had spread across the entire supercontinent of Pangaea. Fossils have been recovered from what is now South Africa, Antarctica, India, China, Russia, and Mongolia — regions that, at the time, were connected to each other as parts of a single unified landmass.
The animal’s global distribution, once palaeontology had catalogued it thoroughly, became one of the key pieces of evidence for continental drift. The German meteorologist Alfred Wegener, proposing his theory of moving continents in 1912, pointed to the fact that identical Lystrosaurus fossils were being found on continents now separated by thousands of kilometres of ocean. His argument was, in effect: this small herbivore did not swim between them. They must have been connected.
He was right, and Lystrosaurus was one of the specific animals whose bones proved it.
Why “dominance” here matters
The Lystrosaurus story is a specific reminder about what evolutionary success actually looks like.
The animal that dominated Earth more thoroughly than any other land vertebrate in the planet’s history was not an impressive-looking creature. It was not fast, not strong, not particularly clever, not equipped with any exceptional weapons or defenses. It looked, by most modern aesthetic standards, unremarkable — a small, squat, pig-turtle-shaped herbivore with two tusks and a beak.
What it had, that mattered more than any of those traits, was a combination of hardiness, generalism, and timing. It could eat a wide range of plants. It could survive in a wide range of conditions. It was flexible enough to occupy varied habitats. And it happened to be alive at exactly the moment when almost everything else that could have competed with it was dead.
Dinosaurs would eventually replace it. So would mammals. So would every other class of large terrestrial vertebrate that has since existed. Lystrosaurus’s dominant window was brief in geological terms, a few million years at most, and by the Middle Triassic it had been outcompeted by newer, faster, more specialised species.
But for that brief window, it did what no impressive animal ever managed. It inherited the Earth.
The champion, as it turned out, was not the strongest or the smartest. It was the one still standing when everyone else had fallen down.