Imagine receiving a photo of an animal and being asked to determine whether it inherited the Earth.
The creature in the image resembles a large pig in size. Its body is stout and barrel-like, its legs are short and a bit splayed, and its feet are broad. Its head has an unusual reptilian shape, finishing with a wide, blunt beak similar to that of a turtle. Two small tusks jut out from its upper jaw, and it lacks any other teeth. Its eyes are small, its expression inscrutable, and its general appearance is reminiscent of both a boar and a snapping turtle.
You would most likely respond with no. There is nothing in this creature that implies domination. No signs of speed, strength, intelligence, or apex-predator prowess. Nothing indicating it would one day out-compete every other land vertebrate on the planet, traverse all continents unchallenged, and leave more fossils behind than any other terrestrial animal ever.
But it did. The creature in the picture is Lystrosaurus. And for a brief and remarkable period during the Early Triassic, around 251 million years ago, it accomplished what no other terrestrial vertebrate had achieved before or after.
It became nearly everything.
What “nearly everything” actually denotes
In the fossil record from the Early Triassic, particularly in well-studied sites in South Africa, Antarctica, India, and China, remains of Lystrosaurus comprise about 90 to 95 percent of all terrestrial vertebrate fossils unearthed.
Not 90 percent of a single family. Not 90 percent of herbivores. Ninety to ninety-five percent of every vertebrate species that existed on land during that period. In a whole ecosystem covering multiple continents of a still-unified Pangaea, this one squat pig-turtle-shaped creature constituted almost the entire fauna of large land vertebrates.
No other land creature in the 500-million-year timeline of complex life on Earth has ever come close to such a level of supremacy. Not dinosaurs. Not mammoths. Not humans collectively, in terms of sheer numerical dominance across all land ecosystems at once. In certain intervals of the Early Triassic, virtually every four-legged creature you encountered anywhere on Earth would have been a Lystrosaurus.
The research documenting the findings from the end-Permian extinction, authored by Michael Benton and colleagues, is the origin of the widely referenced statistic. The Benton 1983 estimate of ~90 percent dicynodont dominance has stood the test of further paleontological investigation and continues to be recognized, four decades later, as the established characterization of Early Triassic terrestrial ecosystems.
How this occurred
The reason Lystrosaurus attained this level of dominance is not that it was an evolutionary wonder. It was, in most aspects, a rather unremarkable herbivore.
What set it apart, uniquely, was its continued existence.
Approximately 252 million years ago, at the interface between the Permian and Triassic epochs, Earth underwent its most extensive mass extinction event. The End-Permian extinction — often termed the “Great Dying” — obliterated around 96 percent of marine species and 70 to 75 percent of terrestrial vertebrate families. The reasons stemmed from a combination of massive volcanic activity from the Siberian Traps, catastrophic greenhouse gas emissions, ocean acidification, oxygen scarcity, and cascading ecological decline. It represented the closest complex life on Earth has come to complete extinction.
Most terrestrial vertebrates did not endure. The gorgonopsians — the apex predators of the late Permian, saber-toothed and formidable — vanished entirely. Most therapsid herbivores went extinct. Most reptilian lineages perished. The land was effectively vacated.
Lystrosaurus, particularly a species known as Lystrosaurus curvatus, was among the few land vertebrates that survived.
The reasons behind this are still a matter of debate. Some paleontologists suggest that its burrowing behavior enabled it to withstand the atmospheric changes that wiped out surface-dwelling species. Others have highlighted specific anatomical traits — a barrel-shaped chest that allowed for large lungs, tall neural spines for efficient respiratory muscles, and short internal nostrils — that may have been adaptations for coping with low-oxygen environments. Still, others have determined that its survival was largely a stroke of luck.
Regardless of the exact cause, when the extinction concluded, Lystrosaurus found itself alive on a planet that had lost nearly all its prior companions.
There was nothing left to predate it. There was almost no competition for the plants it consumed. Every ecological niche once filled by other herbivores was now available.
Lystrosaurus spread out to occupy virtually all of them.
What true dominance genuinely looks like
Within just a few million years post-extinction, Lystrosaurus populations had proliferated across the entire supercontinent of Pangaea. Fossils