For Millions of Years, Earth Was Dominated by a Single Vertebrate Genus

It’s not humans. How a survivor of a super-extinction repopulated our planet

The true face of utter and total domination. This guy ruled the Earth.Photo byWikimedia Commons

There are more than 8 billion humans alive at this moment on Earth (unless something has gone horribly wrong). But humans aren’t the only dominant mammals.

It’s incredibly difficult to accurately count the total number of other animals, but one estimate suggests there are certainly more rats than humans. There’s also an estimated 1.4 billion cattle and 1.1 billion sheep, as well as over 18 billion chickens.

That’s a decent blend of top animals.But at one point, there was basically only one animal living on Earth (on land, at least).

Say hello to Lystrosaurus.

Possibly one of the most successful animals in existence.

The Permian Extinction, or the “Great Dying”

252 million years ago, something awful happened. It was so awful that we still don’t know what it was, but it killed just about everything.

That’s not an exaggeration; the mass extinction event that marked the end of the era we called the Permian period killed an estimated 57% of biological families, 83% of genera, 81% of marine species, and 70% of terrestrial vertebrate species.

Trilobites? Gone.

Ancient fish? Gone.

Corals and anemones? Wiped out.

9 different orders of insects were rendered extinct.

And almost all the reptiles, the largest life form at the time, were also killed.

The extinction didn’t kill everything, or else there’d be nothing to regrow into the life that now flourishes on Earth. But it was severe enough to set back regrowth by an estimated 4–6 million years. Full recovery, with well-developed ecosystems and apex predators like we see today, likely took close to 30 million years.

During that recovery period, a few small groups of animals that found a successful niche managed to flourish — none more so than a sub-order called dicynodonts.

The rise ofLystrosaurus

In this post-apocalyptic period, plants recovered faster than animals. As the base level of the food chain, plants loved an empty environment that they could colonize, and they thrived with all their former predators now extinct.

Until along came Lystrosaurus.

We’ve found four different species of Lystrosaurus skeletons, ranging in size from 2–8 feet in length, and most standing no more than a foot or 2 in height. They were herbivores, with a beak, two tusks like a pig, and grinding teeth for consuming plants, with leathery, hairless skin.

They seemed to have been one of the first animals to emerge after the Permian Extinction, and they thrived. For a few million years, as far as we can tell from fossils, the only land vertebrates were Lystrosaurus.

Imagine that world. Plants, insects, some fish in the seas — and four species of small, pig-like plant-eating dinosaurs. That’s it.

There’s a number of theories about why this particular creature endured an extinction event that killed just about everything else:

• Lystrosaurus may have been able to enter a hibernating state called torpor, as suggested by thin growth rings in fossilized tusks.
• Lystrosaurus likely could burrow, given its short, strong legs (great for digging) and stronger fore-leg muscles. That may have provided some protection, and improved survival in oxygen-poor environments.
• Lystrosaurus may have been a more generalist herbivore, and managed to subsist on the few species of plants that survived the extinction event.
• Lystrosaurus likely reproduced and matured quickly, letting them take over once slower-growing competition was eliminated.
• It could have just been luck. (Yes, scientists will admit this — and no matter their adaptations, luck certainly played a role.)

How do we measure success?

Lystrosaurus isn’t around anymore. (Even though it lived 250 million years ago, it’s more closely related to mammals, today, than it was to the dinosaurs and today’s lizards. So humans, in a very distant way, are the living descendants of Lystrosaurus!)

Is success measured by how long a species, unchanging, has managed to exist? If that’s the case, the winners are sea sponges and jellyfish, both pretty much unchanged for over 500 million years.

Or is success measured by dominance of the planet’s biosphere?By that measure, Lystrosaurus likely was the most successful animal to exist, and its record won’t be matched unless there’s another mass extinction, with its own incredibly lucky sole surviving species.

Lystrosaurus didn’t possess our level of intelligence, of course, and didn’t build a complex civilization or launch objects into interstellar space. On that front, humans have it beat.

But humans haven’t managed to stick around for millions of years, and it’s looking increasingly uncertain that we’ll be able to persist for as long as Lystrosaurus maintained its top spot.

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Life is an ever-evolving game of king of the hill, and changing field conditions can make it easier — or harder — for a particular species to keep its spot. About 250 million years ago, a massive extinction swept the board, clearing the way for a small band of herbivores to become one of the most dominant groups of all time, for millions of years.

Perhaps this is a nice reminder; we don’t need to be apex predators, or the fastest, or the strongest. If a small, burrowing, stubby-legged herbivore can be the most successful land animal on Earth for millions of years, you can succeed as well!

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