This is Scientific American 60-Second Science. I'm Christopher and Daljata.

Just like cows, sheep, and bison roam the earth and herds today, so too did plant-eating dinosaurs.

And it appears they began flocking together much earlier than we used to think,

just as the Jurassic period was beginning to unfold.

This is really a critical time in the evolution of dinosaurs. This is pretty early off.

So the idea is that this type of social behavior may actually contribute to the evolutionary success of dinosaurs.

Jahan Ramazani of the Massachusetts Institute of Technology is a geochronologist in his words,

I day things, and I day old things, things in the millions and billions of years, not the really young stuff.

In this case, Ramazani was dating tiny zircon crystals, embedded in a fossil bed in Patagonia,

near the southern tip of South America. Those crystals dated back to nearly 193 million years ago.

And the fossils preserved there, an array of nearly 200 specimens of a plant eater named Musaurus Patagonicus,

provide a snapshot of a dinosaur at all stages of its life, eggs and hatchlings, clumps of juveniles, and then further out adults.

So this kind of undisturbed distribution of fossils, and this kind of age segregation,

basically shows that these dinosaurs had had a kind of a social structure.

They lived in a colony, and everybody has got things to do, duties with respect to the youngs and the juveniles.

The study in the journal Scientific Reports suggests dinosaurs developed complex social behavior

40 million years earlier than we used to think. And Ramazani says the work also advances longstanding questions

about the social structure of dinosaurs.

Was it more like primitive taxa, like the crocodiles, or looked like the more evolved types of animals, like birds and mammals?

And we are beginning to see that, yes, it looks more like a mammal or more like a bird-type colony.

Whatever type of social structure it was, the scientists hypothesized that it helped large, plant-eating dinosaurs first spread across the planet,

kickstarting tens of millions of years of dominion on Earth.

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