Triassic Park: On the origin of (dinosaur) species

by David B. Williams
Thursday, January 5, 2012

Fossil discoveries in the past decade reveal that the earliest dinosaurs lived alongside a diverse collection of reptilian beasts during the Triassic. Steve Brusatte, AMNH

Ask a third grader what happened to the dinosaurs and she will tell you that an asteroid killed them all. Many adults even know what caused the demise of the dinosaurs: A massive bolide crashed into the Yucat√°n Peninsula in Mexico about 65 million years ago, setting in motion a series of environmental changes that killed off 60 percent of life on Earth. But if you ask people about the origin of dinosaurs 165 million years earlier, you get blank looks. Even many paleontologists have little to say about the subject.

The traditional story about the origin of dinosaurs has centered on a classic evolutionary theory of one group arising and replacing another. Fossil evidence from South America, including some found in the 1960s, appeared to show that when dinosaurs first evolved about 230 million years ago during the Triassic, they were better adapted than other land animals, and thus slowly took over. By the Jurassic and Cretaceous, dinosaurs and crocodiles were the only large land-based vertebrates.

But over the past decade, more and more fossil discoveries have revealed a different story. The earliest dinosaurs lived alongside a diverse collection of reptilian beasts throughout the Triassic — many of which held their own against dinosaurs. The new fossils also show that the ultimate success of dinosaurs probably involved a bit of luck.

“Previously, we thought the story of dinosaur evolution was comparatively simple,” says Bill Parker, a paleontologist at Petrified Forest National Park in Arizona. “But now we find out it wasn’t that easy.” As so often happens in science, a new paradigm is emerging on the rise of the dinosaurs.

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