Steve Brusatte, Professor Michael Benton and colleagues at the University of Bristol said their research shows dinosaurs didn't proliferate immediately after they originated.

"Our research shows the rise of dinosaurs was a prolonged and complicated process," said Brusatte, noting dinosaurs originated about 230 million years ago and survived the Late Triassic mass extinction that killed about 35 percent of them. That allowed herbivorous dinosaurs to expand into the niches left behind.

The researchers said the rapid expansion of carnivorous and armored dinosaurs didn't occur until after a much bigger mass extinction at the Triassic-Jurassic boundary, when at least half the species then living on Earth became extinct.

The study also shows dinosaurs evolved into big predators and long-necked herbivores long before becoming abundant or diversified into the many different species we know today.

"It just wasn't a case of dinosaurs exploding onto the scene because of a special adaptation," Brusatte said. "Rather, they had to wait their turn and evolved in fits and starts before finally dominating their world."

The study is reported in the journal Biology Letters.