Over 200 million years ago, the dinosaurs ruled the Earth. This is an undeniable fact, however, the elements that propelled them at the top of the hierarchy are now being questioned by a new study set to appear this week in the journal Science.

Dinosaurs and crurotarsan asrchosaurus, ancestors of today’s crocodilians, co-inhabited the Late Triassic for over 30 million years. Although fierce “competitors” at the time, their evolution scale reveals similar rates and disparities, which suggests that dinosaurs were not necessarily the superior ones.

Despite all that, the dinosaurs ended up being the ones ruling the Earth, and the big question “WHY” seems to have finally found an explanation. According to a recent study led by Stephen Brusatte from the American Museum of Natural History, the dinosaurs simply got lucky.

About 200 million years ago, the Earth came under a mass extinction event, which greatly affected the crurotarsans. As a result, the ones of them that did survive suffered declining evolutionary rates and increasing disparity. This meant that from the crurotarsans, once dinosaur equals, the crocodiles were the only ones left.

A detailed fossil analysis revealed similar evolutionary rates and disparities for both dinausaurs and crurotarsans prior to the extinction moment. This suggests that if it hadn’t been for the unlucky event, dinosaurs and crurotarsans would have continued as equals, as there was no real superiority of one group or the other.

Logically speaking, if dinosaurs were indeed superior to crurotarsans, they should have presented faster evolution rates, or perhaps crurotarsans should have presented signs of a slower evolution. None of that happened, which indicates that dinosaurs ruled the Earth when nature got crurotarsans out of the way.

But that’s not all! Even if the two groups had continued co-exiting like before, recent studies indicate that crurotarsans may have been more successful than dinosaurs.

After studying over 60 species of crurotarsans and dinosaurs, scientists concluded that although they had similar evolution rates, crurotarsans were in fact more diverse, which according to Brusatte, means they could have become superior to dinosaurs.

While some paleontologists believe the new theory to be quite challenging, taking a different approach to the classical stories on dinosaur evolution and role, others believe it to be unsupported.

“Organisms don’t become extinct at random, and they don’t succeed at random,” said Kevin Padian, paleontologist at the University of California, Berkley, as quoted by National Geographic. “[Dinosaurs] grew faster, they had higher metabolic rates, they were bipedal, and they presumably more alert, agile, and lightly build.”

However that may be, the point is that there is more to dinosaurs ruling the Earth than we thought, and new ideas take us one step closer to establishing the circumstances that led to the rise of the dinosaurs.