A surprising new study indicates that dinosaurs involved very rapidly.

It took just 5 million years for dinosaurs to evolve from their reptile predecessors into the thunder lizards we think of when we hear the name, according to a Live Science report.

Scientists had thought that it had taken between 10 and 15 million years for the early dinosaurmorphs to turn into dinosaurs, but now they have found in a study that the timeline was far, far shorter than that.

Randall Irmis, who is a paleontologist at the University of Utah and a curator at the Natural History Museum of Utah, said the finding “really narrows the amount of time between the appearance of these early dinosauromorphs and the first dinosaurs,” he said according to the report.

Dinosaurs differed from dinosaurmorphs in that they had the ball and socket hip that could rotate easily as well as additional vertebrae that resulted in stronger hips and therefore led to larger leg muscles to allow them to run faster. They also developed an additional hole in their skulls so they could cool off more quickly after an especially vigorous activity, the report states.

To come to their conclusions, the researchers looked at a mineral called zircon to help them date animals found in the dinosaurmorph rock layer. They examined levels of uranium, a radioactive element, a measured its decay. Using this method, they were able to precisely determined how long ago a particular piece of zircon crystal form, and therefore date the nearby dinosaurmorphs.

Their findings were quite astounding: dinosaurmorphs in the rock layer were between 234 and 236 million years old, which would place it 5 to 10 million years younger than scientists had previously expected.

It’s a fascinating finding that could lead to a better understanding of dinosaur evolution.