The study suggests that a massive volcano near India spewed toxic gas into the atmosphere for thousands of years. And eventually, scientists say that gas killed off the dinosaurs.
The scientists tracked ancient lava flows and looked at how fast the lava spread to come to their conclusion.
Dinosaurs were wiped out about 65 million years ago.
In recent decades, scientists had concluded a massive asteroid killed them off. They said it sent dust into the air that blocked out the sun.
The scientists behind the volcano study say it's just a theory and it's possible we may never know what actually killed off the dinosaurs.
The findings from the new study were presented at the annual meeting of the American Geophysical Union.