Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, according to an international team of researchers. It was all about the asteroid.
Source: In death of dinosaurs, it was all about the asteroid — not volcanoes — ScienceDaily
Sixty-six million years ago, an asteroid hit the Yucatan Peninsula in Mexico and produced cataclysmic disruptions that, it is believed, killed off about 75% of species (the K/Pg extinction). But many researchers think there must have been other factors at work.
Source: Smithsonian: The asteroid strike was only one factor in dinosaur extinction | Uncommon Descent