In a barn fire getting the horses out of the barn is difficult because the horses will run back into the barn for security.
What happens to a horse in a barn fire? The horse has much larger lungs proportionally to its body than a human being has. The horse will die as it breathes the smoke. We humans for a little longer can enter the smoke to get the horses out if possible.
That is what happened to the dinosaurs. The larger animals would have had very large lungs when the meteor hit. The mammal that survived a vol-like animal in China our forerunner was underground where the particles would not have been as bad.