Back in the early 90s I had the opportunity of participating on a paleontological expedition to the badlands of Montana. The soil was built up over hundreds of millions of years and flooding cut through the soft soil leaving a stratigraphy that is dramatic and easy to read. You can even see the Chicxulub ejecta, a chocolate brown horizontal line about the width of your hand.
Now whole dinosaur skeletons are a rare find. You can spend a whole season tramping through the badlands and never find two bones that go together. But individual bones are more common, and bone fragments are more common still, and experts can often identify the group of dinosaurs or even the species of dinosaur a bone fragment came from, often a surprisingly small fragment of bone.
What we were doing was assembling a database of species found by layer, which in turn maps to era. What the PI was finding was a shift towards species with anatomical adaptations to deal with heat. His opinion was that there was already a climate driven adaptive stress on the dinosaur population, which turned the aftermath of the Chicxulub impact into a knock-out blow.
So the idea that there was more going on than an asteroid impact is hardly new. People were thinking that way twenty years ago.