How did dinisaurs die?

This really isn't a simple question to answer, as it involves a massive array of data. So massive, in fact, that it has been the subject of debate for centuries up until a few years ago. A final picture was completed, and most of the scientists can now sleep easy at night. Here is the entire hypothesis in full (you might want to sit down for this.)

The fact of the matter is that the dinosaurs were in recline long before the 65.5 million year mark. We have found far fewer dinosaur genera from the K.T. boundary than from, say, 90 million BC. Not only dinosaurs, but just about everything else was in a period of struggle. Where an entire menagerie of pterosaurs- for example- once glided, only one or two species remained. This is believed to be caused by a rare surge in volcanic activity, among other things. The constant threat of poisonous fumes, falling soot, and overcast skies made periods of drought long, birthrates short, and times tough for life here. However, while this did push them, it is unknown whether this would have wiped them out for sure.

What really brought the dynasty to its knees, though, was the coup de grace, the infamous Baptistina asteroid chunk. This six-mile long piece of rock hit the Gulf of Mexico with the estimated force of 100 teratons (100 trillion times the force) of TNT. The entire rock layer below it was shattered and blasted in all directions. A cloud of fire and sheer force demolished the open landscape as far away as Canada, and created mega-tsunamis miles high that raced around the globe. Debris from the initial blast rained down from the sky for days. The tectonic plates buckled, sending an upheaval of earthquakes and volcanoes. Wildfires of clearest origin destroyed much of the forest and plant life left.

Whatever survived this still faced the maw of the aftermath. All of the dust, debris, and ash from the previous events hovered over the sky, simply sitting. The planet was launched into a nuclear winter: it grew very cold very fast, and everything was deprived of sunlight for hundreds, maybe thousands of years. All of the plants which the dinosaurs fed off of withered away. The herbivores were starved and died off. The carnivores enjoyed a brief period of plenty, but eventually depleted their source and slowly, but surely, died off as well.

We as humans may be asking ourselves- how did we live while everything around us died. Well, I'll tell you.

I don't know.

With everything that survived the extinction, there was another that defied it.*

It's practically set up so that there's no real formula for who died and who didn't. We do know, though, that by some odd chance, they all weighed less than fifty pounds. We also know that we owe some thanks to the dinosaurs- if they lived, where would we be?...

*Mammals survived because they went underground, but birds couldn't burrow back then. Maybe it was because they were warm-blooded, then? But sharks and crocodiles survived as well. You can take it from here...