Who was our ancestor when the dinosaurs died?

The asteroid impact that killed the dinosaurs was one of the worst days in the history of the Earth and yet our ancestor survived. I've been trying to find out what we know about who that was? Does palaeontology have any idea? If so, what fossils do we have? And what does all of this have to do with a little mouse thing eating flowers? Couldn't have done this without the help of Andrew Schwartz!