This feels like two separate books squished together. It starts with a primer about the universe that explains the problem of dark matter, then goes on what feels like a tangent to go in depth about asteroid impacts and the consequences, then it goes back to dark matter -- no dinosaurs so far and we're over 80% of the way through -- and then it finally very briefly ties in the dinosaurs.
It's not badly explained, but it's a bait-and-switch.