This is a series of books that starts off with a bunch of humans being abducted and sent back in time roughly 65 million years. They start to build a civilization and take dinosaurs to help out. They are also able to climb very tall cliffs and glide on air currents to travel and scout.
Unbeknownst to them, they were sent back in time by aliens trying to prevent a galaxy wide takeover from other aliens, as it was found out too late that humans have some sort of innate resistance/ability that can stop these would be conquerors.
The other issue is that the timing of everything will make it so that after the humans wipe out the alien invaders, they will in turn be wiped out by the asteroid that kills off the dinosaurs.