In this alternate world, the aliens did establish a foothold at Roswell in 1947, and proceeded to take over the world with the assistance of resurrected Neanderthals as their henchmen. The Sons of Humanity are ready to rise up against them, using the club Terra Incognita as their clandestine headquarters.
The dinosaurs were not killed by a falling asteroid, but continued to evolve. Some species developed sentience, domesticating others the way humans tamed horses and cattle, parallelling our history in remarkable ways. In their
"middle ages" reptilian knights meet in battle, riding harnessed tyrannosaurs in defense of their clans' honor.