I think this is the best idea, beause
[Dinosaurs are kinda weird, this is a Post-apocalyptic game, not Jurassic park
Military… well, may… posibblie, somewhere.
The other options are WEIRD
the best option are mutants.
They appeared from an incident of radiation.
they´re ugly, crazy, and a very large group, they habit at Radtowns, caves, dark places. What else?
at night they will follow you, try to kill you, come from nowhere and creep your from outside of you house making noises.
and then you can add Military, with their bases, getting atacked from the mutants, so you heard creeping noises, a shoots at night.
Idk, if you like the idea Comment, if dont, get away.
PD: SORRY FOR MY BAD ENGLISH!!!