Basic biology would have it that in their natural environment deep underground, these voracious carnivores must have been feeding on a population of herbivores with at least ten times their biomass. I'm not sure what the underground herbivores feed on, but presumably there's a whole underground flora that gets by without photosynthesis. These herbivores must be pretty ferocious themselves, since they have forced the egg-laying bats to evolve such deadly teeth and talons. Though slower than the bat-things, eventually they too will figure out how to crawl through the same hole to the surface.
So I'm thinking sequel: "The Bleat," in which a race of killer sheep invade the eastern U.S., and every action scene begins with a terrifying "Baaaaa!" At first the desperate humans just try to kill them, for instance by tying cowbells around their necks to attract the killer bats, but eventually our heroes learn to shear them and use the wool to make bat-resistant winter garments.
So I'm thinking sequel: "The Bleat," in which a race of killer sheep invade the eastern U.S., and every action scene begins with a terrifying "Baaaaa!" At first the desperate humans just try to kill them, for instance by tying cowbells around their necks to attract the killer bats, but eventually our heroes learn to shear them and use the wool to make bat-resistant winter garments.