Time Safari, Inc. run by a rich multimillionaire (Ben Kingsley), uses the time travel technology for profit, where fat rich guys can go back in time and shoot a dinosaur to death. But they can't change anything in fear of changing the future. Even the smallest change could radically alter the present time. When one of the trips in time goes awry, something is changed. Huge trees and vines are growing in the middle of the city (Chicago), carnivorous insects are eating people and soon there are the descendents of the dinosaurs, primate-like creatures that look like a cross between a veloceraptor and a baboon. It's up to the company's lead scientist (Ed Burns) and the original creator of the time device to set things right.
As time travel movies this is intriguing, as the event they keep on going back to involves the same Allosaurus dying. They get their via the time portal five minutes before it sinks into quicksand and before a nearby volcano explodes. So by killing this creature, which will die in moments anyway, they aren't changing any event. The bullets the use are also made of frozen nitrogen so they soon vanish after use.
It's no big secret that what they accidently kill in the past-a butterfly (it's on the dvd cover). The original tale is the Ray Bradbury short story, but made into a feature film feels like it's a bit stretched out. The computer effects are decent and a futurist Chicago is convincingly portrayed ( I think most of the movie was done against Green Screen, like SKY CAPTAIN AND THE WORLD OF TOMORROW). Still, it is a movie worth spending time with.