That scene at the very end where the butterfly flies off, still alive and so history won’t be altered? Umm… isn’t there going to be a giant volcanic eruption in just a minute or two that will kill every lving thing in the area? The butterfly was doomed to die anyway.
I think we’re supposed to assume that this area is on the edge of the explosion, and that anything that could, say, run or fly would be able to get away – hence only being able to shoot the one dino that was trapped in tar.