Since this is a totally fantasy question, I'd take some totally fantasy guns. Or, in this case, I'd take the US Army's 1st Armored Division, plus air support, since 120mm HE rounds from an M1 Abrams would put a hurting on Mr. T-rex, and those velociraptors would have a hard time getting into an armored tank. Ma Deuce on top would be pretty useful too, as long as you've got plenty of cover in all firing arcs. The .30-cal co-ax gun would work for dealing with little dinos, as well. Then, if you have some M2 Bradleys, you can use their 25mm Bushmaster chain guns to deal with the smaller predators, like the good old velociraptors. HEI-T rounds would put a hurting on fast-movers like that. And man, oh man, would a brachiosaurus steak taste great after a long day of blowing up T-rex. What better way to engage a big herbivore like that than an AH-64D Longbow Apache with their 30mm chain gun, and perhaps a few Hydra 70 rockets and maybe an AGM-114K in the mix?