Small Herbivore A & B: (Dryosaurus and Gallimimus)
This batch of herbivore selection comes from the observations of utahraptor and their direct needs. Currently they need more accessible prey items than just a juvenile tenontosaurus as they don't stand to an adult in singular combat. This dictates the necessity of two smaller dinosaurs that not only could fall prey to adult utahraptors, but juveniles as well. Dryosaurus and gallimimus are most likely to fit this bill, as they are agile but not so large a singular utahraptor could not hunt them even at respective peak physical sizes.
Medium Carnivore: (Carnotaurus)
Well, if you have two prey items in the fields, you need a proper hunter for it. Carnotaurus is perfect from the retro roster of dinosaurs that offsets the utahraptor's superior maneuverability for sheer speed, restricting it to an ideal hunter in the plains. The introduction of carnotaurus will also put tenontosaurus out of its current position of simply standing their ground against any predator save for the largest of utahraptor packs. Lastly, the somewhat fragile build of a carnotaurus will not make it immune to the offensive of a group of utahraptors in adulthood, while its younger years makes it extremely susceptible to lone utahraptors.