Rod of the Great Beast
This fearsome-looking bone rod can be wielded as a +3 mace. More importantly, when the command word is spoken, the wielder can bend a dinosaur to his will. The dinosaur gets a save; if the save is unsuccessful, the dinosaur will accept and carry the rod-holder as a rider. The effect lasts for as long as the rod-holder owns the rod and keeps it about their person, although actually guiding the dinosaur requires the rod to be held in one hand. Controlled dinosaurs are slightly but not greatly more docile than usual when the rod-holder is not about: using carnivorous great beasts as mounts is likely to result in the loss of stablehands (assuming one can find help willing to approach such a creature).