Despite humans living on Earth in Dragonball Z, there are also several dinosaurs alive as well.
Gohan constantly finds himself being chased by a hungry T-Rex. He also makes friends with an injured brachiosaurus, but it is eaten by the T-Rex. Pretty soon, Gohan is able to easily outrun the T-Rex and slice off pieces of its tail to cook and eat. After a while, it's Gohan who's chasing the T-Rex around. Gohan also observes a large heard of triceratops while fending for himself in the wild.
During a series of filler episodes involving Krillin, Gohan, and Bulma on a fake Namek, a gigantic dinosaur picks up a Dragonball and carries it into a lake full of acid, where it is killed. It is later revealed that both the dinosaur and the acid were an illusion, as was everything else on the fake Namek, as they were imaginary quests constructed by the devious Raiti and Zaacro
Captain Ginyu Saga
Bulma is chased by a T-Rex on Namek, but it is killed by Krillin and Gohan.
Bulma appears to be chased by a huge pack of T-rexes and triceratops, but it turns out they are only running from Frieza's immense power as he transforms.
Great Saiyaman Saga
Maraikoh appears to be a dinosaur, though he also resembles a dragon. He advances into the quarterfinals and beats Frogue, but is defeated by Goku in the semifinals. He is later seen during the Kid Buu Saga.
Gohan and Goten own a pet dinosaur named Chobi. Chobi has a mother, and also a father named Toh Toh. Chobi is kidnapped by greedy circus man Mr. Musuka, and Gohan, as Saiyaman, attempts to save him, but during a struggle between Saiyaman and Videl, Chobi calls his parents and they attack the city. Gohan is forced to knock Toh Toh out to stop him attacking Videl. The family is reunited, and Mr. Musuka is arrested for stealing an officer's handgun.
Also Goten finds two dinosaurs while Gohan is training. The first is a baby who reminds him of Icarus. The second is big, and whips Goten away with his tail. Gohan thinks Goten could have been killed, but at that point was unaware that he was just as powerful as him, able to turn Super Saiyan.
Kid Buu Saga
Several dinosaurs are seen giving Goku energy for his Spirit Bomb.
Broly: Second Coming
The monster that attacks Zalador and Coco's village is a dinosaur who looks similar to the one from the fake Namek. Goten, Trunks, and Videl set a trap for it, resulting in Goten and Trunks torturing and killing the monster and they and the inhabitants of the village cook and eat it.