Stumpy is a male T. rex who got his name after his left arm, which was almost ripped off after a territorial fight.
Stumpy and a bigger and more aggressive male T. rex, known as Jack Palance, are fighting at a seashore over a territory. Both males made a fighting display including roaring. After a short fight Jack Palance grabs Stumpy's arm and almost rips it off.
We see Stumpy again with his mate Tinkerbelle, as his two babies play. They fall asleep and the pair chase a little Pachycephalosaurus into a log. However, Jack was there, and Jack cannibalizes the two offspring. Then Stumpy and Tinkerbelle check and find the babies have been eaten. At night Stumpy comforts Tinkerbelle.
The next day they attack and kill a Triceratops, and eat it, but the cannibalistic rival of their's, Jack Palance, returns again, staring at Tinkerbelle, and Stumpy and Jack have a reunion. Then they bite each others snouts, and a splash of blood was torn off of Jack, but Jack was bigger and so recovers quicker, biting Stumpy's neck. He sees the front limb and Jack tries to bite it off, but Tinkerbelle comes from behind and bites Jack's leg, before her mate is free and knocks over Jack, and Jack lands his throat into the horn of the Triceratops carcass, and dies. Later that night, Stumpy and Tinkerbelle are seen cuddling with each other. Tinkerbelle stands up showing she is ready to mate, Stumpy gets up and walks to her and gets into the mating position. Tinkerbelle takes a step forward, stomping an eggshell of their previous young, it then pans out showing them mating.
Later in the episode, the female lays a clutch of eggs, and scares her mate away. Later, a pack of Troodon arrive, surrounding the nest to take an egg. A Troodon takes an egg, but Stumpy grabs the Troodon and kills it, but drops and breaks the egg. He then scares away the pack. Months later, in the morning, Tinkerbelle starts digging the nest, but only a pack of mammals get out, with all, except one egg, eaten. The female hatches the lone egg, and the baby hatches.
Later, on the day of the impact of the asteroid, the baby T. rex has became a teenager and leaves his parents to mess with a Ankylosaurus.
Later, when Junior come out of a cave he was hiding in, he finds his parents dead.