Rex was a male Tyrannosaurus and member of Bloodtooth's pack. He is now known to have been the brother of Bloodtooth.
Rex made his first appearance in season 3 episode 1, where he and Bloodtooth attempt to hunt down Hammer. He made another appearance in season 3 episode 4, where he chases a young Hadrosaur with the rest of his pack. However, the Hadrosaur gets a huge advantage in the chase, and so Rex and the rest of his pack give up. However, Nigel continues because he is full of energy and eventually gets lost.He appeared in every other episode with the Tyrannosaurus pack, until he was killed by a stampeding herd of sauropods in season 3 episode 11.
- Rex is named after his species, tyrannosaurus rex.
- He appears to be the least popular member of the Tyrannosaurus Pack , as very few fans were upset with his death.
- Rex was first thought to be Bloodtooth's mate until episode 2 of season 3 where it was revealed that Grant was Bloodtooth's mate.
- Because Rex died in the same episode as his brother Little Tyrant, his death was subsequently overshadowed, as Little Tyrant had more of a following than his older brother before their subsequent demises.