Rex, Abby Maitland's beloved pet, is a Coelurosauravus from the Permian period – about 250 million years ago – and is unusually active and intelligent for a cold blood. He first appeared in Episode 1.1 and has been the mascot of the show ever since.
He returnes in Primeval Revived.
He is discovered in the Forest of Dean by a young boy, Ben Trent, who contacts the zoo where Abby Maitland is working. When she arrives at the boy's home he suggests Rex may be the modern gliding lizard Draco volans, but Abby discredits this theory, saying the child may have discovered a new species.The two journey into the Forest of Dean to see if they can find out more about Rex where they discover a dead cow lodged in a tree. When Rex runs away from Abby, she follows him and becomes separated from the boy. In the process of trying to recapture Rex she discovers that he can fly, or at least glide very well. The others find Rex shortly after discovering the Scutosaurus, he is later taken to the Home Office where the researchers there examine him — however they scare him and he escapes, gliding through the building. Rex finds an open window and glides out. However he quickly returns enticed by Abby's lizard food.
When Nick Cutter goes through the Forest of Dean anomaly, he tries to take Rex with him, but Rex sneaks back through shortly before the anomaly closes and is taken home, secretly, by Abby and kept as a pet. (Episode 1.1)
Later, Connor implies that he will reveal that Abby has Rex unless she gives him a kiss, in order to show off to his friends who have dropped him off at her place that he may stay in the spare room of her flat. (Episode 1.4)
Connor Temple, now staying with Abby, leaves a window open and Rex flies out to the back of Connor's car. Connor transports him all the way to a golf course, where Rex escapes. Connor chases after him, and the pair are attacked by a Pteranodon. They eventually get away unharmed, but Rex runs off again. Abby is furious at Connor for letting him escape, and for not keeping his presence a secret. After much searching, Rex is eventually found and returned home. (Episode 1.5)
Rex is shut in a freezer by Caroline, he nearly freezes but Abby manages to save him. (Episode 2.4)
Shortly after Connor Temple breaks up with Caroline Steel by text, the disgruntled and upset Caroline lures Rex out and then attacks him. Rex manages to avoid the items she attempts to throw at him, but is hit by a tennis racket Caroline has armed herself with. Rex is shown to have been injured and is unconscious. When Connor and Abby return to their flat Rex is gone, kidnapped by Caroline. (Episode 2.5)
Caroline takes Rex to Leek's creature collection. But when all the creatures are released, Rex is too. Rex is shot in the leg by an armed guard, but the injury was not fatal, he later escapes with Connor, Abby and Caroline. (Episode 2.6, Episode 2.7)
Rex is briefly seen in Abby's flat and wakes up Connor by eating the vegetables on his face. (Episode 3.1)
Jack Maitland, Abby's brother, loses Rex in a card game to friend. Rex is put on the internet for sale but Connor gets him back by persuading Jack's friend, Tony, with help from Becker and his Special Forces cohort. (Episode 3.6, Episode 3.7) Abby brought Rex to Lester's flat as he was feeling lonely. He is immediately curious of Sid and Nancy, Connor's pet Diictodon, and communicates with them. (Episode 3.9)
Rex returns in Primeval Revived
Rex's first appearence in Primeval Revived is Episode 1.3, where he is seen being fed by Abby and Sam in the menagerie, along with the other creatures.