Rex came through an Anomaly from the Permian to the Forest of Dean in the present day, and was found by a boy who lived nearby named Ben Trent, who contacted Wellington Zoo about the lizard. When the chief reptile keeper, Abby Maitland arrived to take the lizard to Wellington Zoo, she realised that he was not the flying dragon like Ben believed. The two took him into the Forest of Dean in search of the exact place where Ben found the creature.
In the forest, they discovered a dead cow lodged in a tree and heard low distant growling. Ben ran off home in terror and Abby quickly tried to follow with Rex, but they got separated from Ben and became lost. A Gorgonopsid then arrived, and Rex flew into a thicket of bushes and Abby likewise hid until the predator had left. Abby continued to search for Ben, until night fell and the two came across a Scutosaurus and met Nick Cutter, Connor Temple, Stephen and Claudia Brown. Cutter and Stephen Hart were fascinated by Rex when they noticed him.
The following morning, Rex was taken back to the Home Office and examined by scientists in a laboratory. However, the scientific instruments startled Rex and he flew out when a scientist opened the door. Rex glided through the building, startling employees and avoiding the team and defecating on James Lester's shoulder, until he perched by an open window. Abby tried to entice Rex with reptile food, and though the lizard initially flew out through the window, he quickly returned to Abby.
The following night, Cutter took Rex with him back into the Permian through the Forest of Dean Anomaly, and let Rex fly off. However, Rex came back through to the present just before the Anomaly closed. With the Coelurosauravus now marooned in the present, Abby kept Rex as a household pet and did not tell the others about his return.
Abby kept Rex in her flat and turned the thermostat up to the high temperatures of his natural habitat in the Permian that he was adapted for. When Connor Temple moved into Abby's flat, Abby tried to hide Rex in a tank under a blanket from him, but Connor found Rex and realised he had returned.
When Connor left in a rush to deal with a new Anomaly incursion, he unknowingly left a window open, and Rex escaped through outside. Rex then snuck into Connor's car without the latter noticing, and thus Connor unknowingly took Rex in his car with him to Wimbledon Golf Course.
When Connor stopped the car, Rex came out onto the roof and Connor noticed him. Connor tried to coax Rex back into the car, but Rex escaped and flew off. Connor followed Rex onto a fairway, where the two were attacked by a Pteranodon. Rex managed to escape being eaten by the Pteranodon, and ran off into the woods again.
Connor and Abby later found Rex in the woods, cowering from a flock of Anurognathus that were roosting in a nearby tree. Once the Anurognathus had flown off, Connor and Abby caught Rex, and returned him to Abby's flat after the incursion was dealt with.
Rex watched as Abby taught Connor how to talk to women, and at one point Connor jokingly referred to Rex as the barman of their skit.
When Rex first met Caroline Steel after Connor brought her to Abby's flat, he took an instant disliking to her and was more aggressive towards her.
When Rex ruined the food that Caroline had prepared for a meal with Connor, Caroline, while alone with Rex at Abby's flat, trapped Rex in Abby's freezer. Abby found Rex in the freezer that evening, freezing to death, and she and Connor managed to recuperate him.
Rex later rested near Connor the next day when Connor was grieving over Abby's supposed death, and he later glided around Abby the following day when she returned to her flat.
Shortly after Connor broke up with Caroline by text, Caroline lured Rex out with a bowl of fruit and then attacked him. Rex managed to dodge and avoid the various household items that Caroline threw at him, but Caroline was ultimately able to knock him out and capture him by hitting him with a tennis racket.
When Leek took Connor, Abby, Caroline and Jenny to the Creature Prison's cage room to witness the feeding time, Abby found Rex in his cage and tried to reach out to him.
When the Creature Prison's security system was disabled by a computer virus, Rex was freed from his cage with the other creatures and escaped into the bunker. Rex eventually met up with Connor, Abby, Jenny and Caroline and led them to a service shaft leading out of the bunker. Rex was non-fatally shot and injured by an armed guard, and was carried out of the bunker by Caroline.
Abby prompted Rex to wake Connor up one morning by eating vegetables off of Connor's face.
When Jack Maitland was left in charge of Abby's flat and played poker with several friends there, Rex danced to music that was being played. Jack eventually resorted to betting Rex in the game, and lost him to Tony.
Tony took Rex back to his house and put him up for auction on the Internet. Connor was eventually able to force Tony to give Rex back by intimidating him with Hilary Becker and the latter's Special Forces cohorts.
When Jack stole Abby's handheld Anomaly detector, Rex caught him with it and appeared to scold Jack for stealing it.
Abby brought Rex over to Lester's flat to have Sid and Nancy, two Diictodon that were staying there with Connor, as company. Rex and the two Diictodon communicated and showed curiosity about one another.
After Connor and Abby disappeared on a mission into the Future, Rex was kept in the ARC's Menagerie after the organisation was revived. When Abby returned from the Cretaceous a year after she and Connor went missing, she went to the Menagerie and saw Rex flying and playing above the Columbian Mammoth in the Menagerie. Rex noticed Abby and the two happily reunited.
Rex escaped the Menagerie and flew around in the ARC. When the ARC's new bio-scanner detected Rex, it locked him and Philip Burton in a lab and sent the ARC into lockdown. The system then began to gradually suck the oxygen out of the room, and so Rex and Philip slowly began to suffocate.
After Connor cancelled the lockdown, he and Jess Parker rushed to the lab, but found that Rex had already suffocated. However, Connor was able to revive Rex by placing him in a box filled with oxygen. He was subsequently returned to the Menagerie.
Due to the inconveniences of keeping and caring for the creatures in the ARC's Menagerie, Philip planned to have all of them, including Rex, put down. Abby tried to move Rex and the other creatures out of the ARC and hide them at a private zoo, but her plan was thwarted. However, Lester was able to blackmail Philip into withdrawing his plans.
When a swarm of Future Beetles invaded the ARC and sent it into lockdown, Rex escaped the Menagerie into the ARC's car park when the Beetles started chewing through the ARC's walls. Later, when Connor programmed the First Man-made Anomaly to release a gamma ray into the ARC to kill the Future Beetles, Abby called out for Rex. Rex came to his owner, and allowed her to take him to the ARC's panic room to shelter from the gamma ray. Rex was presumably returned to the Menagerie after the lockdown was lifted and the ARC repaired.
Rex was shown to be highly curious and unafraid of his modern surroundings, which is why Abby found the need to protect him from the present world. When he was being examined by Home Office scientists, he made no attempt to escape, instead seeming to try to play with the scientists, playfully batting at their utensils. (Episode 1.1) It is possible Rex had a really good memory for a reptile, as he remembered Abby and rekindled with her after not seeing her for a year. (Episode 4.2)
After he was taken by the ARC and placed in the Menagerie, Rex was still playful and curious, but seemed to be a bit unaware of his surroundings; as he kept playing with Abby when a gamma ray was about to go off, (Episode 5.4) and he at one point accidentally triggered a bio-scan system's lockdown protocol which almost resulted in him and Philip getting killed.
Rex was also smarter than he seems, knowing immediately that Caroline Steel was not to be trusted. (Episode 2.2) He also bonded very quickly with Abby and would always be with her and do as she said. He even followed her out of Leek's bunker and distracted a guard, being shot in the process, so that Abby could escape. (Episode 2.7)
- Episode 1.1
- Episode 1.2
- Episode 1.4
- Episode 1.5
- Episode 1.6
- Episode 2.2
- Episode 2.3 (picture)
- Episode 2.4
- Episode 2.5
- Episode 2.6
- Episode 2.7
- Episode 3.1
- Episode 3.6
- Episode 3.7 (mentioned, picture)
- Episode 3.8
- Episode 3.9
- Episode 4.2
- Episode 4.3
- Episode 4.4 (mentioned)
- Episode 5.4 (latest appearance)
- Rex is the only creature (discounting humans) to appear in every series of Primeval so far (the Future Predator technically only appeared in Series 4 in flashbacks).
- Rex's "voice" was based on the sounds of a Racoon with element of Frog added to give the chirping/barking noices.
- As the series continues, Rex's wings become more bat-like, starting as rounded sails and then progressing into folding wings similar to a bat's. Some fans have suggested that they change as he gets older.