Sid and Nancy, along with around a dozen other Diictodon, came through an Anomaly to a hospital in present day West London. One of them was captured by Connor Temple and Hilary Becker when it fell out of the ceiling and into a hospital trolley Connor had with him. The other tried to return through the Anomaly with the other Diictodon in response to another Diictodon's distress call, but the Anomaly closed just before it could go back through. With the two Diictodon now marooned in the present day, Connor and Abby Maitland decided to keep them and named them Sid and Nancy.Jack Maitland was going to be staying at Abby's flat and that he needed to move out, he decided to take Sid and Nancy with him. ARC, and so he kept Sid and Nancy there with him in a cage. Sid chewed out of the cage while Connor was asleep and ran amok in the ARC; disabling the Anomaly Detection Device by chewing through its cables, and escaping whenever Connor came close to catching him. At one point, Sid travelled through the ARC's ventilation to the air vent of a lab. Connor tried to catch Sid, but Sid eluded him once again. At the end of the day, Connor was able to recapture Sid and fixed his and Nancy's cage. James Lester's flat temporarily, he took Sid and Nancy with him. On the way to the flat, one of the two Diictodon that was in the boot of Lester's car at the time also chewed up Lester's classified files in there, much to Lester's anger.
After moving with Connor into Lester's flat, Sid and Nancy continued to be a source of grief for Lester. One night, one of them partially ate Lester's invite to a dinner with the Chinese ambassador, and also chewed up Lester's coat, until Connor got it to let the coat go and Lester scared the Diictodon off with a snarl.Rex over to Lester's flat so that Sid and Nancy could keep him company, and Sid and Nancy were immediately curious to Rex and communicated with him.
After Connor and Abby disappeared on a mission into the future, when the ARC was revived, Sid and Nancy were kept in the new building's Menagerie with the other creatures that the ARC had failed to return to their own time periods.
- Sid's name is a reference to punk rock star Sid Vicious and Nancy's to his girlfriend Nancy Spungen. Also, in Episode 3.2, Cutter at one point jokingly referred to Connor and Abby as 'Sid and Nancy', which may be where they got the name idea for the two Diictodon.
- Although Sid and Nancy haven't been seen since Series 3, the producers of Primeval have confirmed that they are in the Menagerie after Connor and Abby were marooned in the Cretaceous for a year.