Sid is a male Diictodon from Primeval.
He came out of an anomaly with a huge group of Diictodons. He tried to get back to the Permian, but the anomaly closed and he was adopted with the Primeval team with a female Diictodon named Nancy.
Sid is also seen in episode 3.4 where he was at Connor's house with Nancy.
In episode 3.3, he escaped out of his cage in the ARC. During that, he was in the vent in the lab where a patch of deadly Future Fungus so Connor tried to get him down, but he escaped. Sid was recaptured.
One of the Diictodons was chewing on the papers that were classified.
In episode 3.9, Sid and Nancy play with Rex, a Ceoluroceravus.