The Permian was a period in Earth's history. It was dominated by a harsh, arid and volcanic environment, and it was ruled by reptiles, most of which were the ancestors of mammals.
Visits and incursions
Episode 1.1
An Anomaly to the Permian opened up in the Forest of Dean in the late 1990s. A Gorgonopsid came through and attacked Helen Cutter, who escaped into the Permian through the Anomaly and started her travels through time. The Anomaly was open eight years later (presumably having either reopened, or stayed open since the 1990s), and a Coelurosauravus came through and was named Rex. A Scutosaurus also came through, but was later scared back through the Anomaly by the Home Office team.
After obtaining legal permission from James Lester, Nick Cutter went through the Anomaly into a hill range in the Permian with Rex and Captain Tom Ryan. Ryan and Cutter found the remains of a camp their future selves had left on a second mission to the Permian in their near future, then returned through the weakening Anomaly. Rex returned through as well just before the Anomaly closed, and he and the Gorgonopsid were marooned in the present. The latter creature was killed by Stephen Hart, and Rex was kept by Abby Maitland at her flat.
Episode 1.6
An Anomaly to the future opened in the Permian and a family of Future Predators came through. The Forest of Dean Anomaly reopened, but linked to several years earlier in the Permian than it had the previous time it was open. After finding one of the Future Predators feeding in the Permian, Helen Cutter retreated through the Forest of Dean Anomaly to the present from the Future Predators, and the Predators followed her.
After capturing the young of the Predator family, Nick, Helen, Captain Ryan and two other soldiers travelled with them into the Permian through the Forest of Dean Anomaly, to locate and contain the future Anomaly. The mother Predator also followed them through in pursuit of her young, and killed Ryan and the two other soldiers. A Gorgonopsid then killed the mother Future Predator and all but two of the Predator young. Nick and Helen subsequently buried Ryan and abandoned the camp, and thus the camp became the one Nick and Ryan discovered on their first mission into the Permian. Nick and Helen then returned through the Forest of Dean Anomaly; and while Nick decided to stay in the present, Helen went back through into the Permian to find the future Anomaly on her own.
Episode 2.7
At some point in the new timeline, either Helen or Oliver Leek's mercenaries captured two Scutosaurus for Leek's creature army, possibly from the Forest of Dean Anomaly. The Scutosaurus presumably died when the creatures were locked in the Creature Prison's cage room and killed each other.
Extinction Event
When Helen Cutter, Jenny Lewis and Jake Hemple's SAS alpha team travelled through the Anomalies to unite with Cutter in Tunguska, they went through a new Anomaly from London into the Middle Permian. The team passed through a group of Dimetrodon to get through another Anomaly, to a Spaghetti Junction, but not before the disturbed creatures bit and badly infected one of the men.
Episode 3.3
An Anomaly to the Permian opened in a West London Hospital and a group of Diictodon came through. Most of the Diictodon returned through the Anomaly, but two were marooned in the present when the Anomaly closed before they could return through. They were subsequently taken in by Connor Temple and Abby Maitland, and named Sid and Nancy.
Episode 4.4
The McKinnon School Anomaly may have led to the Permian or the Triassic, as a pack of Therocephalians came through.
Undone
An Anomaly to the Permian opened up at a university campus in Canada, and a female Lycaenops came through before the Anomaly closed. Later, the Anomaly briefly reopened, and a male Lycaenops (apparently the mate of the female) came through before the Anomaly closed again. Both the male and female Lycaenops were ultimately killed in the present after being shot and their bodies were stored in the Special Projects Group's freezer until their bodies could be returned.
Real life
The Permian period lasted from approximately 299 to 252 million years ago. During the Permian, the world was dominated by a single supercontinent surrounded by oceans, and the majority of the land was dominated by arid desert. The weather was extreme with very, very cold winters and very, very hot summers. At the end of the Permian there was a mass extinction which wiped out 95% of life. Due to the arid conditions, reptiles rose to dominance in the Permian. The Permian ended with largest-scale mass extinction event in Earth's history, with 90% of marine life and 70% of terrestrial life dying out.