Walking with Monsters

Very late into production it was discovered that Megarachne, the basis of the giant spider seen in the Carboniferous segment was actually an eurypterid or sea scorpion like those seen in the Silurian part. The crew decided then to rename their now obsolete creature "Mesothelae", after the most primitive group of living spiders. There were Mesothelae spiders in the Carboniferous, but just not that big.

There are two widely available variations of the show's original British version:

• One that has all three episodes being separate. This version has previews and recaps at the beginning and end of each episode. Also, at the very end there is a never-before-seen shot of an Allosaurus walking on a Jurassic plain.
• The other version combines the three episodes into a one-and-a-half hour long movie, with the episodes flowing together. This one lacks the new shot of the Allosaurus. It begins with primordial Earth being shown from afar, whereas the other version lacks this shot and starts out with a closer view. It also has an extended ending, with more stock footage taken from Caminhando com os Dinossauros (1999) as the narrator talks about the mammals' ancestors. The other version lacks this scene.

Edited into Primeval: The Chase Continues (2009)