As always in the Ice Age animated franchise the best sequences centre on Scrat, the Sisyphean half-squirrel, half-rat, determinedly chasing an acorn around the prehistoric world to disastrous effect. In this fourth instalment he triggers continental drift and pulls the plug on Atlantis. The main narrative is more conventional, with soon-to-be-extinct creatures such as the mammoth and sabre-toothed tiger behaving like 21st century middle-Americans as they attempt to survive while doing battle against a band of pirates clearly inspired by Captain Jack Sparrow's Caribbean corsairs. Of the latter we've long since had too much.