On their journey to find Roshan's human family, Manny, Sid, and Diego stumble upon an ice cavern. The cavern contains perfectly-preserved frozen animals that have since been extinct. Some of them appear to have been Sid's ancestors.
All of the mammals begin their annual migration to avoid the winter. Sid the Sloth's family leaves without him, as they do every year, while Manny the Mammoth migrates in the opposite direction to avoid the warm weather.