Devonian

The Devonian was an era of Earth history.

In a surreal event, the Seventh Doctor stood on a Devonian beach and tried to convince a lungfish to return to the sea. He watched it grow stubby legs and become an Ichthyostega, two million years early by his count. (PROSE: Transit)

The illusion of the horizon in the Worldsphere was a legacy of the first animals to crawl onto the Devonian beach and look at the sky. (PROSE: The Also People)