Ichthyostega was a stegocephalian (likely a stem-tetrapod?) that lived from 365 to 360 million years ago. It was not a true amphibian; the first amphibians actually appeared in the Carboniferous, long after Ichthyostega died out.
Hell on earthEdit
Ichthyostega wouldn't appear until the end of the episode, and it is depicted feeding and hunting on surviving Bothriolepis.