Ichthyostega measured about 1.5 meters in length. It had seven digits on each hind limb (the front limbs have never been found), and a finned tail. Ichthyostega was one of the first animals to use lungs as primary breathing organs and the adult's skeleton was well-adapted for both aquatic and terrestrial life.
Ichthyostega was closely related to Acanthostega, but the former was more well adapted to life on land than the latter. There are four known species of Ichthyostega, all from the same time and place: I. stensioei, I. watsoni, I. eigili, and I. kochi.
All four species of Ichthyostega were described in 1932 from Greenland. Some additional specimens were collected from the area during the next twenty years.
Ichthyostega was probably a carnivore.