Acanthostega is an extinct genus of four-limbs animals (tetrapods) in the late Devonian period, about 360 million years ago ^{1), 2), 3)}.

Acanthostega is 60cm in length ²⁾. Their forelimb has eight digits, but hindlimbs are unknown (the hindlimb of Ichthyostega has seven digits) ^{1), 3)}.

Acanthostega has fish-like covered internal gills, extensive tail-fin ^{1), 2), 3)}. These characters suggest that they are more close to fishes rather than amphibians, and could not walk on land.

Acanthostega probably lived in the shallow swamp such as a part of its head was above the surface of water or not so.