416-359 million years ago



Acanthostega is the oldest tetrapod known from Greenland, 360 million years ago.

While Acanthostega is recognized as the most primitive amphibian, there are a number of aspects of its skeleton which link it to sarcopterygian fish and demonstrate that it was not fully adapted to locomotion on land.Acanthostega still retained a number of primitive features from its sarcopterygian ancestors: fully functional internal gills, gill struts, a primitive ear, no attachment of the pelvis to the vertebral column, the absence of an ankle (wrist not preserved), a shoulder bone (anocleithrum) which connected the shoulder to the skull as in fish, and a tail fin with dermal rods (as in fish; these rods were different from those of all sarcopterygians in that they were unbranched and unsegmented). There are a number of derived features that identify it as the first amphibian: multijointed fingers and toes, the shape of its limb bones and girdles, and the loss of some opercular bones of the skull found in fish.