The wyvern visage is an item obtained as a very rare drop from Fossil Island wyverns found in the Wyvern Cave. Skeletal Wyverns do not drop the wyvern visage; they drop the draconic visage instead.
A player creating the ancient wyvern shield.
With level 66 Magic and level 66 Smithing, it can be used to create the ancient wyvern shield by using it on the northern strange machine in the House on the Hill while having a hammer and an elemental shield in the inventory. If players attempt to use the two items on each other instead, a message in the chatbox will state Perhaps some of the magical apparatus on Fossil Island can help join these two items.
When the player creates the shield, they will receive 2,000 experience in Smithing and Magic, but the player's magic level will be completely drained. When this occurs, a chatbox message will appear, stating At a great cost to your personal magical energies, you have crafted the wyvern visage and elemental shield into an ancient wyvern shield.
For an exhaustive list of all known sources for this item, see here