They are part of the quest , which is part of The Sons of Hodir quest chain. Upon starting the quest, the character is placed upon one of these proto-drakes, which then flies to join the pack circling the Temple of Storms. The character must then repeatedly use a to pull himself to another Hyldsmeet Proto-Drake and engage in combat against the Frost vrykul riding it.
This mount has no special abilities. Only a "leave vehicle" button is provided. Employing it can be hazardous if the character does not have a means of coming to rest safely on the earth below.
The preferred means of getting off this vehicle is to target a Column Ornament around the Temple of Storms, and use the harpoon to swing to the pillar.