Haast's eagle

The "weather-beaten" skull of a Haast's eagle was used by the Faction Paradox member Mother as her ceremonial mask. To match, her spouse, Father, wore a mask made from the bleached skull of an Argentavis. (PROSE: Going Once, Going Twice)

Behind the scenes
In the real world, Haast's eagle is believed to have been the largest species of eagles in Earth's history (matching the Argentavis, one of the largest flying birds, in general).