The Sellaran bird is an enormous type of bird Pretender rode on when he was first disgraced and fled from Wulder's presence. They are extinct by the time of DragonLight as the eggs they laid rotted in their nests until they laid no more. It is indicated that they have been extinct for a long time as Bardon is unable to recognize the picture of one.
The Followers used this animal as their symbol, which was one of the hints that the organization was allied with Pretender. They also claim that these birds were large and strong enough to wipe out the dragons.