Sources : Sea-stag

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.8): It is a sea-stag [cervus marinus], as the Liber Kyrannidarum says, which is called a polmorarius. He raises his horned head above the waves and seduces birds to sit upon him as if to rest or to eat his flesh; but he suddenly seizes those who are at rest and kills and devours them. - [Badke translation/paraphrase]