 The type species is "Mesadactylus ornithosphyos".The holotype is BYU 2024, a synsacrum of seven sacral vertebrae, featuring a unique—for a pterosaur—complete fusion of the spinae into a supraneural blade, a character, as the specific name indicates more typical for birds, at first leading Jensen to assign the fossil to a bird, "Palaeopteryx".Further referred associated remains include arms bones, pectoral girdle bones, vertebrae (including cervix and sacral), and femora.