A noun dubium (Latin for " dubious name ", plural: Nomina dubia ) referred to in the zoological nomenclature a scientific name that can be assigned to any taxon safe. Cause may be lost original material ( type material ) or the material used for the first scientific description no clear particulars.
In the 19th century some dinosaurs have been described by insufficient archaeological material, for example. So Trachodon mirabilis long time considered as Hadrosauridae, but are his scientific description based teeth without species-specific characteristics. The description of Aachenosaurus based on fossil wood, which has been confused with bone.
Unlike a noun is a noun nudum dubium a valid (valid ) name that can be named as a synonym of another taxon, since it satisfies the formal requirements for a scientific description. So the noun was dubium Antrodemus in older literature as a senior synonym and thus valid name for the robbery dinosaur Allosaurus. Merely due to the fact that Antrodemus is associated with only a non-specific tail bone, which can not be associated with Allosaurus Allosaurus is the valid name for this taxon.