The name Aachenosaurus refers to two fossilized fragments of material that were originally thought to be jaw fragments from a duck-billed dinosaur (a hadrosaur). However, the fossils turned out to be petrified wood, to the great embarrassment of the discoverer. The fossil's name means "Aachen lizard", named for the Aachenian deposits of Moresnet (which was a neutral territory between Belgium and Germany), where the fossils were found.
Aachenosaurus was found and named by the scientist (and abbé) Gerard Smets, on October 31, 1888, who named the type species Aachenosaurus multidens. Based on these fragments he determined that the specimen was a hadrosaur reaching an estimated 4 to 5 meters in length which might have had dermal spines. He defended this conclusion, citing that the fossils had been examined visually with the naked eye, magnifying lenses and with the microscope. However, his error was soon demonstrated by Louis Dollo. Smets at first tried to defend his original identification but was again proven wrong by a neutral commission and withdrew from science completely from pure embarrassment.