"Gadolosaurus" is the informal name given to a genus of ornithopod dinosaur from late Cretaceous-age rocks in Mongolia. Though the name was made public in 1979, it has never been formally described, and the name is considered a nomen nudum. The name "Gadolosaurus" first appeared in a book by Japanese paleontologist Tsunemasa Saito. It came from a caption to a photo of a juvenile dinosaur skeleton; this small individual was only about a meter long (39 inches). The skeleton was part of an Soviet exhibition of fossils in Japan. Apparently, the name comes from a Japanese phonetic translation of the Cyrillic word "gadrosavr", or hadrosaur, and was never meant by the Russians to establish a new generic name.
Because it is an informal name, with a suspect history, it has not attracted much professional attention. However, it has appeared in many popular dinosaur books, with varying identifications. Donald F. Glut in 1982 reported it as either an iguanodont or hadrosaur, with no crest or boot on the ischium (both characteristics of the crested lambeosaurine duckbills), and suggested it could be the juvenile of a previously named genus like Tanius or Shantungosaurus. David Lambert in 1983 classified it as an iguanodont, but changed his mind by 1990, when it was listed as a synonym of Arstanosaurus. What may be the same animal is mentioned but not named by David B. Norman and Hans-Dieter Sues in 2000; this material, from the Soviet-Mongolian expeditions of the 1970s, had been listed as Arstanosaurus in the Russian Academy of Sciences, but is currently under study for a future description, and more bones have been found in the intervening years. These bones were found at Baishin Tsav and were assigned a tentative Cenomanian age.
- Saito, Tsunemasa (1979). Wonder of the World's Dinosaurs. Tokyo: Kodansha Publishers. late 71.
- Glut, Donald F. (1997). "Barsboldia". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. p. 202. ISBN 0-89950-917-7.
- Glut, Donald F. (1982). The New Dinosaur Dictionary. Secaucus, NJ: Citadel Press. p. 280. ISBN 0-8065-0782-9.
- Lambert, David; the Diagram Group (1983). A Field Guide to Dinosaurs. New York: Avon Books. p. 153. ISBN 0-380-83519-3.
- Lambert, David; the Diagram Group (1990). The Dinosaur Data Book. New York: Avon Books. p. 63. ISBN 0-380-75896-2.
- Norman, David B.; Sues, Hans-Dieter (2000). "Ornithopods from Kazakhstan, Mongolia and Siberia". In Benton, Michael J.; Shishkin, Mikhail A.; Unwin, David M.; and Kurochkin, Evgenii N. The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 462–479. ISBN 0-521-55476-4.