), the only valid species within the genus, is based on a poorly preserved and incomplete skeleton collected by Russian scientists in 1914 from the banks of the Amur River, China in a layer of the Maastrichtian-aged Yuliangze Formation and the remains represent a large hadrosaurid.

[1] The holotype of M. laosensis, which is based mainly on an ilium and other fragmentary remains,[3] comes from the Aptian-Albian-aged Grès supérieurs Formation in Laos and was named by Hoffet (1944).

Brett-Surman (1979) first considered it a nomen dubium,[6] though some later workers have continued to see it as a valid taxon (Chapman et Brett Surman, 1990,[7] for example).

Most recently, Horner et al. (2004) listed the type species as a nomen dubium in the second edition of The Dinosauria.

Brett-Surman (1979) considered M. mongoliensis a distinct genus, which he named Gilmoreosaurus[6] and Horner et al. (2004) considered M. laosensis a nomen dubium;[8] This leaves only Riabinin's original species, M. amurensis, as a possibly valid taxon.