had arrived back to New York, the Mongolian material was given to Barnum Brown to study. Brown was renowned for his field collection of dinosaurs, but he was too busy to attend the Asian expeditions. He did extensive work on the material and had prepared names for the new species, but for unknown reasons he ceased work on the project before its completion. Instead, the fossils were sent to the Smithsonian and would be described and named as new species by Charles W. Gilmore. The Smithsonian had little in terms of a dinosaur fossil collection and Gilmore as such was more reliant on the literature than first hand comparisons in his studies. Despite this, his work in the field is considered to be of high quality. He published his findings in 1933, describing both hadrosaurs as well as several other dinosaurs. One of the hadrosaurs, then thought to be a lambeosaur, was the novel genus Bactrosaurus. The second, known from at least four individuals and thought to be a hadrosaurine, was named as a new species of Mandschurosaurus, M. mongoliensis. This choice was made tentatively; Gilmore was mindful of the possibility his species may later require its own genus, but did not currently feel there was sufficient difference from M. amurensis for this. Gilmore's description of the species' anatomy was rather brief and would prove inadequate to understanding the taxon decades later; he provided no clear diagnosis (a list of what traits establish a species as different from its relatives). Another issue caused by Gilmore's work was that all the material, from all the individuals, was catalogued under a singular specimen number. Later palaeontologists thus had to recatalogue all of the elements under more modern standards. Following its original naming, Gilmore's species would remain poorly understood and received limited attention from other palaeontologists. Despite this, the occasions it was discussed often brought major taxonomic changes. One persistent issue surrounding the taxonomy of the Iren Dabasu hadrosaurs was the nature of cranial material found at the Bactrosaurus quarry. Gilmore assumed, based on its association with the rest of the Bactrosaurus material, that it must belong to that genus; no other elements at the site were inconsistent with just one species being present. He was perplexed, however, by its lack of a hollow-crest, something thought universal among lambeosaurs. He did consider the possibility it belonged to M. mongoliensis, and also noted its