In his 1905 paper naming "Albertosaurus", Osborn described two additional tyrannosaur specimens that had been collected from in Montana and Wyoming during a 1902 expedition of the American Museum of Natural History, led by Barnum Brown. Initially, Osborn considered these to be distinct species. The first, he named "Dynamosaurus imperiosus" ("emperor power lizard"), and the second, "Tyrannosaurus rex" ("king tyrant lizard"). A year later, Osborn recognized that these two specimens actually came from the same species. Despite the fact that "Dynamosaurus" had been found first, the name "Tyrannosaurus" had appeared one page earlier in his original article describing both specimens. Therefore, according to the International Code of Zoological Nomenclature (ICZN), the name "Tyrannosaurus" was used.