 In 2007, John Foster suggested that the differences usually cited to differentiate "Amphicoelias altus" from the more well known "Diplodocus" are not significant and may be due to individual variation.Foster argued that "Amphicoelias" is probably the senior synonym of "Diplodocus", and that if further research bears this out, the familiar name "Diplodocus" would need to be abandoned in favor of "Amphicoelias", as was the case with "Brontosaurus" and its senior synonym "Apatosaurus".In 2015, Woodruff and Foster reiterated this conclusion, stating that there is only one species of "Amphicoelias" and that it could be referred to "Diplodocus" as "Diplodocus altus".