 Previously, Dinheirosaurus was classified within a Diplodocidae excluding Apatosaurus, for the differences anatomically are quite great. Bonaparte & Mateus found that a few features present suggested that Dinheirosaurus was more derived than Diplodocus, but plesiomorphic features also present conclude that they branched separately and Dinheirosaurus is not the descendant of Diplodocus. A 2004 study by Upchurch et al. found that Dinheirosaurus was an intermediate diplodocoid, along with Cetiosauriscus, Amphicoelias, and Losillasaurus.
