Atlantosaurus (Marsh,1877)  > A. montanus (Marsh,1877) von Huene, 1906) >> Titanosaurus montanus (Marsh,1877 / Lydekker,1877) >>> Apatosaurus montanus (Marsh,1877) >>> Brontosaurus montanus ((Marsh,1877) Kuhn,1965)

2 1/2 sacral centra Atlantosaurus montanus, originally named Titanosaurus montanus, musn't confuse with titanosaurids. Marsh's 1877 genus Titanosaurus was preoccupied by Lydekker's Titanosaurus (the typical titanosaurid), proposed a few months earlier in 1877. That's the only connection between Atlantosaurus and titanosaurids. The type sacrum of Atlantosaurus montanus is indeterminate but probably belonged to an Apatosaurus.