Apatosaurus
Valid species

Many species of Apatosaurus have been designated from scant material. Marsh named as many species as he could, which resulted in many being based upon fragmentary and indistinguishable remains. In 2005, Paul Upchurch and colleagues published a study that analyzed the species and specimen relationships of Apatosaurus. They found that A. louisae was the most basal species, followed by FMNH P25112, and then a polytomy of A. ajax, A. parvus, and A. excelsus. Their analysis was revised and expanded with many additional diplodocid specimens in 2015, which resolved the relationships of Apatosaurus slightly differently, and also supported separating Brontosaurus from Apatosaurus.

The cladogram below is the result of an analysis by Tschopp, Mateus, and Benson (2015). The authors analyzed most diplodocid type specimens separately to deduce which specimen belonged to which species and genus.
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