Excelsus

Because of this, Riggs recombined Brontosaurus excelsus as Apatosaurus excelsus.

Elmer Riggs reclassified Brontosaurus as a synonym of Apatosaurus in 1903, transferring the species B. excelsus to A. excelsus.

Among the many notable differences are the wider—and presumably stronger—neck of Apatosaurus species compared to B. excelsus.

Based on comparisons with other species proposed to belong to Apatosaurus, Riggs also determined that the Field Columbian Museum specimen was likely most similar to A. excelsus.

Despite this, at least one paleontologist— Robert T. Bakker —argued in the 1990s that A. ajax and A. excelsus were in fact sufficiently distinct for the latter to merit a separate genus.

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.