>Brontosaurus is a genus in the subfamily Apatosaurinae, which includes only it and Apatosaurus, which are distinguished by their firm builds and thick necks. Although Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 paper, which found Brontosaurus to be valid. However, the status of Brontosaurus is still uncertain, with some paleontologists still considering it a synonym of Apatosaurus.
And:
>Almost all 20th-century paleontologists agreed with Riggs that all Apatosaurus and Brontosaurus species should be classified in a single genus. According to the rules of the ICZN, which governs the scientific names of animals, the name Apatosaurus, having been published first, had priority; Brontosaurus was considered a junior synonym and was therefore discarded from formal use.
>Brontosaurus is a genus in the subfamily Apatosaurinae, which includes only it and Apatosaurus, which are distinguished by their firm builds and thick necks. Although Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 paper, which found Brontosaurus to be valid. However, the status of Brontosaurus is still uncertain, with some paleontologists still considering it a synonym of Apatosaurus.
And:
>Almost all 20th-century paleontologists agreed with Riggs that all Apatosaurus and Brontosaurus species should be classified in a single genus. According to the rules of the ICZN, which governs the scientific names of animals, the name Apatosaurus, having been published first, had priority; Brontosaurus was considered a junior synonym and was therefore discarded from formal use.