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Welcome back, Brontosaurus!

After over a century with its unique genus status declared null, the Brontosaurus has been officially declared distinct from Apatosaurus.

Brontosaurus as it was thought to have looked in the 19th century, semi-aquatic with the boxy skull. Image public domain

Every child learns about and learns to love the Brontosaurus -- the gigantic sauropod named for thunder. Learning, therefore, that it has been considered not a distinct genus at all, but an Apatosaurus under another name since 1903, is an epic dinosaur let-down.

According to a new study, though, the Brontosaurus can officially now be reinstated as its own discrete genus, distinct from the Apatosaurus.

Brontosaurus was discovered by prolific paleontologist Othniel Charles Marsh -- who is responsible for the discovery or description of dozens of new species, partially due to his participation in the Bone Wars of the 19th century -- the rivalry between Marsh and fellow paleontologist Edward Drinker Cope to discover the most dinosaurs.

In 1879 Marsh announced that he had found two almost complete sauropod skeletons at Como Bluff in Wyoming -- missing, crucially, their skulls. He modelled the skull on the skull of another sauropod he had found that had a similar build -- Camarasaurus -- and called one of the skeletons the Brontosaurus excelsus, or "noble thunder lizard".

But in 1903, after Marsh's death in 1899, another sauropod was discovered that resembled both Apatasaurus ajax and Brontosaurus. Because Marsh and Cope had rushed many of their descriptions due to the rivalry between them, paleontologist Elmer Riggs concluded that there were not enough differences between Brontosaurus and Apatosaurus to warrant two different genera, so he folded Brontosaurus into the latter, renaming it Apatosaurus excelsus.

Brontosaurus skeletal reconstructions by Marsh in 1883 (top) and 1891 (bottom). Images public domain.

The name stuck around, though -- until the 1970s, when researchers discovered that Apatosaurus (and Brontosaurus) was more closely related to Diplodocus than Camarasaurus -- and that its head, rather than having the boxy shape associated with Camarasaurus, was more slender and horse-like. Multiple skulls were reassigned to Apatosaurus -- and the idea that Brontosaurus was a mistake was cemented.

But according to a new study conducted by paleontologists in Portugal and the UK, there are in fact enough significant difference to warrant classifying Brontosaurus once again as its own genus.

"Thanks to several new and relatively complete finds, we were now finally able to reassess the validity of all the species of Diplodocidae, and study their relationships in more detail then anybody else before,"explained Emanuel Tschopp, a Swiss national who led the study during his PhD at Universidade Nova de Lisboa in Portugal.

"It's only normal that such a study, also has some unexpected outcomes that overthrow years of research, like the resurrection of Brontosaurus."

Artistic reconstruction of the brontosaurus. Davide Bonadonna CC BY-NC SA

The 300-page study, published in the journal PeerJ, examines 81 different skeletons, 49 of which belong to the Diplodocidae family, across 477 morphological characters using statistical approaches to establish a boundary between species and genera -- making it the most extensive phylogenetic analys of sauropods ever completed.

"This detailed data on Diplodocidae allowed us to basically recreate their branch on the tree of life from scratch. This led us to three main findings: first, we found conclusive evidence for an additional, new genus within the group, which we call Galeamopus. Second, Supersaurus, a genus previously known from the USA alone, now also includes the Portuguese genus Dinheirosaurus," Tschopp said.

"And finally, we found that differences between the genera Apatosaurus and Brontosaurus are numerous enough to revive Brontosaurus as its own genus, a name which has long been considered invalid in the scientific community."

Study co-author Roger Benson of the University of Oxford noted that there are distinct dinosaur genera with fewer differing traits from other members of their families.

"The differences we found between Brontosaurus and Apatosaurus were at least as numerous as the ones between other closely related genera," he said, "and much more than what you normally find between species."