This is Brontosaurus as researchers imagined it in the late 1800s: aquatic, and with a large, robust skull.creative commons

The iconic dinosaur Brontosaurus is set to be reinstated as its own unique genus after over 100 years of being misclassified as Apatosaurus.

Brontosaurus – or thunder lizard – has been considered to be from the genus Apatosaurus since 1903, with scientists deciding at this time that the difference between the two were so minor it was better to put both in the same genus.

Skeletons of Apatosaurus and Brontosaurus were found in in the 1870s - but both were without skulls. Researchers eventually concluded that because of similarities in their bodies, they were two species from the same genus.

Because Apatosaurus was named first, this was the one that was used under the rules of scientific naming.

However, an "exhaustive" study by palaeontologists in the UK and Portugal has now provided conclusive evidence Brontosaurus is distinct and can be reinstated as its own genus.

Brontosaurus can be reinstated as its own genus after exhaustive study, scientists say.Davide Bonadonna, Milan, Italy

History of Brontosaurus

Researchers excavated numerous new dinosaur skeletons in the 1870s, with famed palaeontologists Mash and Cope coming across two massive partial skeletons of long-necked dinosaurs. These were sent to the US, where they were described as Apatosaurus ajax, the 'deceptive lizard' and Brontosaurus excelsus.

However, neither had a skull, so Marsh reconstructed one for Brontosaurus based on another long-necked dinosaur, Camarasaurus – which later turned out to be wrong.

Years later another team from the Field Museum in Chicago found another skeleton similar to both Apatosaurus and Brontosaurus, leading palaeontologists to believe Brontosaurus and Apatosaurus were two species from the same genus – but as the latter was named first, Brontosaurs became Apatosaurus excelsus.

The study, published in the journal PeerJ, uses numerous new findings of dinosaurs similar to Apatosaurus and Brontosaurus over recent years to show how different Apatosaurus and Brontosaurus actually were.

Emanuel Tschopp, who led the study, said: "Our research would not have been possible at this level of detail 15 or more years ago, in fact, until very recently, the claim that Brontosaurus was the same as Apatosaurus was completely reasonable, based on the knowledge we had."

The authors used statistical approaches to calculate the differences between other species and dinosaurs from the diplodocid genus.

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

Explaining how they have managed to reverse over a century of research, study collaborator Octávio Mateus said: "It's the classic example of how science works. Especially when hypotheses are based on fragmentary fossils, it is possible for new finds to overthrow years of research."

Brontosaurus family treeTschopp et al/PeerJ