Brontosaurus thunders back after a century in exile

Brontosaurus (foreground) and Diplodocus depicted by Charles R Knight in 1897 (Wikimedia commons)

Bianca Nogrady
ABC

More than 100 years after it was banished from existence, Brontosaurus can be reinstated as a dinosaur genus, according to a detailed study of the iconic dinosaur's family tree.
 
Palaeontologists from the UK and Portugal conducted a comprehensive anatomical survey of 81 specimens of the Diplodocidae superfamily of large long-necked dinosaurs, which includes Diplodocus, Apatosaurus, and once again, Brontosaurus.

Published today in the journal PeerJ , the researchers argue that their analysis overturns a century-old decision to classify the dinosaur as an Apatosaurus rather than a genus of its own.

'Brontosaurus' is not only one of the most charismatic dinosaurs, but one of the most controversial.
The headless skeletons of two large long-necked dinosaurs were discovered in 1870 and described by US palaeontologist Othniel Charles Marsh. The first was named Apatosaurus ajax -- the deceptive lizard, the second was named Brontosaurus excelsus -- the thunder lizard.

Marsh wrongly reconstructed the skeleton of Brontosaurus excelsus using the head of another long-necked dinosaur, Camarasaurus.

Shortly after Marsh died, palaeontologists discovered another skeleton that was similar to both Apatosaurus ajax and Brontosaurus excelsus. They decided that Brontosaurus was not anatomically distinct enough from Apatosaurus to warrant its own genus, so it became Apatosaurus excelsus.

"What palaeontologists of the time had done was they'd compared the anatomy of the bones and made a subjective decision that these things were relatively similar and might as well be the same," says co-author Associate Professor Roger Benson, a palaeontologist at the University of Oxford.

"In 1903 that decision was made, but Brontosaurus is incredibly iconic and somehow it refused to die in the public imagination, even though scientists thought that it was not a distinct thing."

The final blow to Brontosaurus happened in the 1970s, when researchers showed that Apatosaurus was not closely related to Camarasaurus, but to yet another dinosaur from the same area: Diplodocus.
Recently many more specimens have been discovered, allowing for a more comprehensive comparison across specimens by Benson and colleagues, who have reconstructed the entire branch of the Diplodcidae family tree.

"If we've got lots of specimens and we've got detailed quantitative info about their anatomy, then for every comparison between two specimens, we can come up with a number that's the difference between them," Benson says.

Lead author Dr Emmanuel Tschopp says there were a number of anatomical features that distinguished Brontosaurus from Apatosaurus.

"Even though both are very massive and robust animals, Apatosaurus has a more wide neck than Brontosaurus has, so I think that's the most visual and obvious thing to distinguish the two," says Tschopp, a post-doctoral research at the University of Nova Lisbon.

Family tree

While the return of Brontosaurus will no doubt capture the public imagination, the greater worth of the study is its detailed redrawing of the Diplodocidae family tree, says palaeontologist Dr Steven Salisbury of the University of Queensland.

"People might wonder why that hasn't happened until now, but sauropods [large, four-legged plant-eating dinosaurs] are notoriously difficult to work on because they're so big and awkward to look at," says Salisbury, who was not involved in the research.

Adding to the confusion, many of the sauropod specimens were discovered in the late 19th century, and some were incorrectly reconstructed and mounted, Salisbury says.

There was also an initial rush to name specimens during this period known as the 'Bone Wars', some of which were later challenged as more bones were discovered.

"It highlights how science and particularly taxonomy works," Salisbury says.

"Names are proposed for specimens -- and those names may come and go depending on what people think of a species or genus or a taxon -- but importantly, if you've got specimens to look at all the time you can test those ideas, so names are really just tests of ideas relating to taxonomy."

In addition to reinstating Brontosaurus, the team also discovered a new genus, which they called Galeamopus, that had previously been considered to be just another species of Diplodocus.

At the same time, they concluded that another genus -- Dinheirosaurus -- was not distinct enough from the Suprasaurus genus to warrant its own and was therefore subsumed back into Suprasaurus as a species only.