Marsh "discovered" two long-necked dinosaurs around the same time. The first he named as Apatosaurus ajax (the presciently named "deceptive lizard") and the second was dubbed Brontosaurus excelsus. But the Apatosaurus skeleton wasn't very complete when he jumped the gun and declared it a new genus. Later fossil findings seemed to sit right between the species of these two supposed genera, suggesting that they were all more closely related than Marsh had assumed.
Once the species were all lumped together into one genus, it meant the first name given to their group won out over the mistaken second genus. So Brontosaurus became defunct, with the species rolled into Apatosaurus.
But in the new study, researchers claim that there really are enough differences between Apatosaurus excelsus and Apatosaurus ajax to put them back into separate genera. That would mean a rebirth of the Brontosaurus line.
On the one hand, there aren't very clear rules about defining one genus from another -- it's really just a matter of scientific consensus -- so such a declaration should be taken with a grain of salt. But they didn't set out on some pro-Brontosaurus crusade.
The researchers wanted to better understand how the genera Diplodocus and Apatosaurus are related, so they analyzed 81 different specimens based on 477 different characteristics. The group found another fossil that they believe deserves its own genus, as well: Diplodocus hayi, which they've renamed Galeamopus hayi. Plucking Brontosaurus out from among the masses was an unexpected bonus.
"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," co-author Roger Benson of the University of Oxford said in a statement.
But this isn't a be-all end-all victory for Brontosaurus. Science is a process, and just as these researchers believe they've proved previous efforts incorrect, further information may put Brontosaurus back out in the cold.
John Whitlock, an associate professor at Mount Aloysius college who wasn't involved in the study, thinks the research will contribute to an important debate: Just how are we defining different genera? It's all based on how "distant" scientists think one species is from another, he said, and that metric needs to be more solid than it is now.
"It’s going to be a long time before we get there, probably, but this paper is a big start in terms of getting the debate going," Whitlock said. "At the end, though, we’re going to be in a much better place in terms of truly understanding the evolution of the lineages we study, and that’s exciting."
When it comes to the return of Brontosaurus, Whitlock doesn't expect much controversy. "It matches up to a suspicion that I think a lot of workers had -- that there is a lot of diversity in Apatosaurus that might be going unrecognized," he said. "And it really is a catchy name."
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