The Brontosaurus Would Like to Know: What Is a Species, Really?

A new paper reverses the 1903 demotion of the beloved dinosaur genus—and calls into question the way we classify the natural world.

They're real, and yet they're not.  (Atomazul/Shutterstock)

In 1989, the U.S. Postal Service released a collection of 25-cent commemorative postage stamps celebrating a series of dinosaurs. The stamps featured the tyrannosaurus, and the stegosaurus, and the pteranodon. They also featured, however, the brontosaurus, or the "thunder lizard"—which had been reclassified under the genus apatosaurus ("deceptive lizard") in 1903.

This was an egregious mistake, but an understandable one. The brontosaurus—the gentle giant that ate plants and sneezed on children—has spent the past century-plus as, if not an actual genus, then a cultural one. Tyrannosaurus, stegosaurus, triceratops, ... and brontosaurus. The sauropod was like the fourth Beatle, only more beloved. Sure, the long-necked lizard might not have technically existed; in another sense, though, the brontosaurus was more real in the human imagination than the apatosaurus ever was.

So it was big news, this week, when a new paper brought some redemption—for brontosaurus fans, for Linnaean taxonomy, for the U.S. Postal Service. A team of scientists, cross-referencing the digital scans of bones from hundreds of long-necked dinosaurs, is claiming that the brontosaurus deserves to be reinstated as a genus unto itself. Deceptive lizards here; thunder lizards there. As Roger Benson, one of the study's co-authors, explained to Wired: “It was a number of small differences that were important, but probably the most obvious features that would help distinguish the two is that the Apatosaurus has an extremely wide neck, where brontosaurus' is more high than wide.”

You could say a lot of things about that little taxonomic shift, but one of them is that the brontosaurus—something that existed, and then didn’t exist, but then existed in a broader sense, and now exists in the actual sense again—is a tidy reminder of the ongoing churn of scientific knowledge. The sun, the center of it all and then very much not. Caffeine, both healthful and harmful. Jurassic Park’s velociraptor, which was, in reality—as far as we know—much more like a feather duster than like an agile T. Rex. And, of course, Pluto. The late, lamented Pluto.

From a scientometric perspective, occasional updates to the rambling facts of our world are to be expected: Facts are contingent, and we’re always learning new things, and science is a discursive discipline, and all that. From a more human perspective, though, the dynamism of scientific truths can be jarring: If you can just, one day, take away the “planet” from “My Very Educated Mother Just Showed Us Nine Planets,” what else can you do?

The good and the bad news is: a lot. The whole Brontus interruptus saga may be close to the heart of every kid who had a dinosaur phase growing up—and every adult for whom that phase continues—and it may have been made more interesting because of its roots in the fascinating "bone wars" of the 19th century. Beyond that, though, it isn’t unusual. Taxonomies, despite their promise of easy categorization, can be wonderfully, and also somewhat terrifyingly, fluid. That thing we think about as an animal unto itself—Ursus arctos, Homo sapiens sapiens, Aptostichus angelinajolieae—is a human construction more than anything else.

“Species delineation is more than meets the eye,” Paul Sereno, a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence," told me. That’s in part because of the fact that genetic diversity isn’t always expressed phenotypically, in terms of animals’ appearances. It’s also because animals don’t just evolve, over long stretches of time; they also, of course, grow and change—in size, in color, sometimes in sex—over the course of their lives. Which means that understanding how species relate to each other, as environment-sharers and Darwinian competitors, requires more than one-off encounters with them. The biggest challenge to understanding what a species is, ultimately, may simply be one of human exposure. According to one paper, there are an estimated 8.7 million species on Earth; some 86 percent of those, the paper claims, have yet to be described.

There's reason to believe, too, that the percentage of those mystery species will soon drop drastically. Our abilities to observe animals in their habitats, for one thing, are improving. Digital technologies in particular mean that there are more people than ever walking around with cameras to record biological diversity. We’re living in the age of the “Internet naturalist,” as Atlantic contributor Rose Eveleth put it, and that means more information, and more nuance, about the genetic diversity of the natural world.

And that means: more species. New taxonomies. Amended classifications. As Sereno puts it, “we’re in the midst of a mini-revolution in understanding how many discrete genetic packets and species are present today.” And all that means, in turn, that we can expect more news like the resurrection of the brontosaurus—for animals both long-dead and still-living. “We’re constantly revising,” Sereno says, “because material is constantly being found.”