What’s in a name? Sometimes plenty, as the U.S. Postal Service (USPS) found out in 1989 when it issued colorful dinosaur stamps, including one for Brontosaurus. Paleontologists and educators loudly protested that the correct scientific name for the iconic beast was Apatosaurus—a fact that even lay dino aficionados and many 8-year-olds took pride in knowing. The Smithsonian Institution accused USPS of favoring “cartoon nomenclature to scientific nomenclature.” It didn’t help that the stamps were officially launched at Disney World.

Now, a dinosaur-sized study of the family tree of the Diplodocidae, the group that includes such monstrous beasts as Apatosaurus, Diplodocus, and Barosaurus, finds that USPS got it right: The fossils originally called Brontosaurus show enough skeletal differences from other specimens of Apatosaurus that they rightfully belong to a different genus. The study, published online this week in the journal PeerJ, brings the long-banished name back into scientific respectability as a genus coequal with Apatosaurus.

“I didn’t start out trying to resurrect Brontosaurus,” says lead author and paleontologist Emanuel Tschopp. He was just trying to better understand the evolutionary relationships among all Diplodocidae as part of his Ph.D. thesis at the New University of Lisbon. Indeed, paleontologists are impressed by the scope of the new study, which included 81 skeletons and 477 skeletal features or characters, far more than any previous analysis. “Emanuel’s data set is now the largest published so far” for plant-eating dinosaurs, says Philip Mannion, a paleobiologist at Imperial College London. The name change is likely to stick, adds paleobiologist Paul Upchurch of University College London: “I will be happy to start using Brontosaurus again.”

How Brontosaurus lost its name in the first place is the stuff of dino legend. During the “Bone Wars” of the late 19th century, paleontologists Edward Cope and Othniel Marsh marauded through the American West bitterly competing for dinosaur fossils, which led to some rapid and slapdash descriptions. In 1877, Marsh published a brief note on one of his skeletons, calling it Apatosaurus (“deceptive lizard”). Two years later he published an equally brief report on a supposed new genus, Brontosaurus (“thunder lizard”). By 1903, paleontologists had decided that the two beasts were too similar to be divided into separate genera. Because Apatosaurus had been named first, it had precedence under the rules of scientific nomenclature. Paleontologists confirmed this conclusion in the 1970s, and know-it-all children have instructed their parents that “Brontosaurus” isn’t a valid name ever since. (The taxon had its defenders, including evolutionary biologist Stephen Jay Gould in his “Bully for Brontosaurus” essay.)

In the new analysis, Tschopp looked at every Diplodocidae specimen he could get his hands on. These plant-eating dinos lived in today’s North America and Europe between 160 million and 145 million years ago; their long necks and tails stretched up to 35 meters from end to end. Tschopp examined bones in 18 different museums in the United States and Europe and studied photos and drawings from other specimens. The idea was to get a high-resolution family tree by examining many individual specimens, rather than focusing only on fossils that represent an entire species. The study included six specimens of Apatosaurus excelsus, as Brontosaurus has been called since 1903.

Tschopp and colleagues found that A. excelsus differed from the three other recognized species of Apatosaurus in at least a dozen key characters across the skeleton. That’s as many differences as seen between genera long accepted as distinct, such as Diplodocus and Barosaurus. For example, a true Apatosaurus has a bulkier neck and was “even more robust than Brontosaurus,” Tschopp says. But Brontosaurus also has some features that Apatosaurus lacks, such as a rounded expansion of one edge of its shoulder blade and a longer bone in its ankle.

Given these anatomical differences, “It would be unfair to lump Apatosaurus and Brontosaurus together,” Upchurch says. Mannion agrees, and also endorses the team’s finding that another Diplodocidae genus, Eobrontosaurus, should be included within Brontosaurus, giving the dinosaur a few additional species to call its own.

Some paleontologists have reservations. “It’s going to force us to ask questions about what we really mean by genus and species in a paleontological context,” says paleontologist John Whitlock of Mount Aloysius College in Cresson, Pennsylvania. “Is it more useful to distinguish specimens as Brontosaurus and Apatosaurus than it is to distinguish A. excelsus from other species of Apatosaurus? I don’t know, but I hope it’s the start of a conversation.” He and others, including Tschopp himself, note that the characters used aren’t cut-and-dried and could be scored differently by others.

Upchurch thinks this kind of detailed taxonomy could help resolve questions such as how diverse dinosaurs were just before they went extinct about 66 million years ago. Others welcome the resurrection of an icon. “Brontosaurus has a prominent place in the public imagination,” Mannion says. “It can only be a good thing that it is back with us. … It shows that science develops through time and that it’s possible to change our minds, even about long-held views.”