If you grew up loving Brontosaurus only to be told it wasn't a real dinosaur, it's time to rejoice: the gentle giant may have received a new lease on life.

The giant sauropod, long thought to be an Apatosaurus that someone got wrong, was actually its own type of dinosaur all along, scientists say Tuesday in PeerJ.

In fact, Apatosaurus and Brontosaurus were different enough to be separate genera, rather than related species of the same genus.

The finding comes from a study on the evolution of diplodocids, the family to which these dinosaurs belonged. These giant herbivores lived in North America, Europe, and parts of Africa during the late Jurassic period, between 160 million and 145 million years ago.

“They’re a very widespread family, and we wanted to know more about relationships within the family,” says co-author Octávio Mateus, a paleontologist at the Universidade Nova de Lisboa in Portugal.

The new study revises the diplodocid family tree to feature Brontosaurus as an (old) new genus.

The Dino That Never Was

Brontosaurus has a colorful history. Named by O.C. Marsh in the 1880s, the dinosaur was identified in 1903 as a member of the Apatosaurus genus, which Marsh had found a few years earlier.

Since taxonomy honors the name that came first, Brontosaurus excelsus became Apatosaurus excelsus.

But the evocative name—which means "thunder lizard" in Greek—would live on for decades, until 1970s researchers ended the debate by showing that Brontosaurus and Apatosaurus had very similar skulls.

So the “thunder lizard” was condemned to the realm of the scientifically invalid, becoming the dinosaur that “never even existed.”

A New Order

Classifying dinosaurs from a fossil record is difficult, says Mateus. For one, “bones can’t tell us whether animals could reproduce with each other”—a good sign that they’re of the same species.

But the discovery of several diplodocid specimens in recent years has allowed a new approach: specimen-based analysis. Given enough specimens, scientists can examine and compare bones to show how animals are related.

Researchers looked at 81 diplodocid specimens, noting the presence or absence of each of 477 skeletal features. Closely related species shared a lot of these features, while species from different genera—like Brontosaurus and Apatosaurus—had much less in common.

Since skeletons vary between individuals as well, the researchers looked for a minimum number of clear differences—and at where the animals lived—to determine whether dinosaurs were actually different species.

Their findings showed that the diplodocid family should be expanded to include two more genera—Brontosaurus and Galeamopus.

On the other hand, it turns out that Dinheirosaurus and Supersaurus were really just a single genus.

View Images This is Brontosaurus as researchers see it today -- with a Diplodocus-like head. Illustration by Davide Bonadonna

Secrets in Stone

These fossils have been at the mercy of the elements for more than a hundred million years, but we can be pretty confident that Brontosaurus is back, says Mike Taylor, a paleontologist at the University of Bristol in the U.K.

It’s not unusual for bones to be distorted by natural forces, and allowing for warping is “part of the process,” Taylor says.

“What’s outstanding about this study is the extraordinary level of detail,” Taylor adds. “It’s going to be very easy for people to build on what they’ve done.”

Applying this method to other dinosaur families will help scientists understand evolution etched in fossil records, says Mateus.

And more dinosaur family secrets could lie waiting to be uncovered.