Two scientists spent months debunking a long-standing dinosaur classification. Then, they used dinosaur bones discovered in Colorado, previously misidentified as the defunct label, to identify an entirely new species.
The bones were unearthed from the famed Morrison Formation in Colorado between 2021 and 2022 by private fossil hunters, according to a journal article published last week in by those scientists.
The partial skeleton, which is missing its skull, was previously identified as a , but Susannah Maidment and Paul Barrett with quickly realized that didn’t quite fit.
Maidment said they were “immediately skeptical” of the Nanosaurus label when the museum received the fossils in January 2024 because that species of dinosaur was named nearly 150 years ago from fragmentary remains or bone imprints on rocks, not skeletons.
“There are no diagnostic features that allow us to say, ‘This is what a Nanosaurus is,’ so the first thing we had to do was get rid of it,” Maidment said. “It wouldn’t be recognized as a species (if discovered) today.”
When Nanosaurus was first named in 1877, few dinosaurs had been discovered, so the minimal characteristics that its fossils preserved would have been unique, she said.
Now, hundreds of small dinosaurs have been documented internationally and the Nanosaurus fossils aren’t useful in identifying them, Maidment said. It made more sense to wipe the slate clean and start from scratch.
The next step was discovering what the dinosaurs under the label were. The answer? A variety of small, misidentified dinosaur species thrown under the umbrella label.
“A new dinosaur is named, on average, once a week,” Maidment said. “Every time someone names something new, we all have to go back and revise what we thought we knew. … We’re constantly revising and going back through our collections and discovering we’ve got new specimens that we didn’t realize.”
The process of identifying a new dinosaur is long and hard, so when it happens, the paleontology community uses that data to judge its knowledge of species and continue evolving, she said.
Maidment and Barrett named the partial skeleton discovered on private Colorado land in Moffat County, an area called the Skull Creek Estates near Dinosaur, Enigmacursor mollyborthwickae, according to the article.
The fossils were sold through an antiques dealer and eventually made their way through a London art gallery to the museum, Maidment said.
Curators in London put the skeleton on display at the Natural History Museum last Thursday, the same day the article reclassifying it was published.
The two-legged herbivore was small and fast, with long legs, large feet and a small head, according to Barrett.
“It was living on the floodplains and alongside river systems, running under the feet of things like Diplodocus and Ceratosaurus and Stegosaurus and all your favorite dinosaurs from when you were seven,” Maidment said.
Scientists said the dinosaur discovered was only about one meter long, but there are signs that it wasn’t fully grown, according to a .
“One feature we look at in dinosaurs are the neural arches,” Barrett said in the release. “These are the top section of vertebrae, and form separately from the lower parts. They gradually merge as an animal gets older, so by examining them, you can see whether it was still growing.”
Many of the fossils’ arches were not yet fused, he said.
Barrett and Maidment said more discoveries could continue coming out of the Morrison Formation, where this fossil was found.
The from the Late Jurassic Period is named after the Colorado town but spans across the western United States, according to the National Park Service.
“While the Morrison Formation has been well-known for a long time, most of the focus has been on searching for the biggest and most impressive dinosaurs,” Maidment said. “Smaller dinosaurs are often left behind, meaning there are probably many still in the ground.”
Maidment said many discoveries in the Morrison Formation area feel like “trophy hunting” as people search for the biggest bones or the pointiest teeth.
“There’s a bias against small dinosaurs,” she said. “It also means that we don’t have a great picture of ecosystems and … what was living in these environments. And that affects our whole understanding of food webs and ecology and our world.”
Many small dinosaurs are out there waiting to be correctly classified in museum collections or unearthed from the ground, Maidment said. As people continue to work and learn, these discoveries will continue.
