New dog-sized dinosaur species discovered

A drawing of what the Enigmacursor mollyborthwickae might have looked like. (Bob Nicholls Art via CNN Newsource)

Scientists have discovered a new species of dinosaur — one that was dog-sized and roamed what is now the United States around 150 million years ago alongside familiar dinosaurs like stegosaurus and diplodocus.

The Enigmacursor mollyborthwickae, as researchers named it, was about the same size as a Labrador retriever, with a tail that made up about half of its length, according to a study published in the Royal Society Open Science on Wednesday.

Although many of its bones were unearthed from the Morrison Formation in Colorado in 2021-2022, its skull and parts of its vertebral column were missing, leaving scientists unsure of its precise length.

“These very small plant-eating dinosaurs are pretty rare (to find),” Professor Paul Barrett, a researcher at London’s Natural History Museum who co-led the study, told CNN.

“Actually finding a substantially completed skeleton rather than a few bits and pieces of bones is not common and as a result they’re fairly poorly known.”

The skeleton will be displayed at the Natural History Museum from June 26.

This dinosaur was quite “lightly built” and weighed around the same as a collie, said Barrett. It was a herbivore and would have walked on its long hind legs, which “suggests it was quite a speedy runner” allowing it to make a “quick getaway” from predators, Barrett added.

He and his colleague, Susannah Maidment, began investigating this specimen after a London art gallery, which was displaying the dinosaur, got in contact with them.

They were eventually able to work with the gallery to find a donor who could help bring the skeleton to the museum. The species name honors that donor, Molly Borthwick, while the genus name is Latin for “mysterious runner.”

By carefully examining the bones, Maidment and Barrett concluded that this specimen had unique characteristics unlike any other previously known species. In particular, its thigh bone was particularly distinctive, with different sorts of muscle attachments than other dinosaurs, Barrett said.

It is most closely related to Yandusaurus hongheenis, a three-metre- (9.8-foot) long dinosaur that has been found in China. This suggests the species was widely distributed, Barrett said, hypothesizing that other fossils of it simply haven’t been found yet.

Scientists believe this specimen was not yet fully grown as some of its vertebrae had not yet fused but, because of the way the fossil was prepared before it came to the Natural History Museum, they can’t be certain. It is also not clear how the dinosaur died because there aren’t any obvious signs of illness or injury in its bones.

New species of dinosaurs are unearthed or identified relatively frequently, about once a week, said Barrett. But finding small dinosaurs like this is much rarer, partly because they’re overlooked by fossil hunters searching for bigger, more impressive dinosaurs and partly because smaller skeletons are more likely to be ripped apart by predators and scavengers.

Finding these smaller dinosaurs which are often left in the ground “gives us a more complete idea of what those ecosystems were like,” Barrett said.