New species of mystery dinosaur that ran by riverbanks unveiled

Researchers have discovered a new smaller herbivorous dinosaur, naming it Enigmacursor mollyborthwickae - and said it could be the first of many new species found in Western USA

22:59, 25 Jun 2025

A new small herbivore has been discovered and named Enigmacursor mollyborthwickae(Image: Bob Nicholls Art)

A new species of dinosaur that once ran along the North American riverbanks is now on permanent display at the Natural History Museum in London.

Researchers have named the new smaller herbivorous dinosaur, Enigmacursor mollyborthwickae - Enigmacursor means mysterious runner, while the species name honours Molly Borthwick, whose generous donation allowed for the purchase and display of the dinosaur.

The dinosaur was discovered in the Morrison Formation a sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America.

[Dinosaur at Natural History museum]

The new species of small dinosaur was found in a prolific area for fossils in the US(Image: Guy Bell/Shutterstock)

The area has produced some of the most famous dinosaurs in the world, such as Allosaurus and Stegosaurus but smaller dinosaurs are sometimes ignored.

Dinosaur expert Professor Susannah Maidment was a co-lead author of the research into Enigmacursor and said that the new species could be the first of many small dinosaurs found in the western USA.

Susannah said: 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. Smaller dinosaurs are often left behind, meaning there are probably many still in the ground.

[Dinosaur, Natural History Musuem]

Experts believe there are lots of smaller dinosaurs still to be discovered(Image: Guy Bell/Shutterstock)

Enigmacursor shows that theres still plenty to discover in even this well-studied region, and highlights just how important it is to not take historic assumptions about dinosaurs at face value.

The paper was published in the journal Royal Society Open Science, and visitors can now see the new dinosaur on show in the National History Museums Earth Hall Mezzanine.

The story of Enigmacursor begins during the end of the Late Jurassic between 152 and 145 million years ago. At the time, the Morrison Formation would have been a vast network of rivers and floodplains stretching across large parts of the western United States.

Huge, long-necked herbivores like Diplodocus would have roamed the landscape, while carnivorous theropods like Ceratosaurus would have stalked the riverside.

Trying to keep out of their way would have been a variety of smaller dinosaurs, including Enigmacursor.

Its long legs would have allowed this small herbivore to dart away from danger, keeping it one step ahead of its predators, and this speedy lifestyle inspired the dinosaurs name.

The dinosaur was only around one metre long, but there are signs that the dinosaur was not fully grown, says co-lead author Professor Paul Barrett.

He said: One feature we look at in dinosaurs are the neural arches. 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.

We can speculate that Enigmacursor probably wasnt that old, as it doesnt seem to have many of its neural arches fused in place. However, the way the fossil was prepared before it was acquired by the Natural History Museum has obscured some of these details, so we cant be certain.

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Its also unclear exactly how the animal died, as there are no obvious signs of injury or illness in the bones. In any case, the remains of Enigmacursor ended up buried within the Morrison Formation, waiting to be found millions of years later.

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