Scientists have discovered a new dog-sized dinosaur species that ran around the feet of its bigger ancestors 150 million years ago. The Labrador-sized Enigmacursor was originally wrongly classified as a Nanosaurus, a generalised term for small herbivorous dinosaurs from the late Jurassic period. The particularly-small Enigmacursor measures just 64 cm tall and 180 cm long, archaeologists said, and is thought to have roamed the landscape alongside much larger dinosaurs including the Stegosaurus.

The bones set to go on display at the Natural History Museum this Thursday will be the most complete specimen of its kind, and also marks the first new dinosaur to be unveiled at the museum since 2014. Dinosaur expert Professor Susannah Maidment said the USA’s Morrison Association, searching for remains along North American riverbanks had traditionally focused on “searching for the biggest and most impressive dinosaurs”.

“Smaller dinosaurs are often left behind, meaning there are probably many still in the ground,” she told the BBC.

“Enigmacursor shows that there’s 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 creatures, which are thought to have roamed the western United States between 150 and 145 million years ago, would have been among the varieties of small dinosaurs trying to keep out of the way of their carnivorous counterparts, including the Ceratosaurus species.

Its small legs would have enabled it to quickly run away from danger – and contributed to the name Enigmacursor, which means “mysterious runner”.

Paleontologist at the Natural History Museum Professor Paul Barrett said the breakthrough discovery would help to shine a light on the early small dinosaurs that evolved into large and “bizarre” animals.

He told the BBC that these species were “very close to the origins of the large groups of dinosaurs that become much more prominent later on”.

“Speciments like this help full in some of those gaps in our knowledge, showing us how those changes occur gradually over time,” he added.

“When you’re looking for those very big dinosaurs, sometimes it’s easy to overlook the smaller ones living alongside them. But now I hope people will keep their eyes close to the ground looking for these little ones.”