Grapefruit-sized depressions found in rocks on the Isle of Skye have revealed that a type of stegosaurus once wandered the landscape, researchers say.
The newly discovered tracks form a single line, a few metres long, with a right-left pattern and two different-sized prints – as would be expected for an animal on all fours – with one set larger and triangular-shaped, and the other set smaller and further forwards.
“Those proportions match up quite well to the hands and feet of stegosaurus skeletons,” said Dr Stephen Brusatte, a palaeontologist and co-author of the study from the University of Edinburgh. “These footprints are the first evidence we have that this very major, very iconic group of dinosaurs lived in Scotland.”
Brusatte added that the dinosaur who made the prints was about the size of a cow, while the prints themselves are the size of a grapefruit or small teapot. The team add that the tracks were found in sedimentary rocks thought to be about 170 million years old, which formed from mudflats that once bordered a lagoon.
Stegosaurs – hefty, armoured plant-eaters with upright plates running down their backs and a spiked tail – are a major group of dinosaurs, yet Brusatte noted there are few bones or tracks that date from this time anywhere on Earth.
“It looks like [this group of dinosaurs] was starting to evolve, to spread around, during this middle part of the Jurassic, and we are seeing these fleeting glimpses of them as they are starting off their evolution,” he said.
The new study, published in the journal Plos One, follows previous finds by the team, including tracks which revealed that as well as huge, long-necked plant-eating dinosaurs known as sauropods, Skye was once home to meat-eating dinosaurs, probably theropods.
As with that study, the newly discovered prints were found at Rubha nam Brathairean, or Brothers’ Point, on the east of the island, albeit at two different sites.
In addition to the stegosaurus prints the team found other tracks, with about 50 prints discovered in total.
“There are some three-toed prints with claw marks that were made by theropods, but there were no sauropod tracks at these sites,” said Brusatte, noting that tracks of the latter were previously found further into what was once the lagoon, suggesting sauropods splashed through shallow water rather than walking on the mudflats.
However, some of the newly discovered three-toed prints were larger than others and had stubby toes which, the team suggests, could have been made by another type of dinosaur – plant-eating, bird-hipped creatures called ornithopods, a group that includes duck-billed dinosaurs. But Brusatte said more evidence was needed.
“If we find bones of big ornithopods on Skye I think that will be a pretty good sign that some of these tracks were made by ornithopods,” he said.
The team say the new findings expand our understanding of the community of dinosaurs that once roamed the Scottish isle.
“It would have been overrun with … so many different types of dinosaurs: meat-eaters, plant eaters, big ones, small ones, ones that were running around, ones that were wading in the water, ones that had long necks, ones that had plates on their backs,” said Brusatte. He added that in the middle Jurassic, Skye was not the chilly, windswept environment we know today – it was closer to the equator.
“It was an island in the middle of the ever-widening Atlantic with this subtropical, wet, humid, hot climate with rivers draining mountains in the middle of the island, emptying out into the ocean; and then beaches and lagoons fringing the coasts – and these places were havens for dinosaurs and for all kinds of other species,” Brusatte said.
The team say the latest finds highlight the importance of re-examining well-known areas, noting that one of the sites has been scrutinised by palaeontologists and geologists for decades yet its secrets remained hidden until a storm shifted some boulders.