American Scientist

Popular depictions of dinosaur interactions favor conflict, with plant-eating sauropods locked in desperate struggles for survival against fierce meat-eating theropods. Yet the quieter moments of coexistence were likely more common than the life-or-death battles. Indeed, prehistoric predator and prey likely drank together from freshwater lagoons, similar to how animals today congregate around watering holes, according to a recent discovery of 131 fossil footprints on Prince Charles’s Point in Scotland’s Isle of Skye. The discovery of the 167-million-year-old trackways at the remote shoreline, combined with advanced imaging techniques, has revealed an ancient hub of Jurassic dinosaur activity.

Although the footprints are out on the surface of the rocky beach, they weren’t recognized until 2019. To image all of them, a research team from the University of Edinburgh flew a drone with a high-resolution camera across the site, which took 4,500 pictures at many angles. The overlapping images allowed the team, led by Tone Blakesley, to reconstruct the track site using a technique called photogrammetry.

Blakesley, a paleontology and geobiology PhD student, described the process as essentially merging the photos to create a view in three dimensions. As he explains, “The computer software which we import those images into is going to say ‘Okay, so we’ve got this footprint that’s located at this point in each set of images. Now that I know where it is in each image, I can cleverly reconstruct where it is in virtual space.’”

As Blakesley and his team reported in a recent issue of the journal PLOS One, they generated three different types of models. The first was a texture map, basically a single photograph of the area stitched together from all the pictures. The second type was a digital elevation model, or DEM, which represents the height of the region (see two images below). The third type was a contour map, which displays the elevation as well as the shape of the area using concentric rings.

“The DEMs allowed us to accurately take measurements between specific points within our footprints, to be able to more accurately calculate things like a dinosaur’s stride,” Blakesley says. Fossilized footprints can also tell paleontologists about the behaviors and tendencies of dinosaurs within their environments, such as their preferred areas and whether they were in a hurry to get there.

The team’s 3D models revealed fine-grained details of the footprints more clearly than field observations. The researchers were then able to draw track outlines to classify the footprints into shape-based groups called morphotypes, one for meat-eating theropods and one for long-necked plant-eating sauropods.

The sauropods, which were likely two to three times the size of an elephant, left behind large, flat, circular impressions on the beach. Their footprints are surrounded by what appear to be moon-shaped ridges, which further revealed what the Isle of Skye looked like around 167 million years ago. Skye was an island then, in the middle of the prehistoric Atlantic Ocean with a radically different climate. Steve Brusatte, a paleontologist and member of the team, says Jurassic Era Skye “was a subtropical, lush, verdant environment.”

At that time, Blakesley says, “dinosaurs were walking across a thin layer of sand that was deposited over hardened mud. Whenever a sauropod walked through that sand, their feet pushed the sand horizontally across the mud and then upwards to form these wide mounds that surround each of these very flat footprints.”

The team identified the other footprint morphotype as belonging to carnivorous megalosaurs, car-sized distant ancestors of Tyrannosaurus rex, of which there are scant fossils. But you wouldn’t know that from looking at the tracks here. “These theropod footprints dominate these sauropods considerably,” Blakesley says. “There are way more individuals represented at Prince Charles’s Point than there are at any other lagoonal setting recorded on Skye.” Blakesley and his team hypothesize that the large number of megalosaurs indicated their preference for freshwater lagoons, not a pack mentality.

Even though the megalosaurs outnumbered the sauropods, the modeled trackways showed no signs of dinosaur conflict. According to Blakesley’s interpretation, “They were milling around. There are no chase scenes happening. There’s no hunting in action. They were walking at about 8 and a half kilometers per hour, and they would have probably been in the same vicinity.” As paleontologists seek to understand more about dinosaur behavior and how they interacted with one another, studies like this reveal how tracks were made and influenced by ancient environments.

The Jurassic was a period when dinosaur diversity was really taking off. By this time, dinosaurs had spread to more places around the world, growing and forming iconic physical traits such as long necks and spine plates. Brusatte emphasizes how this was a time when “so much of that underpinning of dinosaur evolution was happening in the Jurassic.” Rock from the Jurassic is globally rare, making these footprints doubly valuable to the scientific community.

This remote bay is significant for another historical reason. On June 21, 1746, Scottish rebels Flora MacDonald and Charles Edward Stuart—known as Bonnie Prince Charlie—sought refuge on these shores. As Brusatte says, “Prince Charles’s Point is a place where Scottish history and prehistory blend together. It’s astounding to think that when Bonnie Prince Charlie was running for his life, he might have been sprinting in the footsteps of dinosaurs.