Hundreds of footprints from massive long-necked dinosaurs have been discovered near Duntulm Castle on the Isle of Skye in Scotland.
The ghostly impressions, which date back 170 million years, provide an exciting and rare glimpse of Middle Jurassic sauropods, which were among the largest animals ever to roam the planet.
The tracks, described in a new paper published today in The Scottish Journal of Geology, have wowed paleontologists with their sheer numbers and level of preservation. Normally, animal tracks are quickly eroded, but the lagoon floor upon which these dinosaurs tread tens of millions of years ago was especially conducive to fossilization, etching the footsteps of the animals into the Earth for millions of years.
"[W]e can't tell exactly what species made the tracks," said University of Edinburgh paleontologist Steve Brusatte, who led the research, in an email interview with Motherboard. "But we can tell that they were made by fairly primitive, but quite large, sauropods. So, early relatives or ancestors of the famous ones like Diplodocus and Brontosaurus."
The team thinks these giants ran about 50 feet from head to tail, and weighed about 22,000 pounds
Though the exact taxonomic identities of these ancient creatures remains unclear, Brusatte and his colleagues were able to estimate their sizeable dimensions. Given that the largest of the footprints measures about 70 centimeters across, the team thinks these giants ran about 50 feet from head to tail, and weighed about 22,000 pounds.
In addition to the multitudes of sauropod tracks, the site included a random interloper with a single tridactyl—or three-digit—footprint. This may have been left by a dinosaur from either the ornithischian or theropod branches of the family, but it's difficult to tell with only one specimen.
The tracksite is a boon for paleontologists, especially considering that fossils from the Middle Jurassic period are scarce. "The fossil record is so capricious," Brusatte said. "Some time periods or places are really good for fossils, others not so much so. It largely comes down to dumb luck."
"In the case of Skye, it was part of an island during the Middle Jurassic," he continued. "There were big rivers on the land which emptied out into the sea, with the deltas flanked by lagoons. So there were many different environments for animals to live in, and many different environments for preserving rocks. That's probably one reason why we find so many fossils compared to other parts of the world. But part of it is also that these fossil-bearing rocks are exposed along the coast, so they are accessible and always eroding, exposing more fossils."
Not only did these ancient lagoons support a rich habitat for dinosaurs—and the right conditions to preserve their earthly remains—they also shed light on longstanding debates over sauropod behavior.
"Probably the single most important thing about this tracksite is that the tracks were made in a lagoon," Brusatte told me. "Many decades ago it was thought that the big sauropods must have lived in swamps, because no way such colossal animals could support their weight on land. Then in the 1970s that idea was proven wrong—sauropods were well-adapted for living on land, as shown by their skeletons."
"But this footprint site, as well as some other recent discoveries, are turning back the clock a little bit," he said. "They show that these big dinosaurs really did spend at least some time around the water, and even in the water. […] Why? We don't know yet. Maybe these lagoons were a ready source of food, or offered protection from predators. But regardless of the answer, this discovery and the other recent ones are inspiring us to reimagine the lifestyles of these most incredible of ancient creatures."
Moreover, Brusatte pointed out that dinosaur tracks provided a kind of immediacy that bones and teeth lack. Skeletal remains tell us an awful lot about dinosaurs, no doubt, but they are often scattered around by scavengers, washed away by river currents, or otherwise deposited far away from the natural habitat in which animals lived and died.
Tracks like those found in Skye, in contrast, tell us exactly where these dinosaurs were hanging around 170 million years ago. "The real animals were physically there," Brusatte told me. "And many of them, and over multiple generations. That really blows my mind […] Looking at the mad jumble of tracks it looks like a dance floor, like a dinosaur disco."
What's more, the tracksite is submerged under the ocean during high tide, resulting in some of the deeper tracks morphing into lush tidal pools as the water recedes. The fact that tiny ecosystems are blossoming in the footprints of bygone giants is a genuine mind-boggler, and is sure to be just one of many fascinating insights to emerge from this bonafide dinosaur disco on the Isle of Skye.