Some 167 million years ago over what is now Scotland’s Isle of Skye, a winged reptile, possibly as big as an albatross, soared over a subtropical lagoon, nabbing fish and squid in its toothy maw as dinosaurs thundered across the shorelines.
Somehow this reptile perished, and its carcass was quickly entombed in sediments on the bottom of that lagoon. In 2017 a chance discovery along Skye’s wave-battered coastlines revealed the resulting fossil: the best of its kind found in two centuries.
Unveiled today in the journal Current Biology, the fossil—called Dearc sgiathanach (pronounced “jark ski-an-ach”)—is spectacularly well preserved, with portions of the skull, limb bones, tail, ribs, and vertebrae still intact. The fossil joins elite company: Not many sites around the world preserve pterosaurs well, and fewer still preserve them from this ancient time period.
“Usually when we get to describe fossils … it’s a scrap of a femur, a bit of a beak,” says paleontologist Natalia Jagielska, a Ph.D. candidate at the University of Edinburgh and the study’s lead author. “Luckily with Dearc it’s extremely well-preserved—so well-preserved, it’s kind of an anomaly.”
Jagielska’s team also contends that Dearc is the biggest well-preserved pterosaur ever found from the Jurassic period, which lasted from 205 million to 145 million years ago.
As with modern birds, size in pterosaurs is often spoken of as wingspan, the combined breadth of an animal’s two membranous wings, each one kept taut by an outrageously long fourth finger bone. Later pterosaurs found in other parts of the world, such as Quetzalcoatlus, reached gigantic wingspans of 33 feet or more during the Cretaceous period, which lasted from 145 million to 66 million years ago.
By contrast, Dearc dates to the middle Jurassic. Fossils from this earlier time are rare, and before Dearc, scientists had found little hard evidence that pterosaurs from the period achieved wingspans bigger than six feet (1.8 meters). Now, the discoverers of Dearc estimate that its wingspan was at least 6.2 feet (1.9 meters) and possibly more than 8.2 feet (2.5 meters). That size puts Dearc in the ballpark of today’s biggest birds.
Dearc adds to Scotland’s paleontological heritage as the first new pterosaur to be named from the country since Mary Anning—a pioneering fossil collector and paleontologist—found the pterosaur Dimorphodon in 1828.
“This is probably the nicest skeleton that’s been found in Britain since the time of Mary Anning,” says National Geographic Explorer Steve Brusatte, a paleontologist at the University of Edinburgh and the study’s senior author.
Fighting the tide
The first vertebrates to evolve flight, pterosaurs were the rulers of the Mesozoic skies: an extraordinarily diverse group of winged reptiles that ranged from fuzzy creatures with wide eyes and frog-like mouths to giraffe-size titans with a fighter jet’s wingspan. With teeth adapted to pinning down the sea’s slippery prey, sharp eyesight, and wings bigger than an NBA player is tall, Dearc now joins these hallowed paleontological ranks.
But this valuable fossil almost didn’t make it out of the ground.
For years, Brusatte has explored the Isle of Skye in search of fossilized bones and track sites, including the footprints of long-necked dinosaurs so big their footfalls look like tidal pools. Dearc emerged from the island’s limestone during a May 2017 expedition led by Brusatte and funded by the National Geographic Society.
On the morning of May 23, team member Amelia Penny was surveying a site on Skye’s northern coast when she noticed a dark object weathering out of the rock. Had Penny been there weeks earlier, she wouldn’t have seen it: Recently, powerful gusts had stirred the coast’s waters enough to move boulders that had been covering the fossil’s slab.
Over lunch, Penny showed Brusatte a picture of what she had seen, which Brusatte recognized as the partial jaw of a pterosaur. Even from the bits peeking out of the rock, the team could tell that this pterosaur was big—and, by the looks of it, extremely well preserved.
As a rule, pterosaurs fossilized poorly: Their bones were lightweight and filled with air sacs, which was great for flight but terrible for ensuring the bones’ survival through the fossilization process. What’s more, the pterosaur fossil record is skewed toward juveniles, with fully developed adult bones rare and scrappy.
From then on, Brusatte’s team scrambled to save the fossil. The island’s dig sites lie within sheets of rock on wave-pounded coastlines, getting submerged and then exposed with each rising and falling tide.
The next day Brusatte summoned a local museum owner and contractor, Dugald Ross, to cut the fossil slab out of the rock with a diamond-tipped saw. But as Ross got to work, the team quickly realized that the fossil wasn’t just a jaw, or even just a skull. It was most of the animal’s skeleton.
Suddenly, the team had to cut out massive slabs of rock as the rising tides threatened to swallow up the site. With each piece of the fossil that came out of the ground, they had to carry it up slope, dry it off, and apply a stabilizing material called a consolidant to the fragile, exposed bones. “We’re racing the tides to cut it out,” Brusatte says.
By 4:00 p.m., with water lapping across the fossil slab still embedded in the rock, the team came to a grim realization: They could not get the rest of the pterosaur fossil out of the ground until the next low tide around midnight.
To give the frail bones the best chance of surviving as the waters rose, the researchers covered the fossil in consolidant, crossed their fingers, and hoped it would withstand the water. The tactic worked, and the team ultimately carried the 400-pound slab away in a wheelbarrow the following evening.
“I would say it’s, by far, the most important thing we’ve ever found in any of my trips—and it’s certainly the most stressful one to collect,” Brusatte says. “I’ve never been more elated but also just more terrified, because there were so many steps where it’s just like, What could go wrong?”
Flying in crowded skies
With the fossil out of the ground, the team transported it to the collections at the National Museums Scotland in Edinburgh, where preparator Nigel Larkin painstakingly cleaned it of excess rock and consolidant. That’s where Jagielska got to work.
A geologist by training, Jagielska had previously studied Skye’s rocks, and she had experience with the anatomy of birds. Here was a chance to study a type of flying animal at once familiar and utterly alien.
For more than two years, Jagielska carefully measured the pterosaur’s bones and compared them against those of known pterosaurs. The Skye pterosaur, in many respects, resembled the well-known Rhamphorhynchus but was much bigger.
To figure out the pterosaur’s wingspan, Jagielska measured the wing bones of better-known related species and worked out the relationship between those individual bones’ lengths and the animals’ overall wingspans. She then used this relationship to predict Dearc’s wingspan as between 2.2 and 3.8 meters, which overlaps with the wingspans of modern albatrosses.
Jagielska and Brusatte’s team also CT-scanned the fossil, which revealed an approximate model of its brain shape—including the optic lobes, the regions associated with sight—and the structure of the pterosaur’s inner ear. Team member Greg Funston, a postdoctoral researcher at the University of Edinburgh, sliced into one of the pterosaur’s bones to look at its internal structure, which revealed that this Dearc specimen was still immature. However big Dearc was when it died, it had more growing to do.
Jagielska and Brusatte say that the size of Dearc will help researchers make better sense of the global fossil record in pterosaurs, as it provides a reference for interpreting less complete bones found in the U.K. and elsewhere.
The fossil also shows that in space and time, there were pterosaurs that fell in between the early Jurassic’s relative pipsqueaks and the giants of the later Cretaceous. “It is surprising to find a larger pterosaur in the Middle Jurassic, yes—but personally, I was kind of expecting this gap to be filled,” says Taissa Rodrigues, a paleontologist at Brazil’s Federal University of Espírito Santo who wasn’t involved with the study.
Scotland may show further hints of a highly diverse pterosaur fauna: In a preliminary report that hasn’t yet passed peer review, a separate team of scientists announced on February 16 that they had found a pterosaur on the Isle of Skye that belongs to a different branch of the family tree than Dearc does.
The two discoveries reinforce the Middle Jurassic’s evolutionary importance. During the first half of the Jurassic period, many different groups—including dinosaurs, mammals, and even flowering plants—are thought to have diversified rapidly, possibly stoked by the ongoing breakup of the supercontinent Pangaea. When combined with other pterosaurs from around the world, the Scottish fossils suggest that pterosaurs diversified a lot during this period, which is also roughly when the feathered dinosaurs that evolved into birds started to develop gliding and, later, powered flight.
“One can almost imagine the pterosaurs looking at all this going, It’s pretty busy up here already!” says David Unwin, a University of Leicester paleontologist who co-authored the preliminary pterosaur study. “That’s really quite surprising, that there is sufficient bandwidth for all these different fliers and proto-fliers to survive alongside each other.”
However, unlike Rodrigues, Unwin is not yet convinced about Dearc’s proposed size. Rhamphorhynchus, the animal used to estimate the new pterosaur’s wingspan, had uniquely long, exaggerated wing bones, he says. That means size estimates based on its limbs could risk skewing high. Unwin argues that the wingspan of Dearc probably wasn’t bigger than seven feet across.
Regardless of Dearc’s ultimate size, it still stands out as a superlative Scottish fossil and an important link back to the discoveries of Mary Anning—a fact that fills Jagielska with pride. Working two centuries apart, the two paleontologists have given us a fuller view of Scotland’s Jurassic skies.
“Anning is considered to be this not only feminine but also working-class symbol,” Jagielska says. “I feel this kind of connection.”