The 83-million-year-old fossil, found in 2014 at a paleontological site in Alabama, adds to growing evidence that these weird wonders on wings were sometimes snacks for dinosaurs, prehistoric crocodile relatives, and large fish. After all, pterosaurs were not just bags of bones and leathery skin, as people might assume.
“Pterosaurs actually had a lot of meat on their skeletons,” says Michael Habib, a pterosaur expert at the University of Southern California who was not involved with the latest find. “They were not the skinny animals often depicted in films and art. The flight muscles in particular would have made a great meal.”
The chewed-up wing bone of this particular pterosaur, a Pteranodon, suggests that it had a 15-foot wingspan. But the animal may have weighed just 60 to 90 pounds, which would have made it easy prey for a large bony fish or a Squalicorax, an extinct shark that reached up to about 15 feet in length. (This pterosaur found in Canada was about the size of a house cat.)
And according to the new study, published in the journal Palaios, the marks on the ancient bone match up nicely with the teeth spacing of two fossil fish: Squalicorax and a four- to six-foot-long barracuda-like species called Saurodon.
“This one was unusual, because it showed what we interpret as bite marks from two different groups of animals,” says lead author Dana Ehret, a paleontologist at the New Jersey State Museum in Trenton.
“This is a very exciting find, because feeding traces on pterosaur bones are rare,” Habib adds.
So Many Sharks
While preparing the fossil at the University of Alabama Museum, Ehret’s coauthor and then-graduate student T. Lynn Harrell was initially concerned that he’d damaged the bone while removing surface chalk. But it soon became clear that a series of darker parallel grooves were instead evidence of a predator.
“He thought I was going to be mad at him,” Ehret says. “But as he prepared it, he recognized that there were four [marks] parallel to one another, and that they represented a feeding trace.”
To investigate further, the pair started to pull the fossil jaws of various carnivorous fish out of the museum’s collection to compare them to the marks. They realized that the dark grooves and more subtle serrated scratch marks lined up almost identically with the teeth of Saurodon, and Squalicorax.
Many fossils from late Cretaceous Alabama appear to have been nibbled by sharks, including sea turtles and dinosaurs, which are often “covered in predation marks,” says Ehret. Parts of Alabama were then submerged by shallow, warm waters that were the gateway to the Western Interior Seaway, a massive body of water that ran down the center of North America, splitting the continent in two.
Based on the fossil record, this highly productive region was brimming with sharks: “I’ve never seen so many shark teeth, and I’ve collected all over the world,” Ehret says. “It was just so abundant with different sharks.”
Uncovering the Tooth
Pteranodon also inhabited this coastal environment during the late Cretaceous, making a living snatching smaller fish from the shark-filled waters. Pterosaurs could float, but being less buoyant than birds, they probably didn’t sit on the surface for long, adds Habib. Some species, including Pteranodon, did likely plunge into the water for prey.
“They could then quickly take back off from the surface. But these diving pterosaurs might have been vulnerable to sharks just after they entered the water,” he says.
It’s certainly plausible that a predatory fish leapt out of the water to grab this Pteranodon or took one at the surface, Ehret says, although it’s hard to know for sure based on just this one bone. It’s also possible that the animal died near the shore and was scavenged when it washed out to sea. (Of course, some larger pterosaurs could turn the tables and prey on dinosaurs.)
Mysteries endure in part because pterosaurs with these kinds of feeding traces are very rare, says Mark Witton, a pterosaur expert at the University of Portsmouth in the U.K. The animals had fragile, air-filled bones that would more likely have shattered under the force of a shark bite.
“The record is small, but it is growing,” says Witton, who is the coauthor along with Habib on an upcoming paper about a Pteranodon vertebrae with a tooth embedded in it from an even larger shark called Cretoxyrhina, which reached up to 23 feet in length.
Of more than 1,100 known specimens of Pteranodon, Witton estimates that perhaps half a dozen have evidence of shark bites, most of which have not been studied in detail.
He praises the latest work by Ehret and Harrell because they have “gone to town to demonstrate what the identification of the [predatory] animals were … It’s nice to know what species were interacting in this way.”