"Spinosaurs were better adapted to get at fish than other carnivorous dinosaurs, and so had access to a food source that their allosaur-like contemporaries didn't," Holtz said. Holtz is not one of the study authors.
One English spinosaur specimen—called Baryonyx—was found to have fossilized fish scales, etched by digestive acids, in its body cavity. A juvenile Iguanodon bone associated with the same fossil hinted that Baryonx was not solely a fish eater. However, until now there was no direct evidence of what other species spinosaurs consumed.
Toothless Wonder
The new tooth-embedded fossil may confirm that spinosaurs—like crocodiles—also hunted or scavenged other kinds of prey.
The specimen consists of three vertebrae belonging to a pterosaur, estimated to have had a 3.5-meter (11.5-feet) wingspan. Pterosaurs are flying reptiles, with membranes of skin for wings, and hollow bones.
The skeletal fragment was discovered in what's known as the Early Cretaceous Santana Formation of rocks from northeastern Brazil. (The Cretaceous period started 144 million years ago and came to an end with the demise of the dinosaurs 65 million years ago). These rocks are famous for yielding remains of fragile and rarely preserved pterosaur bones.
The spinosaur tooth may have belonged to the up-to-8-meter-long (26-foot-long) spinosaur species, Irritator challengeri, which is known from the same Brazilian rocks.
The animal's tooth could have broken off while it scavenged a dead pterosaur carcass or even when it ambushed a live individual, Buffetaut said.
"Now we can suppose dinosaurs sometimes ate pterosaurs," he said, adding that one other pterosaur fossil had previously been discovered with an embedded dinosaur tooth.
The fragile nature of pterosaur bones means that they have never appeared associated with the gut cavities of other fossilized animals—the bones would have been fully digested or chewed to the point of unrecognizability. Researchers therefore have few clues as to what species preyed on pterosaurs.
Fossil Behavior
The fossil represents an "interesting little bit of extra information about spinosaur biology, and is one more clue about the range of diet these things had," commented Angela Milner, vertebrate paleontologist at the Natural History Museum in London, England. Spinosaurs were almost certainly scavengers as well as fish-eaters, agreed Milner, one of the researchers behind the description of Baryonyx.
"Any find where you have evidence of a direct interaction between organisms is great, because otherwise we are limited to speculation, in terms of understanding the behavior of fossilized animals," Holtz said.
It is possible that spinosaurs preyed on pterosaurs regularly, he said. Many pterosaurs hunted fish, like spinosaurs did, so they would have been present in the same habitats— near coasts or inland bodies of water.
"When grounded, pterosaurs would have been pretty susceptible to attack," Holtz said. "Though dramatic, it's also not totally out of the realm of possibility that it was caught on the wing," he added.
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