A Dinosaur’s Pterosaur Lunch

From The Smithsonian Dinosaur Tracking blog: A Dinosaur’s Pterosaur Lunch

Though only about the size of a turkey, Velociraptor still looked like a formidable predator. With snatching hands, a jaw set with recurved teeth and, of course, a retractable claw on each foot, almost every end of this dinosaur was sharp. But what did this well-equipped Cretaceous killer actually eat?

One of the prime candidates for a Velociraptor entree has been the small horned dinosaur Protoceratops. A truly spectacular fossil cemented the connection between these dinosaurs. In 1971, a Polish-Mongolian expedition to the Gobi Desert found “fighting dinosaurs“—a Velociraptor and Protoceratops preserved in the throes of fatal combat. While the Velociraptor had kicked its deadly foot claw into the neck of the Protoceratops, the little ceratopsian had crushed the right arm of the predator, and the two remained locked together in death. The trouble is that we can’t know why these two dinosaurs were fighting. Was the Velociraptor trying to hunt the Protoceratops? Or was the little predator itself attacked by a territorial Protoceratops? That the dinosaurs battled each other is obvious, but the reason for their combat remains a mystery.

But a recently described fossil confirmed that Velociraptor or a very similar dinosaur ate Protoceratops flesh. In 2010, paleontologist Dave Hone and co-authors reported a set of Protoceratops bones that had been scratched and scored by the teeth of a small predatory dinosaur. How the horned dinosaur died was unclear, but the toothmarks indicated that the carcass had almost been entirely stripped by the time the carnivorous dinosaur came along to pick off the remaining scraps. Since Velociraptor shared the same habitat and was of the right size to leave the bite marks, the dinosaur is a good candidate for being the scavenger.

Another fossil provides an even closer connection between Velociraptor and its prey. In a paper to be published in Palaeogeography, Palaeoclimatology, Palaeoecology, Hone and co-authors Takanobu Tsuihiji, MahitoWatabe and Khishigjaw Tsogtbaatr describe part of a Velociraptor meal preserved inside the dinosaur’s body cavity. Represented by a single bone, the gut contents show the dinosaur had fed upon a pterosaur.

The broken pterosaur bone was probably inside the dinosaur’s stomach when it died. How that bone found its way into the Velociraptor digestive system is another matter. Based on the anatomy of the bone and the pterosaurs that were around at the time, Hone and colleagues hypothesize that the ingested pterosaur was an azhdarchid, one of the long-legged, long-necked pterosaurs that included the largest flying animals of all time.

This particular pterosaur was not a giant by pterosaur standards—Hone and colleagues estimate that the animal probably had a wingspan over six feet across and weighed more than 19 pounds. But it would have been large compared to the relatively small Velociraptor that consumed it. This would have made the sharp-beaked pterosaur “a difficult, and probably even dangerous, target [for] a young dromaeosaur,” Hone and co-authors suggest, and therefore “unless the pterosaur was already ill, infirm or injured, it seems unlikely that this would be a case of predation.” And the fact that the dinosaur consumed a large bone further suggests this might have been another instance of Velociraptor scavenging. If the pterosaur carcass was fresh, the Velociraptor probably would have consumed the available soft tissues first. The fact that the dinosaur ate bone may be an indication that the pterosaur had been picked over and there was only a little meat left clinging to the carcass.

This isn’t the first time evidence of small dromaeosaurs scavenging on pterosaurs has been found. In 1995, paleontologists Philip Currie and Aase Roland Jacobsen reported a partial skeleton of an azhdarchid pterosaur that had been bitten by a small predatory dinosaur. A tooth embedded in the skeleton identified the scavenger as Saurornitholestes, a dromaeosaurid cousin of Velociraptor from Cretaceous North America.

Although Velociraptor is often celebrated as a vicious and cunning predator, the accumulating evidence shows that the dinosaur wasn’t above scavenging. This isn’t surprising. Even highly active predators will regularly scavenge if the opportunity arises. And while I consider the ballyhooed argument over whether Tyrannosaurus rex was primarily a hunter or scavenger to be dead and buried—the tyrant dinosaur was certainly both hunter and scavenger—it is worth noting that even small, apparently highly predaceous dinosaurs at least occasionally scavenged. In outlining his case for “Tyrannosaurus the scavenger,” paleontologist Jack Horner pointed to Velociraptor as the epitome of what a predatory dinosaur should look like. Yet this new paper, as well as other recently reported indications of dinosaur hunting and scavenging, underscores the fact that the hunting-scavenging dichotomy is too narrow a view on nature. As Hone and colleagues wrote near the beginning of their paper, many carnivores hunt and scavenge. The trick is figuring out which type of flesh-acquisition behavior was more important to a particular species.

Frustratingly, though, we’re more likely to find evidence of dinosaur scavenging than active predation. Relatively small predators like Velociraptor, which may have specialized on even smaller prey, are especially troublesome in this regard. Unless someone is lucky enough to find a small mammal, dinosaur, or other creature in the gut contents of Velociraptor, we may never know what this dinosaur primarily hunted. When predatory dinosaurs wrenched tattered bits of flesh from denuded carcasses, though, they often left tell-tale signs of damage behind, and these traces are more likely to be preserved than are gut contents. Despite its celebrity, we are still just beginning to put together a picture of how Velociraptor hunted and fed.

For more details on the pterosaur-eating Velociraptor, including some excellent art by Brett Booth, visit Dave Hone’s blog Archosaur Musings.

References:

Currie, P., & Jacobsen, A. (1995). An azhdarchid pterosaur eaten by a velociraptorine theropod Canadian Journal of Earth Sciences, 32 (7), 922-925 DOI: 10.1139/e95-077

Fowler, D., Freedman, E., Scannella, J., & Kambic, R. (2011). The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028964

Hone, D., Choiniere, J., Sullivan, C., Xu, X., Pittman, M., & Tan, Q. (2010). New evidence for a trophic relationship between the dinosaurs Velociraptor and Protoceratops Palaeogeography, Palaeoclimatology, Palaeoecology, 291 (3-4), 488-492 DOI: 10.1016/j.palaeo.2010.03.028

Hone, D., Tsuihiji, T., Watabe, M., Tsogtbaatr, K. (2012). Pterosaurs as a food source for small dromaeosaurs Palaeogeography, Palaeoclimatology, Palaeoecology : 10.1016/j.palaeo.2012.02.021