Velociraptor is not an animal that needs much introduction. Ever since 1993’s Jurassic Park, the genus has been a staple in dinosaur toy lines, books, cartoons, and films. The Jurassic Park and Jurassic World films depicted Velociraptors as incredibly social animals that made up for their relative small size by hunting in packs. But how much of that is really supported by the science?
The group of sickle-clawed dinosaurs called dromaeosaurids have been known to scientists for quite some time. Dromaeosaurus albertensis, the animal the group is named after, was described by William Diller Matthew and Barnum Brown in 1922, and Velociraptor mongoliensis was described by Henry Fairfield Osborn in 1924. However, the group would remain relatively obscure in the public’s eye until the 1969 description of Deinonychus antirhoppus by John Ostrom.
Ostrom’s description of Deinonychus was immensely important to the field of dinosaur paleontology, as his paper notes the similarities between Deinonychus and birds, and Ostrom’s description of Deinonychus as a fast and active predator did a lot to dispel the notion that dinosaurs were large, ungainly creatures, which had dominated much of the popular thinking for the previous half century. Another aspect of Deinonychus would help create the notion that it was a social animal, and perhaps a pack hunter.
Deinonychus fossils have been found associated with the herbivorous dinosaur Tenontosaurus with regularity. Tenontosaurus is an ornithopod dinosaur that could measure up to 6.5 meters in length. Resembling the duckbill hadrosaurs that would come later, Tenontosaurus lacked defensive armor or horns to protect itself from predators.
Still, it was a large animal compared to Deinonychus, which grew to only about 3 meters long. The existence of multiple assemblages of Deinonychus and Tenontosaurus together led Ostrom and W. Desmond Maxwell to propose that Deinonychus was a pack hunter that worked in groups to bring down larger prey. A newer study, a 2020 paper by J. A. Frederickson et al that analyzed the chemical isotopes in Deinonychus teeth, calls that assumed social behavior into question.
When most people think of pack-hunting, they imagine some sort of family unit, akin to a pride of lions or a pack of wolves, with the adults bringing down prey and the younger animals getting access to the kill. Analysis of modern reptiles that don’t have this social structure has shown different isotopes in the teeth of young reptiles compared to their adult counterparts, showing the change in diet as the animal grew older and became able to take down larger prey.
The study on Deinonychus teeth showed vast differences in the isotopes found in the small teeth of juveniles and the larger teeth of adults, suggesting a change in diet that would be inconsistent with the popular image of Deinonychus hunting in family-oriented packs. The study notes, though, that this finding doesn’t exclude mob-hunting strategies exhibited by crocodiles and Komodo dragons, where adults often gang up on a singular prey item and bring it down together, before going back to a more agonistic lifestyle after feeding.
Great. So which is it?
As with our look at a swimming Spinosaurus last year, trace fossils help offer some clues that body fossils don’t. In 2007, Rihui Li et al published a paper describing eight trackways from Shandong Province, China. The trackways are interesting because they show animals walking on two toes, with a third toe seemingly raised from the ground. This type of imprint matches what scientists have long suspected from deinonychosaurs (the group of dinosaurs that includes dromaeosaurids and their close relatives, the troodontids), all of which had a toe with a specialized claw that was presumed to have been carried off the ground when the animal walked.
Because no body fossils (that is, fossils of the animal itself) were found with these footprints, they were given an ichnogenus and inchnospecies – Dromaeopodus shandongensis. The Dromaeopodus prints are also large, with some of the better preserved ones measuring 28.5 cm long. Given that size and the evolutionary history of deinonychosaurs (large dromaeosaurids are mostly known from the early Cretaceous period, while larger troodontids are mostly known from the later Cretaceous), Dromaeopodus tracks are believed to have been made by a dromaeosaurid of comparable size to Achillobator giganticus, which measured approximately 5 meters in length.
However, what is perhaps most interesting is that six of the trackways were placed very close together, and all heading in the same direction, at the same time, at about the same speed. The fact that none of these trackways overlap strongly suggests they were made by a group of six large-sized individuals moving together as a group. While this doesn’t offer any evidence of hunting behavior, it does suggest a level of gregariousness that could be conducive to cooperative hunting.
Social behavior is hard to determine from fossils, and animal behavior is incredibly complex. Lions and tigers are both members of the same genus (Panthera), existing at the same time, and yet have wildly different social norms. It’s incredibly unlikely that dromaeosaurids, which existed for upward of 70 million years and ranged widely in size and shape (from the four-winged, meter-long Microraptor to the 6 meter-long Utahraptor) would have exhibited anything close to uniformity when it comes to social behavior.
Every February, to help celebrate Darwin Day, the Science section of AIPT cranks up the critical thinking for SKEPTICISM MONTH! Skepticism is an approach to evaluating claims that emphasizes evidence and applies the tools of science. Every day this month we’ll be highlighting skepticism in pop culture and skepticism of pop culture.
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