Velociraptors on air: from theory to practise
Previously we saw that flight was present in the deinonychosaurs Rahonavis, Microraptor and Archaeopteryx, and might had been more widespread across Deinonychosauria than previously thought, in other small species such as Anchiornisand Jifengopteryx, or even in the juveniles of most if not all species. Here, we will analyse how much these assumitions are supported by availiable evidence.
Deinonychus and Velociraptor: the iconic “raptors” provide good reasons for the usage of that word
Deinonychus is quite interesting in that it illustrates the arboreal adaptations of Dromaeosauridae applied to killing prey. It’s strong forelimbs and sickle claws, developed by it’s tree climbing ancestors, became even more well developed as it became specialised in killing larger prey. However, considering it lived in dense swamp forests, and co-existed with much larger predators like Acrocanthosaurus, tree climbing wasn’t abandoned; while the adults might had been terrestrial, the juveniles show considerably more developed pedal claws, suggesting that they were clearly arboreal.
The arm bones are also longer (Parsons, W.; and Parsons, K. (2006). “Morphology and size of an adult specimen of Deinonychus antirrhopus, (Saurischia, Theropoda)”. Journal of Vertebrate Paleontology 26 (3 sup.): 109A.); this suggests that the juveniles were presumably capable of gliding, or even limited powered flight, considering how robust the arms of Deinonychus were, rendering them thus an exadaptation for flight turned into efficient tools for grabbing prey. Currently, integrument evidence to suggest if this is possible is unknown, but it is reasonable to think that this was possible for juveniles at least reaching up to a third of the known adult size.
Another iconic dromaeosaur that shows tendencies towards aerial locomotion is Velociraptor, which also provided the first unambious evidence of feathers in eudromaeosaurs.
Velociraptor is much different from Deinonychus in that is it smaller, lived in an arid ecosystem, and had clear evidence of quill knobs on the ulna (although it is probably just a matter of time until they are found in Deinonychus as well). Quill knobs are not present in all feathered dinosaurs (several modern birds, like flamingoes, lack them), so their presence inVelociraptor is an indicator that it’s wing feathers were probably quite rigid (incidently further discrediting the notion that the rachises of non-ornithothorace maniraptors were always weaker than those of modern birds). This rigidity could suggest one thing.
Besides Velociraptor, unambiguous quill knobs so far have only been preserved in Microraptor and Rahonavis, deinonychosaurs that were clearly volant. In the case of the latter, the ulna and the radius were considerably long than in the other known volant species, indicating that Rahonavis presumably was adapted to soaring. Thus, it is not unreasonable to think that the juveniles of Velociraptor were perhaps capable of exploting the thermals that formed on ancient mongolian deserts, and thus were capable of soaring. Indeed, it has been noted that quill knobs are absent in flightless birds, further suggesting that Velociraptor had use for robust feathers, at least during part of it’s lifetime. It is less likely that adults engaged in soaring, but they could possibly have practised WAIR if necessary; this is a possibility that has already been adress (Turner, A.H.; Makovicky, P.J.; Norell, M.A. (2007). “Feather quill knobs in the dinosaur Velociraptor“.Science 317 (5845): 1721.).
Thus, both Deinonychus and Velociraptor show that flight or at least gliding was a possibility for the juveniles of eudromaeosaurs, the most derived dromaeosaurs. This is consistent with the general assumition that dromaeosaurs improved their flight capacities over time, as appearent in Microraptor and Rahonavis.