Deinonychus and Velociraptor used their killing claws to pin prey, like eagles and hawks

By Ed Yong | December 14, 2011 5:01 pm

The sickle-shaped “killing claws” of dinosaurs like Deinonychus and Velociraptor have captured the imagination for decades. They were held aloft from the second toe, and were far bigger than the neighbouring claws. In Jurassic Park, Alan Grant tells an annoying child that the dinosaurs used their claws to disembowel their prey with slashing motions. That seems unlikely – they didn’t have a suitable cutting edge. Others have suggested that they were used for climbing onto larger prey.

But neither idea made sense to Denver Fowler from Montana State University, who has put forward a very different idea about how these animals used their infamous claws. He compared the feet of extinct dinosaurs like Deinonychus to those of living dinosaurs like eagles, hawks and other birds of prey. Both groups are known as “raptors” and Fowler thinks that they share more than their nicknames.

In his vision, which he calls the “ripper” model, Deinonychus killed small and medium-sized prey in a similar style to a hawk or eagle dispatching on a rabbit. Deinonychus leapt onto its target and pinned it down with its full body weight. The large sickle-shaped claws dug into its victim, gripping tightly to prevent it from escaping. Then, Deinonychus leant down and tore into it with its jaws. The killer claws were neither knives nor climbing hooks; they were more like anchors.

It’s a simple idea, but a potentially important one, for it casts Deinonychus’s entire body into a new light. Fowler thinks that it flapped its large feathered arms to keep its balance while killing a struggling victim. And its feet, which were adapted for grasping prey, would have given its descendants the right shape for perching on branches. Fowler says, “It really helps to make sense of the weird anatomy of these little carnivorous dinosaurs.”

Fowler’s interest began years ago when someone mentioned to him that some birds of prey have a slightly larger claw on their second toe, just like Deinonychus and its entire family – the dromaeosaurids. He soon got his chance to check that. He was going through local museum collections with colleague John Scanella, when he stumbled across a box full of bird of prey feet.

By analysing his collection, and comparing them to videos of their owners in action, Fowler showed that the shape and size of a bird of prey’s feet provides important clues about how it kills. Some use their talons as precision stabbing weapons; others use them to suffocate their prey; and yet others use them as cages.

When Fowler brought Deinonychus into the mix, he found that its feet most closely resemble those of eagles and hawks (the accipitrids) than to other birds of prey. When he looked at specific features of dromaeosaurid feet, the similarities to birds of prey stood out even further. “We saw the same parallel adaptations in the birds of prey and the fossils,” he says.

Deinonychus has a foot adapted for grasping. Its metatarsus, the bone between the ankle and toes, was surprisingly short and stocky, like that of an owl. It would have given the foot a strong grip at the expense of running speed. The fourth toe could have improved the grip even more by moving round to oppose the first one. And the joints in the foot were very mobile, all the better for resisting the struggles of prey.

This idea of Deinonychus sitting on top of small prey seems at odds with classic picture of this predator working in packs to bring down larger quarry. But again, modern birds show how the same grasping motions might have worked against big targets. Golden eagles can kill reindeer. They dig their talons deep into their victim’s back, holding on while the struggling reindeer widens its own wounds. Deinonychus might have used the same strategy to kill larger prey.

Tom Holtz Jr, who studies predatory dinosaurs, says, “Prey-riding is also common in the Galapagos hawk – there’s classic footage of them taking down marine iguanas much bigger than they are. They pin them down, and flap away as the iguanas take them for a ride.” Philip Currie from the University of Alberta also mentions the famous Mongolian “fighting dinosaurs” – a Velociraptor found in pitched battle with a Protoceratops. “It confirms that dromaeosaurids were seeking prey animals of their own approximate body size.”

Not all dromaeosaurids had a grasping foot. Earlier ones like Sinornithosaurus had a relatively long metatarsus. So did the group’s closest relatives – another lot of small hunters called the troodontids. A long metatarsus would have given them a longer stride and a faster sprint. Fowler thinks that dromaeosaurids and troodontids both evolved from fast-running ancestors. From there, they went down different paths. Troodontids took their fleet-footed adaptations even further, and chased down their prey. Meanwhile, the dromaeosaurids sacrificed speed for grasping strength, and evolved into ambush hunters with strong but slower feet.

“The paper provides a very nice explanation for aspects of dromaeosaurid anatomy that have always bothered me and others,” says Currie. “Deinonychus, Velociraptor and their relatives are often referred to as fast and agile, but their hindlimb proportions and peculiarities of their hips are inconsistent with such an interpretation.”

Fowler thinks that his ripper model explains other odd features of dromaeosaurids beyond their feet. For example, their jaws weren’t very strong or sturdy, but you don’t need an especially strong bite or robust jaws if your prey is fully restrained by massive talons. (Hawks and eagles too have relatively weak bites for meat-eating birds).

The ripper model could also explain the weird arms of dromaeosaurids. Their hand bones suggest that the claws could exert a lot of force. However, their arms didn’t have a wide range of motion and they bore long flight feathers that might have got in the way. They look like arms that were adapted for flapping rather than for clawing or grasping.

Fowler suggests that they could have used these odd limbs in two ways. First, they could have circled them around their prey, covering it in a cloak of feathers to either hide it from rivals or trap it even further. Modern birds of prey do this – it’s called “mantling”. From within the mantle, the dinosaurs could have used small movements of their claws to pull back prey that had escaped from the feet.

Second, by flapping their arms, dromaeosaurids could have kept their balance while trying to dismember the prey between their legs. Modern raptors do exactly this – they use their wings and tail to get their body weight pressing down on top of their prey, and then to keep themselves there.

If Fowler is right, his model has important implications for the evolution of flight. The dromaeosaurids would have been very nearly ready for life in the trees. Their grasping feet, with opposable toes, could easily have adapted to grip branches as well as prey. Their flapping arms, used to balance themselves, could have adapted to help them fly. These animals were positively pre-adapted for life in the trees. Perhaps the graceful wings and perching feet of a blue tit got their start with bloody murder on the ground.

It’s an intriguing idea, which gets over the thorny question of “What use is half a wing?” Even wings that couldn’t hold dromaeosaurids aloft would have been useful for “stability flapping”. But Fowler admits that there are problems with the idea. “I’m not sure we’ve quite got there yet,” he says. “We can get to the point where you have all this vigorous flapping but taking that to a mode of locomotion – what’s the evolutionary pressure for that? We’re working on developing that part of the model.”

“As many of these things that involve behaviour and fossils, it probably extrapolates somewhat beyond the evidence but it’s hard to do anything with fossils that doesn’t suffer from that,” says Peter Makovicky, who studies raptors (the prehistoric ones). “It’s better tested than some of the other ideas that have been proposed,” he says.

Reference: Fowler, Freedman, Scannella, & Kambic. 2011. The predatory ecology 1 of Deinonychus and the origin of flapping in birds. PLoS ONE.

Images: restoration by Nobu Tomura; feet by Didier Descouens



Comments (25)

  1. If I remember correctly, the “slashing” hypothesis of claw use came from some of the early finds of Deinonychus. I don’t think Creighton invented the hypothesis for Jurassic Park.

  2. I didn’t suggest that – just used JP as an example.

  3. Craig B

    Is it possible that flight evolved from the raptors ambushing their prey by dropping on them from tree branches? Would this plus competiton for food be a possible ‘evolutionary pressure’ or does the term mean something more precise than that? If proto wings were used for balancing it is not a huge step (sic) to directing the drop and from there on to actual manouvering in the air and flight.

  4. Given that earlier, smaller dromaeosaurs like _Sinornithosaurus_ and _Microraptor_ had less specialized feet and they show clear arboreal adaptations, isn’t it as likely–if not more likely–that larger, later dromaeosaurs co-opted their feet and wings for prey capture? That would again bring up the “flightless dromaeosaurs” hypothesis, but in a different context.

    I saw this talk at SPV 2010 (I think) and was intriuged then. I really like this idea–it does explain a lot about big dromaeosaurs. I wonder if the really big guys like _Utahraptor_ and _Achillobataar_ practiced the same kind of “mantling” behavior.

  5. @Zach: Sinornithosaurus and Microraptor do not show any unambiguous arboreal adaptations (this was also recently published by Dececchi & Larson, 2011: which is referenced in our paper). In our paper we discuss how grasping adaptations may be useful for an arboreal lifestyle, but they may be more parsimoniously explained as predatory adaptations. Further, these basal dromaeosaurs have a subarctometatarsalian metatarsus which is a cursorial adaptation (something else we discuss in the paper). It is difficult to see how this would be selected for in an arboreal animal.

    A correction: basal dromaeosaurs have grasping proportions of the toes, it’s just that they have a long metatarsus, so they wouldn’t have had as much leverage (grip strength).

    Thanks for the post Ed. Really good.

  6. Zach, the authors suggest exactly that: that this is an exaptation of a more widespread grasping foot for a particular predator mode.

  7. Kurt Kohler

    What beasties do the two feet in the second image belong to?

    Oops! Never mind. A flyover shows they’re both Deinonychus.

  8. Actually, the authors suggest both possibilities: either a tree-grasping first or a hunting first. They favor the hunting first, but I disagree with some of their reasons for rejecting it.

  9. I’m not sure it’s possible to segregate the origins of tree-grasping and hunting technique in this instance.

    Hunting is basal to the group and the specific killing techniques of any given carnivore will be adapted to the environment – in modern taxa members of the same species can use different techniques under different conditions. It may simply be that ambush hunting by a fairly generalist predatory deinonychid in a storeyed habitat led to the coevolution of adaptations for tree grasping and a ‘ripping’ killing technique.

    Heck, it may be that the ‘ripping’ killing method would work better with an ambush from an elevated position, increasing the impact force. This would provide a good reason for aerodynamic feather development, as a mechanism for controlling the trajectory of the ambush leap. But can we ever know?

  10. Okay, now I’m a little confused. What came first–grasping feet for branch-hugging or grasping feet for prey capture?

  11. Trond Engen

    Ooh, I love this. Thank you Ed, thank you Denver, thank you all! My thought when reading was: With the toes specialized for hunting, could the hand claws have been adapted to help with climbing or — stretching it — to grasping onto branches when gliding?

  12. lkr

    With this ‘dive-bomber’ hypothesis in play, I suppose it’s only a matter of time before somebody names a new dromaeosaur “Stukasaurus” or “Helldiveria”??

  13. Juicyheart
  14. Juicyheart

    If these things are ambush predators. Could feathers help them with that? Both lengthening their jump and distracting the prey by making a larger creature suddenly being present and changing the color scheme of the environment. I remember seeing a YouTube video of a cuttlefish doing that to an octopus.

  15. Juicyheart

    If these things are ambush predators. Could feathers help them with that? Both lengthening their jump and distracting the prey by making a larger creature suddenly being present and changing the color scheme of the environment. I remember seeing a YouTube video of a cuttlefish doing that to an octopus. Could these proto wings help a raptor climb the ribs of a sauropod? Could a pack of these kill a cerotop by jumping and fluttering past the horns and frills, to inflict weakening wounds? Were they the first bronco riders?

  16. Juicyheart

    I thought I was updating my second post with my third post. Damn iPhone interface. Sorry for the inconvenience.

  17. Juicyheart

    Could the frill of a cerotops be designed to keep a raptor, or pack of raptors, off the neck, rather than to keep a tyrannosaur from biting into it

  18. Henrique Niza

    I didn’t yet read the entire paper but can also this suggest a hunting strategy from the trees onto to prey by dromaeosaurs with suitable size to arboreal life-style?

  19. this answers the creationist myth that a half formed wing (eye in the original) is useless

  20. yogi-one

    So Jurassic Park is wrong–Bummer! So is are those great scenes in the latest Godzilla remake where the baby godzillas/raptors are chasing the humans around in the coliseum.

    I guess it was bound to be as our understanding of the dinos evolves…

  21. Mysti

    A fossil of velociraptor showed it using it’s large claw to stab the neck of a protoceratops,(died whilst doing it), I figure deinonychus would have done the same, though this makes sense,
    the use of the sickle claw could vary between the different dromeasaurids or be used two or more ways by a species even.

  22. Amtoine Grant

    I strongly object to most inferences drawn from the “Fighting Dinosaurs”. Such as “It confirms that dromaeosaurids were seeking prey animals of their own approximate body size.”- Phil Currie. Why? if the Protoceratops wa sthe agressor, how would the final scne be any different? It wouldn’t. The Velociraptor appears to be doing the ONLY thing it can do from the position it died in. In fact, the ONLY evidence we have for dromaeosaurs hunting naything their size or larger results in casualty for so-called hunter. How does nobody seem to notice this? ie. Multiple Deinonychus die in the process of subduing a Tenontosaurus and the conclusion is they do this on a regular basis? I’d imagine the exact opposite.

  23. monstrinho

    This has bothered me since i first saw deinonychus with the half wings. Sure they would have just been a fragile encumbrance in a fight with a much larger adversary. Feathered heads would have been a sticky mess too. Vultures have bald heads for this reason.

    Perhaps the wings would also have allowed for fast changes of direction when running. Something to think about.

  24. Spaulding

    Like others have already commented, there are suggestions that the common ancestor of Paraves have four gliding wings to travel between the trees and claws adapted for climbing. If that’s how it was, it seems as if the ancestors of the birds continued to adapt to a life in air, while their relatives returned to ground. I think Microraptor and other Paraves descendants that did not belong to the bird’s line, were all small and birdlike. Later species became bigger and more adapted to ground. The Troodons were as you know specialized for a life after sunset, chasing the small prey they just to hide from predators during the day. To chase this kind of prey, you need speed, while there is no need for powerful feet to pin them to the ground.

    And, as mentioned in the article, the velociraptors did have strong claws on their wings. If the wings were used for flapping only, it would be waste of energy and tissue to develope these strong fingers. It may not be clear how their used the claws on their hands, but they were there for a reason. I would assume there is also a limit for how big you can be and still ride on the top of you prey while using the wings to keep the balance. Could Utharaptor have done the same?

    One possibility is that they used the finger claws to grab the prey before the claws on their legs could do their jobs. They would also bend the arms in a similar way seen in birds today, keeping them out of way while not in use, instead of letting them hang to the side or holding them in front of themselves in what is described as a zombie like manner (or the monster villains in Scooby Doo).

    Deinonychosauria also seem to have some advanced features not found in early birds, indicating that they split with the birds’ ancestors a long time ago. Personally, I like the idea of these dinosaurs as primitive birds that returned to the ground, whre they added some complex features to their anatomy. That would also explain their wings, which they kept from their tree dwelling ancestors. But since the Paraves seems to have evolved from a gliding species with four wings, what does that say about the Veloriraptors’ legs? Did they too have similar feathers as their arms, maybe even rudimentary, or were they just like the legs of most of today’s birds? I would love to have seen what they could have evolved into if they just hadn’t been extinct.



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