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Friday, 26 September 2014

Does Deinonychus really have one of the most powerful bites of all dinosaurs?

Quick sketch of Deinonychus antirrhopus with expanded, bone-puncturing jaw muscles, a requirement of having a bite as strong as a modern alligator. Say what? Read on...
There's a part in Michael Crichton's Jurassic Park novel where Velociraptor attempt to bite through bars to reach a people-shaped lunch. Presumably, they're meant to give readers something to rally behind seeing as one person in the line of fire is Ian Sodding Malcolm - I'd be chewing through steel too if it meant we could enjoy a few moments without another preachy monologue. Crichton describes them as hyena-like in their ability to bite through steel, delivering thousands of pounds of pressure per square inch and gnawing their way through thick metal bars in 15 minutes.

Dromaeosaurids biting through steel bars - heck, any animal biting through steel bars, including hyenas - intuitively sounds like crazy talk*. But was Crichton at least right about the strong bites of dromaeosaurids? I've been doing some investigating on dromaeosaur jaw muscles for a new palaeoart commission, but I've come unstuck. Here's why.

*Is there any substance to claims about modern animals biting through steel? Given that tooth enamel is only very slightly harder than straight steel, I wonder how long teeth would last when gnawing through anything but the thinnest metal sheet.

Recently, Gignac et al. (2010) presented a suite of bite marks on Tenontosaurus bones argued to show Deinonychus as capable of deeply puncturing bone with powerful bites. The tooth gouges match those of large Deinonychus in many aspects (bite mark size, shape, correspondence with dental arcade) and broken teeth associated with the same Tenontosaurus corroborate suggestions that Deinonychus fed from the carcass. Other teeth, not from Deinonychus, were also at the site, but their owner does not seem to have left any other obvious traces. Experiments with modern cow bones suggest Deinonychus needed a whopping 8200 N to puncture Tenontosaurus bones to the degree seen in the fossil remains. This value puts Deinonychus bites on par with those of adult alligators and leaves hyenas in the biomechanical dust. It also grants Deinonychus one of the highest estimated bite forces of any dinosaur, even greater than animals of much larger size. The tooth marks only match the largest known Deinonychus individuals, possibly indicating that juveniles were incapable of delivering such bite forces. Because Deinonychus puncture wounds are rare, Gignac et al. argue that puncturing bones was not common in Deinonychus, and that their powerful bites were primarily used for aggressive behaviours instead.

Bitemarks in the radius of Tenontosaurus specimen FMNH PR 2261, below, compared to the dental arcade of Deinonychus antirrhopus, above. This is one of many pathologies on FMNH PR 2261, almost all of which have been attributed to Deinonychus feeding behaviour. From Gignac et al. 2010.

For artists, Gignac et al.'s paper has important implications. Generating 8000 N of bite force requires a lot of muscle, so we might predict that Deinonychus jaws had the same swollen jaw muscles of modern crocodiles to generate all those bone-smashing newtons. This is at odds with other reconstructions of Deinonychus, where the jaw muscles do not atypically alter the contours of the face. I don't know how visible expanded, crocodile-like jaw muscles would be on deeply feathered maniraptorans, but reconstructions with sparse or naked faces would certainly need to take this on board. I've had a quick play about with this concept in the conservatively feathered Deinonychus above.

Problem is, Gignac et al.'s conclusions are not uncontested. Biomechanical assessments of Deinonychus jaws have found they were mechanically weak and ill-suited to delivering powerful bites (Therrien et al. 2005; Sakamoto 2010; Fowler et al. 2011). Therrien et al. (2005) estimated Deinonychus bite force at a relatively wimpy 15.7% of alligator jaw power, which Gignac et al. translate into 1450 N. This isn't unimpressive - as strong as that of a 30 kg wolf - but a far cry from an alligator-like bite, and certainly deflates our reconstructed jaw muscles to their traditional size. On the face of it, I certainly find the arguments for weak jaws more convincing. Hyenas and alligators have robust, wide and solidly-built skulls with generous room for jaw muscle placement, whereas the skull of Deinonychus is full of holes, is relatively narrow and slender, and with comparatively little room spaces jaw for muscles.

So, what to do? Jaws with relatively small muscles have been the norm in Deinonychus palaeoart since its discovery, but is it time we changed that? Were their jaws actually visibly and powerfully muscled as inferred by their trace feeding evidence, or is there something missing here? Is it significant that lower estimates of their bite forces match those of animals which can also puncture bone (wolves - see Haynes 1982)? If anyone has anything to add, please let me know...

References

  • Fowler, D. W., Freedman, E. A., Scannella, J. B., & Kambic, R. E. (2011). The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS One, 6(12), e28964.
  • Gignac, P. M., Makovicky, P. J., Erickson, G. M., & Walsh, R. P. (2010). A description of Deinonychus antirrhopus bite marks and estimates of bite force using tooth indentation simulations. Journal of Vertebrate Paleontology, 30(4), 1169-1177.
  • Haynes, G. (1982). Utilization and skeletal disturbances of North American prey carcasses. Arctic, 266-281.
  • Sakamoto, M. (2010). Jaw biomechanics and the evolution of biting performance in theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences, 277(1698), 3327-3333.
  • Therrien, F., Henderson, D. M., & Ruff, C. B. (2005). Bite me: biomechanical models of theropod mandibles and implications for feeding behavior. The carnivorous dinosaurs, 179-237.

25 comments:

  1. Also, it's possible that the maker of those bites was not Deinonychus but another taxon. For example, isolated teeth from the mid Cretaceous of North America indicate a possible basal tyrannosauroid.

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    1. Thanks Andrea. Gignac et al. mention that one bite mark might be attributable to a tyrannosauroid, but seem convinced that the others are Deinonychus because of their slender shape. Given that early tyrannosauroid maxillary teeth are quite slender and the conflicting biomechanical evidence for a bone-crushing Deinonychus bite, I wonder if this needs a more detailed reappraisal.

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    2. So there's evidence of bone crushing basal tyrannosaurs in Cedar Mountain? I've heard erroneous referral of teeth from there to Tyrannosaurids before, to be fair.

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  2. Having handled Deinonychus skull material, I am extraordinarily dubious of the idea that this is a framework that could generate and withstand alligator-level bite forces.

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    1. I'm reminded of a comment Larry Witmer made about claims for powerful biting in Dimorphodon: "such a musculature system probably would not have had the opportunity to contract more than once!"

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  3. Rodents are known to gnaw on metals and concrete to wear down the biting surfaces of their front teeth, although steel generally defeats even them. A common ploy to keep mice out uses cement mixed with wire wool, so whilst they can probably cope with some steel, they don't really like it much.

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    1. Many rats and especially some of the denser-toothed terraphagous rodents use evergrowing teeth to compensate for their gnawing through various materials that are significantly denser than enamel, including but not limited to steel and concrete. This depends on the relatively thickness, but for the most part iron nails, concrete walls, etc. are not a barrier to rats; but then their jaws are suited for extremely high pressure at precise points: the upper incisors bear a notch in most rodents that occludes the tip of the lower incisors, providing a high-pressure zone that uses the structure of the teeth themselves to enhance the concentration of force, which is how they are able to eat through metal, bone, brick, wood, and some stone (conglomerate, mostly). Such examples of high-power feeding seem to be produced as relief from stress; a happy rat is a calm rat and prone to chewing just food, but an unhappy rat is very antsy and will chew ... anything.

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  4. I doubt alligator raptors, but if this is the case I'd certainly finally be convinced with Deinonychus hunting Tenontosaurus.

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    1. There already is convincing evidence of Deinonychus having hunted Tenontosaurus: http://www.jstor.org/discover/10.2307/4523664?uid=2&uid=4&sid=21104693326717

      -Hadiaz

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    2. Hadiaz beat me to it - I was going to link to the same paper. In short, there are multiple associations between Deinonychus and Tenontosaurus across at least two formations, the Cloverly and Antlers. We're not just talking about shed teeth, either: a number of associated partial skeletons have been recovered. It does seem that these two species were somehow linked, and a predator/prey relationship is perhaps the most parsimonious.

      The 'ill feeling' towards this relationship, which I think my account for your scepticism, is artistic rather than scientific. Especially for Tenontosaurus, it seems these animals cannot be rendered outside of mortal combat with one another. As much as the evidence points towards Tenontosaurus and Deinonychus being prey and predator, they almost certainly did other things which we could be showing in art. You're probably aware that John Conway directly addressed this in All Yesterdays:

      http://archosaurlove.tumblr.com/post/49756928795/all-yesterdays-has-a-page-spread-set-aside-for

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    3. I understand that - but given the size difference there is just no way it could have killed one.

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    4. 1stly, the size difference btwn Deinonychus & Tenontosaurus is about the same as that btwn wolves & bison or moose (& thus, probably not too big).

      2ndly, even if the size difference was too big, there are still the facts that 1) Deinonychus probably hunted Tenontosaurus in packs (See the paper linked in my previous comment), & 2) Deinonychus packs probably favored Tenontosaurus sub-adults (Again, see the paper linked in my previous comment).

      -Hadiaz

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  5. I think the conclusion that something else left those impressions in the Tenontosaurus bone is the most parsimonious here. More robust cousin of Deinonychus? Small tyrannosaur? Who knows. Fascinating though.

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    1. Thanks Sam - see Andrea's comment above for further discussion.

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  6. There are theropods from the Cloverly that were much larger than Deinonychus (e.g. see the large indeterminate tooth figured by Ostrom, 1970).

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    1. The 'other theropod' idea seems to be quite popular, and I think it's probably the best answer to this quandary. Would a significantly larger theropod suit these traces though, given their size?

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  7. I did a Deinonychus muscle recon for a 2002 paper-link below. There's nothing particularly special about it, though I did wrap pterygoideus ventralis around to the lateral mandible but that may need to be revised. We built them on a sculpture but had the real material in hand. Having seen that material, I can't imagine how it could achieve croc-level bite forces. With bite marks like that, maybe the animal did bite Really hard, but that could spell the end of those teeth. Casey. http://www.oucom.ohiou.edu/dbms-witmer/Downloads/2002%20Bimber%20et%20al.%20Augm.%20Paleo.pdf

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    1. Thanks for the comment and links, Casey. It seems at least mammalian carnivores are more careless with their teeth than may be expected. The chance that they will break at least one tooth exceeds 25%, so it may be that some dinosaurs were similarly reckless with their teeth.

      Given the comments here, the number of bites on this Tenontosaurus specimen, and rates of dinosaur tooth replacement, I'm suspect we're dealing with a theropod that could routinely bite into bone without consequence, which probably wasn't Deinonychus.

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  8. I tried to post this comment multiple times yesterday and my internet kept crapping out, so apologies if 3 of these show up at some point...

    I'm also very skeptical of an alligator-like bite force in Deinonychus, but it is really most parsimonious to assume that the deep puncture bites in the Tenontosaurus bones were created by something much larger, even though (according to Gignac) their distribution and architecture perfectly matches Deinonychus dentition? And then that the mystery larger dinosaur also didn't leave any other traces, like shed teeth?

    Maybe Tenontosaurus just had remarkably weak bones for its size... :p

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    1. Witton actually alludes to the presence of teeth that do not belong to Deinonychus in this article.
      "Recently, Gignac et al. (2010) presented a suite of bite marks on Tenontosaurus bones argued to show Deinonychus as capable of deeply puncturing bone with powerful bites. The tooth gouges match those of large Deinonychus in many aspects (bite mark size, shape, correspondence with dental arcade) and broken teeth associated with the same Tenontosaurus corroborate suggestions that Deinonychus fed from the carcass. Other teeth, not from Deinonychus, were also at the site, but their owner does not seem to have left any other obvious traces."

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    2. Yeah, but if those "other teeth" don't fit the dentition implied by the bite marks on the Tenontosaurus bones as well as Deinonychus teeth do, then we aren't really any closer to solving the mystery.

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  9. Would it be possible for an animal with dentition that was similar to Deinonychus to be able to produce the requisite bite force of 8200 N?

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  10. Sorry this is so late to the party, but is it possible these deep gouges are evidence of Tenontosaurus falling upon, or crushing Deinonychus while Deinonychus was taking a bite, thereby driving the teeth in? Might explain the apparently massive forces necessary to drive those teeth in and the broken teeth? Another possibility might be that the decomposition of the bone in a moist, acidic environment had softened the bone somewhat? Love your blog, by the way. It's most informative and always offers fresh perspectives.

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  11. I think the tyrannosauroid explanation is the most interesting. It seems possible, given the recent finding of Siats and its association with small tyrannosauroids, which haven't yet been described in any detail (Zanno and Makovicky, 2013). I'm willing to bet there was a tyrannosauroid of some type existing at the same time and place as Deinonychus. Hopefully the answer will eventually be solved.

    Great blog, Mark. I really admire your art and writing!

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  12. As for living animals biting through steel, quite a few fish can bite through steel eladers, especially piranhas.

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