Venomous dinosaurs

A paper soon to appear in PNAS (and not yet online) suggests that some dinosaurs might have been venomous.  The title, however, leaves no wiggle room: “The birdlike raptor Sinornithosaurus was venomous.”

A team of scientists from China and Kansas noticed that a fossil specimen of the feathered theropod dinosaur Sinornithosaurus millenii (see pp. 40-44 of WEIT) had long maxillary teeth that were grooved (see Fig. 1 below).  Such grooved teeth are often seen in venomous animals:   glands secrete the venom into channels in the jaw, which deliver it to the base of the teeth. It then mixes with saliva and the toxic cocktail is drawn into the tooth grooves by capillary action.  In venomous reptiles like the gila monster, these teeth deliver a poisoned bite that doesn’t kill the prey but puts it into a state of shock.

S. millennii also had a space on the jaw (“maxillary fossa”) that could have housed a venom gland, and jaw channels that might have collected the secretions.  The authors also note that the morphology of the skull is also consistent with a venomous predator: the snout is narrow and the skull has a “tall later profile with a large gape,” suggesting that the dino had a relatively weak bite and therefore needed help from venom to incapacitate its prey.

They conclude that “Sinornithosaurus was a venomous predator that fed on birds by using its long fants to penetrate through the plumage and into the skin, and the toxins would induce shock and permit the victim to be subndued rapidly.”  [Note: some have suggested that S. millenii might have been an ancestor of modern birds, but Gong et al. clearly disagree, since they envision birds as being its prey.]

The reason this paper was PNAS-worthy is because if the report is true, this would make S. millenii the first known venomous dinosaur, and of course dinosaurs are the ultimate charismatic macrofauna.  Anything new about them is sure to get wide attention.

Ed Yong has a more detailed report at  on Not Exactly Rocket Science , including statements from dissenters who argue that the evidence for venom use is less than airtight. Perhaps the authors should have been a bit more cautious in their title!

Fig. 1. Photograph of the holotype of S. millenii (IVPP V12811) showing dentition with venom grooves (vg). mxf, maxillary fang (from the paper).

Fig. 2. Sinornithosauris millenii. Illustration by Mick Ellison (from WEIT).

h/t: Ed Yong for the pdf.

_________

Gong, E., L. D. Martin, D. A. Burnham, and A. R. Falk. 2009. The birdlike raptor Sinornithosauris was venomous. Proc Natl Acad Sci U S A early edition

(If you’re interested in punctuated equilibrium and cryptic species in marine microfossils, see also Hull, P. M., and R. D. Norris. 2009. Evidence for abrupt speciation in a classic case of gradual evolution. Proc Natl Acad Sci U S A 106:21224-21229.)

12 Comments

  1. Posted December 22, 2009 at 3:43 pm | Permalink

    That’s cool! With venomous bird-predators running around, I suspect that more than a few mesozoic birds will be found to have toxic feathers, similar to the extant hooded pitohui bird.

  2. Posted December 22, 2009 at 4:11 pm | Permalink

    Well, cool.

    The abrupt speciation paper linked at the bottom is subscriber-only. (Though I can probably get access through my university student account.0

  3. Insightful Ape
    Posted December 22, 2009 at 5:32 pm | Permalink

    But this is confusing. Snakes are lepidosaurs, dinos are archosaurs. Only distant shared ancestry. If true it would be quite an odd case of converging evolution.
    Any thoughts Dr Coyne?

    • J.J.E.
      Posted December 22, 2009 at 7:19 pm | Permalink

      Google Platypus venom for some REAL convergenc.

      • Ed Yong
        Posted December 23, 2009 at 8:25 am | Permalink

        See also this post I wrote on convergent evolution among the venom proteins used by shrews and Mexican beaded lizards. Bryan Fry’s done a lot of work on convergent evolution of venom proteins and there’s a hell of a lot of it going on.

      • newenglandbob
        Posted December 23, 2009 at 8:51 am | Permalink

        Ed Yong: “this post” has no link.

      • Insightful Ape
        Posted December 23, 2009 at 2:52 pm | Permalink

        I am still not convinced. Convergence involving molecular structures is one thing. Anatomical convergence is a different thing, and much more complicated. It is possible, I guess. But is it also possible that the adapted teeth may have had some function other than poison delivery?

      • J.J.E.
        Posted December 23, 2009 at 11:18 pm | Permalink

        So, snakes have both hypodermic needle fangs as well as grooved fangs. The grooved model is probably the easiest to evolve because teeth already come in a variety of shapes with crevices, peaks, bumps, points, crowns, etc. I don’t see convergence of a groove to be very innovative. And the very interesting and innovative hypodermic model ISN’T observed in the fossil. So, the less likely convergence route isn’t taken.

        And finally, convergence is common in biology, even for structures as complex as the eye. So I don’t see what is unusual even if this was an example of a more complex type of convergence.

  4. SWH
    Posted December 22, 2009 at 7:06 pm | Permalink

    My thoughts went along the same lines as my primate colleague above. I guess poisons are found in several different groups of animals, including fish, amphibians, reptiles, birds and mammals. However delivery by modified teeth is not that common and implies an aggressive rather than defensive use (as in the feather toxins of the hooded pitohui bird mentioned by Rick). Convergent evolution is a possibility but I do wonder whether there might be some other explanation for this tooth shape. I would agree with Jerry that a somewhat more speculative title would be in order – if only to give the authors somewhere to hide if another explanation surfaces.

  5. newenglandbob
    Posted December 22, 2009 at 8:34 pm | Permalink

    I just recently read in Carl Zimmer’s “The Tangled Bank” about beta-defensins in early tetrapods for fighting bacteria evolving into venom genes that are found in Gila monsters, some lizards, iguanas and of course snakes. Now we can add dinosaurs to the venom club.

  6. Curtis Croulet
    Posted December 23, 2009 at 12:31 pm | Permalink

    Why would S. millenii preying on birds contradict it being a possible bird ancestor (4th paragraph above)?


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