Into the air!

Mike Habib (right) with Musings favourite Luis Rey

Mike Habib (right) with Musings favourite Luis Rey

This time out, say hello to Mike Habib‘s work on quadrupedal launching. Just how did those giant pterosaurs get into the air?

It has been long recognized that the largest pterosaurs far exceeded the size of the largest known flying birds.  A new paper by Mark Witton (also in the Wellnhofer volume – details here) suggests that the famous giant azhdarchid, Quetzalcoatlus, probably weighed in around 250 kg.  All this business about size naturally raises the question of how pterosaurs managed to launch in the first place.

Take-off is generally the limited step with regards to the size limit of flying animals.  Traditionally, pterosaurs have been assigned a bird-like launch sequence, in which the animals launch off of the hindlimbs in a bipedal fashion.  Oddly enough, no one seems to have ever actually tested this assumption in the literature – apparently it was just intuitive.

Like a lot of intuitive thoughts, however, there are some serious problems with the bipedal launch model for pterosaurs (not the least being the whole giant size thing).  I went about testing this model using structural mechanics.  The overall approach boils down to this: birds, which always launch bipedally, generate over 80-90% of their launch force from the initial push of the hindlimbs.  That is, the initial leap or run gives them most of the power for take-off.  This means that the bones of the hindlimb have to be very strong in large birds.  We call this “positive allometry”: as birds get bigger, their hindlimbs get disproportionately stronger.  By contrast, the forelimb skeletons of big birds are rather gracile and slim.

zhejiangopterus-skeleton-wittonIf pterosaurs actually launched like birds, with the hindlimbs producing most of the force, then the ratio of their bone strength values should be about the same as birds, and big pterosaurs should have slender wing bone elements (especially the proximal elements, like the humerus) and big, robust hindlimb bones.  Well, it turns out that the opposite is actually the case: pterosaurs have whopping huge forelimb bones and very slender hindlimb bones, and this gets more exaggerated in big pterosaurs (image of Zhejiangopterus courtesy of Mark Witton).

My conclusion is that pterosaurs didn’t launch like birds at all.  Instead, it is more likely that they pushed off the ground with all four limbs – what we call a quadrupedal launch.  In this model, the forelimbs provide most of the initial power (requiring beefy arms).  Interestingly enough, it also solves the size problem – a quadrupedal launch allows even the true giants to take off from the ground, while a bipedal launch is actually quite impossible for a 250 kg Quetzalcoatlus (unless it doesn’t mind breaking a leg).  These structural data do not absolutely clinch a quad launch model, of course (we need launch track-ways for that), but it does provide rather compelling evidence for a serious reworking of our models of pterosaur take-off, and our estimates of their maximum size range.

Edit: This work has also broken on the news, so you may have seen this mentioned elsewhere already, including here.

18 Responses to “Into the air!”

  1. 1 Zach Miller 08/01/2009 at 9:33 am

    One of my blog commentors, upon seeing my frustrating in trying to imagine such a takeoff, pointed me in the direction of the vampire bat, which launches quadrapedally and does it very well, so I’m sold. I think an animation or series of pictures would help “solidify” this concept in people’s minds, though. My brain was frazzling trying to envision an azhdarchid pterosaur vaulting with all four limbs until I saw the bat diagram.

  2. 2 Mike Habib 08/01/2009 at 11:32 am

    Zach, you make an excellent point about the need for an animation. It is such a good idea, in fact, that I have a biological illustration MA student doing exactly that! I’m advising her thesis project, and we have just finished obtaining very high resolution surface scans of Anhanguera (thanks to a loan from the AMNH in New York, and scans by Digital Dimensions in Baltimore, Maryland). We are now at the stage of articulating the digital model and prepping it for attachment to the physical parameters from my Matlab programs. In the end, it will be an exact, 3D launch animation of one of the best-known pterosaurs. When certain embargos lift down the road, perhaps we can do the same for Quetzalcoatlus.

  3. 3 Taissa 09/01/2009 at 12:42 am

    Congratulations to Mike, that’s very interesting!! And Dave, using a photo from the meeting suited perfectly well, by the way. Hopefully you won’t publish the one you’re making me a scary face? =D

  4. 4 Zach Miller 09/01/2009 at 3:18 am

    AWESOME. Please let me (or at least David) know when the animation is complete!

  5. 5 David Hone 09/01/2009 at 1:17 pm

    Taissa, you are safe – I didn’t use the ones taken by Helmut of you working on Ludodactylus. I do have them on file however…

  6. 6 Nathan Myers 14/01/2009 at 4:28 pm

    By day she wanders her domain, nodding occasionally to sample its faunal abundance. By moonlight she takes to the air, marauding far and wide, plunging to snatch the offspring of dangerous borderland mega-predators while they sleep. Who can stop her? Who can stir from slumber in time to mark her ascent? Truly she is terror from the skies, a Maastrichtian ninja.

    • 7 Graham King 14/01/2010 at 8:27 pm

      Whoop! You should develop that as a children’s book, Nathan; get accurate pterosaur restorations to the young! & profit wildly!

  7. 8 Edina Prondvai 14/04/2009 at 9:34 pm

    I got excited about this animation, too! Please, inform me as soon as it gets finished! Cheers!

  8. 9 Amin Khaleghparast 06/05/2013 at 7:32 pm

    for Dr. Mike Habib

    What is your opinion?
    please send your advice to my Email:

    Best regards, Amin Khaleghparast (a lonely creative biologist from Tehran, IRAN)

    • 10 David Hone 09/05/2013 at 2:28 pm

      Mike tells me he’s mailed you about this. I’ve had a quick look and my only substantive comment would be to extend the main wing down to the ankle, that’s really where is should be in these guys. Other than that, nice stuff!

  9. 11 Amin Khaleghparast 15/05/2013 at 5:53 pm

    Dr. David Hone
    Do Dimorphodon have a triangle tail membrane or rhombic? How and why?

    please send your advice to my Email:

    I never receive any answer by Dr. Mike Habib….he and Dr. Mark Witton are my popular scientists…I know both them are very busy in their work but I hope you ask them send me their valuable opinion about my my Dimorphodon…then I can correct my art!

    about your answer….I do not draw any wing membrane yet???

  10. 13 Amin Khaleghparast 16/05/2013 at 10:45 pm

    Thank you for your answers….I start to correct my Dimorphodon Skeleton again…after I perform it, I will send you!

    Best regards, Amin

    About Amin Khaleghparast:
    I am a Young Muslim Iranian Male Biologist (Born 22 Oct 1985). I have a Bachelor of science (B.Sc.) degree in “General biology” field and a Master of Science (M.Sc.) degree in “Biology-Genetics” field in same Iranian University (Islamic Azad University_ Tehran Science and research Branch).

    my Email:

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