Observant readers might have noticed the several recent references to 'big news in a big journal' coming soon, or on 'how a Tet Zoo article evolved into a peer-reviewed technical publication'. Yes, not all of Tet Zoo is idle nonsense written for fun; at least some of it results in actual peer-reviewed result: you know, the stuff that's made me the fulfilled, famous, financially successful person I am today. And long-time readers might recall the threat, from way way back in April 2006, that 'Why azhdarchids were giant storks' represented '... the better part of a paper on the subject [of azhdarchid palaeobiology]. At some stage I'll re-vamp it for publication... perhaps with Mark [Witton] as co-author'. Well my friends, that day has arrived...
As most people in the world will know by now, my plan to co-author a full technical study on the subject of azhdarchid palaeobiology has finally come to fruition, and the figurative fruit of our loins is let loose on the world today. Even better news is the fact that this research is published in PLoS ONE and hence is 100% open access: go here for the paper (Witton & Naish 2008). I will not bore you with all the details, you can read them for yourself in the paper. Anyway, my version of the azhdarchid story has been told before. Here, I want to make a few random points.
Firstly, Mark and I have - believe it or don't - set up a new blog entitled Azhdarchid Paleobiology (American spelling because PLoS ONE is an American journal). It's basically a very dumbed-down summary of what we say in the paper, but it includes some nice sexy pictures that anyone can download and use for free. For yet more quasi-supplementary info, Mark's thoughts on the project will be up on his world-famous flickr site here.
Let's begin with some of the basics of azhdarchid morphology, in case you've forgotten. While azhdarchids were very large (the wingspans of the biggest species exceeded 10 m: picture right down below is Mark's restoration of Hatzegopteryx to scale with a person), they actually had proportionally short wings: the wing finger was abbreviated, with notably short distal-most phalanges. Given that data currently indicates that pterosaurs had broad wing membranes that incorporated much of the hindlimbs (go here on Tet Zoo ver 1 for the details), we reconstructed azhdarchids with proportionally short, broad wings, the aspect ratios of which compare well with those of birds and bats that engage in static soaring (Witton & Naish 2008). Azhdarchid hindlimbs were proportionally long. Note that we find azhdarchids to be relatively heavy, at least compared to most other published estimates. As I mentioned here, the entrenched view that pterosaurs were 'ultralight airbeings' (with even giraffe-sized forms with 10 m wingspans being estimated at 60-90 kg) is extremely suspect, and a mass of 250 kg for a Quetzalcoatlus-sized animal seems more reasonable. I can't provide all the support for that last assertion as it forms the basis of a paper (by Mark) currently in press.
The azhdarchid rostrum is very long, straight and sub-triangular in cross-section, with a pointed tip. It most recalls that of extant storks like the adjutants and marabous (Leptoptilos). Hooked bill tips - like those present in some dip-feeding birds (birds that pick prey up from the water while still on the wing) - are absent, as are the pits that would indicate the presence of pressure-sensitive organs like those seen in sediment-probing birds. The sub-triangular cross-section of the rostrum is unlike the laterally compressed bill shapes of stabbing birds like herons [shown here: Ardea cinerea]. In contrast to the rostrum, the cranium is short. The occiput is located right underneath the cranium, and the jaw musculature is inferred to have been weak. Easily the most unusual detail of azhdarchid morphology, however, is the neck: most of its length is composed of elongate, cylindrical vertebrae, and we infer from interlocking processes, the shapes of the zygapophyses, and other details that cervical motion was pretty restricted, especially ventrally.
Fine-tuning the model: 'terrestrial stalkers'
By comparing these features with the different hypotheses of azhdarchid lifestyle, I concluded (back in April 2006) that azhdarchids probably behaved like storks: more specifically, like the most generalised of storks, those that 'patrol marshy areas and flooded meadows as well as dry grasslands'. Mark essentially agreed with this view, suggesting also that azhdarchids might have been waders, foraging in shallow water as well as in terrestrial environments (Witton 2007).
Our new look at the data has led us to fine-tune all of this. Read the paper if you want all the details, but a detailed review - the first ever - of the taphonomic and morphological evidence explains how the data supports a strongly terrestrial lifestyle for azhdarchid species. The azhdarchid fossil record has a strong and conspicuous 'terrestrial signal': in fact, in many parts of the world, azhdarchids can - at least as far as we can tell from the fossil record - be considered a typical component of Late Cretaceous terrestrial ecosystems. Footprints inferred (on a very strong basis) to have been produced by azhdarchids show small, compact, well-padded feet. Not what you'd expect for wading, swimming or climbing, but suited for strong terrestriality.
And those anatomical details I reviewed above (the relatively short wings, the long hindlimbs, the long, stork-like rostrum, etc.) all point to a terrestrial lifestyle where terrestrial foraging in terrestrial environments was important. Quite why azhdarchids had the bizarre stiff neck that they did remains mysterious, but while its restricted range of motion is clearly at odds with several of the lifestyles that have been proposed for azhdarchids (like scavenging, dip-feeding and sediment-probing), we argue that it would have worked well for animals that were continually reaching down to pick things up from the ground. Indeed minimal degrees of fore- and hindlimb flexion are required for azhdarchids to do this (as shown in adjacent figure, from Witton & Naish 2008).
So a convincing body of evidence indicates that azhdarchids were 'terrestrial stalkers': proficient walkers that picked up prey from the ground. We were not able to find any evidence showing that azhdarchids were specialised for aerial feeding (that they grabbed prey while on the wing), as several other pterosaurs workers have proposed, and there are good reasons for thinking that sediment-probing was not an available option for these animals.
If azhdarchids were terrestrial stalkers, are they the 'mega-storks' I've argued previously? The problem here is that not all storks do the same thing, and most stork species are tied to aquatic habitats. A second extant group might serve as even better analogues, and these are the ground hornbills, or bucorvids (adjacent Bucorvus photo from Honolulu Zoo. More centipede eating!). With robust hindlimbs, well-padded feet specialised for terrestrial striding, and elongate jaws that are used to pick up terrestrial prey, they are also terrestrial stalkers, and good analogues for azhdarchids as we imagine them. Someone should study the inferred visual fields of azhdarchids to see if they might have been able to do any of the neat stuff that ground hornbills can do (namely, see their own bill tips, and use their immense eyelashes to shield their eyes in bright sunlight). Mark has already wondered out loud whether he should have given his azhdarchids big eyelashes. Hmm, haven't ground hornbills have been used on Tet Zoo before? Err, moving on...
Die you skim-feeding bastard, die!
Annoyingly popular among pterosaur workers has been the idea that azhdarchids were skim-feeders*: that they flew above the water surface, trawling their lower jaws through the water and snatching prey up when it was detected (presumably via touch). Some people have questioned our assertion that pterosaur workers ever really favoured skim-feeding as an azhdarchid mode of life. In fact, a check of the literature finds specific statements about the possibility of skim-feeding in azhdarchids made by Nessov (1984), Kellner & Langston (1996), Martill (1997) and Prieto (1998). Kellner & Campos (2002) published a whole paper in which they proposed that tupuxuarids, which are close kin of azhdarchids, were Rynchops-like skim-feeders [adjacent image shows Witton diagram of Rynchops skull, with rhamphothecae].
* Skim-feeding is sometimes referred to as skimming. I prefer the former term. Skimming is what you do to flat stones.
The notion that azhdarchids might have been skim-feeders has always struck me as bizarre and as an immediate non-starter: skimmers (Rynchops), the only animals that routinely skim-feed, are very odd, exhibiting a long list of unique, striking adaptations that aren't seen in other birds, and none of their bizarre specialisations are present in azhdarchids (or indeed in tupuxuarids, or in any pterosaurs for that matter). At the risk of sounding harsh, I have to wonder if the palaeontologists who have claimed skim-feeding for azhdarchids have in fact ever really looked at either Rynchops, or at Zusi's (1962) comprehensive and much-cited monograph on the anatomy and behaviour of Rynchops. For more on this see both Witton & Naish (2008) and Humphries et al. (2007), and Mark's article here.
Alas, as shown by statements made at the Munich pterosaur meeting, and by the description of the awesome new Triassic pterosaur Raeticodactylus (Stecher 2008), the myth of the skim-feeding pterosaur just won't die. Please pterosaur workers, please, look at the skull of Rynchops and/or read Zusi (1962) before you talk about skim-feeding in pterosaurs again.
To the future!
One of the main reasons why some palaeontologists prove so straw-graspingly clueless when it comes to imagining lifestyles is that they're unaware of which morphological features are associated with which lifestyles in extant animals. But that's not really their fault, as (comparatively speaking) bugger all published research exists on form and function in living animals. Indeed Mark and I discovered this when researching the functional anatomy and lifestyles of seabirds. Things are changing, but slowly, and I'm reminded of a comment made (by Colin McHenry) at the CEE Functional Anatomy meeting: palaeontologists have all the questions, neontologists have all the data.
I want to end by noting that this view of terrestrial, ground-hunting azhdarchids is by no means unique to Witton and Naish. Indeed several other workers have promoted this view before we came along, and at least some of our colleagues are in strong agreement with us. What I find particularly exciting is that several other studies on Cretaceous pterosaurs, due to be published within the next few months, also conclude that at least some pterodactyloid pterosaurs were strongly terrestrial animals, adapted for life in terrestrial environments. Given that many of us, myself included (Naish & Martill 2003), have long been saying how pterosaurs were all analogues of sea- and/or waterbirds, this is neat stuff.
Refs - -
Humphries, S., Bonser, R. H. C., Witton, M. P. & Martill, D. M. 2007. Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biology 5, No. 8, e204 doi:10.1371/journal.pbio.0050204
Kellner, A. W. A. & Campos, D. de A. 2002. The function of the cranial crest and jaws of a unique pterosaur from the Early Cretaceous of Brazil. Science 297, 389-392.
- . & Langston. W. 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park. Journal of Vertebrate Paleontology 16, 222-231.
Martill, D. M. 1997. From hypothesis to fact in a flight of fancy: the responsibility of the popular scientific media. Geology Today 13, 71-73.
Naish, D. & Martill, D. M. 2003. Pterosaurs - a successful invasion of prehistoric skies. Biologist 50 (5), 213-216.
Nessov, L. A. 1984. Pterosaurs and birds of the Late Cretaceous of Central Asia. Palaontologische Zeitschrift 1, 47-57.
Prieto, I. R. 1998. Functional morphology and feeding habits of Quetzalcoatlus (Pterosauria). Coloquios de Paleontología 49, 129-144.
Stecher, R. 2008. A new Triassic pterosaur from Switzerland (Central Austroalpine, Grisons), Raeticodactylus filisurensis gen. et sp. nov. Swiss Journal of Geology DOI: 10.1007/s00015-008-1252-6
Witton, M. P. 2007. Titans of the skies: azhdarchid pterosaurs. Geology Today 23 (1), 33-38.
- . & Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271
Zusi, R. L. 1962. Structural adaptations of the head and neck in the black skimmer. Publications of the Nuttall Ornithological Club 3, 1-101.
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Really neat stuff. Congrats on the published paper!
Now, this would be so awesome if you could do a trackback... ;-)
What's with "Azhdarchid Paleobiology" when it could be 'Kool Azhdarchid Paleobiology On the Web!' or KA-POW!
Seriously, congrats, Darren and Mark.
Wondering: Do you think full-grown Azhdarchids could fly? If the 250 kg weight estimate is correct, I doubt that they could have got off the ground (for long). Forgive my skepticism, but the reconstructions seem to indicate a relatively defenseless scrabbler, despite the huge beak (the stiff neck would have made them vulnerable from behind). Size is important (in defense), but these guys started as babies. Might they have gone through a youth in which they could fly, but have given it up when they got too big?
(as always, good answers raise more questions.)
p.s. your study made the front page of yahoo!
You made Yahoo's front page.
"Flying reptiles ate dinosaurs
Huge "winged lizards" once dined on
T-Rex babies, a new study finds."
The evidence would be long gone, of course, but I have to wonder whether some analog to the Hawaiian Islands or Cuba was home to relatively small, flightless azhdarchids that terrorized the local rodent-analogs and large insects.
Also . . . do you think it's possible that something like an azhdarchid might have been occupying a similar niche back in the Hauterivian or thereabouts?
Awesome stuff. I always wondered about mesozoic waders, but woul dnever have guessed that azhdarchids would be among them like this.
I wonder, though, about the mechanics: This guy looks really top-heavy. Is there anything in the back vertebra (like large neural spines) suggesting the capability to support this huge head in this position? (I skimmed over the paper but could not find anything there as well)?
Well, I came about this in a roundabout way. Greg Laden turned me on to the paper, after which I emailed Darren, congratulating him, then I see that he's posted about the paper AND a whole new accompanying blog! You've been busy, sir! :-) Congrats again. Wonderful paper. I'm too tired right now, but I'll be linking to everything tomorrow morning.
OT: How come 'Quetzalcoatlus sp.' doesn't have a real name yet? Is someone working on it?
And, of course, congrats to Mark Witton. His illustrations, as always, serve as a reference point and point of inspiration for yours truly.
Well first of well done to you and mark. The first I heard of this theory/paper was back when I was still an undergraduate! Some interesting stuff, and more impressive is as mark mentions on his flickr site: You convinced dave. Talking of flickr I can't fathom how you could possibly have posted about pterosaur skim feeding with out put up the most scientifically accurate Pterosaur Xmas card known to man (maybe) - I talk of course of my 2007 card ( here) lol
Congratulations for a paper!
Some random babble:
1. What of your research is attributable to specific azhdarchid genus, and what to some generalized azhdarchid which may have not existed? Related species of storks have different lifestyles.
2. Quetzalcoatlus sp. at least is usually reconstructed with short legs and improbably long neck. This guy at least seems a swimmer like pelicans. Analog of pelicans being the closest relative of Shoebill in Sibley-Monroe taxonomy? Did you check functional anatomy of pelican neck?
3. Many wading birds do have short feet (e.g. flamingos, stilts and godwits). Presence of web feet on azhdarchid track seems also indicate wading lifestyle.
4. Did these guys have leg and arm musculature to sustain prolonged walking?
5. What about positive proof from storks and hornbills, particularily their neck anatomy? They seem not to have inflexible necks.
6. Could azhdarchids have neck with specific bending points?
7. If you cling to it, let your illustrator draw a mass emergence of baby titanosaurs from a nest, and flock of azhdarchids gathering to pick babies. Per analogy of white storks over locusts and marabous over wildfire.
Excellent paper! Congratulations to you and your colleague!
A polo shirt with a small embroidered azhdarchid at top left would be awesome...[/frivolous nonsense]
Many thanks to all for comments. Very brief responses...
-- Even weighing 250 kg, azhdarchids were capable flyers as demonstrated by estimated wing musculature and planform. There is no reason to assume flightlessness.
-- Azhdarchids in the Hauterivian? We're not yet sure when azhdarchids originated, but the ages of their closest relatives suggest an origin some time round the Barremian-Aptian. That might change though.
-- Could they support the big head? Yes, obviously :) They evolved a solution that didn't rely on tall neural spines: we propose that the interlocking cylindrical cervical verts and nuchal ligaments provided the required support.
-- Quetzalcoatlus sp.: no-one really knows what is happening with Quetzalcoatlus, it is in limbo. Some people say Quetzalcoatlus sp. is a distinct taxon, others that it's just small individuals of Q. northropi.
Responses to Jerzy (thanks for critique)...
1. So far as we know at the moment, all azhdarchids are enough alike in proportions and morphology for one proposed lifestyle to fit them all. No evidence yet for divergent lifestyles as seen in, e.g., extant ciconiids. See the paper.
2. If Quetzalcoatlus is reconstructed with short legs, those reconstructions are wrong. Long legs. Nothing like a pelican, and nothing like a swimmer at all. Pelicans have elongate, flexible neck (I can send you photos) and differ from azhdarchids in most other anatomical details. Shoebills have very elongate spreading toes suited for their marshy habitat (contrast this with compact, narrow azhdarchid feet) and broad, dorsoventrally flattened (platyrostral) bill with rostral hook. Very unlike azhdarchids. See the paper.
3. The wading birds you mentioned have a high degree of digital divergence (toes II and IV spread far to the side relative to III) - up to 90 degrees. Nothing like azhdarchids, where all the toes are subparallel, forming narrow foot. The azhdarchid foot is, sorry, absolutely NOT suited for wading. See the paper.
4. Little is known about musculature, hard to make speculations on something like endurance. Slim, elongate, narrow hindlimbs do look suited for committed walking, and unpublished data on forelimb strength (spoken about by Mike Habib at Munich pterosaur conference) shows that azhdarchids could run and even launch quadrupedally. Pterodactyloids in general - and dsungaripteroids and azhdarchoids specificially - were highly capable terrestrial animals.
5. The stiff azhdarchid neck doesn't quite have any analogue, but as explained in the paper it would work well for a terrestrial stalker. Bucorvids exhibit some cervical fusion, indicating that a restricted range of cervical motion relative to arboreal relatives is ok for terrestrial stalkers.
6. See the paper.
7. Yes, cool idea.
Damn! Those are some scary motherfuckers!
Plus, the head wasn't as heavy as it looks. Skull fragments of Hatzegopteryx look like styrofoam. And of course azhdarchids were toothless -- mammalian molars at least are insanely heavy...
Thank you - fascinating and entertaining.
I'm still having trouble imagining those things getting airborne from a late cretaceous savannah - 250kg is a lot of weight to have to lift. What has changed though, having read your paper (and thanks for issuing it through PLoS ONE so it's free) is that now I want to believe it!
You even managed to include ground hornbills - to my mind one of the most fascinating groups of birds extant. People make a big deal about the big mammals on the African plains and forget the role of birds - the large storks, raptors and ground hornbills are very significant components. In my opinion watching the behaviour of ground hornbills was way more interesting than watching the lions and antelopes etc. The idea that storks and ground hornbills scaled up (a lot) could be a model for azhdarchids is intriguing and wonderful.
Once again thanks.
Congratulations on the paper, and to Mark Witton on his fabulous artwork.
The guys at Objective Ministries would surely like to get their hands on one of these! Can you oblige, perhaps with help of Drs Victor Frankenstein Michael Crichton?
Very intersting work here.
Out of interest, how do you pronounce the word "azhdarchid"?
Had to post this up here - check out THE SUN's (the most tabloid of tabloids for those outside the UK) take on the story - and how they have modified marsk comparison drawing some what...
Congrats on a very cool paper. You made the front page of Sciencedaily. My vote for illustration is an enraged large theropod snapping futilely at an azhdarchid taking off with a nestling.
Pterrific! Cryptic Pterosaurian Bigfoot found!
Any niche parallels to South American screamers? Aren't screamers carnivorous wetland but terrestrial birds?
Given the featherweight construction of that humongous beak and its enormous volume compared to that skinny neck, I have to wonder whether it was used for display. Perhaps the biggest beaks (probably flashing the most color in season) were used to show dominance, drive off lesser individuals, attract mates, etc. Maybe the biggest azhdarchids were pushing the limit of how ornamental the beak could be and still be functional.
Also, if they had mating dances like albatrosses or cranes, wow. If somebody tries to revive the TV-safari-into-the-past genre, that would be something to see!
I read this and Mark's Flickr site, and I have to say this is a stunning bit of new thinking (even if, as the authors humbly note, it's not 100% new). Kudos to Darren and Mark for making a good case for an idea that seems, intuitively, quite strange.
Musing of an admitted amateur:
The main question that gives me pause is whether the largest of these creatures were capable of a quick takeoff while stalking on flat ground - a necessity for survival in an environment with big, fast, bipedal predators. They look awfully vulnerable if actually caught on the ground, especially given the largely unsupported membranes of pterosaur wings - one good tear, and theyre ground-bound. (I know the wing "fabric" was reinforced with actinofibrillae, but a tear does not have to go all the way across the wing to cause a serious loss of lift. A tear on the trailing edge would have been particularly bad. And that quadruped posture puts the critical wing membranes right down near the ground, as oppoosed to the wings of storks.)
Taking off from flat ground would have required intensive flapping, and I've always read the largest pterosaurs didn't show the musculature necessary for that. The debate has gone back and forth on this, but my intution is that the raised weight estimate would lend support to those who think the pterosaurs were relatively weak flyers, spending much of their time gliding and needing at least a downhill slope to take off.
Im a bit puzzled that evolution did not select for bigger feet, which would allow for the fact that ground isn't simply flat - it has soft spots and holes and so on, and it would be advantageous to be able to walk in mud or marshy spots as well as firm ground. Still, if you look at the weight difference between these critters and, say, an apatosaur, the relative foot size isn't unreasonable.
It's also hard to think of a stiff neck as being an advantage for this animal. You'd think evolution would have pushed toward a flexible neck, allowing for feeding at all levels (prey in trees, on uneven ground, etc.) without requiring the predator to maneuver the whole neck and often the body. We do know some marine reptiles had relatively inflexible necks, and I can't think of a good reason for that, either. Unless maybe it was simply the cost of maintaining more neck muscles when they were not critical to survival?
Again, great work guys. I'll be curious to see how the scientific debate (which is likely to be heated) develops over this idea.
I am not a professional either, but--Could the stiff neck be an adaptation for absorbing some of the mighty whacking force of the beak being put to use?
And perhaps they normally didn't fly far, just springing up and flapping out of the way of attackers, where it wouldn't matter that they were headed back down in a few seconds. If they were able to land with that big beak pointed at the attacker's vulnerable bits, perhaps it would think twice about pressing on. To start longer journeys with some advance notice, it would walk up the nearest rise to catch the wind.
Also, how fast might they have been able to go on all fours? I'm having trouble picturing the gait imposed by those weird forelimbs.
First off - great job Mark and Darren! I am immensely pleased to see you guys pulling the type of attention you deserve for this. And, of course, the illustrations are wonderful - I have commented (with great honesty) in several cases that Mark's pterosaur illustrations are among my very favorites. Truly as good as you can find anywhere.
In any case, for those that were asking about launch (especially Matt):
"The main question that gives me pause is whether the largest of these creatures were capable of a quick takeoff while stalking on flat ground - a necessity for survival in an environment with big, fast, bipedal predators."
Using a quad launch, a large azhdarchid would have no trouble taking off in a hurry. I've done a model, using a vault-ballistic launch system (quite simple), of the 250 kg Q. northropi with the planform given in the paper - with that build, and a very reasonable flight muscle mass fraction, the animal launches from a standstill, in no wind, from the ground, in 0.60 seconds. Note that this requires no running, it is a leaping launch. The key is using all four limbs - that engages the flight muscles in the initial leap, which makes it very powerful (much more so than the bipedal driven launch in birds).
"...but a tear does not have to go all the way across the wing to cause a serious loss of lift. A tear on the trailing edge would have been particularly bad. And that quadruped posture puts the critical wing membranes right down near the ground, as oppoosed to the wings of storks.)"
The wing membrane could take more abuse and still function than you might think. A minor tear at the trailing edge would not ground the animals. Also, the wing tips are reinforced in a manner that specifically makes them surface-impact tolerant. More so than in other pterosaurs (as evidenced from my own work and that of Jim Cunningham).
"Taking off from flat ground would have required intensive flapping, and I've always read the largest pterosaurs didn't show the musculature necessary for that. The debate has gone back and forth on this, but my intution is that the raised weight estimate would lend support to those who think the pterosaurs were relatively weak flyers, spending much of their time gliding and needing at least a downhill slope to take off."
Yes, that view is well represented in the literature, but it is riddled with errors. One problem is the persistent misconception that raw weight is the critical factor for a flying animal. In reality, it is the power to weight ratio that matters. Obviously, low weight helps this ratio, but only if power is not reduced. The super light versions of pterosaurs are actually *less* flight worthy - they are so thin and low muscled as to be practically incapable of flight. Heavier estimates actually improve flapping capacity, because the flight muscle fraction increases. This is also much more consistent with the osteology, which clearly indicates high muscle masses and large loads on the bones. Large pterosaurs would have flown unpowered for long stretches, to be sure, but they could flap powerfully when need be, and launch quickly. In fact, azhdarchids have *increased* flapping and launching capacity relative to other pterosaurs - that's why they could get so darn big. It also means they were the best at getting off the ground - which jives quite nicely, I think, with Mark and Darren's work.
Also, the launch sequence does not require frantic flapping. This is also a common model, but is also shackled by a misconception - namely, there is a persistent tendency to think that flying animals force themselves into the air with their wings. In reality, the initial impulse comes from the walking limbs (hindlimbs in birds, both forelimbs and hindlimbs in pterosaurs and semi-terrestrial bats). 90% of a bird's initial launch force comes from the legs. Flying vertebrates generally first leap, then engage the wings (albeit in rapid succession). Burst launching birds will engage the wings a bit earlier, towards the end of the leap, but the hindlimbs still provide most of the force. There is no reason to expect that pterosaurs used a running launch, or that they need slopes or special wind conditions.
Wow. Mike, I cannot tell you how happy I am to read this - all you have to do now is get it into print :)
[in press for Zitteliana right?]
Thanks to everyone for commments.
Thanks very much. You are of course, correct about 90% of a bird's launch force being provided by the legs: I was thinking the air resistance and weight of this large animal as it rose vertically would be proportionately more challenging and would require flapping from the start. That's an intuitive reaction, not a calculation, so I have no problem with being wrong.
My thought concerning a tear on the trailing edge was that it would have been especially vulnerable to further tearing as the wing stretched tight and was then subjected to the lift/downforce as the wing flapped. I'd also expect a trailing edge tear to "spill" more air from the area under the wing than a similar tear hemmed in on all sides. I do agree there must be some margin for damage, or the species would have been unlikely to prosper regardless of its lifestyle. (I know much more about aircraft than about biological wings, and I have a prejudice: I never liked the pterosaur wing design, successful though it obviously was. The force operating at right angles to the section of the leading-edge "finger" halfway between the hand and the wingtip of a huge, flapping Quetzalcoatlus wing must have required a great piece of evolutionary engineering to deal with. I'm presuming the knuckle joints were very strong as well as flexible, but even so....)
"Heavier estimates actually improve flapping capacity, because the flight muscle fraction increases. This is also much more consistent with the osteology, which clearly indicates high muscle masses and large loads on the bones."
Agreed, though there's a point of diminishing returns, as (IIRC) the muscle mass increases by the cube of the cross-section while the strength only increases as the square. You are saying the optimum point on the curve for this beast is higher than most reconstructors have calculated, and that the physical evidence for the amount of muscle has been seriously misread. I don't doubt your work, but I would expect to see a lot of objections from the guys who did those earlier reconstructions. I'm curious whether the peer review process was contentious.
OK, that's all this particular amateur is going to throw out there. Thanks again to you and to Darren and Mark for giving us a really thought-provoking revision to paleontology. (I never put much stock in cryptozoological "thunderbird" reports or claims of surviving pterosaurs, but imagine just for a moment people actually meeting this monster on the ground or seeing it swoop low overheard. The term "cardiac arrest" comes to mind. I hope the guys making Jurassic Park 4 see this material.)
I used to groan at the depiction of the big pterosaur in JP2 or JP3 that stomped along the catwalk, but now it looks as though Spielberg's folks were closer than it appeared at the time to the actual beastie.
Now I have to wonder how much they might have been able to carry while in flight, either in their paws or on their backs.
Congrats to your and Mark on the paper, it looks fantastic and it is great to finally see this work out. Now, we just need to get Jim and Mike's work published so that we can start finding a synthesis to the debate on azhdarchid feeding habits. However, I have some comments on the paper's thesis:
Aren't these large azhdarchids you've modelled as ground stalkers rather overdesigned for that habitus? They don't actually require to be that large for this behavior, which seems to be a selection towards another direction, which I am on the fence about (sea-skimming).
Similarly, the length of the neck, without effective ventriflexion, seems overdesigned for a group that are plucking anything from the ground. This is at odds with such a maneuver, in fact. You and Mark brought a parallel to hornbills, which have very flexible necks, and do not require such long and slender limb structure to motivate. Why not under-size the body and limbs, and make the neck more flexible? This would seem to be more conducive to such a model, yet instead the limbs are not THAT terrestrial in design, and the neck and head are heavily built for a stiffened function, whichever that was.
Perhaps lastly, this doesn't not in anyway explain some of the cranial features, which don't relate to a probing OR a plucking strategy, and certainly do not need a well-developed ventral butress of the mandible paired with a dorsal butress (or crest) on the cranium. This verticalizes the forces acting on the skull, rather than translating them to the tipis in such pluckers/probers.
Finally, "skimming" can be applied to any of the animals with skim the surface of waters with their jaws, including some gulls, terns, and frigate birds. BTW, in America at least, we call stone skipping "stone skipping", rather than "skimming".
Awesome post... I look at the storks and cranes here in Florida totally differently now. This is why i check the blog every day. This has become my favorite place online for hard science news.
Nice job! Congratulations!
Darren - you are correct, the launch paper is in press with Zitteliana. Well, the first launch paper, at any rate. There will be more to come, and I hope to co-author some work with Jim Cunningham down the road.
Matt - your thoughts on issues of drag while launching are very reasonable; I'm sure you were quite familiar already with much of the information I shared, but I wanted to be thorough for the sake of the broad readership here at Tetrapod Zoology. Like you said, the intuitive reaction and the calculated result often differ. I have had that experience several times with my own expectations. On a more technical note, with regards to take off drag and required force: the quad launch dynamic actually improves the drag regime, because it delays the production of induced drag and parasite drag until late in the launch cycle when the wings are deployed. During the quad leap, only profile drag really matters.
"My thought concerning a tear on the trailing edge was that it would have been especially vulnerable to further tearing as the wing stretched tight and was then subjected to the lift/downforce as the wing flapped."
Good point. I have a couple of thoughts on how the wing was structurally reinforced against tear propagation, but more on that some other time.
"Agreed, though there's a point of diminishing returns, as (IIRC) the muscle mass increases by the cube of the cross-section while the strength only increases as the square."
Also an excellent observation. There are some mediating factors, however. One is that anaerobic power proportion tends to increase with size, so power drops off less rapidly than expected from simple scaling (see work by Marden). Of course, this has a negative impact on muscle endurance, but that is off-set by the ability of large flyers to reduce flapping frequency (either having slow stroke cycles, or having bursts of faster strokes separated by unpowered phases). I tend to refer to this as "gait mediation", though others may have a better name for it. In any case, gait mediation and muscle fiber composition both conspire to delay the point of diminishing returns.
Note, as well, that pterosaurs get a bit of an advantage by double-use of the primary launch system - the forelimbs provide most of the launch power and then also power flapping. That gives them much more leeway for expansion of pectoral/forelimb musculature, because it doesn't become unused payload during flight. By contrast, birds have the limitation that extra-powerful launching gear (ie. large hind limb muscles) become extra payload during crusing flight.
Jaime A. Headden: If you read the paper
Humphries, S., Bonser, R. H. C., Witton, M. P. & Martill, D. M. 2007. Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biology 5, No. 8, e204 doi:10.1371/journal.pbio.0050204
it will show how unlikely (or even impossible!) a pterosaurs skim feeding was. Marks near death experienced which involved a model and metal parts snapping under the stresses of skim feeding are further evidence against skim feeding!
Great stuff - and by far the most productive comments thread I've seen yet on SB, too:)
It seems pretty ironic that a paper about grounding pterosaurs should take-off in such a dramatic way. (Thanks folks: I'm here all week. Try the veal.)
Seriously, to all the people saying nice things about the paper and its authors, thanks very much. Darren and I put a lot of thought into the PR for this thing, but I don't think we thought we'd ever get the overwhelming public reaction that we did, so thanks for that. On a more personal note, thanks to all those saying my pictures are nice: it's especially great to have the more informed internet palaeocommunity say such things, and, frankly, I never get tired of being told that my images have changed the way people think about pterosaurs.
Anyway, that's enough sentiment for one morning: back to the cold, hard mistress that is my only slightly assembled PhD thesis.
Congratulations, folks. I first saw your paper mentioned in a short article in the UK freesheet Metro - although they did describe azhdarchids as birds. I didn't know whether to laugh or cry...
Clearly they're using a total group concept of Aves.
Very nice and apt.
Darren, and Mark, this looks great, and I'll need to read it through again more thoroughly later.
Congratulations on the recognition and PR.
Those are awesome creatures. They deserve their own book - and film. They do, they do!
(I'm guessing even a selection of sound effects true-to-their-life would awe).
Thanks for paying them such devoted attention.
Judging from footprints, pterosaurs generally were very good and fast walkers. I've been to Crayssac...
Also, ground hornbills eh? Since they came up when discussing the intelligent "dinosauroid", I can't help but wonder what an intelligent azhdarchid "pterosauroid" would look like...
Congratulations Darren and Marc! It is really great to see how much popular attention you did get. Today I saw your names and Marc´s reconstruction drawing (of the pterosaurs, not of himself)even in the online news of one of Germany´s biggest journals. You have a big advantage towards many other paleontologists who could also publish interesting news even for the mainstream data, because with Marc you have a very skilled illustrator, and good pictures are eyecatchers and sell much better than bald headlines alone.
I really hope there will be amazing new publications of you in the near time (BTW, how is the work on your tetzoo-book?).
I have also a random question: How big were the brains of this giant pterosaurs?
Sordes: you're too kind.
"How big were the brains of this giant pterosaurs?"
Not enormous, really. Take a look at Fig. 3 from our paper, and focus on the cranium: see how depressed the orbit is? There aren't any azhdarchid skulls preserved three-dimensionally, but if they follow the standard pterosaur convention then everything dorsal to that, more or less, is laterally compressed bone with no thinking capacity whatsoever. Hence, the brain is squeezed in between the dorsal margin of the orbits and above the housing for the temporalis musculature, and, relatively speaking, that's not a huge amount of room.
Now you need a little pterosaur plastic figurine to add to your collection - perhaps sell a bunch of them as part of the PR ;-)
Safari produces a toy azhdarchid: you can see it, with my other pterosaur toys, here, but it's not very good... (and is flying rather than walking).
Has anyone calculated what minimum wind speed would be required for one of these beasties to simply spread its wings and take off without flapping?
It's the pics, Mark. The Hatzegopteryx looking down, as if affronted, at the human and another plucking up a baby sauropod are just the sort of thing to communicate in a very immediate and intuitive way what you're proposing. You and Darren should be feeling very, very pleased with yourselves.
I notice that Nature describes it as "not much of a flier".
Not much of a flier? That thing can get airborne in 0.6 seconds! Imagine T. Mom turning her back for *two seconds* (just to get a coffee fer-gawds-sake), and this crazy azhdarchid plummets to the ground, BAM! ("alights"? forget it!), snatches up Junior, and leaps into the sky before she can even put her cup down.
These things were Maastrictian Ninjas. I'll bet they had a mean kick, too.
OK, "Maastrichtian" ninjas.
Darren and Mark would have us picture sedately strolling patricians, nodding to acknowledge the occasional cowering, comestible peasant. Perhaps, perhaps. But must appearances deceive? Could not both be true? By day, leisurely touring her uncontested domain, she idly samples its faunal abundance. By moonlight, the celestial marauder ranges far abroad, plunging to snatch mega-predators' offspring from their very nests before exploding once more skyward. Who can stop her? Who can stir from slumber in time to mark her ascent? Truly she is terror from the skies.
Thanks for this information Mark. I already thought that their brain were very small compared to their size...but you never know, so why not ask an expert.
Neil and others:
Regarding "skim feeding." I am not referring to the method employed by Rhynchops, but that rather done by soaring surface "skimmers" such as Fregata, which dip then snatch. This requires a different mechanism and was originally suggested for keel-snouted ornithocheirod pterosaurs such as Anhanguera.
As for the paper, yes, I do have it. While my comments there would be fairly limited as I am not a mathematically-minded person and couldnot model the relative forces that would be tested, I offer this critique.
It is not enough, I think, to argue skimming doesn't work, when there are 1) different ways to skim, and 2) you offer no alternative models to explain the features which have been forwarded as skimming adaptations (or rather, since the term "skimming" is a touchy one, "volant surface feeding" or somesuch techy terminology). While 2 is not required by the authors, it allows the authors to develop research and not make broad statements about what can or cannot feed in such a manner.
For example, pelicans skim feed, and their jaws are designed to operate (in a quick, snatching motion) under the very environments the authors were testing for, and the tests the authors performed would likely not have given the pelecanid jaw a clean bill of health because it is 1) not ventrally braced, 2) flat on the oral surface, and 3) possessed a very short symphysis relative to jaw length (a very short portion of the jaw, compared to Rhynchops actually depresses into the water's surface.
The authors show that some pterosaurs CAN reduce their drag through water, but do not explain that in the taxa which do not, this drag can be reduced in other ways. For example, anglation of the mandible can alter the drag coefficient on the jaw itself, it can actually allow the jaw to maintain position in the water as long as the impelling force was NOT reducing velocity, etc. The paper (and the thesis of this paper) was that this drag simply stops the skimming effect. I would contend that it does not, and that it isn't the only effect that inhibits a given jaw from being a "skimming" jaw.
The authors do not tell us what or why some pterosaurs appear to possess mechanical adaptations for resisting torsion of the jaw at the tips with ventral bracing. The jaws are ill-suited for cracking nuts, let me tell you, especially being so large as to render nuts almost irrelevant to diet. Pterandodontids, along with Zhejiangopterus with similar jaws, do not appear to possess features that adapt them to, well, much of anything else (though I do understand Quetz and such have different jaws, and this model does seem to work for them better). Finally, dorsal bracing of the capitate musculature on the posteroventral surface of the expanded occiput allows the neck to possess a massive amount of bracing. Such an expanded occipital region occurs in several other pterosaurs, most of them ornithocheiroid, that also seem to have "skim-feeding" adaptations. A "nuchal" crest forming from the back of the skull into an occipital crest to increase the length of these muscles, as perhaps expressed most strongly in pteranodontids which possess regions that seem to anchor very long dorsal cervical and temporalis musculature, argues we are looking at very strong jaw and skull bracing versus forces that can only be keyed to feeding in some manner.
Jaime: what frigatebirds and pelicans do cannot be - and shouldn't be - described as skim-feeding. Frigatebirds are 'dip-feeders', reaching posteroventrally to pluck prey from the water, pelicans are divers or lungers, and I am not aware of any observations where they do anything like dip-feeding or skim-feeding. Do you have specific references in mind? Other than in Rynchops, facultative skim-feeding has only been reported in a few narrow-billed terns.
Are there different ways to skim-feed? Please back this assertion with some citations or something.
On the drag stuff, I'm afraid you've lost me - are you talking about the Humphries et al. paper here? There is a lot more to being a skim-feeder than having reinforced jaw joints and wide occipital regions, and those two features in particular are perhaps the 'least important' as they're seen in other animals too (though note that pterosaur jaw joints still don't approach the super-reinforced condition we see in Rynchops).
I suspect you're playing devil's advocate.
"Who can stop her? Who can stir from slumber in time to mark her ascent? Truly she is terror from the skies."
You know what that reminds me of? A flying battleship.
Part of your pic is in this week "Economist".
Actually, even better pic might be Quetzalosaurus swallowing a person with elegant stork-like tossing into the air. BTW, could 250kg pterosaur pick 70kg food item this way?
Darren is leading the way in peer-reviewed blogging. :-)
Unsurprisingly, I have to agree with Darren and the 2007 investigations into skim-feeding. Firstly, as Darren says, skim-feeding is a specific foraging method quite exclusive to Rynchops: the other birds you mention feed in quite different ways. Our paper dealt specifically with Rynchops-style foraging, which is the bird pterosaur workers refer to when discussing skim-feeding in pterosaurs. Because pterosaurs and birds share an overall similar body plan (i.e. the basic flying tetrapod layout), I disagree that there is more than one way to skim-feed: open jaw (but not neccessarily the entire mouth - Rynchops has a highly kenetic skull that means it's jaw tips are open but it's mouth is closed when foraging) to submerge mandible in water, keep the body clear and fly along until you hit something. Ignoring foraging methods like diving, lunging, surface gleaning (because these aren't skim-feeding), how many other ways are there for a volant tetrapod to trawl the water surface with its jaws?
We didn't explain the purpose of the so-called 'skim-feeding adaptations' because there are no skim-feeding adaptations in pterosaurs: the whole point of the comparative anatomy section in our paper was that the idea was flawed from the start. Without going into detail, the features that were touted as supporting skim-feeding typically didn't (e.g. azhdarchid necks, the Thalassodromeus jaw) and, looking at the rest of the skeleton showed that other essential adaptations simply weren't there. There are some weird attributes to pterosaur anatomy, sure (like the aforementioned Thalassodromeus butter-knife mandibular symphysis), but nothing that supports a skim-feeding hypothesis. Now, we could've tried to explain these features (indeed, one reviewer asked us to), but the whole skim-feeding mess arose from authors doing similar things: find one or two anatomical features and base a whole ecology around it. This is not the way to investigate the lifestyle of an extinct organism: the whole picture - functional morphology, trace fossils, taphonomy - should be considered and every piece put in place. Hence, rather than just chucking another half-assed pterosaur lifestyle hypothesis out there, we thought we'd be sensible and leave it for another paper. Like Witton and Naish (2008). I hear that's quite good.
Reducing drag in the way you describe might work, but bear in mind that decreasing angulation also decreases foraging depth. Big skim-feeding pterosaurs would need a whole lot more food than Rynchops, so, if anything, they would need to increase trawling depth to get enough food to sustain themselves. Check out the way Rynchops skims: pretty much the entire mandible (about 12 cm, I think) is submerged to maximise foraging depth, and this allows it to eat fish and crustaceans of 2 - 3 cm length. A Thalassodromeus or giant azhdarchid wouldn't last very long on 2 - 3 cm fish, so they would need to dunk more of their symphysis in to grab food proportional to their body size. Plus, if our biomechanics are correct, you would need to reduce drag a huge amount to make skim-feeding viable for anything with more than a 2 m wingspan.
As for adaptations in the jaws for resisting torsion: this is not really exclusive to skim-feeding. Bracing that is more indicative of skim-feeding (shock-absorption at the articular, increased mandibular depth against bending forces, big sites for jaw muscle attachment to hold the jaws in place while skim-feeding [pterosaurs would have to do it with open mouths - no kenesis in their skulls]) are all noteably absent. Plus, while large pteorsaurs have sculpted occiputs, they maintain relatively slender necks that are far more important in skim-feeding than most people realise. When the head gets pulled underneath the body in a skim-feeding impact (and it will, what with the forward momentum of the body, the relatively stationary object and the force of the impact), most of the shock is dealt with in the neck. You need a flexible, strong neck to cope with being rammed backwards and then be pulled forwards: most pterosaur necks - if any, actually - are not up to that task. It's been said at least twice in print now: for azhdarchids at least, the neck rules out skim-feeding right away - no question. The pronounced nuchal line on things like Hatzegopteryx and Pteranodon is almost certainly a reflection of their size: their huge heads have to be anchored with something (I mean, they're light, but still over a metre long, so let's not kid ourselves that they weigh nothing at all) and the dorsal regions of the occiput will anchor soft-tissues resiting gravity. Add to this the fact that most pterodactyloid necks (including azhdarchids) appear to flex more dorsally than ventrally and may even have a dorsally arced neck when held neutrally, and it's hardly surprising that the sites for soft-tissue anchorage in the dorsal occiput are most pronounced. There's not great lateral bracing, though (something else we see in Rynchops, so I doubt their necks were particularly well braced.
Thanks for the heads-up: I didn't know we were in there. Apparently we're in the print edition, too. Nice.
Good news: they answered your question, too:
"At five or six metres high, Quetzalcoatlus could easily have eaten young dinosaurs. Or young humans, had they been around 65m years ago."
[see http://www.economist.com/science/displaystory.cfm?story_id=11449813 for the full story]
So there you have it: The Economist says pterosaurs could eat young (and presumably lightweight) people. I can't argue with a publication like that, so I'd best stop drawing my young self next to them, then. It's all right: it's my birthday in a month, so I'll be safe then.
Wonderful paper, congratulations!
Have I said I love your blog/s?
I saw an article on London' Metro "newspaper" about your paper, with the predictable headline: FLYING DINOS STALKED THEIR PREY ON THE GROUND. The same article goes on to refer to Azhdarchids as dinosaurs and/or birds, and claims they lived 230 million years ago. Oh well...
Also, the Azhdarchid-Bucorvid analogue is very interesting... maybe I can do a "Drahcosophont" simillar to Avisapiens. And they can copy it too...
Re: azhdarchid feeding habits, would their beaks be any good for cutting up prey? Or would they just swallow prey whole?
The later would imply a pretty low ceiling for how big baby dinosaurs/people/teletubbies they could eat.
How difficult it is to hide from something you can't find.
I don't know if you know, or were possibly responsible, but your research has already found its way onto wikipedia!
Mark and Darren are in Wikipedia under "pterosaur", but not "azhdarchid", yet, the more appropriate spot. Somebody here could correct that.
I see references to special adaptations to allow their mouths (azhdarchids', not Darren's and Mark's) to open extra-wide. That seems like a Clue. Are there any notions floating around to suggest why or how an azhdarchid might benefit from extreme gaping?
So is there any evidence that they hunted together or is the picture on top just an example of artist license?
Tuesdays metro couldn't seem to make its mind up if your Azhdarchids were " Giant flying dinosaurs " or "toothless birds [which] had wingspans in excess of 10m".
What's wrong with science journalism these days?
So, feeding ecology in pterosaurs is not my focus nearly so much as locomotion is, but here are a few thoughts:
- Azhdarchoid pterosaurs share a whole suite of traits that make them the best launchers, the best ground runners/walkers, and the most powerful flappers among pterosaurs. These traits are most extreme in azhdarchids, and explain the ability to obtain large size. They also suggest, to me, that the basal state for azhdarchoids was semi-terrestrial feeding.
- Some azhdarchoids could have secondarily derived a fish-feeding ecology, but I would suggest that we cite more than coastal location of fossils to support this. Peregrine falcons nest on sea cliffs, but I wouldn't call them a marine bird.
- Azhdarchids cannot reach the space directly in front of their body, nor can they reach laterally very much. That suggests to me that simple reach distance is so important as to have overwhelmed other factors. So, perhaps they fed on elevated items often (fruit, arboreal animals?). Alternatively, perhaps the preferred habitat was very heterogenous, and often included bodies of water - a reaching neck would allow for feeding from both the ground and out a ways into the water, without the need for compromising the walking-adapted foot morphology.
Darren/Mark: what are your thoughts on this? I still find it odd that azhdarchids cannot reach the space near their body (ie. constrained minimum reach), nor can they reach laterally. Broadly speaking, what do you see as the cost/benefit tradeoff in that regard? You discussed the neck a fair bit in the manuscript, or course, but I'd be interested in elaboration regarding your thoughts on the advantages of the lengthened cervical series.
That's funny that I see the ground hornbill article mentioned again, just after I've finished my own variation of Darren's "dinosauroid."
I like Andy's suggestion of a speculative "intelligent pterosaur" - but a question for Darren and Mark: with all that brainpower geared toward balance and flight mechanism, was there much room (or need) for any kind of real intelligence?
Nemo will likely beat me to this one.
I don't know if you know, or were possibly responsible, but your research has already found its way onto wikipedia!
I note in passing that Darren and Mark are now, courtesy of the Sun, officially recognised Boffins.
Richard: Battleship? Somehow I'm thinking of something more like a "Huey" helicopter troopship.
I don't seriously mean to suggest they hunted by moonlight, as romantic as that would be. "... for no sooner would a flock of half a dozen silk-winged leather-bodied Fuolornis Fire Dragons heave into sight across the evening horizon than half the people of Brequinda are scurrying off into the woods with the other half, there to spend a busy breathless night together and emerge with the first rays of dawn all smiling and happy and still claiming, rather endearingly, to be virgins, if rather flushed and sticky virgins." (*Pace* Douglas Adams)
The choice of whether to stalk and peck or to plummet, snatch and leap would naturally have to depend on whether anything else big and beefy (chickeny?) was already on the ground. The tenderest, most appealing morsels visible from above would tend to have defenders nearby, but not always near enough by.
Richard was referencing that most amazing of monster B-movies, The Giant Claw. Yes, it's as big as a battleship. Like a flying battleship. Some kind of.... flying battleship.
Darren: So, the visuals for Mike Habib's paper have already been released.
Hi Darren, I was wondering what is the source for the Q.sp vertebrae figured in the paper. Are they Witton originals, based on personal observation or is there a Quetz reference out there that I dont know about?
... and apologies to Richard Hing for my obtuseness, with thanks for provoking Darren to post his link to that most amazing visual aid (which, incidentally, demonstrates the value to azhdarchids of their capacity for extreme gaping, vis-a-vis parachutists).
Tuesdays metro couldn't seem to make its mind up if your Azhdarchids were " Giant flying dinosaurs " or "toothless birds [which] had wingspans in excess of 10m".
What's wrong with science journalism these days?
Editors who feel that "These things that you've never heard of which were sorta kinda related to dinosaurs and birds but not much but anyway they were awesome take my word for it" risks losing the reader before the lede.
Not that I'm justifying it.
Wow, excellent read. And I've just heard the Economist short mention of yours in their latest audio and written edition. Pity I couldn't see the pictures...
Holy cow, congratulations! I missed all the publicity your paper got due to being in a tent in the middle of no-where, but now it's time I stopped lurking around here and did a bit of incoherent fan babbling. I'm no scientist so my opinion is worth next to nothing, but I am totally won over by your argument and fabulous illustrations.
...Oh, and "Die you skim-feeding bastard, die!" should be a t shirt, preferably depicting an Azhdarchid violently dispatching of one.
Let's do it. Actually, I've spent the last two days assisting in the making of an internet movie (all will be revealed), and we came up with an alternative, even better phrase... We were inspired by Samuel Jackson and a movie that involves legless squamates and a flying machine.
After inserting the missing comma, that is. :-}
You know Dave, you are mentioned. Let's see if that bit makes the final cut...
(missing comma? What?)
Die, skim-feeding bastard, die!
By analogy, there's supposed to be one in "you know, Dave". I once was in a mailing list where someone kept writing "that is the problem David", when in fact he was the problem... :-)
Okay, I haven't read the actual paper yet, but could it be that such adaptations as the azhdarchids':
- large size and height
- long but rather inflexible neck, and
- very long beak
... taken all together, had the beneficial survival-enhancing effect of ensuring that even as the animal fed from the ground, its eyes were always fairly high off the ground, the better to spot any approaching predators from as far away as possible?
(Whereas a smaller, shorter, shorter-necked, shorter-faced pterosaur that was always bending its neck to bring its face down near the ground would be relatively more vulnerable to being sneaked up on?)
So rather than posing a problem for the evolution of such large, gawky-looking pterosaurs, perhaps the presence of large, relatively fast-moving (?) theropod predators actually helped drive the evolution of the azhdarchids' distinctive traits of large size, giraffe-like proportions and posture, and stiff neck that inhibited the lowering of the head.
(Kind of like the way the placement of a horse's eyes so far back on its skull makes it a little easier to see an approaching predator while the horse's muzzle is buried in the grass -- only in the case of the azhdarchid, the adaptions for "always keeping an eye out for predators" are more extreme.)
Azhdarchids actually have smaller eyes for their skull size than any other pterosaur - well below the eye size you may expect for them, actually (compare the orbit size of Zhejiangopterus with the similarly sized Anhanguera, for instance). What's more, their eyes are positioned far lower on their skulls than is typical of other pterosaurs - diagnostically so, in fact. By contrast, birds and mammals that always keep an eye-open for predators tend to have eyes positioned very high in their crania. As such, we may assume that azhdarchids were not under enormous pressure to look-out for predators.
There is a general trend in neoazhdarchians (that is, Tupuxuridae, Chaoyangopteryidae and Azhdarcdhiae) for lowering the eye-socket, and because even small forms (the recently described Shenzoupterus is only 60 cm long from snout to tail, including that massive head) have depressed orbits suggests that was a trait selected for independently of size. The predator-deterring large size of azhdarchids did not allow them to stop watching for predators, basically: they stem from ancestral forms that already had lowered orbits, suggesting they all share a common function. In modern birds, lowered orbits can reflect a need to see the jawline: herons have low eyes to aim their strikes effectively, and long-beaked toucans and hornbills have low eyes to see any food they're manipulating. Neoazhdarchians may have done the same thing: with their long jaws, they almost certainly would've needed to engage in a bit of gulp-and-throw behaviour, chucking food - a baby sauropod say - back into the jaw further with flicks of the jaw and anterior neck. I really did mean to mention something about this in the paper.
As for theropods vs. azhdarchids, there's certainly been some rumblings about the vulnerability of azhdarchids when foraging on the ground. My answer to this is fourfold: 1) lots of them were humungous (I hear some of them could look giraffes in the eye), and humungous animals tend to recieve a lot less predator attention than large ones; 2) for their size and power, they're also pretty lean. OK, so there may be up to 250 kg of pterosaur-flavoured joints to go around on some, but that's not much food for a 6-8 tonne monster theropod, and littler animals may have had difficulty catching and killing bigger forms. It's probably far more efficient use of a marauding tyrannosaur's time to kill a slower, fatter hadrosaur; 3) they could fly and, as anyone who's been keeping up with azhdarchid-related comments here and elsewhere will know, aerodynamic boffins (they know who they are) have said repeatedly that azhdarchids would take off from a standing start in next-to-no-time at all; 4) lots of modern birds spend the vast majority of their time grounded, but we don't see them being massacarred by modern predators. Sure, they get caught out every now and then, but no-more so than any other ground foraging animals. Hence, I come back to a point that needs to be emphasised more: the Mesozoic was not a prehistoric killing field where anything standing still for more than a second was devoured by a massive reptile. Azhdarchids would've been eyed-up and devoured by predators, sure (there are even azhdarchid fossils that show bite marks from Saurornitholestes - note that this is rightly assumed to be scavenging, though), but they wouldn't have been particularly vulnerable. All right, their foraging strategy may have brought them into the line of fire more than that of, say, Nyctosaurus - an animal that appears to have been extremely volant, but wandering around on the ground would not open an azhdarchid buffet for every theropod in town.
Hmm. Should've but that on AzhPal.
And into my quote folder it goes.
Thanks for the response, Mark.
What I'm wondering is this, though: Okay, so the orbits of azhdarchids were lowered to allow them to sight along their jawline and look at food they had caught in their beak-tips and needed to manipulate -- a beneficial adaptation independent of size or stance.
Even given that, I am still wondering if the azhadarchid's stiff, giraffe-like posture and reduced ability to bend their necks down, in combination with their tendency to attain large size, had the effect of keeping their eyes high above the ground in absolute terms, even if the position of the orbit themselves was was not optimized another few inches higher for far-seeing, but was better positioned to see the tips of their own jaws. This would be a compromise of functions, then -- "I can see my own jaw tips but I can also see a good ways out around me" rather than an optimization for being a good look-out only.
Oh, wait. On the other hand, you noted that their eyes were disproportionately small, even for their larger size -- and I assume smaller size means reduced visual acuity. So I guess that puts the kibosh on my "azhdarchids were under pressure to be fairly good living watchtowers" hypothesis right there.
I'm not a paleontologist or a functional anatomist or even a biologist of any sort -- just an interested layman. I was just throwing that out there. I always appreciate learning from the pros.
I can see what you mean about the length of the skull and neck always keeping the eyes relatively high: that height advantage would almost certainly be handy for spotting all sorts of stuff.
Oh, just to nip any suggestions that azhdarchids were blind and found their way around using sonar in the bud, I should point out that azhdarchid eyes are not tiny, beady little things, but that they were certainly on the lower end of the orbital size-scale.
very thanks for this interesting work. I am quite surprised but you have added such a lot of poofs that I can't desagree anything... I don't understand only one point: in your pictures they walk on four legs.
Because all known pterosaur tracks show the animals walked on all fours, and because this fits their anatomy very well, while bipedal walking was not even possible for many, perhaps even all, pterosaurs.
thank you for the answer. I didn't know this!
You don't "skim" flat stones--you "skip" them!
Not in Britain you don't.
Hah, you're definitely getting a chance to spread the gospel of the storklike pterosaur, nice illustration of Lacusovagus in this LiveScience article!
Your new analysis of the probable lifestyle of Azhdarchids, based on anatomy rather than oft-repeated assertions, is yet another reminder that nothing in paleontology is set in stone, and we should always keep our minds open to new information. Good analysis, and good job, guys!
There is good way to check your theory. Hope that you have a possibility to conduct the small statistical study. Having Done him(it), you will be able persuasively to prove or refuse their own discourses.
It is Necessary to check, there is amongst discovery skeleton copies, having with jammed fractures of the bones - especially wing? If P the flying lifestyle before death, that fracture of the bones of the wing of the Hands (but possible, and legs - if web bore up and to him) - was for it fatal and such copy must not be nor one. And opposite if such there is, that this partly proves that they could lead the successful overland life, not rising in air. In the event of traditional constant overland lifestyle, must be a not infrequent events jammed amputated flying finger, more so that they, probably were only disturbed in this case.
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Not the right post to comment on, but I couldn't find a better one.
NewScientist.com has, today, an article
about pterosaurs taking off.
They cite Mark Witton (and Mike Habib), but not you.
Also, Â«Sciences et AvenirÂ»