That pesky clearance problem

I have received quite a few questions over the last year or two about wing clearance during takeoff in pterosaurs.  This seems to be a sticking point for some, as evidenced by the problem rearing it's ugly head again with the recent Chatterjee et al. GSA conference spectacular (see earlier posts below).  It would seem prudent to lay out some of the issues surrounding this problem - or, more specifically, to explain why this isn't really such a huge problem after all.

Because of the way that flying animals scale, larger, long-winged species with greater flight speeds flap with lower amplitudes than smaller species (on average, that is).  Interestingly enough, this means that the amount of clearance required by large flyers is comparatively small, so long as they can get up a good bit of speed on takeoff.  To examine this issue more closely and quantitatively for giant pterosaurs, we can look at something call the Strouhal number.

Strouhal Number is a dimensionless parameter that describes the "gait" of a flapping flyer (or really, anything that is oscillating its propulsion system in a fluid).  As it turns out, because of vortex shedding efficiency constraints, animals are remarkably constrained with regards to their Str during cruising flight: it only varies from about 0.2 to 0.4 including everything from insects to large birds.  There is a great explanation of this number, and its application to flying animals, here (I've shared that link elsewhere to good effect).

Str for a flapping flyer can be calculated as the ratio of flapping amplitude to the product of frequency and velocity.  The largest pterosaurs probably flapped at a rate just over 1 hertz in cruising flight, and likely had minimum steady state speeds near 12 m/s and a cruising speed a good bit greater, say around 20 m/s or more. 

Now, during launch, the animal probably only gets up near steady state stall speed (incidentally, it doesn't have to, contrary to what you often read in basic biology textbooks), and the Str can rise above the 0.4 mark that we might expect during cruising.  Let's let the Str rise to 0.50 and constrain the launch velocity to the min steady state stall speed above.  That still gives us an amplitude for the very tip of the wing in Quetzalcoatlus of 5.6 meters.  Of that total arc, about 40% of it is upstroke, so that leaves a required glenoid height at the end of the launch phase of 3.4 meters or so.  Given that Quetzalcoatlus had a glenoid height of about 2.5 meters while standing, it turns out that very little leaping is required at all for sufficient clearance (less than 1 meter).  The animal still needs to jump, but nothing extraordinary is required.

How giant pterosaurs are struggling to take off from the sinking ship of science journalism

This week, it emerged that the giant azhdarchid Quetzalcoatlus was an atrophied, under muscled animal that was weak and inefficient at takeoff, and could only launch through use of running bipedally with flapping wings, headwinds and downward sloping ground. The newly proposed idea of quadrupedal launch, where pterosaurs became airborne via powerful leaping with all four limbs (Habib 2008) is hokum, being the stuff of fantasy and overly zealous application of bat launch strategies to flying reptiles. 70 kg is the maximum mass that these giants and all other flying animals could achieve, and recent discussions that they were considerably more massive (Paul 2002; Witton 2008; Henderson 2010; Witton and Habib 2010) are plain wrong.

At least, that’s what a recent press release by Sankar Chatterjee and colleagues would have us believe. (Above image: the pterosaur launch battleground. At top is a quad launching Hatzegopteryx, a giant azhdarchid; below, is a bipedally launching Quetzalcoatlus using taxiing, headwinds and a slope to become airborne. Hatzegopteryx is from Witton [2013]; Quetzalcoatlus is from Chatterjee and Templin [2004]) Speaking at the Geological Society of America 2012 conference recently held in Charlotte, N.C., Chatterjee (of the Museum of Texas Tech University; most notable within recent pterosaur research for his contribution of windsurfing tapejarids to the Attenborough pterosaur documentary) and colleagues outlined why he considers much of the recent discussions of giant pterosaur flight dynamics to be flawed in a short presentation, and decided to disseminate their ideas further through the public press. Although the press reports for this story have been relatively widespread, the response from pterosaur researchers to this release has been generally negative, largely because the claims do little to address the recent developments and hypothesis shifts within pterosaur flight studies and largely parrot the findings of Chatterjee and Templin’s 2004 paper on pterosaur flight. Pterosaur.Net’s own Mike Habib, one the key modern researchers on pterosaur flight, offered this take on the release:

“Unfortunately, this looks like the argument comes down to ‘but we got a different answer in 2004!’ Yes.  We know, and for five years I've explained why it is probably wrong.  Oh well.”

Chatterjee et al.’s abstract and press release do not explain why the many arguments supporting pterosaur quad launch (see here and here, for a start) are problematic or why arguments and methodologies to estimate relatively high masses for pterosaurs (here) are incorrect. Instead, they’ve decided that such scientific rigour doesn’t matter, and gone straight into informing the public that giant pterosaurs took flight in the way described in their presentation, and that all other opinions on the matter are wrong.

By bigging up their abstract rather than a peer-reviewed publication in which their methodological details and discussion are explained in detail, Chatterjee et al. have given the impression that their work is more scientifically credible than it actually is. Science journalists have lapped the release up, presumably because giant pterosaurs are cool, but they have not mentioned the lack of a detailed peer-reviewed study behind the findings, nor (in the majority of cases) bothered to find out what other palaeontologists make of the story. This is not the first time this sort of outreach has happened. The proceedings of other conferences and un-reviewed articles have given us infamous press stories such as the ‘Triassic kraken’, vampire pterosaurs, and the suggestion that all dinosaurs were aquatic. And these are just examples from recent memory.

As a scientist concerned about effective and accurate scientific outreach, I find this sort of journalism very worrying. I have no problem with off-kilter ideas like those proposed by Chatterjee et al., but their desire for press attention without applying appropriate scientific rigour is extremely concerning. They have not documented their studies in a scientific paper, sought the opinions of other experts in peer review to construct a scientifically sound hypothesis and news piece. Instead, they went straight from the ‘idea’ phase of their project to media broadcasting, which, as I see it, has three effects. Firstly, it risks misleading the public if their ideas fail to meet scientific scrutiny (most of the ideas mentioned thus far in this article are guilty of this, and I strongly suspect the same is true of the Chatterjee et al. story). Secondly, it undermines the integrity of the scientists behind the story. The idea that “any publicity is good publicity” does not apply to scientists. Within academic circles, you become “the guy who went public with [crazy idea]”, which doesn’t do your reputation, or that of your institution, any favours. Thirdly and perhaps most importantly, such practises undermine science generally. It’s no wonder that palaeontology is often viewed as a speculative and unsubstantiated discipline when a lot of our press work concerns unsubstantiated, often ‘fringe’ or highly controversial ideas being presented as credible hypotheses. This only creates confusion among people as to what the leading hypotheses on given topics are or, when press stories have gaping holes in logic (e.g. the Triassic kraken, aquatic dinosaurs) show scientists as bumbling, foolish individuals incapable of using common sense.

This is a serious problem which we, as scientists and scientific communicators, need to address. Many people are generally sceptical of scientists and their conclusions, concocting up ideas of scientists in scaremongering conspiracies for grant money, or seeking media attention to justify their employment at publically funded museums and universities. The manner in which scientists frequently present unsubstantiated work to non-academics does little to help restore our reputation with these individuals. While it’s of fairly trivial concern whether the public, or anyone for that matter, knows the ins-and-outs of pterosaur launch, all scientists need to think about the broad perception of science by the public. Scientists researching our many severe, modern crises need to be taken seriously, and press reports that expose incomplete or shoddy scientific work negatively impact this perception. Fairly or not, many people, tar all scientists with the same brush (for proof, check out the comments section on any science story publicised by the Daily Mail). We should be working to enhance the reputation of science among the public so that scientific opinions on critical issues like our on-going losses of biodiversity, climate change, sustainability of our lifestyles, energy conservation, and other real, genuine problems are trusted and taken seriously. Scientists leaping for the press with hypotheses that have yet to be suitably tested only present scientists as attention seekers, incompetent or both, and we cannot afford to perpetuate this idea further.

Of course, the fault does not only lay with the scientists. Science journalists also need to raise their game, becoming more circumspect when following and writing up of press stories, noting the state of the research involved, gauging its context within its field and, perhaps in some cases, ignoring clearly bogus, fringe reports entirely. I have worked with a great number of people involved in the scientific media who clearly do not have any interest in science beyond their job, and these are the worst people to be trying to turn the sometimes complex hypotheses of scientists into digestible material for laymen. As Brian Switek shows on a daily basis at Dinosaur Tracking, you become an exemplar science journalist not by just being a deft writer, but you have to give a crap about science too. Failure to fact check and presenting ideas inaccurately is miscommunication, which is clearly an enormous failing for an individual employed to dissemination of information.

In short, we need to stop thinking about scientific outreach as purely an exercise in getting the most attention possible to our research or science news articles. These short-term goals are damaging to science as a whole, which is what science communicators are meant to promote. Science communication is an opportunity to educate non-academics with new and exciting results of good scientific practise that have helped develop our understanding of the world and our place within it. We should take the responsibility that this task requires fully and seriously if we want our scientific voice to be listened to.

References

• Chatterjee, S. and Templin, R. J. 2004.  Posture, Locomotion and Palaeoecology of Pterosaurs. Geological Society of America Special Publication, 376, 1-64.
• Habib, M.B. 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, B28, 161-168.
• Henderson, D. M. 2010. Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology, 30, 768-785.
• Paul, G. S. 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. John Hopkins University Press, Baltimore, 472 pp.
• Witton, M. P. 2008. A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana, B28, 143-159.
• Witton, M. P. 2013. Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. [In press]
• Witton, M. P. and Habib, M. B. 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PLoS ONE, 5, e13982.

Embarrassing questions on Quetzalcoatlus

You can’t queue up at a supermarket checkout nowadays without being bombarded by celebrity lifestyle magazines. They glare at you from the impulse-buy shelves with paparazzi shots of stars looking flabby, pregnant, boozy or unhappy and garish, block capital headlines scorn celebs for revealing their mortal flaws. There is probably a deep-seated psychological reason to their popularity, perhaps reflecting the desire people have for gossip or reassuring somewhat insecure readers that it’s OK, people with stars on Hollywood Boulevard aren’t perfect either. The thing that strikes me, though, is that a lot of the people splashed all over the front pages of these rags have very little substance behind their fame, becoming famous because they took they posed semi-nude for a tabloid newspaper, are related to someone else in the public eye or appeared on telly for five minutes on a reality TV show. These are the empty celebrities, the ones that you assume have some reason for being known but, when investigated in more detail, are actually quite devoid of substance. It’s rare that these tabloid-fodder achieve international fame: to do that, you’ve at least got to be associated with an internationally-released product or hung-out in high-profile political circles. In some respects, then, becoming a real international household name requires a little more substance than your local, lower-grade celebrities. Talent, though, is handy but not strictly necessary.

There are definitely fossil animals that are the equivalent of A-list celebs, the sort of critters that every five year-old knows and that press releases strive to mention, no matter how tangential their work is to them, to gain more kudos. They’re the animals that the public know and love, the likes of Tyrannosaurus, Triceratops, woolly mammoths and sabre-toothed cats. Typically, these animals do have some substance to them: while their taxonomy may be confused or controversial, they definitely ‘exist’. Some pterosaurs are in this club too, with Pterodactylus (or probably ‘pterodactyls’) or Pteranodon being at the top of the list, and Quetzalcoatlus, everyone’s favourite superpterosaur, just behind (detail of a new image above). Thing is, though, Quetzalcoatlus may be a fraud. Yes, that’s right: there may be so little substance to its existence that its status as a household palaeontological name is undeserved: it’s a local celeb masquerading as a big shot. That’s controversial stuff and, no doubt, several of you have just sprayed your monitor with coffee shot through your nose at the very idea of such a thing. But mop up that liquid, dry the screen off, and we’ll see why I’m suddenly being so nasty to one of the cornerstones of Azhdarchidae.


Giant, yes; diagnostic, maybe not
As I’m sure you all know, Quetzalcoatlus stems from the Maastrichtian Javelina Formation of Texas. Remains of several animals that would be referred to this genus were found from 1972 – 1974 and were briefly described by their discover, Douglas Lawson, in 1975 (Lawson 1975a). Quetzalcoatlus was erected in the same year (Lawson 1975b) with fragments of a giant left wing (including a famous complete humerus, TMM 41450-3; see image, above) being used as the holotype for the type species, Q. northropi Lawson, 1975b. A bunch of smaller individuals that were represented by substantially more complete remains were discovered at the same time and initially referred to the same species (Lawson 1975a, b) but, later, were said to be sufficiently distinct from Q. northropi to deserve their own species (Kellner and Langston 1996). Pending their complete description, however, Kellner and Langston simply called them ‘Q. sp.’ for their work on the Quetzalcoatlus skull.

That all looks above board on the surface, but it doesn’t take much digging to find several massive holes. Firstly, despite the wealth of material that has been referred to it, neither Quetzalcoatlus or Q. northropi have ever been given a rigorous taxonomic definition*. To my knowledge, only Nesov (1991) has had a stab at a Quetzalcoatlus definition but his listed characters are either not unique to Quetzalcoatlus or of questionable validity, so his work is not really useful here. This leaves us without a diagnosis and, accordingly, we simply cannot know if Q. northropi is a valid species or not. What’s more, with Q. northropi being the type species of Quetzalcoatlus, the entire genus must go if the former is sunk.

*You could get away with this sort of stuff in the 1970s, but it’s much harder to be taxonomically slack nowadays. The ICZN (the body that regulates naming of zoological specimens) has recently tightened its rules considerably to make sure that new taxa come with proper holotype allocation, diagnoses and all other due practises (e.g. article 16, International Commission on Zoological Nomenclature 1999), so messes like the one under discussion here should – in theory – eventually become a thing of the past.

In my eyes, this is quite a real possibility. Pterosaur limb elements aren’t normally named because they are not considered diagnostic at generic or species levels: taxa that are based on limb elements alone have been considered nomina dubia by later authors. ’Santanadactylus’ spixi - a set of wrist bones - and Palaeornis cliftii - an isolated humerus – have both fallen into this trap (Unwin 2003; Witton et al. 2009). Unless Q. northropi is unusually distinctive, it’s possible it may be binned too. Adding more concern to this worryfire is that, so far as I can see, the Q. northropi humerus doesn’t look that different from other giant azhdarchid humeri (e.g. Padian and Smith 1992; Buffetaut et al. 2002) and the existence of these other giants nullifies the possibility of using size as a diagnostic feature (though this would be dodgy anyway). The other Q. northropi elements are so scrappy that they’re probably of very little taxonomic utility and preclude the use of limb element proportions in a diagnosis, too. Call me cynical if you like, but it looks like this could be an uphill struggle to me.


The plot thickens
There’s more. With no definition for Quetzalcoatlus, the referral of the Q. sp. material (including that depicted above, from Kellner and Langston 1996) to this taxon is also questionable. The Q. sp. material is what people refer to when talking about the detailed anatomy of Quetzalcoatlus, but we need to be careful: there has never been any justification printed for the allocation of Q. sp. to Quetzalcoatlus: we’ve just been told it’s similar to Q. northropi and can therefore be placed in the same genus. Thing is, Hatzegopteryx, Arambourgiania and Zhejiangopterus are pretty similar animals to Q. northropi too, so why can’t the Q. sp. material been popped in one of these genera instead? You can't argue taxonomic provinence in this instance, either: it's highly likely that there is more than one azhdarchid genus in the Javelina Formation (see my thoughts on this here), so you can’t suggest allocation of Q. sp. to Quetzalcoatlus through association alone.

To be clear, I'm not saying that Q. sp. itself is of questionable validity - whatever you want to call it, Q. sp. is definitely a valid, diagnosable species, I’m just iffy about its allocation to Quetzalcoatlus at present. Note, however, that the story continues outside of material referred to Quetzalcoatlus, too: the status of Hatzegopteryx may also hang in the balance. I don’t have time to go into that now, though.

So, what next?
The resolution of all this is, in my view, quite straightforward. Eagle-eyed readers may have read between the lines of this post and realised that, despite it’s fame, popularity and unearthing almost 40 years ago, there is almost nothing written or illustrated of Quetzalcoatlus. The issues highlighted here will not be resolved without this data and, frankly, a few good photographs and descriptions of Q. northopi would give all the information we need to get started. There is, in fact, a bit of an elephant in the room about Quetzalcoatlus and, foolish though it may be for a bloke looking for a job in the pterosaur corner of palaeoindustry to be so outspoken, it should be flagged up. Without mentioning any names, the Texas Memorial Museum has placed a strict embargo on the release of information about Quetzalcoatlus until the full monographic description has been properly published. This has been promised since at least the 1980s (Langston 1981; Kellner and Langston 1996) and, in the meantime, getting access to the material seems to be extremely difficult. I asked to see the material back in 2006 and was told no. Colleagues of mine have asked the same, and got the same answer. The few friends of mine that have seen the specimens are sworn to secrecy and, if they want to publish even itty-bitty snippets of information about them, they have to ask permission first.

If you ask me, this is all a bit rotten. The Society of Vertebrate Paleontology’s ethical mission statement states that vertebrate palaeontologists of the world are here to:

1. To advance the science of vertebrate paleontology throughout the world;
2. To serve the common interests and facilitate the cooperation of all persons concerned with the history, evolution, ecology, comparative anatomy and taxonomy of vertebrate animals, as well as the field occurrence, collection and study of fossil vertebrates and the stratigraphy of the beds in which they are found;
3. To support and encourage the discovery, conservation and protection of vertebrate fossils and fossil sites;
4. To foster the scientific, educational and personal appreciation and understanding of vertebrate fossils and fossil sites by avocational, student and professional paleontologists and the general public.
   

From the SVP Constitution, Article 12, Code of Ethics.

Aside from the point 3 in this list, it seems that the decades-long embargo on the Quetzalcoatlus material isn't really in keeping with these guidelines. I mean, I get embargoes. I get 'gentlemen's agreements' about publishing rights. But 40 years to publish a specimen description while simultaneously being very cagey about giving access to the material? Seriously guys, what's going on? I'm not sure there's quite enough ground here to go stampeding to the SVP ethics committee or anything, but when is this material going to be properly published and freely available to see?

References

• Buffetaut, E., Grigorescu, D. and Csiki, Z. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften, 89, 180-184.
• International Commission on Zoological Nomenclature. 1999. International Code of Zoological Nomenclature (4th Edition). The International Trust of Zoological Nomenclature, 1999.
• Kellner, A. W. A. and Langston, W. Jr. 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park. Journal of Vertebrate Paleontology, 16, 222-231.
• Langston, W. Jr. 1981. Pterosaurs. Scientific American, 244, 92-102.
• Lawson, D. A. 1975a. Pterosaur from the Latest Cretaceous of West Texas: discovery of the largest flying creature. Science, 185, 947-948.
• Lawson, D. A. 1975b. Could pterosaurs fly? Science, 188, 676-677.
• Nesov, L. A. 1991. Gigantskiye lyetayushchiye yashchyeryi semyeistva Azhdarchidae. I. Morfologiya, sistematika. Vestnik Leningradskogo Gosudarstvennogo Universiteta. Seriya 7, 2, 14-23.
• Padian, K. and Smith, M. 1992. New light on Late Cretaceous pterosaur material from Montana. Journal of Vertebrate Paleontology, 12, 87-92.
• Unwin, D. M. 2003. On the phylogeny and evolutionary history of pterosaurs. In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 139-190.
• Witton, M. P., Martill, D. M. and Green, M. 2009. On pterodactyloid diversity in the British Wealden (Lower Cretaceous) and a reappraisal of “Palaeornis” cliftii Mantell, 1844. Cretaceous Research, 30, 676-686.