Papers via blogposts

Those keeping up with the pterosaurian literature will be aware that the latest issue of Acta Geologica Sinica has a set of papers resulting (at least in part) from the 2010 Beijing Flugsaurier meeting. (And while we’re on the subject, the 2013 meeting in Rio has extended abstract submissions till the 31^st of January, so there’s still time to get them in). I’ve got a couple in there and while people might be more interested in the horribly flattened anuroganthid, I’m more keen to talk about the short review paper I produced.

The title, ‘Pterosaur Research: Recent Advances and a Future Revolution’, might sound familiar and indeed some of the content may too. That’s because it ultimately sprung out of a post that I had over on the Musings and also put up on Pterosaur.net. This is a first for me at least, a paper that resulted pretty much directly from a blogpost.

At the time I’d been writing about rates of discovery of dinosaurs and pterosaurs and what that might mean for future discoveries. It occurred to me that actually the pterosaurs seemed to be going through something of a renaissance in the way that dinosaurs had in the 1970s. We were finding more and more of them, more papers were being published by more researchers, and more of the big questions were either being answered, or at least were being tackled in a rather more systematic way than they had before. It occurred to me that this was worth summarising and producing something more formal. The fact that the next Flugsaurier volume was due meant there was a most suitable venue available and discussions with various colleagues helped me develop the idea and push for it’s inclusion.

If you look back at the developments of the last 10 years or so in pterosaurs, it’s quite a remarkable and rapid progression. That’s not to overlook the huge amount of groundwork that had gone before and the efforts of previous generations, but even quite a few fundamentals that had occurred for dinosaurs decades ago are now being sorted out for pterosaurs. We now have inclusive phylogenies for pterosaurs, we’ve got a good idea of their soft tissue structures and especially the wing, some of the taxonomic and systematics issues of the past are being resolved, we’ve got a major transition in the form of Darwinopterus, cool new taxa like the boreopterids and chaoyangopterids turning up, detailed analyses of flight, take-off, mass estimates, muscle patterns, and skull shapes, we finally, finally, have eggs and we’re even getting serious on behaviour and ecology for analyses of head crests, growth and the like as well as looking at major evolutionary trends like diversification and distribution. We’re even getting attention from the public and serious attention with whole exhibits on pterosaurs, new books, and documentaries, and of course we now have the Flugsaurier meetings themselves, established and (hopefully) regular events that will help keep things ticking along.

So this paper attempts to summarise all of this and in effect provide a statement of the ‘state of the art’ – what do we know and how have we got there, but it is also supposed to be a bit of a celebration of the last decade of research and the gains made by the pterosaur research community. Those in the know will probably realise that the background to this has not been without a significant amount of strife, and while this is not mentioned in the paper, I think it only emphasises how much has been learned despite this limitation. I hope it also provides a sort of counter-point, but also a continuation of Peter Wellnhofer’s piece that kicked off the 2008 Flugsauriervolume. Peter wrote a review of the history of pterosaur research, but pretty much only took it up to the modern era, and with the galloping developments of the last few years, this should bring things more or less up to date.

Hone, D.W.E. Pterosaur research: recent advances and a future revolution. Acta Geologica Sinica, 86: 1366-1376.

The paper is available here (and indeed all of the latest papers are from AGS). Just click on the left hand set of the three series of Chinese characters at the bottom of the page and then add a .pdf suffix to the filename once it’s been saved.

LACM to Boston: G+ Hangout Interview

I recently did a G+ hangout interview with Lorena Barba's bio-aerial motion class out at Boston University.  I broadcasted from the Natural History Museum of Los Angeles County, along with Justin Hall.  Here's the link on YouTube: https://www.youtube.com/watch?feature=player_embedded&v=Mt88TkOlD4g

This was our first go with the "On Air" feature, which automatically records the hangout and sends it to a personal YouTube channel.  I talked a lot about pterosaurs, as well as a bit about Microraptor.

Cheers,

--MH

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.

GUEST POST: Felipe Pinheiro and the Raiders of the Lost Palate

2012 has been a good year for pterosaurs, with several new taxa and important papers being published. This trend continued this week with the description of a fragmentary but intriguing pterosaur palate from the famous Cretaceous Santana Formation of Brazil, authored by Felipe Pinheiro and Cesar Schultz of the Universidade Federal do Rio Grande do Sul. Avenida Bento Gonçalves, Brazil, and Bayerische Staatssammlung für Paläontologie und Geologie, Germany, respectively (image of the new material is shown above. Image courtesy Felipe Pinheiro). Felipe asked if we could big up the paper here at the Pterosaur.Net bog, but I'm a little too pushed for time to write a post worthy of the article, which not only describes the specimen but sheds much needed light into pterosaur palatal anatomy. Felipe was kind enough to provide his own illustrated summation of the story however, so we could still cover the paper here at the blog. On that note, I'll hand you over to our guest blogger, and be sure to check out his open access paper for more details on this new discovery. 

MPW 24/11/12

--

The fragility of pterosaur skeletons is always working against us, the paleontologists devoted to understanding these flying archosaurs. Independently if our research deals with systematics, anatomy or paleobiology, we’re often confronted with the fact that our research subject is badly crushed and a great deal of useful information is simply lost. A very good example of this issue is the pterosaur palate: although new pterosaur taxa are being published all the time, only a handful of well-known specimens have this structure preserved, thus, limiting our knowledge of its anatomy and evolution within the group. Luckily, some rare sedimentary deposits were kind enough and maintained the original, three-dimensional shape of their fossils, allowing the study of otherwise inaccessible anatomical features, like, of course, the pterosaur palates. (Pterosaur specimens showing palatal regions below. Image courtesy Felipe Pinheiro)

Our understanding of pterosaur palatal anatomy changed considerably after the recent work by Attila Ösi and colleagues (2010). Analyzing pterosaur palates under an evolutionary perspective and utilizing the Extant Phylogenetic Bracket as a tool, the authors identified homologue structures between pterosaurs, birds and crocodiles, demonstrating some bones that were misinterpreted throughout the literature. The best example is the conclusion that, in pterosaurs, most of the palate is composed by palatal blades of the maxillae, instead of the palatines. Although this identification was also proposed by some old researchers, like Newton (1888) and Seeley (1901) and, more recently, Peters (2000), common sense was still that the palatines composed most of pterosaur palatal surface.

As the work of Ösi et al. (2010) was mainly focused on stem “non-pterodactyloids”, especially Dorygnathus, a new look on pterodactyloid palate was still needed and this is the main subject of our new paper, titled “An Unusual Pterosaur Specimen (Pterodactyloidea, ?Azhdarchoidea) from the Early Cretaceous Romualdo Formation of Brazil, and the Evolution of the Pterodactyloid Palate”.

Besides describing a new fragmentary (but interesting) palate from the Romualdo Formation (the Early Cretaceous concretion-bearing strata of the Santana Group, northeastern Brazil), we analyzed and redescribed a number of well-known pterosaur specimens with palatal preservation, such as “Pterodactylus” micronyx, Anhanguera and Pteranodon. Also, the palate of the Iwaki Tupuxuara specimen is described and illustrated for the first time. As a result, our work shows that pterodactyloids had often complex palatal morphologies with, sometimes, interesting “reversions” to the non-pterodactyloid condition, with three pairs of lateral openings. Also interesting is the extreme reduction of elements in some taxa, such as the almost vestigial ectopterygoids of anhanguerids. (Possible evolutionary pathways of the pterosaur palate shown below. Image courtesy Felipe Pinheiro.) 

This morphological disparity is probably an evidence of complex feeding habits among derived pterodactyloids, with ecological implications that is, presently, the research subject of our working group, at the Universidade Federal do Rio Grande do Sul, Brazil.

I hope you all read our paper (don’t worry, it’s open access). We’re opened to all kind of criticism and discussions by my personal e-mail: fl_pinheiro@yahoo.com.br.

Enjoy!

Felipe L. Pinheiro

Laboratório de Paleontologia de Vertebrados, Instituto de Geociências, Universidade Federal do Rio Grande do Sul.

References:

• Ösi A, Prondvai E, Frey E, Pohl B (2010) New interpretation of the palate of pterosaurs. The Anat Rec 293: 243–258.
• Newton ET (1888). On the skull, brain and auditory organ of a new species of Pterosaurian Scaphognathus purdoni), from the Upper Lias near Whitby, Yorkshire. Philos Trans R Soc Lond B Biol Sci 179: 503–537.
• Peters D. (2000). A re-examination of four prolacertiforms with implications for pterosaur phylogenies. Riv Italiana Paleontol Strat 106: 293–336.
• Seeley HG (1901) Dragons of the Air: an account of extinct flying reptiles. New York: Appleton & Co.; London: Methuen & Co.

Pterosaur fact checking

I will keep this brief, since Mark already did a great job of responding to the media release from the recent Chatterjee et al. presentation.  One thing to look for in any sort of functional morphology argument is whether the anatomy, the numbers, and the behavior all match up.  One reason the Chatterjee et al. abstract is so immediately concerning is that their own information doesn't jive internally.

Example 1: one of their concerns with the quad launch hypothesis is clearance for the wings after launch.  Now, I've calculated the expected clearance and everything seems fine, but that doesn't mean I'm right.  Maybe someone will find an error at some point.  What is clearly not going to be true, however, is the idea that keeping the feet on the ground (biped running launch) is going to give more clearance than a leap.  It simply isn't possible to get more clearance by not jumping (it might be true that jumping still isn't enough, but it's not going to be worse).  So Chatterjee et al. have a mismatch between their own conclusions and their arguments with the competing model.  The numbers and the behavior don't match up.

Example 2: Chatterjee et al. argue that pterosaurs can't work as scaled up bats, and argue instead that they should work like scaled up birds.  Anatomically, pterosaurs don't match either of these, so the bat argument is a straw man, and the bird argument is moot.  The anatomy and the behavior don't match up.

These are the sorts of arguments that raise red flags in scientific discourse.  On a final note, there are some basic fact checking items that should be looked out for, such as claims about living animals.  From the media story, Chatterjee is quoted as saying "Like albatrosses and the Great Kori bustards, which weigh 20 to 40 pounds, ground takeoff was agonizing and embarrassing for Quetzalcoatlus."

Aside from the problem with the pterosaur analogy, there is the obvious problem that Kori bustards don't have trouble taking off (though they might find it embarrassing; I haven't asked them).  In fact, Kori bustards can leap into flight at a steep angle.  Check this out.  Yes, the bustard tries running to escape, first, but when pressed, it just leaps into the air.  No big runway, no "agonizing" takeoff.  In fact, there is no correlation between running launch and size in living birds or bats.  More on that some other time, but in general, if a YouTube search quickly demonstrates that your commentary is flawed, that's a bit worrisome.

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.

Some pterosaur related goodness

As people might know, I've recently started blogging for the website of The Guardian newspaper in the U.K. Coupled with the Musings, Pterosaur.net and my occasional contributions to other sites like the 21st Floor means that I can be spread a bit too thin these days. As such I'm rather behind on here, despite rather obviously having some top pterosaur-related goodness that I should be talking about.

Most obviously, just a week ago, my first paper come out in which I named a pterosaur. Named Bellubrunnus, this is an absolutely stunning specimen - I mean, just look at it. Inevitably there's a series of posts by me on it and it's implications for pterosaur evolution (here, here, here and finally here). Best of all, the paper is in PLoS ONE and so freely available to all who want to read it.

More recently, Pterosaur.net contributor Luis Rey has set up a blog for his new artwork. One of the first things he's done is a brand new image of Darwinopterus coming in to land on a tree trunk based on a conversation we'd had and a sketch I knocked up for him. Two versions are actually out there and you can catch up with them here and here.

Cross/Guest Post: Thin vs Thick Wings

I have a special treat this evening.  Colin Palmer has been kind enough to write a guest post on the relative performance advantages and dynamics of thin and thick wings, especially in the context of animal flyers.  Colin is located at Bristol University.  He is an accomplished engineer with an exceptional background in thin-sectioned lifting surfaces (particularly sails).  Colin has turned his eye to pterosaurs in recent years, and he has quickly become among the world's best pterosaur flight dynamics workers.  You can catch his excellent paper on the aerodynamics of pterosaur wings here.  Press release on it can be found here.


This is a cross post from Aero Evo.  If you want to comment on the post, I recommend going there, as that means Colin only has to watch one site at a time (remember, he supplied this at of the goodness of his heart!)

--MH

------------------------
Thin And Thick Wings
Colin Palmer

In the early days of manned flight the designers took their inspiration from birds. One of the consequences was that they used thin, almost curved plate aerofoil sections. This seemed intuitively right and certainly resulted in aeroplanes that flew successfully. However towards the end of the First World War the latest German Fokker fighters suddenly started to outperform the Allied planes. Counterintuitively their wing sections were thicker-surely these sections would not cut the air so well so how could they possibly have enabled aeroplanes to fly faster and climb more quickly. But that was what was happening, the Germans had done their research and discovered that a combination of a cambered aerofoil with the correct thickness distribution gave superior aerodynamic performance. Subsequently all aircraft had similar teardrop shaped wing sections and soon there was a massive body of experimental and theoretical work available that enabled designers to select just the aerofoil they required.

Fast forward to the period after the Second World War and an explosion of interest in applying the latest aerospace science to the traditional arts of sailing. Many people looked to aircraft and logically assumed that sailboats would perform better if only they could be fitted with wing sails, like up-ended aircraft wings. Surely this had to be more efficient than the old-fashioned sails made of fabric and wire, just like the earliest aircraft. But the results were disappointing. Not only on a practical level where the wing sails proved unwieldy and unsuited to operating in a range of wind conditions, but perhaps more worrying they offered no obvious performance advantage and indeed in light winds they were significantly inferior, area for area. What was going on? Why didn't the massive investment in the development of aircraft wing sections have anything to offer to sailboats?

The answer lay in understanding the effect of Reynolds number. From the very earliest days of manned flight aircraft were operating at Reynolds number approaching 1 million and as speeds increased so did the Reynolds numbers, so it became customary for aerofoils to be developed for operation at Reynolds numbers of 2 to 3 million or more. But sailboats are much slower than even the slowest aircraft so the operational Reynolds numbers are lower than for aircraft, typically in the range from 200,000 to 500,000, right in the so-called transition region. It turns out that in this Reynolds number range the experience and intuition gained from studies at significantly higher values can be very misleading indeed. In the transition region a curved plate, (membrane) aerofoil can be more aerodynamically efficient than a conventional thick aerofoil.

This transition Reynolds number range is also where most birds and bats operate, and from what we know of pterosaurs it was also their domain. Consequently natural forms are not necessarily disadvantaged by having the membrane wings of bats or pterosaurs or the thin foils of the primary feathers in the distal regions of bird wings.

But there is a complication. A curved plate or, to an even greater extent, a membrane aerofoil has very little intrinsic strength and requires some form of structure to keep it in place and keep it in shape. On sailing yachts this structure is a thin tension wire that supports the headsail or the tubular mast in front of the mainsail. In order to tension the wire for the headsail, very large forces are required which places the mast in considerable compression, normally requiring a guyed structure that can have no direct analogue in nature. Natural forms are restricted to using a supporting structure which is loaded in bending and restrained by attached muscles and tendons. Generally speaking, the bending resistance of a structure depends upon the depth of the cross-section, so as bending load increases the diameters of the bones must increase otherwise the wing will become too flexible.

This is where the apparent superiority of the membrane wing may be compromised, because the presence of structural member severely degrades the aerodynamic performance. The structural member may be along the leading edge of the aerofoil as in the case of bats and pterosaurs, or close to the aerodynamic centre as in the case of the rachis of the primary feathers of birds. In all cases the loss of performance is less if the supporting structure is on the pressure side (the ventral side) of the aerofoil. It is therefore most likely no coincidence that this is the arrangement of the wing bones and membrane in bats and the rachis and vane in primary feathers. It was therefore also most likely that the wing membranes of pterosaurs were similarly attached to the upper side of the wing finger. Even in this configuration there is a substantial penalty in terms of drag, although it may result in some increase in the maximum lift capability of the section, due presumably to an effective increase in camber. (Palmer 2010).

This aerodynamic penalty arising from the presence of the supporting structure may perhaps be the reason why birds’ wings have thickness in the proximal regions, where the performance of such a thick aerofoil is superior to a thin membrane obstructed by the presence of the wing bones. More distally, where the wing bones become thinner or are not present, the wing section reverts to a thin cambered plate formed by the primary feathers. On the bird’s wing the proximal fairing of the bones into an aerofoil section is achieved by the contour feathers with very little weight penalty. This is not possible in bats (and presumably also in pterosaurs) where any fairing material would, at the very least, need to be pneumatised soft tissue, resulting in a considerable weight penalty as compared to feathers. In the absence of aerodynamic fairing around the supporting structure, aerodynamic efficiency can only be improved by reducing the cross-section depth of the bones - the general shape of the section having very little effect. But reducing the section depth results in a large increase in flexibility since the bending stiffness varies as the 4th power of section depth, so there are very marked limits to the effectiveness of this trade-off.

It may therefore be no coincidence that where the cross section depth has to be greatest, in the proximal regions of the wing, both bats and pterosaurs have a propatagium, which means that the leading-edge of the wing section is more akin to the headsail of a yacht, stretched on a wire, than a membrane with the structural member along the leading-edge. Wind tunnel tests have shown that moving the structural member back from the leading-edge, while keeping it on the underside of the wing section, results in a significant increase in aerodynamic performance.

Meet Bellubrunnus: New Pterosaur in PLoS ONE

Dave Hone and colleagues have just published a fantastic description of a new pterosaur in PLoS ONE.  You can read (and download, if desired) the paper here.  This new critter is particularly fun because it has wingtips that curve anteriorly; which is unique among pterosaurs known to date.  Very cool stuff, and if you want to know more, obviously read the full paper, as well as the discussion by Dr. Hone himself at Archosaur Musings.

Here is a section of the Abstract from the original article:

Methodology/Principal Findings
The specimen was examined firsthand by all authors. Additional investigation and photography under UV light to reveal details of the bones not easily seen under normal lighting regimes was completed.
Conclusions/Significance

This taxon heralds from a newly explored locality that is older than the classic Solnhofen beds. While similar to Rhamphorhynchus, the new taxon differs in the number of teeth, shape of the humerus and femur, and limb proportions. Unlike other derived non-pterodacytyloids, Bellubrunnus lacks elongate chevrons and zygapophyses in the tail, and unlike all other known pterosaurs, the wingtips are curved anteriorly, potentially giving it a unique flight profile.

Cheers!

--MH

Pterosaur.Net wades in against ReptileEvolution.com

This has to be quick, as I'm close to emerging from  seemingly never-ending book revision and want to finish it as soon as possible, but something of interest to Pterosaur.Net readers (and, indeed, anyone with an interest in palaeontology, natural history or science communication) has emerged that needs bringing to the widest possible attention. Over at Tetrapod Zoology, Darren Naish has recently published a long, detailed critique of the many problems inherent with a website with worrying Internet presence, David Peters' ReptileEvolution.com. The title of the piece, "Why the world has to ignore ReptileEvolution.com" probably tells you everything you need to know about its content but, if that doesn't spell it clearly enough, its loud message at the top of the page makes the point clearer:

ReptileEvolution.com does not represent a trustworthy source that people should consult or rely on. Students, amateur researchers and the lay public should be strongly advised to avoid or ignore it."

But why should you care? 
In all likelihood, if you're reading this post, you are already familiar with Peters, his website and its sister blog, The Pterosaur Heresies. Even if these names are not familiar however, there is a good chance you have bumped into them when Googling almost any Mesozoic reptile you care to think of. Peters is well-known in palaeontological circles (though perhaps mostly ignored by the professional palaeontological community now) for his unorthodox views on amniote phylogeny and, perhaps more commonly, his sometimes bizarre interpretations of pterosaur anatomy and functional morphology. For years, Peters has been using a technique known as "Digital Graphic Segregation", tracing photographs of fossils and interprets actual bone, marks in the surrounding matrix, and probably preparation, printing and jpeg compression artifacts, to reconstruct the anatomy of fossil animals. Observations on actual specimens are very much of secondary concern and do not factor into this technique much, if at all. This leads to the frequent identification of  features that simply do not exist on the actual specimens (see Peters' reconstruction, above, of Anuroganthus ammoni for an example [source]. Note the number of phalanges in the wing finger, shape of the skull and long, fibrous tail. Go here to compare this with the best-preserved specimen of this pterosaur) and, when fed into a phylogenetic analysis, the resultant trees are understandably completely incongruous with anything seen in 'mainstream' literature. Peters' work has been rightly criticised from all angles (including Bennett 2005; Hone et al. 2009, this, and frequently on the Dinosaur Mailing List) but he retains his ideas in the face of overwhelming evidence to the contrary (i.e. the inability to see the structures he claims to find on actual specimens despite microscopic, and UV observation, and CT scanning). As such, the work portrayed on his website and blog has to be pseudoscience, at best.

Above, ReptileEvolution.com image allegedly demonstrating the  presence of a fifth wing phalanx in the pterosaur wing. Consistent observations of pterosaur fossils, by contrast, suggest they only had four phalanges, or sometimes three.  From here.

This, in itself, is not really the problem. As Darren points out, the Internet is a place for creative, free thinking individuals and, hey, if you cannot express your opinions here, where can you? The issue taken with ReptileEvolution.com is not that it exists, but that it's internet presence has grown to the point that it is now a top-listed site for many palaeo-based searches. Tap virtually any Mesozoic reptile species into Google and either ReptileEvolution.com or the Pterosaur Heresies is likely to be in the first few hits. The situation is even worse for image searches, which are increasingly dominated by the many graphics that Peters' uses on his sites. This would seemingly be because Peters is extremely prolific in his output on these projects, and because most Mesozoic reptiles are poorly covered online.

Those In The Know are, at worst, merely frustrated by this situation, as it skews search results from other hits that may be of interest. Those who are not familiar with Peters' work or sites however, are potentially being mislead by his very professional-looking websites that frequently present their content as hard biological facts rather than the eccentric views of one individual. I have heard anecdotes of news outlets citing ReptileEvolution.com and, not many months ago, we ran into a direct example of one website blindly following Peters' ideas (we weren't impressed). This is a worrying trend.

We have more-or-less ignored Peters' work at Pterosaur.Net, which may seem surprising given that he has dedicated a whole blog, more or less, to deconstructing the 'mainstream' view of pterosaur palaeobiology. ReptileEvolution.com even has a page dedicated to picking holes in the main Pterosaur.Net site! I suppose we have more interest in discussing other topics on our blog than merely rehashing the same anti-Peters arguments over and over. Most of us have had discussions with Peters about his ideas and hypotheses at one venue or another anyway, so I guess we've 'moved on' in some respects. Regardless, I'm sure I speak for my colleagues here at Pterosaur.Net when I say that we are as concerned over the prevalence of ReptileEvolution.com and the Pterosaur Heresies as Darren is at TetZoo, and want to bring these concerns to the widest possible audience. Hence, I urge you to read Darren's discourse if you have not already done so and, if you are concerned about the accurate portrayal of palaeontological science online, then blog, tweet and discuss this issue as much as you see fit. As may be expected, Peters has started a rebuttal of the piece across a number of blogposts, which begins here.

That will have to do: I've gone on far longer than planned. Back to the book...

References

• Bennett, S. C. 2005. Pterosaur science or pterosaur fantasy? Prehistoric Times, 70, 21-23.
• Hone, D. W. E., Sullivan, C. and Bennett S. C. 2009. Interpreting the autopodia of tetrapods: interphalangeal lines hinge on too many assumptions. Historical Biology, 21, 67-77.

They keep on coming

Yes descriptions of new pterosaurs don't quite keep up with the rates of new dinosaurs, but they don't do badly either. This is the skull of Morganopterus, yet another (and yes, arguably one of too many) boreopterids to come out of China in recent years. While the group is already known for having long, low heads with far too many teeth, this one does seem to be going for a record.

It's big too - nearly a metre long if you include the little crest off the back of the head (and there's a small one over the tips of the upper jaw too). Not too many years ago Pteranodon was the only pterosaur known with this kind of posteriorly directed head-crest but now we have Ludodacylus and Morganopterus too so they're starting to be come pretty common in the ornithocheiroids. I'd be far from surprised if a few more didn't turn up in the next few years on new species or better specimens of already recognised taxa.

This is a nice specimen and it seemed too interesting not to share, though I don't have too much to say about it right this minute. Still, if new pterosaurs are your thing, stay tuned, there's something due out Thursday which I hope will turn a few heads.

P.S. The image is Fig 1 in the paper, but this version was kindly sent to me by Lu Junchang.

Cross-Post: Feathers vs Membranes

A recent discussion arose on the Dinosaur Mailing List that included some questions regarding the relative merits of membrane wings and feathered wings, mostly in the context of pterosaurs vs birds. In that spirit, I thought I'd give a little rundown of the relative advantages/costs of each type of vertebrate wing.  This was also posted on Aero Evo.

Avian Wings
Birds are the only flying vertebrates to use keratinized, dermal projections (i.e. feathers) to form their wings.  Feathers have the distinct advantage of being potentially separate vortex-generating surfaces, meaning that a bird can split its wing up into separate airfoils, thereby greatly changing its lift and drag profile as required (Videler, 2005).  Tip slots are the most obvious example of this mechanism, whereby the tip of the wing is split into several separate wingtips by spreading the primary feathers of the distal wing.  The alula, which lies along the leading edge of a bird’s wing, and is controlled by digit I, is another example of a semi-independent foil unit (Pennycuick, 1989; Videler, 2005).  The splayed primaries of a slotted avian wingtip passively twist nose-down at high angles of attack (and therefore at high lift coefficients), and this feather twist reduces the local angle of attack at the distal end of slotted avian wings, preventing them from stalling (Pennycuick, 2008).  Slotted avian wingtips may therefore be nearly "unstallable", though this does not prevent the overall wing from stalling (Pennycuick, pers comm.).  Feathered wings can also be reduced in span without an accompanying problem of slack and flutter – the feathers that form the contour of the wing simply slide over one another to accommodate the change in surface area.  Despite these advantages, feathers have some costs as wing components, as compared to membranous wings.  Feathered wings are relatively heavy (Prange et al., 1979) and cannot be tensed and stretched like a membrane wing (which has ramifications for cambering). Theoretically, avian wings should not be able to produce maximum lift coefficients as high as an optimized membrane wing (Cunningham, pers comm.), but experimental data to determine if transient, maximum lift coefficients actually differ significantly between bats and birds are not yet available (Hedenstrom et al., 2009).

Chiropteran Wings
Bats have a wing surface formed primarily by a membrane stretched across the hand, antebrachium, brachium, and body down to the ankle.  Unlike birds, which have a limited number of muscles that produce the flapping stroke (two, primarily: m. pectoralis minor and m. pectoralis major), bats have as many as 17 muscles involved in the flight stroke (Hermanson and Altenbach, 1983; Neuweiler, 2000; Hedenstrom et al., 2009).  The membranous wings of bats are expected to have a steeper lift slope than the stiffer, less compliant wings of birds (Song et al., 2008).  This results from the passive cambering under aerodynamic load that occurs in a compliant wing: as lift force increases, the wing passively stretches and bows upwards, producing more camber, and thereby further increasing the lift coefficient and total lift.  While there are some advantages for a flying animal in having such a passive system, bats presumably must mediate this effect with the many small muscles (and fingers) in their wings – tensing the wings actively while under fluid load will mediate the amount of camber that develops.  This would be important to mediate drag and stall, though no empirical data currently exist to indicate exactly how bats respond to passive cambering.  The work by Song et al. (2008) also indicates that compliant, membrane wings achieve greater maximum lift coefficients than rigid wings, but data have yet to be collected demonstrating that this holds in vivo for bats and birds.  Compared to birds, the distal wing spar in bats is quite compliant (Swartz and Middleton, 2008).

Pterosaur Wings
The structure and efficiency of pterosaur wings is obviously not known in as much detail as those of birds or bats, for the simple reason that no living representatives of pterosaurs are available for study.  However, soft tissue preservation in pterosaurs does give some critical information about their wing morphology, and the overall shape and structure of the wing can be used (along with first principles from aerodynamics) to estimate efficiency and performance.

It is known from specimens preserving soft tissue impressions that pterosaur wings were soft tissue structures, apparently composed of skin, muscle, and stiffening fibers called actinofibrils, though the exact nature and structure of actinofibrils has been the topic of much debate (Wellnhofer 1987; Pennycuick 1988; Padian and Rayner 1993; Bennett 2000; Peters 2002; Tischlinger and Frey 2002).  Associated vasculature is also visible in some specimens, especially with UV illumination (Tischlinger and Frey, 2002).  Recent work on the holotype of Jeholopterus ningchengensis (IVPPV12705) seems to confirm that the actinofibrils were stiffening fibers, imbedded within the wing, with multiple layers (Kellner et al., 2009).  The actinofibrils were longer and more organized in the distal part of pterosaur wings than in the proximal portion of the wing, which may have implications for the compliance of the wing going from distal to more proximal sections.  The inboard portion of the wing (proximal to the elbow) is called the mesopatatgium, and was typified by a small number of actinofibrils with lower organization, which would have made this part of the wing more compliant than the outboard wing.

The outer portion of the wing, which was likely less compliant the mesopatagium, is termed the actinopatagium (Kellner et al., 2009).   Because pterosaurs had membrane wings, they could presumably generate high lift coefficients, but exactly how high depends on certain assumptions regarding their material properties and morphology (pteroid mobility and membrane shape being two of these factors).

Now, for some punchlines...
Based on the structural information above, we might expect the following regarding pterosaurs and birds:

- Pterosaurs would have a base advantage in terms of maneuverability and slow flight competency.

- Pterosaurs would also have had an advantage in terms of soaring capability and efficiency

- Pterosaurs would have been better suited to the evolution of large sizes (though this was affected more by differences in takeoff - see earlier posts about pterosaur launch).

- Birds will perform a bit better as mid-sized, broad-winged morphs (because they can use slotted wing tips and span reduction).

- Birds would have an advantage in steep climb-out after takeoff at small body sizes (because they can work with shorter wings and engage them earlier).  This might pre-dispose them to burst launch morphologies/ecologies.

Interestingly enough, the fossil record as we currently know it seems to back up all of these expectations.  For example, the only vertebrates that seem to have been adapted to dedicated sustained aerial hawking in the Mesozoic were the anurognathid pterosaurs.  Large soaring morphs in the Mesozoic were dominated by pterosaurs, also.  On the other hand, mid-sized arboreal forms in the Cretaceous were largely avian.

Pterosaur Ontogeny

Yes it's another reposted piece from the Musings (and with some good comments and discussion) but I could hardly not post it here, given the extreme relevance to pterosaurs in general, and a paper I have coming out shortly to be more specific. We have touched on these various issues before, but here's a crack at being much more explicit about the changes in form of pterosaurs as they age.

Not too long ago, Matt Wedel had an SV-POW! post that talked about ways of diagnosing an adult vs non-adult sauropod. Inspired by this and the fact that I have recently been playing around with issues of ontogeny in pterosaurs, I decided to write something similar for the non-avian Mesozoic fliers. If you have a pterosaur specimen in front of you, just how do you know if it’s an adult or not?

Obviously there are some general indicators that are pretty good for vertebrates as a whole that will get you quite a long way (even if this is a new species). Size is obviously rarely a great indicator, but if you have a pterodactyloid with a 20 cm wingspan then it’s going to be a juvenile, and likewise if you have a rhamphorhynchoid coming in close to the 2 m mark it’s very unlikely to be anything but a big adult. Young animals (and especially very young animals) tend to have big heads compared to their body and especially very big eyes compared to the size of the head. A bunch of fusions are absent in young pterosaurs that are present in adults too, just as you’d expect for most animals. The sutures between the centrum and neural arch of the vertebrae will be open in juveniles and closed in adults, and similarly the elements of the pelvis and sacrum, and the scapula and coracoid will be separate in young animals and fused together in adults.

Pterosaurs also have some characters of ontogenetic change that are rather more peculiar to them than vertebrates in general. Very young pterosaurs also tend to have a very grainy texture to the surfaces of their longbones, despite the fact that even embryonic pterosaurs have a pretty ossified set of bones (unlike many young animals). Smaller pterosaurs also tend to have various parts of the skeleton being less ossified and rather amorphous compared to those of adults. The tarsals are often not well ossified and can be missing (well don’t preserve) and if present may be very simple shapes. The carpals tend to look more ‘blobby’ and lack the detailed morphology seen in adults and will be separated into multiple elements whereas in adults the wrist will primarily be formed of just two massive elements (plus the pteroid). Finally, while obviously you would expect skulls to fuse up during ontogeny, pterosaurs do tend to take it one step further than most. Rather like birds, in adult pterosaurs the sutures all but disappear, or even go entirely, such that the skull looks like a single smooth piece of bone. Also as in some birds, bigger pterodactyloids have a notarium and this only fuses up and fully develops in adults. Similar to the point above about absolute size, the presence and development of some form of head crest is indicative, but not a great indicator of age. Yes a massive and elaborate crest in an animal is indicative that it’s an adult, but there could be a fairly well developed crest in an animal that is close to becoming and adult and of course there are taxa without crests and in at least once case it appears that females don’t have crests.

As in mammals, but unlike dinosaurs and birds, pterosaur also have epiphyses. The growing plates at the ends of the long bones physically separate the main shaft of the bone from the proximal and distal ends, so things like the femur can appear to be in three pieces. Obviously as growth slows towards maturity these epiphyses slowly disappear as they fuse into the single element that you would expect to see.

So in short, something that is small, with grainy textured bones, a big head, with big eyes, unossified tarsals, amorphous carpals, no crest, clear sutures in the skull, no notarium, and separated scapulocoracids, pelvis, epiphyses and neurocentral sutures is going to be a young juvenile. And the close these various features get to the opposite condition the closer the animal is likely to be to adulthood.

As ever with such things these are not absolutes, but merely guides. Good guides, certainly – you simply won’t see a notarium in a very young pterosaur, or open neurocentral arches in a big, old adult. However, in terms of determining more subtle difference in age it will be tricky – one animal may have fused up the notarium, but may have incompletely ossified tarsals and another could have the reverse. Although at least some characters do seem to have a bit of a pattern (the scapulocoracoid seems to fuse pretty early in most things) a general lack of numerous specimens of different ages makes it hard to do any more detailed analysis. Still, in terms of gross age (hatchling – young - adolescent - adult) even for a specimen of a previously unknown species with no obvious close relatives, it should be relatively easy to determine the approximate age of the animal.

The Beauty of Big

One rather obvious trait of pterosaurs, compared to other flying animals, is that they had a tendency to get rather large.  There has been much to do about how they could get so large (as most readers of this blog know, I and quite a few others now prefer the explanation that pterosaurs were quadrupedal launchers).  However, it's a bit trickier to tackle the problem of why some of them became so large. 

What might select for giant size in pterosaurs?  It's probably not something that can be answered definitively, but there are some plausible options.  One of them relates to the issue of long-range travel.  I talked a bit about this potential advantage here. The gist is this: being large makes long-distance travel more feasible for most animals, particularly flyers.  Some reasons this happens include:

1) Large flyers can carry more fuel.

2) Large flyers travel at higher speeds, on average.

3) Large flyers are less affected by adverse weather conditions.

4) Large flyers use less fuel per unit body mass, per unit time.

This means that, on average, a big flying animal can go longer between stops on long migrations, and gets to their destination more quickly, than a small flyer.  This might be particularly important for a flyer which feeds on resources that are patchy in their distribution.  This, in turn, might suggest (very tentatively) that animals like azhdarchids had a tendency to travel long distances between food sources.

Of course, there are a host of other advantages to being large, as well: big animals are harder for predators to kill, can eat larger prey, and can (in some cases) better defend young.  For egg-laying animals, large size often improves fecundity.  So there is no way to say for certain exactly why some pterosaurs grew quite large, but it does raise questions of general biological interest.

The Amazing Pterosaur Pelvis

There is a new paper out in Acta Palaeontologica Polonica on the anatomy and diversity of pterosaur pelvses by Hyder, Witton, and Martill.  It's open access, so check it out: http://app.pan.pl/article/item/app20111109.html

Here's the abstract:
Pterosaur pelvic girdles are complex structures that offer a wealth of phylogenetic and biomechanical information, but have been largely overlooked by pterosaur anatomists. Here, we review pterosaur pelvic morphology and find significant differences that correlate well with pterosaur clades identified in some phylogenetic analyses. We find that the length and orientation of the iliac processes, position of the acetabulum, extent of the ischiopubic plate and presence of supraneural fusion in adult individuals are taxonomically informative. Ontogenetic changes in pelvic morphology dictate that osteologically mature specimens are required to assess the development of many of these characteristics. We suggest that pelvic characters can readily be incorporated into pterosaur phylogenetic analyses and may assist in resolving the controversial interrelationships of this group. Distinctive pterosaur pelvic morphotypes suggest considerable differences in stance, locomotory kinematics and hindlimb functionality across the group.

Winglets

I did a quick post over at Aero Evo on winglets here.  The issue of winglet structures in pterosaurs came up and some followers here might find it interesting (see comments section).

Cheers!

It’s dumb, it’s awesome, it’s… Our lives with pterosaurs, part 2

If you’re wondering what’s going on here, or if you’re looking at the right blog, it’s probably because you haven’t read this yet. And yes, we are stooping this low.

 

Pterosaurs in the modern day! What would it be like if some pterosaurs survived the K/T extinction to coexist amongst our modern biota and in modern environments? Such are the questions we're attempting to answer here. Just to remind you, the only pterosaurs under direct scrutiny in these posts are azhdarchids and nyctosaurids as they seem to be the only pterosaur lineages that were present at the terminal Cretaceous. We spent a lot of the last post discussing how we may try to exploit pterosaurs for our own benefit, and in this concluding post we’re going to consider how we may succeed at coexisting with wild pterosaur populations. (Adjacent image: when stork-like animals go wrong)

NOTE: The Blogger upload system has been a real pig this evening, and formatting this post has been nothing short of a nightmare. Apologies in advance for any choppy bits of text or other issues. I have tried to correct errors as I go, but please let me know if I've missed any. 

Meeting the neighbours

Humanity would probably bump into wild pterosaurs fairly often. Azhdarchid pterosaurs, in particular, achieved very wide distributions in the Cretaceous, being absent only from Antarctica (Witton and Naish 2008; Ösi et al. 2011; see map, above, for the distribution of azhdarchid fossils. From my Ph.D. thesis). Azhdarchid fossils show very strong ties to terrestrial environments,either being preserved in continental freshwater deposits and, when they do occur in marine sediments, they tend to be components of mixed terrestrial/marine biotas (adjacent graph is a sexier version of the same data presented in Witton and Naish [2008] on this topic. I’ve not updated it with new data since then, but the statistics will not have changed significantly to my knowledge). Their distribution across the globe suggests they were versatile animals capable of living in different habitats and climates, and their palaeoenvironmental signature hints that they would preferentially frequent terrestrial settings. Modern azhdarchids, then, may be fairly familiar sights to us if they were around today.

We may even find that some single azhdarchid species were found all over the globe. Some of the recent findings on their flight ability are rather arresting, with the 10 m span giants seemingly capable of flight speeds exceeding 100 kph (62 mph; Witton and Habib 2010). Mike Habib's recent SVP talk suggests that they could remain aloft long enough to travel almost halfway round the world in one sitting (Habib 2010) and, to paraphrase him directly, (imagine this being said VERY LOUDLY for full effect. Those who know Mike will understand why), geographic boundaries would mean nothing to these guys. This may mean that the sort of provincialism we see in some modern fliers may not apply to these forms and, indeed, cautionary words on the implications of this have been said with regard to azhdarchid systematics.

We may not find ourselves quite so acquainted with nyctosaurids, however. Their fossils are generally rarer than those of azhdarchids and, to my knowledge, largely constrained the Americas. Their rarity is of particular interest because Nyctosaurus, perhaps the best known of all nyctosaurids, occurs in the Smoky Hill Formation of Kansas, a deposit that has also supplied over 1000 Pteranodon specimens since 1872. I’m not sure how many Nyctosaurus specimens there are around the world, but I get the impression that it may be dozens, not hundreds or thousands (please let me know otherwise if I’m wrong, though). Assuming that this does not reflect other sampling or preservational biases, it seems that nyctosaurids were simply rather rare animals. Their remains, unlike those of azhdarchids, are also found exclusively in deep marine deposits, suggesting they spent much of their time away from land. Nyctosaurid anatomy agrees with their lack of landlubber status: the loss of the three, small manual digits used in walking and embarrassingly small legs do not suggest proficient terrestrial abilities. By contrast, the development of ossified tendons in the forearms of some nyctosaurid specimens (Bennett 2003; Frey et al. 2006) suggests that they put tremendous, continuous strain on their wings, and the wings themselves are super-long and probably very glide-efficient. The impression one gets, then, is of highly volant creatures that probably spent almost their entire lives in the skies over seas and oceans, so perhaps only sailors and fishermen would regularly see them if they were alive today.

Garbage monsters

In developed countries where little or no primary habitats remains, our modern azhdarchids may spend much of their times in rural areas, as this is probably the closest approximation of their natural habitat, and would, perhaps, provide the largest amount of live prey. The feeding habits of azhdarchids have been controversial since they were identified in the 1970s, but, in what is probably the only thorough exploration of their feeding habits to date, Darren Naish and I concluded that they were most likely ‘terrestrial stalkers’, long-legged predators of relatively small animals sought out in sparsely vegetated settings (Witton and Naish 2008). This idea may not be unfamiliar to many of you: not only have Darren and I waxed lyrical about it repeatedly in various blogs and lectures, but it’s now been immortalised on on TV and even in excellent, excellent comic book format (you can also download the full paper for free). Accordingly, I won’t go into details here, but, for the uninitiated, the seemingly proficient terrestrial abilities and long jaws and neck of azhdarchids seem well suited for hunting small game on land and, often, poorly adapted for anything else. The bulk of modern azhdarchid diets may not be too dissimilar to their Mesozoic ancestors, as these ancient forms were likely to primarily dine on small reptiles, amphibians and mammals that would appear, superficially at least, not too different from their modern representatives. Of course, modern azhdarchid diets would lack a certain non-avian dinosaur flavour, and that would presumably be substituted by various mammal species.

Azhdarchid jaws are generalised enough that we cannot rule out some ocassional bouts of scavenging, and it would be silly to ignore the importance of carrion feeding to some modern azhdarchid analogous, the ‘giant’ storks. Some of these birds – particularly the larger Leptoptilos species (e.g. the adjutant and marabou storks) – frequently forage on carrion (Kahl 1987) and, because we humans are disgusting slobs who do not dispose of our garbage properly, they have expanded their taste for lousy food to leftovers on rubbish tips. Other, more familiar birds are also keen rubbish raiders: I’m sure we’ve all seen local crows and gulls riffling through bins or splitting open refuse sacs. I see no reason why azhdarchids would not develop the same behaviours, so we may find some of them colonising urban areas and living off our waste. Perhaps this would mean that some modern azhdarchid species would be fairly resistant to the current global species decline, as the route to evolutionary success nowadays seems to mostly revolve around living off our garbage (well, it is the only resource we’re not running out of). (Image, above, shows said exploitation of waste in action)

If wild azhdarchids did take foot in urban settings, encounters with them may be a little daunting for human residents. As we discussed in the last post, pterosaurs seem to have increased their average body size over time, so later forms were much larger than the earlier. Perhaps we’d feel fairly confident stopping smaller (2.5 m span) animals from spreading rubbish all over our driveways, but would we feel the same about 4, 7 or 10 m span animals? Perhaps not. Plus, did I mention that these pterosaurs may have been gregarious? Several azhdarchid localities have yielded associated azhdarchid skeletons (Lawson 1975; Cai and Wei 1994) or very abundant azhdarchid remains (Nessov 1984; Ösi et al. 2005), suggesting that they were at least tolerant of each other, or perhaps even hanging around in little groups. All told, in this hypothetical world of pterosaurs, we’d probably need to seriously rethink our philosophy on garbage disposal. Probably best to keep the cat in, too.

They can eat my trash, so long as they don’t eat me

Speaking of modern pterosaur diets, an enormous elephant in the room needs to be acknowledged: would we be on the menu? This is a legitimate question, and not because we’re used to Tinseltown pterosaurs having a taste for human meat. Some azhdarchids were so enormous that they could consume people-sized prey (by which, I mean small adults, not just children). We don’t have particularly extensive fossils of giant azhdarchids to test this with, but we do have a key component for answering this question: a giant pterosaur skull fragment comprising the jaw joint and some bones from the roof of the mouth (shown on the left, in ventral view, in the image below). This belongs to the 10 m span Hatzegopteryx, one of the largest azhdarchids known, and is notable for its unusually robust construction of stout bony struts and enormous jaw condyles. By doubling its width we can attain minimum estimate of the complete jaw width, revealing a staggering maw 500 mm across (Buffetaut et al. 2002, 2003). (Image, below, shows the mirrored Hatzegopteryx jaw skull element. The ventral braincase and posterior jaw region of Thalassodromeus is shown for comparison and to scale. Thalassodromeus, by the way, has a jaw of 160 mm width and 700 - 800 mm long. Hatzegopteryx was mucking huge).

We should remind ourselves at this point that we’re a) talking about the minimum width here, so there's possibly room for a little more expansion; and b) these are, so far as we can tell, animals capable of flight, and yet had skull widths that many large dinosaurs would be jealous of. As with many pterosaurs, the asymmetrical nature of the jaw condyle would deflect the lower jaw laterally when opened so that much of the 500 mm jaw width could be used for swallowing food. The posterior palatal region is also highly vaulted, so there is additional swallowing space in the dorsal region oral cavity, too. Combine this with the likelihood of a large gulf between the mandibular rami occupied by distensible gular pouch (known from several exceptionally-preserved pterosaur specimens), and it seems more than likely that Hatzegopteryx could fit a person into its throat.

After that, of course, you’d need to be moved down the long neck, a length up to 3 m if we assume that the giants had necks of comparable proportions to those of smaller azhdarchids. Unfortunately for us, we have good evidence that pterosaur throat tissues were highly elastic and capable of encompassing large prey, so we may slip through an azhdarchid oesophagus without issue. The preservation of a recently-devoured fish in a complete juvenile Rhamphorhynchus specimen reveals just how large some pterosaur prey items were, and how stretchy their throats must have been to accommodate it (see detail of the trunk region of this specimen, below. After Wellnhofer 1975). The specimen in question was preserved in the process of digesting a fish that – as preserved – occupies 60 per cent of its trunk length, but may have been even larger as the anterior end had already been partially digested (Wellnhofer 1975). Pterosaurs, then, may have had small bodies, but they weren't afraid of packing their meals in. Our previous discussions on how giant pterosaurs could support our weight in flight have obvious connotations here, too: if one could support our weight externally, there seems little reason to suggest they couldn’t internally. We may fill their bellies, but we wouldn't impede their locomotion in doing so.

The outlook isn’t looking promising for us, then. Larger members of the populace may be a bit too massive to comfortably digest, but leaner or smaller folks may well be at risk. In any case, giant azhdarchids would be best avoided. If we did encounter one, would our chances of being eaten be high? Perhaps it would depend on context of engagement. On open ground, the 2.5 m long limbs and powerful muscles of giant azhdarchids would almost certainly chase us down and, hey, let’s not forget: they can fly. It's hard to outrun an animal that can fly fast enough to get a speeding ticket on most roads. We may be safe if we could get to cover or a cluttered setting, as the giant azhdarchid bauplan is hardly suited to moving through narrow confines or probing crevices. Without that, though, I don’t fancy our chances. Azhdarchids of this sort may be quite difficult to deal with too, short of simply killing them. Troublesome bears or cats can be moved far enough away from populous areas that they won’t bother people again, but we’d be hard pressed to stop relocated azhdarchids from simply flying back to wherever we caught them. The more I think about it, the more it seems that large azhdarchids would actually be quite a dilemma for us, and one that would probably see most of them being shot. All told, maybe it’s best for us all that they're extinct.

On that bombshell, then, I think that’s enough of this craziness for the time being. Hopefully, someone, somewhere, will have taken something useful from these posts and, if nothing else, we finally have a picture of a cowboy quad-launching a giant pterosaur. With that, I think my work here, and perhaps the respectable portion of my career, is finished. 

References

• Bennett, S. C. 2003b.  New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Palaeontologische Zeitschrift, 77, 61-75.
• 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.
• Buffetaut, E., Grigorescu, D. and Csiki, Z. 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 91-104.
• Cai, Z. and Wei, F. 1994. Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China. Vertebrata PalAsiatica, 32, 181-194.
• Frey, E., Buchy, M. C., Stinnesbeck, W., González, A. G. and Stefano, A. 2006. Muzquizopteryx coahuilensis, n.g., n. sp., a nyctosaurid pterosaur with soft tissue preservation from the Coniacian (Late Cretaceous) of northeast Mexico (Coahuila). Oryctos, 6, 19-40.
• Habib, M. B. 2010. 10,000 miles: maximum range and soaring efficiency of azhdarchid pterosaurs. Journal of Paleontology, 30, 99A-100A.
• Kahl, M. P. 1987. An overview of the storks of the world. Colonial Waterbirds, 10, 131-134.
• Lawson, D. A. 1975. Pterosaur from the Latest Cretaceous of West Texas: discovery of the largest flying creature. Science, 185, 947-948.
• Nessov, L. A. 1984. Pterosaurs and birds of the Late Cretaceous of Central Asia. Paläontologische Zeitschrift, 1, 47-57.
• Ősi, A., Weishampel, D. B. and Jianu, C. M. 2005. First evidence of azhdarchid pterosaurs from the Late Cretaceous of Hungary. Acta Palaeontologica Polonica, 50, 777-787.
• Ősi, A.,Buffetaut, E. and Prondvai, E. 2011. New pterosaurian remains from the Late Cretaceous (Santonian) of Hungary (Iharkút, Csehbánya Formation). Cretaceous Research, 32, 4556-463.
• Wellnhofer, P. 1975. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Palaeontographica A, 148, 1-33, 132-186, 149, 1-30.
• 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.
• Witton, M. P. and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE, 3, e2271.