Sunday, July 15, 2012

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, 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, 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.

Friday, July 6, 2012

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!)


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.

Thursday, July 5, 2012

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.

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.



Wednesday, July 4, 2012

Pterosaur.Net wades in against

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' The title of the piece, "Why the world has to ignore" 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: 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, 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 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 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 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. 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 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...

  • 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.

Monday, July 2, 2012

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.