Posted by: pterofd | January 5, 2010

Hairy wings, silent flight?

The anurognathids are a weird bunch no doubt. A very short tail for a non-pterodactyloid pterosaur, multiple layers of actinofibrils (Kellner et al. 2009), short skull / large orbit (Bennett 2007) and a hairy body (Wang et al. 2002) to name a few of their more obvious structures. I could also mention the three phalanges of the fourth digit but this interpretation appears to have been challenged lately.

During our recent visit to Beijing a couple of my colleagues were fortunate to get to spend a week pouring over the superb specimen of Jeholopterus ningchengensis (IVPP V12705) for some research on membrane composition and structure. The recurring point that cropped up in a number of conversations was that however well preserved the specimen is, anurognathids are just such strange animals that it is potentially dangerous to regard them as being typical for anything other than anurognathids i.e. can we really apply what we know about anurognathid membrane structure / composition to other pterosaurs?

Overview of Jeholopterus (from Kellner et al. 2009).

This will certainly be an interesting question the group will have to consider in the immediate future but in this post I wanted to quickly draw attention to a part of the wing that often gets overlooked…..the hair-like structures along the trailing edge. Kellner et al. 2009 published a small photograph of this but I’m not aware of much in the literature that covers its potential functions (although I’m without a copy of “Deep Time” so apologies if it has been covered before).

Combs along the trailing edge of the wing (or turbine when we enter the realm of man-made machines) are known to reduce the noise produced by the animal during flight by collapsing the vortex shed off the wing. There is quite a bit of literature on this subject but its function in biological flight could warrant further attention. Owls are certainly the most famous example where these structures are used to reduce the noise produced by the wings at frequencies above 2 kHz – i.e. within the hearing range used by both the owl and its prey (Bachmann et al. 2007). As a result owls are masters of silent flight which allows them to approach their prey to a much greater degree than would otherwise be possible.

A) LE of owl primary 10; B) TE of owl primary 10; C) LE of pigeon primary 10; D) TE of pigeon primary 10; E) TE combs of Jeholopterus. Adapted from Bachmann et al. 2007. LE = leading edge; TE = trailing edge.

The examples above show just how similar the trailing edge structures of the wing in Jeholopterus (E) are when compared to those of an owl (A, B) and the obvious differences they have with those of a noisy flier, in this case a pigeon (C, D). While I am in no way trying to compare the functionality of a feather with that of the pterosaur membrane, the presence of trailing edge structures would almost certainly function in a similar way to other noise reduction structures.

Jeholopterus shares a couple of similarities with that of the barn owl: they both use a slow flight while hunting and both were active during times of darkness or at least periods of low light,  but there the similarities end. Jeholopterus was almost certainly an insectivore rather than hunting small vertebrates and so it is not immediately apparent how effective a noise reducing structure like this would have been (hearing range of insects anyone?). So could Jeholopterus have used its trailing edge structures to break down the vortex shed off its wing? If so it would have flapped and glided over the darkening Mesozoic landscape using a combination of slow flight speed, high maneouverability and specialised fibres to reduce the noise frequency of the wings, snapping up insects as it went.  Certainly some food for thought regardless.

References:

Bachmann, T., Klän, S., Baumgartner, W., Klaas, M., Schröder, W. and Wagner, H. 2007. Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia. Frontiers in Zoology 4, doi:10.1186/1742-9994-4-23.

Bennett, S.C. 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81: 376-398.

Kellner, A.W.A., Wang, X., Tischlinger, H., Campos, D.A., Hone, D.W.E. and Meng, X. 2009. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proc. Roy. Soc. B. doi:10.1098/rspb.2009.0846.

Wang, X., Zhou, Z., Zhang, F., and Xu, X. 2002. A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and ‘hairs’ from Inner Mongolia, northeast China. Chinese Science Bulletin 47: 226 – 232.

Posted by: pterofd | January 4, 2010

New Year, Old Problems

Well the holidays are over and its a brand new year, so its back to work for the research group as a whole. While our lastest trip to chilly Beijing wasn’t quite as sucessful as we might have wished for, we got a nice look at the excellent Jeholopterus and Darwinopterus, amongst others, and gave us all a good excuse to sit down and talk pterosaurs for a couple of weeks within too many interuptions. Many thanks to my advisor David Hone for putting up with us for a couple of weeks (Hope the new office is working out nicely).

So with the dawn of 2010 there are too many aspects of pterosaur flight that would like to cover but for the immediate future i will have to be content with working on getting our initial results on the fixed wing models into print and  unveiling our “next generation” models – complete with mobile joints. The fomer of these two tasks is just waiting on one or two body simulations to look into the higher than expected drag  coefficients we observed, but will be polished off before the end of the month and will represent the end point for the first experimental phase of the project. The latter models will take the simulations more than a little closer to representing an actual pterosaur by allowing us to alter the wing shape/sweep, tension and camber – for those interested in which animals we are planning for use it will be a combination of Coloborhynchus (based off the specimen SMNK PAL 1133) and an azhdarchoid pterosaur, most likely Sinopterus. This should give us the best of the high-aspect ratio and low-aspect ratio configurations that pterosaurs used. Of course such a model would be all for naught without a “membrane wing” that can: a) change shape as the the fore and hind limb joints are altered and b) still retain enough tension to function as a reasonable lift producing wing.

Simulating the pterosaur membrane is certainly no simple task however this is the current fixation of project workers Steffie Moeninger (SMNK) and Julian Sartori from the ITV Denkendorf who are working towards a prototype membrane. They themselves have far grander plans for membrane development than the simple wing model  necessary for the next phase of the project but i’ll see if a can’t obtain some photographs of their textile experiments and pursude at them to elaborate a bit of their indivudal goals within the scope of the project. Needless to say the development of pterosaur membranes for industrial/commercial use is in itself an interesting field.

So for the immediate future expect to have more forthcoming posts on membrane simulation, jointed pterosaurs and finally some hard experimental data for people to sink their teeth into. Of course there are any number of other aspects i want to cover, not least the role of the uropatagium and tail during flight along with an updated bit on pterosaur crests which will be a bit more substancial than my own previous attempt (Elgin et al. 2008). Of course there is also Colin Palmer’s latest work on the biomechanics of the pteroid and propatagium (Palmer and Dyke 2009) which i hope to say a few words about.

So a happy new year to all of our readers and stay tuned for further posts.

PS. For all those wondering where on earth the great Quetzalcoatlus is and how we could have passed it over so far – we are in the process of getting a CFD simulation sorted out in collaberation with the University of Karlsruhe which will center around this taxon.

References:

Elgin, R.A., Grau, C.A., Palmer, C., Hone, D.W.E., Benton, M.J. 2008. Aerodynamic charaters of the cranial crest in Pteranodon. Zitteliana B28, 167-174.

Palmer, C. and Dyke, G.J. 2009. Biomechanics of the unique pterosaur pteroid. Proc. Roy. Soc. B. doi:10.1098/rspb.2009.1899, 1-8.

For all those wanting to know where the great Quetzalcoatlus is in all of these experiments we are hoping to get a CFD analysis completed in a couple of months courtacy of the University of Karlsruhe (or KIT as i suppose it should now more correctly be called).

Posted by: pterofd | November 30, 2009

Wind tunnel vs General public

The “day of the open door,” or Tag der Offenen Tür, is an important event for the SMNK and is one of the main times in the year when the general public get to have a look at what actually goes on in a museum behind closed doors.

For us this was an oppertunity to give the public a short tour around the wind tunnel complex at the KIT (formally University of Karlsruhe) and explain in detail exactly what we are trying to do and why shoving model pterosaurs into an air flow was actually important.

Torsten giving an explanation on how the wind tunnel is set up and actually works.

This involved a series of talks about how the tunnel was set up and how it actually worked, as well as discussing how the models were built and what we hoped to achieve next as part of the project.

 

Naturally its difficult to imagine the forces acting on the models when they are fixed in the wind tunnel and so for the last portion of the tour we let a number of willing volunteers take a model and walk into the working section with the air flow on. The results of this were quite amusing but i think that by the end of this everyone had an appreciation of what we were trying to measure and, if nothing else, had a fun time struggling to keep their footing (see below).

Some members of the public experience what it was like to be a pterosaur in a 10ms head wind.

With the largest wing span of any of our models, Coloborhynchus proved a popular choice although a little more work was required to stop it carrying the younger members of the group downstream.

All in all the tour of the wind tunnel facilities was quite sucessful and everyone enjoyed themselves – well worth the long walk in the rain to see.

Events such as these are becoming increasingly important to all project workers at the SMNK as we try to make as many of our research programs visible to the general public and educate people as to what actually happens at their local museum. For many this is quite an eye opening experience as they have little idea that modern museums participate in activities beyond guiding tours of school children around rows of stuffed animals.

The Tag der Offenen Tür thus represents an important event were we as academics are given the possibility to engage with the public and explain and discuss what modern natural science is about. Scientists shouldn’t confine themselves to their “ivory towers” and interacting with the public in this way in as beneficial to us as academics as it it to those who give up some of their weekend to see what we have to say.

 

Posted by: pterofd | November 5, 2009

Could (large) pterosaurs really fly?

Perhaps it might seem a little strange that the first real post of a research group whose sole purpose is to study flight in pterosaurs is asking the question “could pterosaurs actually fly?” There is, however, a little logic to this when some of the more recent headlines about pterosaurs in popular science media read “Giant Pterosaurs Couldn’t Fly, Study Suggests” (National Geographic) and “Were pterosaurs too big to fly?” (New Scientist). Thus it seems this is a good pace to start.

As with any media coverage it is always advisable to get to the source of the headline and the study in question was that of Professor Katsufumi Sato and his extensive list of co-authors, published in the online journal PLoS one entitled “Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs.” For those not familiar with this article their research centres around attaching accelerometers on to five procellariiform species (encompassing shearwaters, petrals and albatross) and recorded the frequency of wing flaps during take off and brief episodes of flapping flight between periods of gliding. This is itself is a novel idea and the paper should be rightly credited with being one of the few examples where data was collected from wild animals in the field, a rather formidable task and one that, without some technological advancements, would be quite impossible. Higher frequencies were associated with take off while lower frequencies were recorded when the animals were actually airborne. To quote from their abstract “In these species, high and low flapping frequencies were found to scale with body mass (mass^-0.30 and mass^-0.18) in a manner similar to the predictions from biomechanical flight models (mass^-1/3 and mass^-1/6).”

So far so good, but were Sato et al. really trying to argue that giant pterosaurs couldn’t fly? By plotting the regression lines of both high and low flapping frequencies against body mass an intersection point is found (as should be clearly illustrated in the figure below) corresponding to the point at which an albatross-like animal would lack the power margin to keep itself airborne if not supported by favourable wind conditions. Any animals heavier than this would simply be unable to flap fast enough to increase their flight speed. The magic number, the point of intersection between the two lines, was 41kg (402.21N), which corresponded to a wing span of 5.1m by their estimates. Thus, their conclusion goes that pterosaurs either larger or heavier than this would be unable to remain airborne in the absence of either favourable wind conditions or thermals.

Wing beat frequencies

High wing beat frequencies (red) associated with take off and lower wing beat frequencies (blue) during flight (figure from Sato et al 2009).

While this data here is certainly useful for putting an upper limit on flapping flight in birds (or more specifically procellariiforms), particularly as previous values have been estimates, e.g. 12 – 15 kg (Pennycuick 1986), we run into a number of problems when applying this data to pterosaurs. Firstly the giant Quetzalcoatlus was not the only pterosaur to exceed this wing span or weight, in fact many “medium-large” taxa including Pteranodon, Anhanguera and Coloborhynchus, to name a few, also grew to wing spans of up to 5m and, based on fossil material that I have seen, some almost certainly got much larger than this.  This point has also been noted before in the figures of Templin and Chatterjee (2004) where larger pterosaurs would have certainly occupy a range in excess of the “mass limit for continuous level flight.”

Secondly while Quetzalcoatlus is the iconic “giant” pterosaur its bauplan differs remarkably from that of the albatross (aspect ratio of ~8 versus 19, wing load of 224N/m^2 versus 155N/m^2) and so a comparison between the two is difficult not least because Quetzalcoatlus has been suggested to thermal soar (rather than dynamically soar), a point Sato et al acknowledge. Other larger pterosaurs, however, were all “albatross-like” and found in marine settings leading to the suggestion that they would have had to inhabit areas of special environmental conditions in order to fly (e.g. the roaring forties of today). Their global distribution in the fossil record and finds on shorelines or sheltered settings rather than exposed on bare islands like albatross today suggest that this was not the case.

Perhaps the most obviously point to consider (and I’ve saved it until last) is that pterosaurs are not birds, even the ones with wing profiles that resemble them. By this I mean that pterosaur muscle configuration, physiology, air-sac development and wing structure, to name a few, are all very different to birds. While all flying animals are constrained by a number of universal factors (e.g. drag reduction, lighter bodies) differences in physiology and structure radically alter the way in which animals fly. Birds and bats for example do not share a maximum or minimum size for flapping flight and in turn insects are radically different to both of these again. Consider that the size range in bats is between 1.9g and 1.5kg while in birds it is much larger 1.5g – 15kg (Altringham 2001). As bats increase in size the mechanical power need for flight also increases along with wing inertia and thus they sacrifice both agility and manoeuvrability which in turn influences what the animal can catch. Bats also appear to link breathing and echolocation pulse emission to the wing beat cycle and it is possible that at a certain size (as wing beat frequency decreases) this period may become too infrequent for effective prey capture (see Altringham 2001). Kilpatrick (1994) also reported on the structural differences between birds and bats where the breaking stress of their humeri was found to be 125MPa and 75MPa respectively. These are just a couple of the many examples that can be readily found and differences in structure and function explain why we do not find albatross-sized bats, Pteranodon-sized birds (Argentavis magnificens aside) or bird-sized insects outside the Carboniferous when environmental conditions were significantly different from today.

Without an in depth comparison of birds and pterosaurs to account for their differences in morphology, physiology and structure it is highly problematic to suggest that pterosaurs above a wing span of 5m simply couldn’t fly. All large pterosaurs are fully equipped for flight as their global distribution attests to and even in the more terrestrial taxa there is no indication that the wings were becoming redundant. It seems appears unlikely that these forms were restricted to areas of very specific environmental conditions (with the possible exception of really big pterosaur that must have required thermals).

Thus in summary while I disagree with the conclusions of Sato et al, generally applying data from a number of procellariiform birds directly to larger pterosaurs, it is nice to finally have some experimental data on the upper range of size of certain birds. The take home message from this is, of course, that if this data is not generally applicable to pterosaurs then it raises the interesting point that whatever pterosaurs did to attain these large sizes, they did it very different to albatross-like birds.

Altringham, J.D. 2001. Flightt.. In: Bats, biology and behaviour. Altringham, J.D. (eds). Oxford University Press, 262pp.

Chatterjee, S. and Templin, J., 2004. Posture, locomotion and paleoecology of pterosaurs. Geological Society of America Special Publication: 376, 1-64.

Kilpatrick, S.J. 1994. Scale effects on the stresses and safety factors in the wing bones of birds and bats. Journal of Experimental Biology: 190, 195-215.

Pennycuick, C.J. 1986. Mechanical constraints on the evolution of flight. Memoirs of the California Academy of Sciences: 8, 83-98.

Sato, K., Sakamoto, K.Q., Watanuki, Y., Takahashi, A., Katsumata, N., Bost, C-A., Weimerskirch, H. 2009. Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs. PLoS One: 4, 1-6.

Posted by: pterofd | November 4, 2009

Hello World

Welcome to the blogspot of the Pterosaur Flight Dynamics Group, a collaboration of various institutions including: the State Museum of Natural History Karlsruhe (SMNK), the University of Karlsuhe and the DLR, Göttingen. As its name suggests, the group focuses primarily on the flight characteristics of the world’s first true vertebrate fliers, the pterosaurs.

It is difficult to remember a time when pterosaurs were quite as popular a study group as they are now, a fortuitous fact given that after over 200 years of scientific study there are still many aspects of their life that remain poorly understood. These range from relatively simple factors such as diet and feeding preferences to more complex issues such as physiology and development. To address the growing interest in pterosaurs from both academic workers and the general public http://www.pterosaur.net was launched earlier this year to educate and inform interested parties about what exactly pterosaurs are as well as discuss several aspects of their biology. While not exclusively dealing with pterosaurs both http://archosaurmusings.wordpress.com and Tetrapod Zoology (http://scienceblogs.com/tetrapodzoology/) occasionally cover some interesting issues.

The purpose of this site is to provide a rather informal outlet for the research group and of course deals almost exclusively with how pterosaurs flew and activities relating to flight. Since the creation of the group at the 6th annual meeting of the European Association of Vertebrate Palaeontology last year there have been a number of interesting developments and even more hours spend sending models, and occasionally group members, down a wind tunnel. Thus this spot will also provide a forum for some interesting results that have come out of the project so far. In summary we hope this site serves as a good resource for anyone interested in pterosaur flight and provides a more detailed look at one of the more intriguing aspects of pterosaur biology.

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