Pterosaur Basics

As part of my ‘science basics’ project on here (assuming it gets further than just a few posts) I thought it worthwhile trying to dial back some of my natural tendency to pitch this blog at a technical level, and try and make it a bit more accessible in general. In other words rather than just banging on about anurognathids, pterosaurs cranial crests and origins, it might be more appropriate to give a very brief overview of pterosaurs in general for anyone not that intimately familiar with them. I do have a bigger project on this very area slowly coming to the boil, but it never hurts to have more information out there, and it gives me an opportunity to do my own summary.

Obviously no matter how simple and straightforward I try and make this, some technical terms and complexities are going to have to be introduced, but hopefully this will be simple enough for almost anyone to be able to follow – we shall see. This is about as concise and simple as I can make it and really is designed to just cover the basics of evolution, ecology, morphology, and more in just a thousand or so words…

Pterosaurs are extinct flying reptiles. This is a pretty good start and covers quite a lot of ground already that I have not bothered with before. They lived worldwide in all kinds of environments and ranged from 35 cm to 13 m in wingspan. They existed from about 225 to 65 million years ago and thus ran alongside the dinosaurs pretty much toe to toe for their entire existence, dying out in the great extinction at the end of the Cretaceous. Although they first appeared in the Triassic period, their origins might extend beyond that by some margin, but fossils of this time are rare, so it is hard to say.

Pterosaur fossils are rare (and the further you go back in time the more rare they become) and even more so than dinosaurs or even birds as their bones were hollow to reduce their weight. This makes them unsuitable for fossilisation and thus rarer than many of their contemporary relatives. Even so, we have thousands of specimens representing around 100 species (though this is still about 1/10th of the dinosaur fossil record). However many pterosaur fossils are from exceptionally well preserved fossil beds and thus are known with skin, beaks, claws, wings and other soft tissues preserved, and not just bones.

Pterosaurs are not dinosaurs (or birds for that matter), but close relatives of them. Their exact origins are still uncertain as pterosaurs are very advanced animals having specialised for flight and thus look quite different to their nearest relatives, making an exact comparison of anatomy very hard. They are certainly reptiles though, although you might not know that to look at a living one.

Pterosaurs could fly. And fly properly (powered flight) not just gliding or soaring, but actively gain height when they wanted to on their own power and take off from the ground. To do this they had a large wing membrane stretched from an elongate finger on their hand that connected to their body. Accessory membranes were present in the crux of the arm and between the legs. Some also had a long tail with a small ‘tail vane’ flap on the end which may have also helped with steering.

There are two major groups of pterosaurs – a scattering of early forms called ‘rhamphorhyncoids’ (the use of ‘’ is a taxonomic distinction unimportant here, but technically correct) and the more derived group the pterodactyloids, with a number of families in each group. ‘Rhamphorhynocids’ were generally small, had relatively broad wings, short necks, short and robust skulls, a large rear wing membrane, were poor on the ground, and had (with one exception), long tails. Pterodactyloids were generally the reverse – big, with, narrow wings, long necks, long skulls (often with no teeth), a smaller rear wing, were good on the ground, and had short tails. Crests of bone and skin were present in many taxa in both groups, though in general they are bigger and more elaborate in the pterodactyloids. While they overlapped in time and space, the pterodactyloids slowly took over as the ‘rhamphorhyncoids’ died out in the middle of their reign.

In the air, pterosaurs were adept fliers and not clumsy gliders as one thought. The shapes of their skulls tell us about their brains and these are in some ways similar to other active fliers – birds and bats. Their wings were complex structures with many specialised layers of tissue that would have put them under the animal’s control and allowed them to perform well in the air. The additional membranes (especially the front one) controlled by a special bone called the pteroid would have helped with steering.

On the ground the ‘rhamphorhyncoids’ were probably pretty poor. Their large rear membrane would have shackled their hindlegs together making walking difficult, and the shape of their hips and upper legs meant that could only really sprawl and not walk upright. Combining this information with the long claws on their feet and we can infer that they were probably far happier in the trees or on rock faces when not on the wing. The pterodactyloids had no such problems, as can be seen by their extensive fossil record of footprints. They had split their rear membrane in two freeing the legs which were brought under the body to allow them to walk far more effectively than their predecessors and helped them diversify to exploit new environments and foods.

There is unsurprisingly quite a bit of diversity in pterosaur morphology and ecology. There are great differences in size, their teeth and beaks, skull size and shape, neck length, wingspan and wingshape, leg length, foot size and more. This allows different animals to exploit different foods and environments from small woodland forms that caught insects in flight with snapping jaws, to flamingo-like filter feeders with thousands of teeth that live on lakes, blunt toothed clam crackers that patrolled coastlines, and huge tooth-less marine forms that hunted fish far out to sea. Soft tissue preserved in some fossils can tell us about beaks, wings, and more and most importantly pterosaurs were covered in a sort of reptilian ‘hair’ that made them furry.

At least some pterosaurs lived in large flocks and perhaps most did. At breeding times, some might have signalled their importance with their elaborate head crests or mating competitions in order to choose their mates. Eggs were probably laid a few at a time and buried in nests (we have three fossil eggs, each with a baby pterosaur inside). Growth was rapid and they probably reached adulthood in just a few years, even those that grew to prodigious sizes. The biggest pterosaurs were as much as 13 m across and weighed in at over 250 kg making them the biggest flying animals of all time.

The age of the pterosaurs came to an end at the same time as the dinosaurs, and presumably the same series of events that affected their cousins were ultimately the cause of their demise. Pterosaurs were though the first vertebrate to achieve powered flight, they lasted for 150 million years and conquered every continent and habitat, not to mention producing species way beyond those of birds in terms of size. They were not ugly, scaled reptiles, poor gliders, simple animals that were out competed with birds (they survived a good 100 million years alongside their distant feathered relations), but fast skilful fliers, with a huge range of species, that were a diverse and important part of Mesozoic ecology for tens of millions of years.

Well, that’s it. I doubt this is of much use to any of my (current) regular readers, and yes there is much that has been omitted, streamlined, glossed over, telescoped, and compressed to a fraction of what it requires at even the most basic level. Things like the pteroid, the notarium, the detailed structure of the wing, air sacs, webbed feet, eggs and more barely even registered if they were mentioned at all. I consider Dave Unwin’s recent pterosaur book a great primer and that clocks in at 300 odd pages, with a hundred or so figures, so this was never going to be an in depth look at the last 250 years of research. Hopefully it will serve as a decent primer for anyone unfamiliar with pterosaurs though and hopefully will still be up to date a year or so from now.

24 Responses to “Pterosaur Basics”

  1. 1 Oliver 21/07/2008 at 11:06 pm

    Thanks for the overview – this regular reader certainly appreciates it (although I like the other stuff too). Keep the mix going…


  2. 2 Will Baird 22/07/2008 at 12:33 am

    I may be mistaken, but wasn’t there a dearth of small form pterosaurs in the late cretaceous?

  3. 3 Nathan Myers 22/07/2008 at 5:22 pm

    Will: Hoarding will not be tolerated!

    A very helpful overview. In lieu of pictures, links might serve, e.g. (If I might be allowed to quibble, I would rather see ramphorhynchus’s tail described as useful for stabilization than for steering. Aeronautically, it doesn’t seem very helpful in steering, but stability is always of grave concern to a flyer.)

  4. 4 David Hone 22/07/2008 at 7:46 pm

    Will, in general that is true, though there are a few taxa that are lats say medium sized (around 4m) that were knocking around in the Late Cretaceous, but i general over time they got bigger.

    Nathan, I deliberately eschewed pictures to see if I *could* write a decent description this short and without them. And as for the tail, no you can’t quibble, ;-) we went over all of this before, and the function and orientation of the tail is still not understood and the term ‘stabilisation’ is a loaded one, whereas the more general ‘steering’ is not, which is why I used it.

  5. 5 Nathan Myers 25/07/2008 at 10:43 am

    On any airframe (pterosaurs included) a rudder-like structure is not useful for steering, as in a boat. It is useful to match the orientation (“yaw”) of the airframe to the direction of flight. Without, the airframe tends to “slip” or “skid”. In the absence of any sort of capacity to alter wing geometry (as in a toy, or damaged, airplane), twitching a rudder can initiate a wing tilt, and thus a turn, but we are certain that pterosaurs were not so limited.

    Use as an active rudder would require extra musculature. Without, a tail vane still helps to minimize slip and skid in the same way that the tail vane on a farm windmill keeps the rotor pointed into the wind. With or without such musculature, its role would be stabilization; it could do a better job with. Either way it would be useless for “steering”, which can only sensibly refer to changing the direction of flight.

    Given better control systems, as in later pterosaurs and modern birds, the vertical surface becomes an unnecessary source of extra drag, and is abandoned.

    I’m sorry to bang on about this, but it’s the aeronautical equivalent of placing pterosaurs in Dinosauria.

  6. 6 David Hone 25/07/2008 at 8:16 pm

    Well not according to the aeronautical engineers I know. One, (who incidentally is a Professor of rudder theory and used to design tail planes for fighters in the UK) tells me that it would work fine. In fact when I first spoke to him about pterosaurs for our flight research, he pulled out a design of a tailplane for a stealth bomber he had created for the British MOD which matched that of a juvenile rhamphorhynchus (it was a diamond shape on a long spar). He was annoyed that he had been beaten to the punch by 150 million years.

    You can argue if you want and sorry to be blunt, I’ll take his word (and that of a number of his and my colleagues) over yours. These things can steer.

    Oh and as for the dinosaur / pterosaur comment, I diasgree there too. As I wrote above, ‘steering’ encompasses ‘stabilisation’, but not vice versa. So it more be more correct to say that I am calling them archosaurs not pterosaurs. Both are right but one is more specific.

  7. 7 Nathan Myers 27/07/2008 at 5:34 pm

    Dave, I think you misunderstood your aeronautics professor friend. There is no question but that such a tailplane could be very useful in flight. What it was useful _for_, though, can only in the loosest possible sense be called “steering”. Any control surface (or, indeed, anything with area) may apply “steering forces”, causing rotation about any central axis, but one mustn’t confuse that with the conventional definition of steering, which is to make the vehicle or animal change direction.

    The mis-terminology might be harmless around here, just as in some contexts one may usefully describe Hatzegopteryx as a dinosaur. It’s not correct, but to many people it provides just the right amount and quality of information.

    Again, I’m sorry to belabor the point. It’s just that I thought that you preferred to avoid that sort of imprecision. If you thinK “stabilizer” is too limiting as a description, you may refer to its role as a “flight control surface” without violence to strict correctness.

  8. 8 David Hone 27/07/2008 at 10:35 pm

    I don’t think I did misunderstand him. And I don’t think I am wrong. I fail to see how a vertical rudder, (when used correctly), could not apply a ‘steering force’ that could cause and active change in direction. That is what rudders do.

    Furthermore as I have already stated repeatedly, we still do not know the true orientation of the rudder, much about its detailed structure, or how it might have been used. Certainly no areodynamic work has been done explicitly on the tail to my knowledge. We do not know exactly (or even generally) what it could and could not do. Therefore I am not going to use a loaded term like ‘stabilisation’ when I can use a general and non-specific one like ‘steering’, which is what I did.

  9. 9 Nathan Myers 29/07/2008 at 9:45 am

    Now I’m certain you misunderstood him.

    Ask any pilot what happens if you just step on the rudder pedal. They will tell you it puts the plane into a “skid”, in which the central axis of the plane does not line up with the direction of motion. The main effect is radically increased drag, as the plane presents much more frontal area than before. Glider pilots sometimes do this deliberately to slow down while landing. The glider nose points to one side, but the glider continues to move straight down the runway. Thus, the rudder on an aircraft operates very much unlike the rudder on a boat.

    In any case, if the tail lacked musculature to enable “stepping on the rudder pedal”, you wouldn’t even get that. What you would get (if the vane was vertical, which you say the rocks suggest) is prevention of skids and slips, which induce drag and loss of control: i.e, stabilization, the more basic function. Add some musculature to wag the tail, and you can have _active_ stabilization, which can reduce drag more. That is not “steering” in any conventional sense.

    In rocketry, “steering” refers to pointing the rocket nozzle in a different direction; the whole rocket will soon be going that way. Modern fighter planes fly more like rockets than gliders. Pterosaurs, I think, must have lacked rocket propulsion, and so are better modeled as gliders. To steer, it would have done what all regular airplanes and flying creatures do: tilt its wings and, if possible, apply a little rudder to prevent slip.

    Aerodynamics and flight theory are far from intuitive. If they were intuitive, we would not have professors of rudder theory.

  10. 10 David Hone 29/07/2008 at 7:44 pm

    Again, several points need raising here, several not for the first time.

    1. We still don’t actually know how the vane was orientated (I favour vertical but I may be wrong).

    2. We still don’t actully know how the tail worked, ‘glider’ or ‘fighter’ or otherwise. If the tail could have rotated about its long axis (possible given the structure of the proximal caudals) all kinds of effecs could kick in at low or high speed.

    3. We don’t know what flight speeds they achieved, but many must have been fast (based on wingshape and inferred musculature) and in any case they could, and probably would, have entered power dives at times which would have involved high speeds and tucked in wings. Thus on your own analogy could act more like fighters, would not have used the wings, and the tail could have helped steer. Peregrine falcons hit, what 200 mph in a dive? Many birds fly in excess of 60mph. These are not glider analogues.

    4. Given the above I still think ‘steering’ is the best term to use in context. We do not know what they coud and could not do, so I will not load the dice against myself by using a pejorative term when a more general and inclusive one is available.

  11. 11 Nathan Myers 30/07/2008 at 9:54 am

    Your hypothesis of rocket-propelled pterosaurs will raise eyebrows in some circles. I predict little support, although Terry Pratchett explored it, with hexapodal flying reptiles, in his Discworld novel, “The Last Hero” (recommended). The notion of rocket-propelled falcons will raise eyebrows elsewhere, as I believe the live specimens examined were found not so equipped. All the falcons I have personally seen flying were either flapping or gliding, once at high (and increasing) speed.

    I can’t imagine what is supposed to be pejorative about the standard name of components of every commercial aircraft ever constructed: aircraft tails are composed of a rudder and elevator attached to, respectively, a vertical and a horizontal stabilizer. On those (typically military or sport) craft without fixed stabilizers, the rudder and elevator are pressed into service to perform active stabilization. Pterosaurs’ head crests must have been used similarly.

    If your insistence on factually incorrect use of the term “steering” is your revenge for the rest of the world calling pterosaurs “dinosaurs”, I guess I’m OK with that — except in an academic paper, of course, where it would be waggish.

    A short course in aircraft operation (typically called “ground school”) can be inexpensive, engaging, and enlightening. Also recommended. Afterward, a model aircraft of your own, with three-axis remote controls (+ throttle), ought to be even more enlightening, and might even be fun. Further recommended.

  12. 12 David Hone 30/07/2008 at 11:29 pm

    I am obviosuly not suggesting they are rocket propelled, merely that they are not necessarily slow fliers akin to gliders and thus your fighter analogy was more appropriate that the glider analogy.

    Furthermore, unlike gliders, pterosaurs were extraordinarily lightweight in construction and as a result, potentially a small moment arm from a tail vane could have a far greater impact on their locomotion than that of even a bird, let alone a typical glider. A large vane on a short tail would have the same effect as a small vane on a long tail, yet rhamphorhyncoids combined a long tail with a large vane, *and* a low mass, *and* muscluature on the tail to amke it active. Once more, and indeed finally, I can only see this as evidence that they *COULD* have used the tail for active steering, thus steerin is the term I will use.

  13. 13 Nathan Myers 31/07/2008 at 1:48 pm

    Evidently you have not lifted and carried (with a partner at the other end) a modern glider, nor rode in one going 150 mph.

    However, the point was never the absolute speed. With a rocket/jet providing a thrust greater than the weight of the aircraft, airframe details become secondary — “with enough thrust a brick will fly” — and what matters most is which way the jet exhaust is pointing. Then steering is a matter of pointing the jet exhaust this way or that. That pterosaurs must have flown like birds and light airplanes, and not like rockets, ought not to be a controversial point.

    Dave, you don’t seem to be getting the central point that, big vane or small, long boom or short, metal or flesh, mesozoic or holocene, deflecting the rudder on an airframe simply does not cause steering to occur. That is not to say nothing happens, just that what happens cannot reasonably be called steering. To insist on the term is to insist on a known falsehood, just as if you were to insist that however azhdarchids really fed, you’re going to call it (“once more, and indeed finally”) skim-feeding.

    This is your blog. You are free to insist on a falsehood. It just seems odd in light of your complaints about journalists.

  14. 14 andy 08/08/2008 at 2:17 am

    Hi David,

    I must say I appreciated this thread a great deal as well.
    As a kid I already had a big passion for dinosaurs, yet pterosaurs never interested me all that much. They were just there, in the books, along the other and more fascinating animals.

    Your threads about them over here have made me change my idea about them. They truly are very interesting creatures.

    Thanks once again!

  15. 15 David Peters 14/08/2008 at 6:51 pm

    With regard to the tail vane issue, one must remember that the only point at which the tail vane could be manipulated was at the pelvis. The whole of the tail was extremely stiff and the caudofemoral musculature was quite reduced to absent. Thus the tail vane, if vertical, would have acted not like an airplane rudder, but more like an arrow vane, passively keeping the rest of the tail in line with the line of flight to reduce drag. Certainly turns would have been initiated by banking, as in modern bats, birds and flying machines.

    The alternate explanation for vanes was that they were a decoration, as in certain living birds of paradise. At present knowledge tail vanes are restricted to just the clade Campylognathoides + Rhamphorhynchus (are there others?) with a minor presence in Sordes. I suggest this because at the base of the tail the freedom of movement was larger in the vertical plane. Thus, standing pterosaurs with vanes could have swung them overhead like metronomes. Since the uplifted tails would have been quite similar in height to the uplifted wing tips (when folded), altogether, with slight folding and unfolding of the wings there could have been three upraised body parts all waving like metronomes in some sort of pterosaurian rhythm.

    Other forms had their own intraspecific greetings.

    The final consideration is: how and when did tail vanes originate? There is where you’ll find your answer. But let’s leave that for another blog.

  16. 16 David Hone 22/08/2008 at 1:29 pm

    Nathan: my complaints about journalists are based on them trying to use scientific terminology incorrectly in a scientific forum, and while this is primarily a scientific forum, I made the explicit statement that this is a simple review and I am using simple language. Steering is in common usage and includes something close to stabilisation as far as the lay public are concerned. I do not complain when journalists call someone a ‘dinosaur’ as being scientifically inaccurate, only when they are explicitly trying to use it in it’s correct context and get it wrong. I am not trying to do that with steering.

    Either way, I still believe I am right, so you can consider it a falshood, but my aero-colleagues are happy for me to use the term in context as above as they themselves do, so I fail to see why I should not.

    As for the rocket issue, it was your analogy, not mine. If I misunderstood it, it was becuase you were not clear. And I will still mantian that until the work is done emperically we will not and indeed cannot know how perosaur flew, so please stop trying to cram loaded terms onto unknown quantities or qualities.

    David: I am going to be frighteningly blunt and say this once. You will probably be offended, but that is your fault not mine: please do not peddle patently false and ungrounded speculation on here or I will simply delete it. If you have any evidence that supports the idea that tale vanes were used for communication, get it published in a proper journal. Speculation is fine based on good evidence, giving it as a fact or tautology based on no evidecne is not.

  17. 17 Nathan Myers 26/08/2008 at 11:40 am

    I guess the lesson is that careful use of terminology is pointless outside one’s own field. But where does that leave journalists? And shouldn’t a pterosaur specialist learn something about flight? (I wasn’t joking in my recommendation to get a full-featured model airplane and learn to fly it well; they’re electric nowadays, and much more pleasant to use.)

    Anyway, welcome back. I’ve missed your postings.

  18. 18 David Hone 26/08/2008 at 2:59 pm

    Thanks for the assessment of my abilities, but as I have now wearily pointed out repeatedly on this thread I am working with several areonautical engineers on pterosaur flight, I have trained (admittley in a limited capactity) in biomechancis and flight, and indeed have more than one paper in press on the subject, in addition to supervising a student in the field. I am happy that I know enough about flight and its terminology. For asolutely the last time, several colleagues are quite happy to call the tail a ‘rudder’ and to say that it ’steers’. These are their terms used in scientific publications and grant applications. Regardless of the rightness or wrongness according to what you want them to mean, I am taking the lead from my peers (indeed superiors).

    In short:
    We do not yet know how the tail works.
    It could be a lateral or vertical arrangement (somehting you have bypassed repeatedly).
    It could move in a number of unusual or unpredicatable ways.
    Bearing that in mind I will NOT use a loaded term like ‘stabilisation’ when we do not, and connot know if that is what it does.
    Regardless, I am taking my lead from senior people in the filed who are quite content to use both the term ‘rudder’ and ‘steering’.

    And once more back to the journalists. If a paper or press release calls a pterosaur a pterosaur, the journalist shold call it a pterosaur, and not change it to pterodactyl or dinosaur. Here he is putting his ideas nto what he wants the terms to mean and not take the lead from those with authroity to give that guidance (indeed people who he actively got the information from in the first place).

    If my engineers call it a rudder, I’ll call it a rudder. The point is to take the lead from people who have more knowledge and experience than you and not to to play with their words. This is what I am doing, yet you still say I am wrong, despite the evidence to the contrary (i.e. my long-term professional relationship to half a dozen people working in the field of aeronautics). They respect my knoweldge of palaeontolgoy and try to each me mechanics and vice-versa. It appears you may have a great knowledge of flight than I, but until you can demonstate you know better than them, I’ll take their word for granted.

    Now please end this debate.

  19. 19 Nathan Myers 27/08/2008 at 1:05 pm

    Dave, I’ve always been in total agreement with your aeronautical authorities. I have tried to help you understand what they must have told you, but your attention is elsewhere. As you request, I will leave the task to others now. If you go back and re-read what I have already posted, you may still learn from it.

  20. 20 David Hone 28/08/2008 at 2:14 am

    My attention is on the task in hand, you however have repeatedly ducked issues put in front of you and challenges to your statements. I have learned from what you wrote, I learned to go back over my own notes and other sources and indeed many describe rudders as providing a ‘steering function’. Not only to they prevent unwanted yaw but can still help steer. Which is what I said.

    In fact I had always said ‘may help steering’ which (once more to the original point that you raised over the definition) had always allowed for it *not* to be used in steering. If you bother to reread what has been written you will see that all I have been doing is challenging your assertions over my definitions and your own analogies.


  1. 1 Four legs good, two legs bad? « Dave Hone’s Archosaur Musings Trackback on 01/12/2008 at 2:10 pm
  2. 2 ‘Rhamphorhynchoids’ and Pterodactyloids « Dave Hone’s Archosaur Musings Trackback on 23/12/2008 at 9:41 am
  3. 3 Pterosaurs as dinosaurs, or not « Dave Hone’s Archosaur Musings Trackback on 18/05/2009 at 8:41 am
  4. 4 One hell of an intermediate – presenting Darwinopterus « Dave Hone’s Archosaur Musings Trackback on 14/10/2009 at 10:51 am

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