Tutorial 3: Pneumaticity

November 3, 2007

It’s come up here a few times already–it’s hard to talk about sauropod vertebrae without bringing it up–but now it’s time to get it out in the open. In almost all sauropods, and certainly in all the ones you learned about as a kid, at least some of the vertebrae were pneumatic (air-filled). Now, this is a very strange thing. Most bones are filled with marrow, so if we find a bone that is filled with air, somebody’s got some ‘splainin’ to do.



Figure 1. Pneumatic bones of various animals. Compare the air spaces in the skull of a cow (A) and a hornbill (B) with those in the vertebrae of a turkey (C) and Apatosaurus (D). The front of the turkey vertebra was worn off with sandpaper. Erosion did the same thing for Apatosaurus. The vertebra, OMNH 1312, has a preserved height of 53 cm, but the neural spine is missing.


How does the air get into the bone?

You probably know more about pneumatic bones than you think, because you’ve carrying some around your whole life. Some of the bones of your skull are pneumatic, and we call the air-filled spaces sinuses. Your sinuses are connected to your nasal passages or the air-filled spaces in your middle ear—but connected by what? These connections are made and maintained by diverticula, which are pouches of epithelium (tissue that lines your internal surfaces) that grow out into the surrounding bones. For example, when you were a baby, pouches of epithelial tissue in your nose pushed up into the bones of your forehead. The spaces enlarged as you grew up, and today they form your frontal sinuses. But those sinuses are still lined with epithelium that is much like the inner lining of your nose, and the sinuses are still connected to your nasal passages, as you may discover when you have a cold. The air-filled pouches of epithelium that fill your sinuses are called pneumatic diverticula. The growth of the diverticula into the bones produces the pneumatic cavities, or holes in the bone, that house the diverticula.

In mammals, pneumatic bones are normally only found in the skull (there are very rare cases of diverticula getting loose and invading the first cervical vertebra). But in birds almost any bone in the body can be pneumatized, by diverticula of the lungs and air sacs. The lungs of birds are very different from our lungs–in fact, they are unique in the animal kingdom. The lungs themselves are small and not very flexible, but they are attached to a system of large air sacs in the thorax and abdomen. These air sacs are empty—in other words, they contain no tissue except a thin lining of epithelium. Like us, birds breathe by movements of muscles and bones, but instead of expanding and compressing the lungs as we do, the breathing movements of birds expand and compress the air sacs, and the air sacs blow air through the lungs. The air sacs are connected in such a way that birds get fresh air blown through their lungs when they inhale, and then again when they exhale (fresh air is stored in some of the air sacs between inhalation and exhalation). This constant flow of fresh air through the lungs (which are arranged into tubes rather than small sacs, like ours) means that birds have the ability to pull much more oxygen out of the air than mammals can.

In addition to providing large amounts of oxygen, the air sacs give rise to a network of pneumatic diverticula. These diverticula spread throughout the body: in between the internal organs, between the bodies of the muscles, and even under the skin. If one of these diverticula comes into contact with a bone, it may press into the bone in the same way that the diverticula of your nasal cavities pressed into the bones of your forehead when you were young. Because the diverticula go just about everywhere, they can pneumatize almost all of the bones in the body. In some birds, such as pelicans, almost the entire skeleton is pneumatic, but in most birds only the vertebrae, sternum, hip and shoulder bones, and humeri and femora (upper arm and leg bones) are pneumatic.



Figure 2. CT slices through cervical vertebrae of Apatosaurus (left) and a swan (right). Although the two animals are very different in size, the construction of their vertebrae is very similar. The Apatosaurus vertebra, OMNH 1094, is 51 cm long. The swan vert is 2.5 cm long (1/20 as large).


What does this have to do with sauropods?

If a bone is pneumatic, the air has to get into the bone through a diverticulum, and the diverticulum has to get into the bone through a hole. So almost all pneumatic bones have one or more large holes on the outside, which are the pneumatic foramina. Human medical histories and experiments on birds have shown that these pneumatic foramina must remain open for a pneumatic bone to develop properly and be maintained. If the foramen is closed—for example, by a disease or injury—the air space inside the bone will eventually be replaced by new bone growth.

In addition, pneumatic bones tend to have relatively large, smooth-walled chambers inside, compared to non-pneumatic bones that are filled with marrow. These chambers have a distinct appearance and they are not easily confused with anything else. So if we find a bone with a good-sized foramen leading to big internal chambers, we can infer that the bone was pneumatized. No other anatomical system makes the same traces on the skeleton.

A lot of sauropod vertebrae are crazy pneumatic. In fact, the only non-pneumatic vertebrae we’ve shown so far are these, and you can see big obvious pneumatic foramina in the vertebrae shown here and here and here and here.



Figure 3. Reconstruction of the respiratory system of a diplodocid sauropod. The left forelimb, shoulder, and ribs have been removed for clarity. The cervical vertebra is AMNH 7535, and the caudal vertebra is OMNH 2055.


Air, air, what is it good faer?

(Sorry, that’s my Scottish brogue coming out.) Pneumatic vertebrae tell us some important things about sauropods as living animals. First, sauropods clearly had some kind of air sac system like that of birds. I’ve spilled a lot of ink on that already, and you can find those papers here. Second, we can use the distribution of pneumatic vertebrae to plot the extent of the pneumatic diverticula. Recall that if a bone is to stay pneumatic it has to remain connected to an outside air source. So if we find pneumatic vertebrae from the front of the neck to the middle of the tail, which is the case in most diplodocids, then we know that pneumatic diverticula spanned that whole distance as well.

Finally, it is surely no coincidence that the largest and longest-necked terrestrial animals had mastered ultralight construction. How light is ultralight? Well, the vertebrae of most sauropods were 60% air by volume, and in brachiosaurids like Sauroposeidon that number could be up to 89%. That’s a handy thing to have if you want to hang a long neck off your front end. Every major sauropod clade–Mamenchisauridae, Diplodocoidea, Brachiosauridae, and Titanosauria–had at least one member with a 9-meter neck, and the first three had members with 12-meter necks.

On a personal level, pneumaticity is also a great intellectual playground. There are so many things we don’t know about how it works, even in living birds. How do these spaces form, and what are the physiological controls? Why all the variation among clades, in birds and non-avian dinosaurs alike? Why are some bones 50% air and others 75% and still others 90%? Why do birds pneumatize the bones of their skeletons in the same order as their dinosaurian ancestors? How do body size and pneumaticity influence each other, in development and in evolution?

Morpheus told Neo that the Matrix is a system, with rules, and some rules can be bent and others broken. I want to be Pneo. I want to understand the rules. I want to see the code.

I want to play, too!

Groovy! Pneumaticity is wicked cool, and you don’t have to have a zillion dollars and an ion reflux pronabulator to get a good look at it. The holidays are coming up, and bringing with them the annual spike in the availability of turkey bones (you can get ’em from the neighbors if you aren’t having turkey yourself). Boil the vertebrae or humeri (the “drumsticks” of the wings) for half and hour or so to get all the soft tissue off, then soak them overnight in ordinary drugstore hydrogen peroxide to degrease them. Then you can use a small hacksaw or a Dremel to cut them open and see the air spaces inside, or you sand off the ends of the bones with sandpaper. The spaces you’ll see are identical to the air spaces in sauropod vertebrae, just a little smaller.

If you’re really ambitious, figure out what the bone-to-air ratio is in turkey vertebrae, and compare that to what you find for the humeri. There are a handful of papers on bone-to-air ratios in bird limb bones, but there is almost zero published data on the same ratios in vertebrae, or on how the bone-to-air ratio compares in vertebrae and limb bones of the same animal. There is a nice opportunity here for someone with little or no formal training to make a real (and publishable) contribution. Gimme a holler if you’d like to know more.

67 Responses to “Tutorial 3: Pneumaticity”

  1. Mike Taylor Says:

    Dammit all Wedel, this is supposed to be Sauropod Vertebra Picture Of The Week, not Dissertation Of The Week. How are Darren and I supposed to keep up with this level of work?!

  2. Matt Wedel Says:

    Hey, I wrote it as short as my conscience would allow! Why do you think I’ve been putting it off for so long? And there’s still stuff I missed. We’ll have to have a lamina tutorial one of these days. I nominate you.

  3. Mike Taylor Says:

    Don’t worry, I already had myself down for the Wilson1999tastic lamina tutorial. Coming soonish … though probably not until after the soon-to-come themed week.

  4. Matt Wedel Says:

    You can tell this is a great blog because each post gets so many comments. Some of them are even from people outside the SV-POW! creative team!

  5. Mike Taylor Says:

    Yes, I have to admit that the Rest Of The World is not really keeping up its half of the bargain around here.

  6. Mike from Ottawa Says:

    “Some of them are even from people outside the SV-POW! creative team!”

    You called? They also serve who only stand in awe.

    That was a great post. I’d read long before that sauropod vertebrae were heavily (or should that be lightly?) pneumatized but that second pic brings it home like nothing else. There’s almost nothing but nothing there.

    The Canada geese I see on my way to and from work each day will seem even more like miniature, bipedal brachiosaurs than they already do.

  7. DDeden Says:

    Hi, I got a few questions.

    So highly pneumaticised vertebrae = lightweight & big. Do diverticuli typically have air flow? Excluding the thoracic air sacs, lungs and trachea, does the epithelium in bones have respiratory functions? Reason for Q: Amphibians can breathe through their naked skin (I guess enough to support BMR of sleep or hibernation), turtles can breathe through their anal-intestinal “gill-like” tissues somehow, but all/most the rest of the reptiles that I know of breathe through their nose and mouth only, and are covered with non-respiratory scales/scutes. The internal air surface area in a highly pneumaticised apatosaurus would have been huge, but I don’t know if any respirational blood-oxygen/CO2 exchange would have occurred there. Same Q for flying Pterosaurs and marine Plesiosaurs…

    The epithelium in human paranasal sinuses during humming produce significant amounts of Nitric Oxide into the nasal cavity, which is anti-biotic and a vasodilator. Do you know if the diverticuli in birds and assumably in dinosaurs has/had a similar activity, either through humming or calling (thinking of the hornbill and rainforest kipunji monkey which has a nasal honk-like call), or some other airflow regulator?

    Baboons in (generally hot-dry) savannas lack paranasal sinuses and have a oral bark-like call, while rainforest Sulawesi macaques have them as do rainforest apes, and I think the sinuses prevent airborne infectious diseases.

    Since many dinosaurs lived in tropical humid marsh – like habitats AFAICT, they may have had similar Nitric Oxide emissions, and this may relate to the various hollow bills, beaks, crests of animals in humid warm wet environments. Opinions and answers appreciated.

  8. Darren Naish Says:

    Over to you Matt! ;)

  9. Matt Wedel Says:


    In birds, the pneumatic spaces in the bones serve no respiratory function, and there is no reason to suspect that they did in dinosaurs, either. The air sacs and the air spaces in the bones are poorly vascularized, so there is little opportunity for gas exchange. As for whether or not air is actively circulated through the diverticula, we just don’t know. I recommended in my 2005 paper that someone ought to have a look at that, but brief asides in sauropod papers may not be the best way to bring the problem to the attention of avian physiologists. Maybe we’ll have more luck here!

    Monkeys seem to have evolved and lost paranasal sinuses over and over. I am very skeptical of any improvement in disease resistance. It seems to have more to do with skull architecture. If the facial bones are wide or thick and have space for sinuses, sinuses form. If the bones are thin and plate-like, sinuses don’t form. That’s my off-the-cuff observation; please feel free to correct me.

    Don’t forget that we find incredible dinosaur diversity in habitats that were seasonally arid, such as the Morrison of the American West and some of the dinosaur-bearing formations in Mongolia. So I fail to see a correlation between dinosaurian headgear and environment. But that’s not my balliwick; if there is evidence that supports this, please let us know.

    Thanks for stopping by and commenting.

  10. DDeden Says:

    Thanks Matt. A second thought on the diverticuli was that if there is no air flow, perhaps in temperate climates and in tropical but cool waters, the dead air spaces may act thermoinsulatively (eg. pelicans). Both structural integrity and acoustic/thermo-insulation of cylindrical columns (bones) improve with internal tensional membranes such as in fig. 2, remniscent of structural foams, seen also in many non-woody plant stems.

    Skull architecture may be influenced by type of habitual feeding (nut vs foliage) as well as both inter specific defense and intra specific competition. I’ll keep an eye on the sinus functions. Being that dinosaurs seem to have been well protected from skin pathogens due to scales and feathers, I expect they were also selected by microbial pathogens for better oral and nasal “armor”, which is why I thought to bring up the disease angle. Thanks again.

  11. cubicle charlie Says:

    Great stuff! And I have a question too. If most of these pneumatized bones contain air instead of marrow, then what’s producing all the red blood cells for both birds and sauropods?

  12. Matt Wedel Says:

    If most of these pneumatized bones contain air instead of marrow, then what’s producing all the red blood cells for both birds and sauropods?

    Good question. In sauropods only the vertebrae and ribs and possibly the ilia (parts of the pelvis) are pneumatic, so there is still plenty of marrow space in the other girdle and limb bones. And in most birds only the proximal limb bones (humeri and femora) are pneumatic, so the distal limb bones (past the elbows and knees) can keep those erythrocytes coming. But then you have a few weirdos, like pelicans, that pneumatize damn near everything, including distal limb bones. I imagine that pelicans must make all of their red blood cells in a handful of bones in their fingers and toes, but I don’t know that for sure. Pat O’Connor probably does; in addition to being the Bird Pneumaticity Mastah, he’s been working on distal limb pneumaticity in particular, and he’s cut up quite a few pelicans.

    It is interesting that as the skeleton becomes pneumatized the erythropoietic bone marrow keeps getting shoved off to the extremities. There is a paper tracing this out in the pigeon. That ref is:

    Schepelmann, K. 1990. Erythropoietic bone marrow in the pigeon: Development of its distribution and volume during growth and pneumatization of bones. Journal of Morphology 203:21-34.

  13. That’s interesting about the RBC production in the more distal digits. Did dinos have spleens? Both horses and marine mammals can produce lots of RBCs in their spleens, I don’t know if their bones also produce much.

    An odd question (even for me!): Could the skull and associated brains be considered simply as a neural/axonal/fat rich pseudo-pneumatic bone cavity, or is it truly an entirely different physiological structure, completely nonanalagous to any other bones or cartilage in the body? Does a femur have fat, blood vessels, nerves in it, like a brain does?

  14. Matt Wedel Says:

    Everything from fish on up has a spleen, so dinos did too. I didn’t know about the spleen as a source of RBCs, but I did some checking and it happens. Maybe that is what the pelican is up to.

    At the level of bone biology, the skull is no different from all the other bones in the body. The bones of the dermatocranium are membrane bones rather than cartilage replacement bones, but they all have nerves, vessels, and marrow (or air), including the femur. The brain is *bounded* by bones, but it is not inside bone the way marrow is inside bone. Remember that the basic vertebrate setup evolved in animals with cartilaginous skeletons.

  15. DDeden Says:

    Thanks, yes human free-divers pay attention to the RBCs released by the spleen during breath hold diving, which activates the release during the mammalian diving reflex, so they can stay down longer and dive more often.

    The temporal bone (under the temples) is the densest bone of the body, yet it (at least the mastoid process) has porosity and even some marrow production. I was interested in how sound carries through air, bone and water, especially in regards to Homo erectus, (and also in Homo neandertalensis and Homo sapiens idaltu) which had a very dense occiput. I speculate that during daily forage diving, sounds were transmitted between a diver and a floating partner via humming and clicking (which later became basis of vowels and consonants), sound carried directly through water and dense occipital and temporal bone to the inner ears which apparently are part of the temporal bone, largely bypassing the flooded middle and external ears entirely. A parallel occurred in echolocating cetaceans, but with far more refined results and further modifications. (Some modern freedivers deliberately flood their middle ears and paranasal sinuses to avoid frequent time-consuming gas pressure equalization manuevers at depth.)

    I’m trying to determine if sound transmitted through water and then only along the very mineralized dense skull surface, into the inner ears, remaining isolated/insulated by the pneumaticised spongey layer, would explain the difference between the inner ear architecture in ape relatives and humans. Thanks again.

  16. Matt Wedel Says:

    Don’t forget that the human temporal bone is a composite of different elements. The petrous portion that houses the ear is extremely dense in most mammals, as you note. The mastoid process is pneumatic in humans and it is part of the temporal bone, but it’s not the part that houses the middle or inner ear. I know that chimps have comparatively broader temporal bones with more pneumatic spaces, based on the work of Ron Sherwood. But that’s where my knowledge of paratympanic pneumaticity in primates ends, so I’m going to refrain from commenting on your functional hypothesis.

  17. […] know) who asked aggressively confrontational questions that gave me the chance to talk about postcranial skeletal pneumaticity live on national television (take that, […]

  18. […] coverage of the wackiness that is Xenoposeidon. I drew the ‘pneumaticity’ straw, not surprisingly, so I get to introduce the anterior and posterior views of the vertebra, which reveal some of the […]

  19. Hi,
    Thanks for a brilliant post and the link to your papers on pneumaticity and avian style respiration in sauropods.
    As a bit of a bird enthusiast I’ve been intrigued by their unique (or apparently not so unique) respiratory system since I first heard of it, and a lot of things about sauropods make a lot more sense once you accept they were using a similar system.
    Just a couple of quick questions, firstly how well developed would this ‘air sac’ respiratory system have been in the common ancestor of the sauropod and theropod lineages? Did both lineages inherit fully fledged ‘avian’ respiration or did each independently adapt a more primitive version along similar lines?
    Secondly how much can the fossil bones alone tell us about the extent of the air sacs and diverticula through the soft tissues?
    Can I just add, as a reader of this blog with no background in palaeontology, that I find these tutorial posts invaluable, thanks and keep up the good work.

  20. Matt Wedel Says:

    Hi Horwood,

    We have pretty good evidence that cervical and abdominal air sacs were present in both sauropods and theropods, which means they were probably present in the common ancestor of Saurischia as well. We can’t put a flow-meter into a Mesozoic dinosaur to see how the air was moving through the lungs, but at least we can say that saurischians had all the respiratory gear they would have needed for avian-style flow-through lung ventilation.

    As for the extent of the air sacs and diverticula in the soft tissues…this is tough. We can sort diverticula into three groups, based on how much we can learn about them from the skeleton alone. First are the diverticula that actually resided inside the bones. We know pretty much everything about the morphology of these things. Second, there are the diverticula that were adjacent to the bones and left traces on the external surface. We know the form and extent of these diverticula where they were in contact with the bone, but the other side–the side facing the soft tissues–is not constrained by bone, so we don’t know the size or shape of the whole diverticulum. Possibly some of these diverticula were just thin skeins of air-filled epithelium right over the surface of the bone, and possibly they were big spheres or ellipses that ballooned out into the surrounding soft tissue. We can’t tell from fossils, and birds haven’t been much help yet, because–and this may seem unbelievable–we have zero measurements of diverticular volume in a living bird. We typically study this stuff by injecting euthanized birds with air or latex and then CTing or dissecting them. But any injection method has the potential to distort the volume in some way, and more importantly, these are all done to dead birds.

    All that stuff goes double for the third group of diverticula, those that don’t contact the skeleton at all. Birds have diverticula among the viscera and muscles and under the skin, and preserving any trace of those in the fossil record would require some kind of miraculous preservation that would make the feathered dinos from Liaoning look like hunks of crap.

    So this is a cool field but it is also occasionally frustrating, because we keep banging our heads against the very limits of what we can detect in fossils, and what we can infer from them.

    If you’d like to know more, I dealt with your first question in more detail in my 2007 paper, and your second question is addressed in my 2005 paper.

  21. DDeden Says:

    Matt, how about the opposite of pneumasticity in vertebrae? Here is a link to a post which includes a ref to dense vertebrae in sabercats.


    (for information (and a referenced paper) about unusually dense bone in sabercats, sea otters and Homo erectus.)

    Are there large sauropds with particularly dense vertebrae and poor pneumatization? If so, any idea why? Small body size? Anti-buoyancy in water? Improved bipedal running?

    Are you aware of any animal which (like Homo erectus and neandertals) had very porous facial bones (enlarged paranasal sinuses) yet particularly dense occiputs?
    I know that a light-weight facial structure is not uncommon, but is that usually accompanied by a thick dense-boned rear skull?

  22. […] to see the unlabeled version). They are facing left, and the giant depressions in the sides are the pneumatic cavities. The centra (C3 and C4 if you’re curious) are propped up on their oversized parapophyses, […]

  23. Graham Peter King Says:

    Matt- thanks! Pneumaticity is fascinating me (so I guess SVPOW is working). I’ll come back to you in a moment.

    DDeden- that is fascinating stuff about sinuses, humming and nitric oxide. Weird! Does that mean when I annoy people as I do by humming rather often, I can claim its physiological benefits in my defence?
    And what exactly is the nitric oxide accomplishing…?

    Matt, pneumaticity – my speculations 1,2,3, following conversation with my Dad about the oddities found here.

    (1) Those cervical air sacs – with flesh-bound surfaces indeterminate – might they have been continuous and patent with the pharynx, allowing unidirectional parallel flow (but in opposite directions) via trachea and putative sac-channels, thus ELIMINATING tidal volume from the respiratory system? (Thinking, sauropods had a heck of a long neck to breathe through, and a lot of dead air to clear before getting to the good fresh stuff. YOU try breathing through a thirty-foot tube… Ok, their lungs were more voluminous than ours, but still…). If so, their breaths would surely have had to go this way: IN through trachea, OUT through the sac-channel… since only the tracheal route (I presume) would have the cartilaginous support to resist collapse under negative pressure.

    (2) Could the sacs have served to cushion the neck against collision? I am thinking (a) a long neck swinging had a lot of angular momentum, pneumaticity notwithstanding, and a tree-trunk standing unnoticed in its path might break something important (Dippy the Diplodocus only having a little brain to navigate with). A little pressurised cushioning would spread the force and extend the period of deceleration, maybe enough for reflex muscular response. Maybe tactile stimuli to the neck of sufficient intensity would trigger a reflex protective (“ouch, puff”) pressurisation of the air-sacs (cf automobile air-bags)? (Bear in mind the reflex arc would be a very long path. Giant axons to speed transmission, perchance?). Maybe neck-jousting was a mating contest, serving as a test of strength, reactions, ability to pressurise airsacs aptly, hence respiratory fitness, etc.

    (3) Acoustic resonating chambers! Maybe it was DDeden’s talk of humming that set me thinking. Suppose sauropods vocalised and set the whole neck thrumming, a big tubular sounding board and signal emitter (and a detector of sympathetic vibes too, I guess). Being amid a herd of vocalising sauropods would be like strolling amidst the pipes of a church organ, or perambulating in the belfry when the bell-ringers are at work.
    Katy Payne at Cornell found that elephants use infrasound to communicate long-distance and out-of-sight amid forest,http://www.birds.cornell.edu/brp/elephant/ELPFAQ.html ; Caitlin E. O’Connell-Rodwell of Stanford University examining the idea they may pick up some infrasound through their feet.
    Rhinos and cassowaries are at it too, it seems.
    (PS how do you do that script thing you do to include links ‘here’?)

    Sauropod necks and pneumaticity; fascinating!

    Sorry to be so… long-winded? ;-D

  24. Graham Peter King Says:

    Oh, the neck-jousting idea was meant to be my point 2(b), I forgot; just in case anyone wondered why there was only (a).

  25. Graham Peter King Says:

    (Finally!!!) What were those lengthily-humming sauropods doing; making so much nitric oxide all day long?

  26. Matt Wedel Says:

    Hi Graham,

    All of your ideas are interesting. It is important to keep in mind that the entire system in present in birds at a smaller scale. Any connection of the cervical diverticula to the pharynx or trachea is pretty unlikely. Birds have had 150 million years to ‘discover’ such a connection (by developmental accident, which is probably how diverticula formed in the first place!). The fact that none of them have done it doesn’t mean it’s impossible, but to me it seems awfully unlikely.

    I’m not wild about diverticula as cushions for neck-whomping. Pelicans have a network of subcutaneous diverticula that evidently looks and functions like bubble wrap. Such a system might have been present in sauropods, but it’s unlikely that we’ll ever know for certain. The diverticula we have evidence for are right up against the bone–by the time the impact force gets there, it’s already been through the skin and muscle, which are subject to damage of their own. Also, Kent Sanders did some tests with inflated ostrich necks on X-ray tables and found that no matter which way you bend the neck, the air on the compressed side goes to the diverticula on the extended side. In lieu of some mechanism to keep the air in one place–which is apparently completely lacking in the diverticula of birds–any hypothesis that depends on pressurization is dead in the water. In short, the diverticula that might have functioned as cushions we have no evidence of, and the ones we have evidence of would seem to make poor cushions. I agree, though, that this area needs some actual testing instead of armchair speculation, which is what I’m doing (the speculation, not the testing–yet).

    Finally, I am fully on board with the idea that sauropods might have communicated infrasonically, but that can be done with a long trachea alone. I’m not sure what the diverticula would contribute. In any case, the whole diverticular system evolved in little critters that almost certainly weren’t communicating by infrasound, so that doesn’t seem to have been a driving factor.

    I hope you don’t think I’m being ridiculously negative. Pneumatic diverticula are strange and wonderful things, and it possible that they have functions we are not yet aware of–even, maybe especially, in birds. But many of the speculative functions are not supported by the anatomy or evolution of the system. That doesn’t mean they might not have evolved later, through exaptation. But for me, there are enough unanswered questions based on the evidence we have.

    What were those lengthily-humming sauropods doing; making so much nitric oxide all day long?

    Hopefully anesthetizing themselves, since they lost so many teeth.

    Yep, I’m going out on that one.



  27. Matt Wedel Says:

    Oops, forgot to mention that I know a little about resonating chambers in ratites, having cut one open.

    If I try to type out the link syntax for you here, it will just show up as a link. But you can find basic HTML syntax all over the place, including Wikipedia. Good luck!

  28. Graham Peter King Says:

    Cheers Matt for the in-depth response!
    Not negative-seeming, no worries. I’m pleased to bat ideas to and fro.

    These ideas were playfully-serious, thrown out from a somewhat engineering-mindset, brainstorming ‘what-ifs’ (not knowing the fossils or literature well myself – actually most of what I have learned on the topic has been from SVPOS in recent weeks!)

    I think, re sacs and sound, that (WHATEVER purpose they mainly served) if the sacs were at all pressurisable (and to sustain airflow, not lapse flaccidly, I would guess they had to be at least minimally so); and if their walls were (overlain by) tensionable tissue; then if the sauropod vocalised, the sacs (just by being there) could tend to resonate somewhat (depending on pitch).
    If they noticeably affected the sound emitted (eg by amplifying vibration or changing timbre), there’d be scope for selection to operate on same… particularly if vocalisations played a key role in establishing herd hierarchy/ attracting mates/ repulsing rivals.

    I am intrigued too by the immune-system and air-filtering implications of all those warm moist cavities which surely would suit bacteria, bloodsuckers and other parasites as appealing niches to colonise (if once breathed inside). How do present-day reptiles and birds fare? Do they have nasal hair (or equivalent) to trap airborne debris? Do bulk air-flow (and ciliated epithelium propelling mucus up and out) suffice to keep pneumatic cavities swept clean?
    (Or is nitric oxide a disinfectant/insect repellent too?!)

  29. […] we might be curious about the ratio of bone to air space. As frequent commenter Mike From Ottawa noted of another pneumatic vertebra, “There’s almost nothing but nothing there.” In […]

  30. […] vertebrae in, for example, his 1859 article on pterosaur vertebrae [Owen 1859]). As you can see in Tutorial 3, the internal anatomy of bird and sauropod centra are so similar that it is difficult not to […]

  31. […] detailed anatomy of the beasts. For Nigersaurus alone, there were cases on vertebral pneumaticity (yay!), the vertebrae themselves (real bones), the detailed anatomy of the jaws (real bones, from the […]

  32. […] everyone who reads this blog surely knows by now, sauropod cervicals were extensively lightened by pneumaticity.  By bringing air into the center of the neck, they were effectively able to displace bone, muscle […]

  33. J Says:


    Do any mammals have pneumatic femurs? If not, what extant animal could a 40cm pneumatic femur come from??

  34. Matt Wedel Says:

    Do any mammals have pneumatic femurs?


    If not, what extant animal could a 40cm pneumatic femur come from??

    Let’s see, 10cm is 4 inches, so a 40cm femur is 16 inches. Pretty darned big. I think it would have to be from an ostrich or another ratite.

    You’re dead certain that it’s a femur, and that it really is pneumatic and not just hollow? I hope those questions don’t sound condescending, I’m just trying to eliminate possibilities. A lot of people don’t immediately grasp the difference between bones that are hollow and marrow-filled, like, say, human femora, and those that are pneumatic.

    Got any pictures you could e-mail me or post online and point me too? This is pretty darned interesting.

  35. J Says:

    Definitely a femur. And I’m pretty sure it’s pneumatic, has a hole which I assume to be a pneumatic foramen. Would that be enough to distinguish between hollow and marrow filled? if not, what other characteristics are there? It has no 1st trochanter and the femoral neck is practically non-existantwhich also make me think it’s non-mammalian.
    i think it’s an ostrich actually, at first I thought it was too wide, too chunky – but I guess that be a weight-bearing adaptation?
    will work on some pics
    It has a big knobbly knee joint which is pretty cool too.

  36. Matt Wedel Says:

    Certainly sounds like an ostrich–their femora are amazingly wide and chunky, with very knobby knee joints as you describe.

    Does it look like this?

  37. Cress Kearny Says:

    I found SV-POW! about a year ago and have enjoyed all your posts, new and old, since then. Among other things the blog explained some sediment-filled cavities, large and small, that have always puzzled me in a large, Late-Jurassic centrum that I bought (sliced) many years ago at a rock shop in eastern Utah. Pneumaticity, without a doubt. But now I read of a study by Daniela Schwarz-Wings in JVP (Issue29, no.2) in which the epaxial muscles of crocodiles are used to infer the musculature along the vertebra of some sauropods. Question for you: such heavy musculature doesn’t fit well with the extensive exterior pneumaticity shown in many illustrations by you and others. A piece on how these studies might be reconciled would be interesting and pertinent.

    Keep up the good work.

    Cress Kearny

  38. Mike Taylor Says:

    Cress, you make an interesting point; but I am not familiar enough with Daniela’s work, and especially not of the prerequisite extant-critter myology, to comment intelligently. Sorry.

  39. Matt Wedel Says:

    Question for you: such heavy musculature doesn’t fit well with the extensive exterior pneumaticity shown in many illustrations by you and others.

    Really? How so not? Daniela has reconstructed exterior pneumaticity as or more extensive than anything I’ve shown. I find her pneumaticity work extremely convincing and her muscle reconstructions at least fairly convincing–that is, I don’t have super-strong reasons to doubt her muscle work, I just know less about muscles and more about pneumaticity.

    In any case, the muscles had to be attaching along the laminae and at the exposed prominences, like the top of the neural spine, the diapophyses, and the rugosities adjacent to the zygapophyses. I don’t think that there is any real debate about that, because the cavities and troughs between the laminae are pretty obviously pneumatic, and the laminae and prominences are all that is left for muscle attachment. The only questions left from a reconstruction standpoint are what attached where and how thick to make the muscles. Even here it is hard for me to comment intelligently because there are a lot of unknowns in scaling up the gloop (soft tissue) that ought to go around the bones, for animals as big as sauropods (see our short, junk-food-themed series on this problem here and here). If Daniela’s slabs of muscle strike you as too thick, I can only shrug. She has done more, and more careful, work on the external pneumaticity than I have and she clearly doesn’t see any conflict.

    I can tell you from dissecting birds from pigeons up to ostriches that vertebrae with substantial external pneumaticity can still anchor surprisingly thick muscles. Figuring out what cross-section of muscular tissue the exposed bony areas (i.e., those not covered by diverticula) of sauropod vertebrae could support would be a wonderful project for someone, but it would start in realms of biomechanics that I understand at second hand and poorly, and rapidly delve into my areas of darkest ignorance.

    Anyway, thanks for the kind words. Sorry to not be more helpful on this one. It is something that Mike and I have discussed a lot, and even brought up with a couple of biomechanists, but we quickly realized that it would be a dissertation’s worth of work at least, with no guarantee of getting a satisfying answer, and we’ve got other fish to fry. But if someone else wants to die on that hill, I will cheer them on all the way.

  40. J Says:

    hey! yes it does look like that!
    But now im confused, so if its pneumatic does that mean it lacks marrow? i thought ostrich femora had marrow…at least that’s what the dog food adverts say?!

  41. Mike Taylor Says:

    A pneumatic bone is one that is filled with air (like a pneumatic drill, both based on the Greek pneuma, meaning breath or spirit. If there’s any marrow at all in a pneumatic bone, it’s negligible in quantity — in fact IIRC one of the outstanding issues in bird physiology is how they get by with so little marrow.

  42. Nathan Myers Says:

    In sentient-bird-world, the bird scientists are bird-agonizing over what use mammals could have for all that marrow.

    (For an impression of sentient-bird-world, see http://www.gunnerkrigg.com/archive_page.php?comicID=562 and following.)

  43. […] and caption recycled from fig. 14 here. Hat tip to Mike from Ottawa for the wonderful […]

  44. […] we covered skeletal details such as regions of the vertebral column, basic vertebral anatomy, pneumaticity and laminae, but we never started out with an overview of the sauropod […]

  45. […] this popular article on pneumaticity (which has instructions for making your own), and way back in Tutorial 3–only the 12th ever post on […]

  46. […] The long answer is that the expression “hollow bones” has caused no end of confusion, because there are at least two ways to interpret hollow: filled with air, or not filled with bone (the former is a subset of the latter). If you mean “not filled with bone”, then the bones of almost all amniotes* are hollow, and the spaces inside are occupied by marrow (most commonly) or air. If filled with air, the bones are referred to as pneumatic, and an accessible introduction to them is here. […]

  47. […] is definitely understandable; imagine how heavy some sauropods would be if their bones didn’t resemble bath sponges, not to mention that they would probably need to eat more calcium than is in the white cliffs of […]

  48. […] are present in the cervical, dorsal, and anterior caudal vertebrae of most sauropod taxa. (See this SV-POW! post for information on pneumaticity in sauropods.) The size of the pneumatic foramen and lack of […]

  49. Frosted Flake Says:

    Thanks Matt.

    You have revolutionized my view of … quite a few things. For one thing, I didn’t realize pterosaurs had superchargers. I thought they just had really thick air.

    Click to access 1451-93720602116L.pdf

    That’s not bad for one page on the internet. Now, I’m off to check out your links. Wish me luck!

  50. Mike Taylor Says:

    The paper you link to is a good example of people in Chemical Engineering departments are not always encouraged to write papers about palaeontology. A classic example of ignoring all the existing literature to find a crazy solution to a non-problem.

  51. Frosted Flake Says:

    Oh come on, Mike. Don’t stop there. Tell us what the real deal is.

    And a link to some data would be nice. I mean, if yours is a constructive comment. If all you wanted to do is call me stupid, well then, aren’t you the bright, shiny little fellow.

  52. Mike Taylor Says:

    Frosted Flake, the data you seek is all over the last 50 years of published literature in palaeo. I wasn’t calling you stupid; I was calling the the paper you linked ignorant. There is no controversy here. Every major point the paper makes is wrong, and any palaeontologist will tell you the same.

  53. Frosted Flake Says:


  54. […] of pneumatic diverticula from the respiratory system, which has been covered extensively on this blog in sauropodomorph […]

  55. John G Leslie Says:

    I really appreciate your article-it is well written and has been a help to me. I am not an evolutionist and I view your data not so much attempting to prove progenic relationships, but rather in structure /function ones. Thanks again, If you would like to correspond off the web I would enjoy it.
    Dr John G Leslie

  56. Mike Taylor Says:

    John, thanks for these kinds words, but in fact this tutorial is by Matt, not me! As it happens, we are both Christians, but also both wholly persuaded by the evidence of evolution. If you’d like to correspond off-Web, you are very welcome to drop me a line at mike@miketaylor.org.uk

  57. […] blue lines are the inferior margins of my maxillary sinuses – air-filled spaces created when pneumatic diverticula of the nasal cavity hollow out the maxillae. You have these, too, as well as air spaces in your […]

  58. […] the "pain in the neck" of heavy bones, and allowed oxygen to flow more freely into their bodies. It's estimated that pneumatic bones made their necks so ultra light that their bones were 60-89% air… (specifically […]

  59. […] but it probably wasn’t broadly distributed as it is in mammals. In the interaction of their air sac systems with connective tissue, sauropods were probably a lot like birds. Most birds don’t have […]

  60. […] between those extremes (some animals beat this by building parts of their skeletons out of [bone tissue + air] instead of [bone tissue + marrow]). We know that sauropod limb bones tend to have thick cortices […]

  61. […] So, skeletal pneumaticity is, essentially, the reduction of parts of the skeleton, usually the axial (spinal) column, to reduce weight (maybe) and to fill with air sacs. And, understandably, it was the other major feature that Seeley pointed to as being unique to saurischian dinosaurs (i.e. not seen in ornithischians). If you would like to read more about this feature, head this way. […]

  62. […] in mind that the centrum was full of air in life, whereas the cervical ribs and the bony struts that support them are just huge slabs of […]

  63. […] before Matt and others were CT-scanning sauropod vertebrae to understand their internal structure, Werner Janensch was doing it the old-fashioned way. I’ve been going through old photos that […]

  64. […] air inside or even alongside the centrum. I wanted to visualize that better so I took my trusty old CT cross-section of OMNH 1094 and pasted it on top of this vert, stretching it a bit in GIMP to improve the […]

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