Airheads

December 8, 2008

human-sinuses

A 3D reconstruction of the paranasal sinuses in a human (from Koppe et al. 1999). You also have paratympanic sinuses that pneumatize the mastoid process of the temporal bone (feel for an inferiorly-directed, thumb-size protuberance right behind each ear).

pig-skull-x-ray

An x-ray of a pig skull, from here. Can you see the outline of the brain-shaped endocranial cavity?

rhino-skull-ct

How about in this x-ray of a rhino skull? Image courtesy of Kent Sanders.

cow-sinuses-small

A sectioned cow skull. The bottom half of the endocranial cavity is exposed in the horizontal cut. The vertical cut shows the tiers of sinuses that make up most of the volume of the skull. I think that the middle tier (the large, butterfly-shaped space) is the front part of the endocranial cavity and housed the most rostral bits of the brain; note that it is completely surrounded by sinuses.

bighorn-small

Part of a bighorn sheep skull. The pneumatic horncores of bighorns are a useful antidote to the idea that pneumatic bones must be weak.

elephant-skull-sectioned-480

A cross-section of an elephant skull, courtesy of Project Gutenberg. The cavity at the back marked ‘b’ is the endocranial cavity that holds the brain. The big tube running through the middle is the nasal airway. Everything else is pneumatic. Note that the brain is entirely surrounded by sinuses.

exploded-proboscidean-skull-480

A blown skull of a proboscidean from the bone cellar at the Humbolt Museum. I snapped this on the last day in collections,  on a mad scramble to get whatever non-sauropod pics (gasp!) I might want later. The bumps to the upper right are the occipital condyles; the skull is in left lateral view facing down and to the left.

alligator-paratympanic-sinuses

Paratympanic sinuses (green) surrounding the brain (blue) of an alligator, from David Dufeau’s homepage. Go there for a lot more mind-blowing images of sinuses. The snout of this gator is filled with paranasal sinuses, they’re just not shaded in here.

rhinoceros-hornbill-480

Sectioned skull of a rhinoceros hornbill, which is pretty much completely filled with paranasal and paratympanic sinuses. Even the lower jaw is pneumatized.

Okay, so now you know that mammals, crocs, and birds are all air-heads. What does any of this have to do with sauropods? Well…

  • Archosaurs and mammals evolved cranial pneumaticity independently. Does that mean that cranial pneumaticity is easy to evolve (since it evolved more than once) or hard to evolve (since it only evolved twice)? This is relevant to the question of how many times postcranial pneumaticity evolved.
  • Archosaurs evolved cranial pneumaticity before they evolved postcranial pneumaticity. Does that mean that postcranial pneumaticity is the application of a pre-existing developmental program (bone pneumatization) to a new anatomical region (the postcranial skeleton)? Or did the developmental control of pneumatization have to evolve de novo in the postcranium?
  • The development of cranial pneumatization in mammals and postcranial pneumatization in birds seems to  follow similar rules. Does that mean that we can apply lessons learned from, say, the development of human sinuses to understand the development of sauropod vertebrae?
  • Sauropods and big-headed mammals like elephants have this in common: at the front end they’ve got a big chunk of pneumatic bone. In sauropods, it’s the neck; in elephants, it’s the head. In both cases the big pneumatic organ makes up close to a tenth of the animal’s volume. I don’t know what else to make of that, but maybe you can get mileage out of it at a cocktail party.

I posted these because I was inspired by Darren’s post on dome-headed elephants, because they’re cool, to maybe demystify sauropod pneumaticity a little, or perhaps to re-mystify skeletal pneumatization in general. You have a pneumatic cavity between your brain and your monitor right now. How much time have you spent thinking about that (when you didn’ t have a sinus headache)?

Next time: more Berlin goodness.

original-gangsta

UPDATE: By utter coincidence, Ohio University put out a news story about Larry Witmer’s work on sinuses yesterday. Hat tips to Yasmani Ceballos Izquierdo, who posted the link on the DML, and to Mike for sending it on to me. As long as you’re going over there, remember that Larry is one of the Good Guys and puts his papers up for public consumption; the new dino sinus paper is here. It’s great, but it makes the pictures I used here look pretty pathetic. Go have fun!

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14 Responses to “Airheads”

  1. Zach Miller Says:

    I am struck by a few things:

    1) Rhinos have big freaking teeth!
    2) Considering how thin-walled the sinus passages are in the hornbill skull, I am tempted to think that their chances of preservation in any dinosaurs skull are next to zilch;
    3) Gators have big brains (although that looks like a juvenile);

  2. Matt Wedel Says:

    1) Rhinos have big freaking teeth!

    Big HEAVY freakin’ teeth. Requiring big neck muscles to lift and drag around. Requiring a big back of the head to anchor those neck muscles. Requiring sinuses to make that big head light enough to lift. Sez me.

    2) Considering how thin-walled the sinus passages are in the hornbill skull, I am tempted to think that their chances of preservation in any dinosaurs skull are next to zilch;

    You could submit this sentence as a Nature paper entitled, “On the fossil record of pterosaurs.”

    3) Gators have big brains (although that looks like a juvenile);

    That is a juvenile. David’s got a whole series of ‘em. He’s doing with croc heads what I can only dream of doing with sauropod vertebrae. If croc heads interest you at all, I strongly recommend having a look at his research page. Oh, and he’s got pretty pics of bird heads, too.

  3. Nathan Myers Says:

    These pictures are made of awesome. I, too, am impressed at the sinuosity of the crurotarsan brain pictured (not to mention the sinufaction of the containing skull). If we needed a reminder that the brain is just an exapted nose, here’s one.

    “On the fossil record of pterosaurs.”

    So, you admit that pterosaurs really do qualify as dinosaurs, conversationally. My work here is done.

  4. Nathan Myers Says:

    Speaking of hornbills and surprising diets,

    basicinstructions.net/?p=830

    (Linked above)

  5. William Miller Says:

    That’s interesting food for thought.

    Has anyone really looked for pneumaticity (cranial or postcranial) in anything except archosaurs or mammals? Could there be secret pneumaticity in large fish, lizards, turtles, or snakes?

  6. Mike Taylor Says:

    In case anyone’s not realised, the last picture in this post is the cover of Matt’s first rap album, produced under the name of Pneu Matt “Daddy” Ticity. Makes a great christmas present!

  7. Andreas Johansson Says:

    Is that amount of sinus asymmetry normal in humans, or is this a pathological specimen?

  8. Matt Wedel Says:

    Is that amount of sinus asymmetry normal in humans, or is this a pathological specimen?

    Nah, pretty normal. The pattern of frontal sinus pneumatization is different for everyone, as individual as your fingerprints or retinal blood vessels, just harder to see. The frontal sinuses are paired structures and each side develops on its own. By itself that doesn’t mean much; the same is true of your hands, eyeballs, and kneecaps, and they usually look about the same. The wild asymmetry and other variations do suggest that whatever controls there are on the system, they’re pretty loose.

  9. William Miller Says:

    Re the pneumaticity of elephant skulls and sauropod necks: Were indricothere skulls pneumatized? If they were, maybe that’s related to large size…

  10. 220mya Says:

    Nathan;

    Pterosaurs are really just stem birds anyway. They just happened to evolve flight independent of Avialae.

  11. DD Says:

    absolutely amazingly aerated awesomeness!

  12. Mike from Ottawa Says:

    Since heads are doing a guest spot on SVPOW, I thought i pass this on a type of carpenter ant, in relation to the exploding heads of sauropods:

    “In at least nine Southeast Asian species of the Cylindricus complex, such as Camponotus saundersi, workers feature greatly enlarged mandibular glands. They can release their contents suicidally by rupturing the intersegmental membrane of the gaster, resulting in a spray of toxic substance from the head, which gave these species the common name “exploding ants”.”

    Has this method of defence been considered for sauropods?

    The above is from Wikipedia, by way of the Myrmecos blog, which despite the handicap of being shockingly deficient in sauropods and their vertebrae is pretty interesting.

  13. Matt Wedel Says:

    Re the pneumaticity of elephant skulls and sauropod necks: Were indricothere skulls pneumatized? If they were, maybe that’s related to large size…

    Indricothere skulls were pneumatized; they look pretty much like the black rhino skull above except the tops of their heads were flatter and they didn’t have a rugose pad for a nose horn. I don’t know if they were more pneumatic than the skulls of smaller rhinos in an ASP sense; it would be interesting to find out.

    the last picture in this post is the cover of Matt’s first rap album, produced under the name of Pneu Matt “Daddy” Ticity.

    Please. My recording name is simply Neu Matt. My first album is Neu Matt: Da City, to be followed soon by an a collection of ballads entitled Neu Matt: Eyes and the grungier Neu Matt: Ick!

  14. Graham King Says:

    Matt Wedel Says:
    December 12, 2008 at 12:58 am
    Please. My recording name is simply Neu Matt. My first album is Neu Matt: Da City, to be followed soon by an a collection of ballads entitled Neu Matt: Eyes and the grungier Neu Matt: Ick!

    I hope to find these albums in the shops soon. Though the tasters online are great!

    I particularly like the tracks on Neu Matt: Ick!, ‘Alley Complex’ and ‘V Airy Ability’.
    There are some very intricate passages in the former; and in the latter, some wild experimentation, and soaring themes I find evocative of pterosaurs.


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