Things to Make and Do, part 6c: fragments of ostrich skull

June 25, 2010

After the third simmering, Veronica the Ostrich Head started to come apart beautifully — more so than she should have done in one or two places, as it became apparent that her skull, as well as being incompletely fused due to presumed subadult age at time of death, was slightly damaged.  Still, I’ve been able to tease the bones apart nicely, remove pretty much all the remaining soft tissue, and figure out where most bits go, well enough that I think I’ll be able to put her back together once everything’s been cleaned.

[Anyone who’s not yet read parts one and two of this ostrich-head series should probably do so before going on to this one — apart from anything else, the pictures will make more sense that way.]

Here’s my girl as she emerged from the pot (cranium only — the mandible was separate by this point).  What may not be apparent here is just how fragile she was by this stage: I had to hold her snout as well as the main part of the skull to prevent it from falling off.  You can see that it’s skewed a little sideways, rotating clockwise with respect to the rest of the skull so that the posterodorsally oriented midline “tongue” of bone is off to the left (our right), and lies alongside the central bulging bone rather than overlying it as in earlier stages.

The squamosals are still in place at the sides of the back of the skull, but they came away very easily, and cleaned up nicely.

I carefully removed the snout, and was astounded to see how very thin the bones that connect it to the rest of the skull laterally are:

The midline bone here apparently is the fused ascending processes of the premaxillae, despite my having said last time that it probably wasn’t — thanks to Nick Gardner for putting me straight.  but what are the posterolaterally directed spines?  Can they also be processes of the premaxillae?  Or are they the maxillae?  I think the former: read on.

It’s hard to tell in part, of course, because of the horny beak which obscures whatever sutures might be up there at the front of the skull.  I don’t want to remove that, partly for fear of causing damage to the bones but mostly just because it’s nice to keep.  What I’d not appreciated until I started this exercise is that there’s no hard demarcation between beak and soft-tissue, but they grade into each other so that the posteriormost preserved parts of the beak are not horny at all, but rubbery — even stretchy.  It’s hard to know how much of this to remove.  If there’s a Standard Operating Procedure, I don’t know it — anyone?  Maybe I’ll leave the snout in a bug-box and let the dermestids decide.  (Let the Dermestids Decide would be a good title for a debut novel, and its Oscar-winning movie adaptation.)

(Of course this continuous gradation between tissue types is familiar to all of us who’ve ever tried to remove the cartilage from a skeleton: in some cases, like the cartilage caps on long bones, there’s clear bone and clear cartilage, but in other cases it’s not so well-defined.  Think, for example, of the partially ossified but partially cartilaginous breastbone of a chicken — take a look the next time you have a Sunday roast.  This is a real problem in cleaning skeletons.)

Once I’d removed the snout, here’s what remained:

On the midline, half way along the remaining skull (i.e. anteromedial of the orbits) is a very fragile self-contained bony capsule which seems to be full of some kind of soft tissue — maybe fat.  It’s not easy to make out its boundaries in this photo, so here is another that I took of the skull after lifting the capsule out — you can see it in the background.  Does anyone know what the capsule is?  My feeble bird-skull literature isn’t telling me anything about this.

With this capsule gone, it was with me the work of a moment to lift out the two big, spongy, soft-tissue masses from in front of the orbits, which you’ll remember I decided not to attempt last time.  A very good decision that proved.  Having removed them, I found a neat cartilaginous midline structure which I’d like to preserve for the final reconstruction of the skull, but which is already changing shape dramatically as it dries up so I fear I’m going to have to let it go.  Anyway, the bony structure of the remainder of the skull is now much more apparent:

I am guessing that the anteriormost lateral bones are the maxillae, which are a super-weird shape.  As you can see, the left bone is broken: its anterior portion is missing.  Happily, I have this bit, and it’s a perfect fit for the posterior part, so a bit of superglue should fix this problem — but it does emphasise just how insanely delicate many of the skull bones are.

I think the “wing” bones projecting laterally from near the back of the skull must be quadrates: if so, then the bones that project anteriorly from them are quadratojugals, which shade into straight, elongate jugals (you can see the junction in the near side of the photo above) and then connect with the maxillae.

The midline bone, which is surprisingly robust, seems to be made up of fused vomers or somethingat the front, and the parasphenoid rostrum to the rear [thanks to Nick Gardner for this and other corrections].  They’re hard to see in this photo, but there’s also a pair of oddly shaped more-or-less horizontal plates ventrolateral to this midline bone (I think they must be the palatinespterygoids) and two longer, narrower bones anterior to these (which might be the vomers, in which case the fused midline bones are something else? are the palatines).

Once I’d removed all these, I was left with a solid braincase fused together with that midline bone that might be vomersmade up of the parasphenoid rostrum and vomers.  And that, with surprising suddenness, was that.

So here is the complete set of skull bones, laid out in something resembling their order in life: top of the skull at the top of the picture, facing left, with vertebrae to their right; bottom half of the skull (mandible first, then palate) at the bottom of the picture, also facing left.  (Sorry that the contrast is not great: the sun was almost down by the time I took this photo):

When I looked at this, I was reminded of a passage in one of Dave Barry’s old columns, ‘Mister Mediocre’ Restaurants, in which he proposed some surefire business ideas, including a place where you could have your non-functional gadgets permanently destroyed:

The idea there was that consumers would bring their broken electronic devices, such as television sets and VCR’s, to the destruction centers, where trained personnel would whack them (the devices) with sledgehammers. With their devices thus permanently destroyed, consumers would then be free to go out and buy new devices, rather than have to fritter away years of their lives trying to have the old ones repaired at so-called factory service centers, which in fact consist of two men named Lester poking at the insides of broken electronic devices with cheap cigars and going, Lookit all them WIRES in there!

Similarly, I found myself thinking: lookit all them BONES in there!

Happily, help was on the way: Nick Gardner sent me a copy of Maxwell 2009, which has a few useful figures, and from these I was able to take pretty good guesses on the identities of more of the bones.  (That’s why I’ve included more guesswork above than in previous articles in this series.)  So I leave you with an annotated version of the photo above, with my best guess at identifying the bones.  PLEASE MAKE CORRECTIONS IN THE COMMENTS — I will make up a revised version of this annotated photo once they’re all in.  For for now, here it is Here is the initial version, which Nick critiqued in the comments:

And here is the corrected version, so far at least:

Now let’s get those corrections going!

References

  • Maxwell, Erin E.  2009.  Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae).  Zoological Journal of the Linnean Society 156:184-200.
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19 Responses to “Things to Make and Do, part 6c: fragments of ostrich skull”

  1. Nick Gardner Says:

    Based on the ref, I sent you, or if you looked at the Digimorph or Witmer Lab 3D specimens for Struthio, you could have seen that those caudolateral processes are in fact from the premaxillae. Like I said before, much of the antorbital skull superficially is premaxilla in birds.

    Onto the other bones:
    What you labelled as vomers? are palatines. What you labelled as palatines are pterygoids. The back portion of what you labelled as vomers that are coming from the braincase is the cultriform process of the parasphenoid (aka ‘parasphenoid rostrum’), the front part is the vomers. You should be able to see some kind of suture between them. Your quadrates in the upper part of the picture are squamosals, but the bottom stuff you labelled as quadrates, those are quadrates (quadrates don’t come in four packs, sorry). You missed the lacrimals hanging out in front of the frontals. The mystery capsule is probably some kind of ethmoidal ossification, maybe the mesethmoid.

    It would be cool if you could get some higher resolution images of the individual elements in different views (rostral, caudal, medial, lateral, dorsal, ventral).

  2. Mike Taylor Says:

    Many thanks for the corrections, Nick. I did refer to Maxwell 2009, and it did help; but not as much as you seem to have expected it would help someone who doesn’t already know bird skulls.

    I don’t know what the heck I was thinking labelling the squamosals as quadrates, especially as I’d correctly identified them in the text. D’oh!

    Yes, I do plan to get a lot of high-resolution images of the individual bones. When they’re available, I’ll make sure SV-POW! knows about it.

  3. Nick Gardner Says:

    well, I really cannot recommend Romer’s The Osteology of the Reptiles enough and also Hanken and Hall’s “The Skull” series that was released through University of Chicago Press during the early 90’s.

    in particular, the second volume “Patterns of Structural and Systematic Diversity” has some great papers illustrating the skulls of basal tetrapods (incl. amphibians), reptiles, and birds.


  4. […] right cervical rib from cervical vertebra 3 of my ostrich, Veronica [see earlier Part A, Part B and Part C for context].  I thought you might like to see the result, so here it is: Third right cervical rib […]

  5. Nick Gardner Says:

    I’m still certain that the mystery capsule is the mesethmoid.

  6. Mike Taylor Says:

    Oh, cool — I didn’t get from your initial comment that you were at all sure about the mesethmoid. In that case, I think we now have everything identified. Many thanks.

  7. Bruce J. Mohn Says:

    Hi Mike:

    If you haven’t already done so, make sure to brace the portions of the premax that connect with the nasals. Otherwise these will curl up during drying. I made that mistake with my emu.

    Best,

    Bruce


  8. Nice posts on the ostrich, I guess I can get one of those from a farm in my country.

    Could be possible to retrieve sclerotic ossicles? they should have gone with cooking, perhaps other method can be used to get them.

    And do you plan to assemble this skull? which adhesive do you think would be most useful?

  9. Mike Taylor Says:

    Jorge, I didn’t see any sclerotic ossicles; and because I clean things down very slowly are carefully (retaining, for example, the sub-1 mm manual sesamoids from my wallaby skeleton) that makes me think that probably there weren’t any. Do they perhaps only ossify late in ontogeny? Veronica seems to have been a subadult. (Or are you even sure that ostriches have them? None of the photos or figures that I’ve seen of ostrich skulls show them.)

    Yes, I plan to assemble the skull (only I’ve exhaustively photographed all the constituent elements). I have no idea at this point what kind of adhesive to use, and would gladly welcome suggestions.


  10. […] is complete!  Here are all the bones of Veronica’s skull [see earlier part one, part two and part three], laid out as they were in life (though of course much more widely separated), all in dorsal […]

  11. Nick Gardner Says:

    Sorry, you must have lost them somewhere. Ostriches have scleral rings (see Hall, 2008), as do all birds, I’m pretty damn sure.

    They probably aren’t included with the other skulls because of having to mount them or w/e.


  12. I´m pretty sure ostriches have sclerotic rings, they perhaps do ossify late in ontogeny.

    Long ago, I used a kind of water-solved wood glue for bones (because of its reversibility), but I guess if you can get a little bit of Paraloid B-72 it will work as well (however, paraloid sets soooooooo slowly…), I have used it a few times.


  13. I would like to build on what Nick said earlier: The midline capsular structure exposed on the skull roof if the mesethmoid (as commonly cited, the homology is less settled). The openings on the sides implicate the olfactory bulbs, and there should be a posterior aperture for the olfactory nerve(s). You actually have two bones there, though: the dorsal of the two, as delimited by a distint suture, is the true mesethmoid; the structure beneath it is a portion of the ossified interorbital septum, and in images after you removes the skull roof, eyes, and lachrymal/nasals/premaxillae, you will note the bone contacts the cultriform process of the parasphenoid.

    You’ve identified the posterior right mandibular ramus correctly; chondrification of the medial mandibular bones (prearticular and splenial) generally results in disappearance of distinct bones, or lack of ossification (they remain cartilage in the jaw). The broad end of one of them indicates it forms part of the butress of the anterior wall of the articular cotylus, and thus is a surangular.

    Fortunately, you don’t have to hunt for the ectopterygoids or the epipterygoids; the former are fused to the palatines in all neornitheans and most ornithothoraceans, while the latter seldom ossify or are fused to the pterygoid as forming a point form tendons of the jaw: your pterygoids should have a small nubbin for the contact, expanded with fusion in later ontogeny.

    Your hyoid bones are two paired ceratobranchials and one epibranchial. These, as their prevalence in typical articulated skull fossils show, are the first structures to ossify as they support massive hyolingual muscles needed for oral processing and swallowing; the epibranchial is (as you say earlier) still cartilage, so it’s amazing it survived.


  14. Question: Can you remove the rhamphotheca from either upper or lower jaw?

  15. Mike Taylor Says:

    I probably could remove the rhamphotheca; I’m not sure that I want to, What would you advise?


  16. In some bird specimens, the rhamphotheca tend to slip right off. It varies, so I don’t know if further soaking would do it, I was just curious if they could also simply be “jiggled” off through careful manual manipulation.


  17. […] 19, 2010 Work continues apace with Veronica, my tame ostrich.  (See previous parts one, two, three and four).  I’ve been photographing the individual bones of the skull — a skill […]


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