Things to Make and Do, part 6f: my dumb observation of the day is that in dorsal view, a partly-assembled ostrich skull looks kind of like a chasmosaurine
July 24, 2010
What’s that? You want proof, you say? Well, I find your lack of faith disturbing; but since you asked, you got it!
What we have here is the part-way assembled skull of our old friend Veronica, in dorsal view, with anterior to the left. The long pointed bones down there are the nasals: you don’t see their anterior ends in complete skulls because they’re covered by the fused premaxillae. Posterolateral to those are the lacrimals, forming those posterolaterally directed spurs. Between the nasals towards their posterior end is the top of the mesethmoid. Behind the nasals and mesethmoid are the frontals, the largest bones on view here; and behind those are the parietals. Ventral to those superficial bones are the palatines (sticking forward and showing on either side of the nasals), plus the pterygoids, the squamosals, and of course the braincase including the parasphenoid rostrum and fused vomers, but those are all hidden in this dorsal view.
Here’s the whole hill of beans in ventral view: this time you can see the parasphenoid rostrum going down the midline, with the vomers fused onto its anterior end; and the pterygoids attached near the base of this process, and the palatines extending anteriorly from them. In this view, the squamosals are the lateralmost projecting bones. Zoom through to the full-sized images to see the cool pneumatic openings up inside the squamosals and the parts of the braincase that they articulate with.
Still waiting to be attached to the cranium: the quadrates (which go on the lateralmost points of the skull); then the quadratojugal, jugals and maxillae, forming a straight line directed anteromedially from the point of the quadrate; and finally the fused premaxillae which go on the end of the snout and join the nasals medially and the maxillae laterally. Those bones will of course obscure some of what we can see at the current stage of assembly, so I thought it would be useful to show you this intermediate stage.
Since I’m here, I may as well show you how the partially reassembled cranium looks in left lateral view, too:
From here, you can really appreciate the weird shape of the lacrimals, with their ventrally directed processes that I think are going to contact the maxillae once I’ve got them attached.
Finally, those of you who have been wise enough to get hold of some red-cyan anaglyph glasses will be able to appreciate this spectacular 3D view of the skull in ventral view. The rest of you: come on, sort it out: they cost maybe a couple of bucks, and they’ll revolutionise your perception of, well, anaglyphs.
Things to Make and Do, part 6e: gloat your eyes, feast your soul, on my ostrich ethmoid ossification
July 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 that’s taken me some time to get good at, and one that I might do a tutorial on some time, to follow up the one on photographing big bones.
Here is a preview of the result of this photography-fest: a multi-view figure of the ethmoid ossification.
The top row shows it in dorsal view; the middle row in left lateral, posterior, right lateral and anterior views; the bottom row in ventral view.
This is a midline bone, or rather complex of bones, that lives between and slightly ahead of the eyeballs, as shown in the photographs of part 6c. The top part is the mesethmoid, which contributes to the roof of the skull between the nasals and ahead of the frontals. Below that is — well, I’m not sure what it’s called. Jaime said in a comment that it’s “a portion of the ossified interorbital septum”, but it’s not like a septum: it’s a hollow capsule with very, very thin walls. Anyone know its proper name?
By the way, I strongly encourage you to click through the image above and see it in its full high-resolution (5943 x 3384) glory. As a taster, here’s a small segment — the rear portion of the dorsal view — in half resolution:
As you can see, that’s some very well textured bone — much more so than is apparent to the naked eye.
SV-POW! is, as I’m sure you know, devoted to sauropod vertebrae. But occasionally we look at other stuff… and you might have noticed that, in recent months, we’ve been looking at, well, an awful lot of other stuff. I’m going to continue that theme here and talk about salamanders. Yeah: not sauropods, not sauropodomorphs, not saurischians, and not even dinosaurs or archosaurs. But salamanders. Don’t worry, all will become clear. This all started back in May 2010 when I blogged about amphiumas over at Tet Zoo. Amphiumas are very unusual, long-bodied aquatic salamanders.
As it happens, amphiuma vertebrae are particularly interesting if you work on saurischians because (drum-roll)… they have laminae. The term lamina is not restricted to structures present only in pneumatic saurischians: I would argue that it should be used for any sheet-like bony process on a vertebra, and I hope everyone agrees with me. Laminae are not common outside of Saurischia, but are present here and there: they’re present in stem-archosaurs (like Erythrosuchus), various crurotarsan archosaurs (including aetosaurs), some neosuchian crocodilians, and silesaurids (Desojo et al. 2002, Parker 2003, Nesbitt 2005, Wedel 2007, Butler et al. 2009). Even weirder, they’re present in Aneides lugubris, the Arboreal salamander of California and Baja California (Wedel 2007). But that’s about it.
Why would a salamander ‘want’ vertebral laminae? The laminae of the Arboreal salamander are presumed to be related to the extensive accessory ossification present in the skeleton of this animal, itself a consequence of adaptation to a peculiar climbing lifestyle. In other words, it’s hypothesised that the function (if I may be so bold as to use that word…) of the salamander’s laminae is nothing like that of the archosaurs that have them.
And now we know that A. lugubris isn’t the only salamander with laminae: amphiumas have them too. They’re clearly figured in the amphiuma literature (Gardner 2003), but (so far as I know) no-one has previously drawn attention to them when discussing archosaur laminae.
Gardner (2003) figured schematic amphiuma dorsal vertebrae that were based on a combination of features present in two of the three living amphiuma species (namely, Amphiuma means and A. tridactylum). On the lateral sides of the centra are structures that – if seen in an archosaur – would almost certainly be identified as anterior and posterior centrodiapophyseal laminae (using, as always, the nomenclature proposed by Wilson (1999)) [see the digram above, from Gardner (2003)]. There are also structures on the dorsal surfaces of the postzygapophyses that look something like laminae: they extend from the posterolateral parts of the neural arch and run across the tops of the postzygapophyses, hence recalling spinopostzygapophyseal laminae. Actually, I’ve just realised that similar structures are also sometimes present in anurans (frogs and toads) where they’ve been called paraneural crests or paraneural processes. These structures do have a ‘known’ function: in amphiumas they’re associated with complex dorsalis trunci epaxial muscles. Unlike the spinopostzygapophyseal laminae of saurischians, the structures in the amphibians are low ridges that don’t contact the neural spines, so it could be argued that they aren’t so lamina-like after all.
But what about the structures on the sides of the centra? Why are laminae present in a group of long-bodied aquatic salamanders? Why are laminae present at all? This question has been asked a few times here on SV-POW! (here, for example), and there are two primary hypotheses. One is that the laminae keep the various air sacs separate from each other, perhaps because they persist while much of the bone around them is resorbed during ontogeny, while the other is that they somehow provide mechanical support and are aligned along lines of stress (for more on this subject see the piece on finite element analysis).
The pneumaticity explanation can’t work for amphiumas (given that they’re apneumatic): does the ‘mechanical support’ one apply instead? We don’t know anything about stress distribution in amphiuma vertebrae – in fact, I don’t think we know anything about the mechanics of amphiumas at all – but it’s possible that the laminae might play this role, especially given that amphiumas have to bend, twist and push with their bodies while excavating burrows.
In conclusion, we just don’t really know what’s going on here. In fact, all we can really do at the moment is wave our arms around a bit and say “Hey, amphiumas have vertebral laminae, too”, and that’s pretty much all I’m doing here. It’s also possible that the structures I’m talking about in amphiumas are very different in detail from the vertebral laminae present in archosaurs: I’ve never even seen a single amphiuma skeletal element and am basing all of this on photos and diagrams in the literature. Nevertheless, it’s something definitely worth bringing attention to. As usual, we stand poised at the abyss, straining our eyes to see into the infinite darkness ahead.
Butler, R. J., Barrett, P. M. & Gower, D. J. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters 5, 557-60.
Desojo, J. B., Arcucci, A. B. & Marsicano, C. A. 2002. Reassessment of Cuyosuchus huenei, a Middle–Late Triassic archosauriform from the Cuyo Basin, west-central Argentina. Bulletin of the New Mexico Museum of Natural History and Science 21, 143–148.
Gardner, J. D. 2003. The fossil salamander Proamphiuma cretacea Estes (Caudata; Amphiumidae) and relationships within the Amphiumidae. Journal of Vertebrate Paleontology 23, 769-782.
Nesbitt, S. J. 2005. Osteology of the Middle Triassic pseudosuchian archosaur Arizonasaurus babbitti. Historical Biology 17, 19–47.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of northern Arizona. Unpublished MS thesis, Northern Arizona University, Flagstaff, AZ, 312 pp.
Wedel, M. J. 2007. What pneumaticity tells us about ‘prosauropods’, and vice versa. Special Papers in Palaeontology 77, 207-222.
Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19, 639-653.
It’s been a while since we last caught up with my wallaby, which I am suddenly going to decide to call Logan. When we saw him last, I was concentrating on his feet, although the initial post does also include a photo of the partially prepped skull in right lateral view.
Back in the day — and this was eight months ago, remember — I wrote “I think that [the skull] would benefit from a third simmer-and-pick session before I put [it] out somewhere for invertebrates to deal with.” That’s what I did, but the results were not encouraging. I put the skull (and first three cervical vertebrae, which I’d prepared with it) into a plastic box with air-holes and left it in the woodshed — an approach that’s worked well for Darren Naish many times, and has also served me well regarding that baby rabbit that I keep meaning to show you. But when I went to retrieve Logan’s skull a few days ago, I found that it had gone mouldy!
There should be a picture of Mouldy Logan here, but I stupidly forgot to take one. So instead here is the fifth cervical vertebra of the Erketu ellisoni holotype IGM 100/1803, with its bizarrely sigmoid centrum, from Ksepka and Norell (2006: fig. 5).
Well, anyway – ouch! I didn’t even know bone could go mouldy. And what I didn’t appreciate at that point is that the mould had also made the bone fragile, brittle — crumbly, even. Not good at all. To get rid of the mould, I simmered the skull and vertebrae gently for an hour or so, then cleaned it up with a toothbrush and some washing-up liquid (or “dish soap”, as you wacky colonials apparently call it). It was at this point that the crumbliness became apparent, of course: the respiratory turbinates were completely gone, and the nasals, having come away from the rest of the skull, broke into three pieces each. Also, the dorsal margins of the maxillae and premaxillae, where they abut the nasals, started to crumble. Finally, the bone directly above the foramen magnum whose name I can never remember came away, and a small chunk came away from the bone that that abuts it to the left. It wasn’t pretty.
Anyway, I cleaned the bones as carefully as I could, then let them soak overnight in dilute hydrogen peroxide before carefully rinsing them and leaving them to dry. The result still looks good, but it’s disturbingly fragile. Here it is:
I also prepared a red-cyan anaglyph of these bones, from an aspect slightly anterodorsal of dorsal. Those of you who have not yet obtained red-cyan glasses for viewing these, get your arses in gear — they are really informative.
Finally, here is a close-up of the crumbling nasal region, and the remaining pieces of the nasal bones. You can see that the bone has lost integrity.
(Those two fragments at the bottom of the picture are, I think, from the dorsal border of the right maxilla.)
And now, gentle reader, I come to you for advice. What can I do to strengthen poor Logan’s skull? I guess there must be some kind of commercially available compound that I can soak it in or paint on to it to consolidate the friable bone? Help me out, please. I don’t want to lose Logan.
And by the way …
I realise that SV-POW! has been heavy on these extant-animal-skeleton posts recently, and correspondingly light on actual, you know, sauropod vertebrae. I hope no-one feels too short-changed: I’ve been assuming that among that constituency that appreciates sauropod vertebrae, there’s a corresponding liking for ostrich and wallaby skulls. Do let me know if it ain’t so (or indeed if it is).