Posts Tagged 'bones'

Dinosaurs labelled

Inspired by the posters featured in this post of mine Mike Taylor has gone and made this picture comparing a sauropod and theropod to show the homology of all the elements.  He’s stuck it up on SV-POW, but is encouraging people to use it in their teaching so I thought I’d repost it here. Thanks Mike and great job.

Guest Post: trabeculae and diamond-tipped saws

Bone thickness model of trebeculae. Courtesy of M. Doube


Today’s guest post comes from Michael Doube. I found out about Michael’s work though my friend John Hutchinson at the Royal Vet College in London who regular readers might well recognise as a major dinosaur researcher, though John often dabbles in extant organisms as a basis for his palaeontological research. In this case Michael and his team were looking at trabeculae, those little supporting threads of bone. Their pattern of distribution can potentially tell us quite a lot about both extant and extinct species and Michael explains:

Continue reading ‘Guest Post: trabeculae and diamond-tipped saws’

Darren Tanke’s Gorgosaurus preparation 15: finishing touches

The Gorgosaurus has entered its final phase of preparation on this side. All the bones are being worked on in a systematic fashion now. Glue that stabilized them mostly went inside the bones, but some is on the outside and rough in appearance or dirty with embedded sand/dust. All this “old glue” is carefully scrapped off and a final clean coat of thin glue applied to the surface where needed. Rough rock areas are being smoothed down. As said in an earlier update, the specimen will be molded in latex rubber. This will likely be done in one piece and how that is made will be covered in future updates if Dave Hone and the followers of this blog are interested [Edit: I most definitely am, it would be great to cover this too! Dave]. It is technically not fossil preparation but an important and often overlooked aspect of the technical side of vertebrate paleontology.

Part of the Gorgosaurus‘s final phase of preparation is getting it ready for latex molding. Molding a fossil is like chess- if you do something to the specimen, it will affect how the mold will be removed in the future? You always have to think ahead. For example a deep undercut under a bone can be molded, but once the latex cures how will it be removed from that deep undercut? Will it come off easy, or (more likely) will it be “stuck” and in the efforts to remove the mold, the bone above is damaged or possibly destroyed. With these thoughts in mind, the Gorgosaurus is being gone over section by section, looking for potential problem areas for molding and demolding as well as general areas of support. Bad undercuts are being fixed. Any low spots are obvious “weak” areas for support and latex will stick more firmly to them than a flat of slightly convex surface. These low areas are filled in. To do this, I first take leftover waste rock matrix from the Gorgosaurus and with a hammer break it up into sand grain consistency. The hole or depression to be fixed is glued and then enough loose sand it sprinkled into the low spot. A dry brush steers the sand in to small undercuts. Larger undercuts can be filled by using a small funnel made out of a piece of paper. The funnel’s tip is put under the undercut (usually meaning the funnel is angled somewhat) and pinches of sand dropped into the funnel until the problem area is filled up- this works great for microcracks only a sand grain wide too. Once this is all done, a very gentle puff of air administered by mouth gently blows away any brush marks in the loose sand. Then the loose sand is glued with acetone-based glue- the same used to stabilize the bones. Being acetone-based, it can be reversed at any time in the future if need be.

The final effect looks fairly good, but never adopts the same color as the untreated rock, but this can be rectified with paint later if wanted. The procedure is shown here in one small area and then a picture of an overall area after treatment is shown. The long and narrow belly ribs in the overall view on the right side are much better stabilized now. You may ask why not just leave the rock in there to begin with and that is usually the plan, but sometimes it is not there (due to a wide crack), or crumbled away into loose unstable pieces, or was deliberately removed for some reason (such as the removal of the postorbital from the antorbital fenestra in an earlier post) and needed to be refilled. We are hoping to start molding the Gorgosaurus block by mid February.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

Ossification and preservation

While obviously working on dinosaurs means that you are primarily looking at fossil bones, these are not always the whole story when it comes to the skeleton. Obviously bits go missing, and whole skeletons are a rarity, unossified parts can also make themselves scarce. However, not all parts of the skeleton always even ossify – the skeleton is not synonymous with bones. Chickens have a mostly cartilaginous sternum for example.

So while a fossil might preserve all of the bones, it won’t necessarily preserve all of the skeleton. Add to the fact that as noted with ossified tendons, not all things that can ossify always do (and of course with tendons, most of them do not) making things harder. Coupled to this is the fact that, as with ossified tendons, there is likely to variation if how such a feature is expressed. You might have half a dozen good specimens with only one preserving a given feature. That might not be missing in the others, it simply ossified in one of them and not the rest. Part of this variation also comes from age, with typically older animals having more bones or parts of bones that are ossified than juveniles (or even other adults if it’s a particularly old individual) so this has to be factored in too.

This is an especially important consideration why trying to track evolutionary changes in groups where certain characters or bones seem to come and go regularly. An example are the clavicles / furcula that I touched on recently. If you match a phylogeny to the specimens we have with furculae / clavicles the picture is a little confusing with the elements apparently disappearing and reappearing multiple times. Part of this will be down to the incompleteness of some fossils, but it’s also likely to be in part due to how these bones ossify. Based on their inconsistent appearance and incomplete preservation in at least some taxa, it’s likely that they were largely present in most, if not all, theropods and merely remained as cartilaginous elements and did not ossify, hence their apparent (but not genuine) absence.

Characters can of course be lost, and reappear (we’ll be dealing with this issue next up) but caution should be taken in assuming that this is the norm. Obviously knowledge of the vertebrate skeleton really helps as some elements are more prone to this pattern of only occasionally being ossified, or ossification patterns changing during ontogeny etc. but the first assumption should not be that an element is genuinely absent, even when there is an apparently complete set of bones present. There’s more to the skeleton than just those lumps of calcium and phosphate based crystals.

Destructive sampling

Sadly not all of the information you might want from a fossil can be obtained just by looking at it. No matter how technological your approach (microscopes, SEM, X-rays, CT scans, synchrotron and the rest) some things, while present, will remain inaccessible. For a start, most vertebrate specimens won’t fit into a scanning electron microscope. CT scanners can only penetrate so much matrix or so much bone. X-rays will only give you a certain level of resolution and so on.

Therefore if you really want to count the LAGs in that femur, or look at those melanosomes in that feather then destructive sampling may be your only option. If you want to do some form of geochemical analysis such as looking at the isotopes then this certainly is your only option. The term might sound rather drastic and imply that you won’t be left with much at the end of it, which while far from the truth, is certainly descriptive. The aim of destructive sampling is to extract the necessary information with the minimum amount of damage, but the crucial point here is that the fossil will be irreparably damaged by this process.

This is typically and understandably seen as a necessary evil in most cases. The damage can be minimised and the information gained can be massive. And of course in many cases it need hardly be noticeable. Isolated dinosaur teeth are for example exceptionally common and in most cases damaged or incomplete, and only the smallest of sample (a few milligrams) is needed to do an oxygen isotope analysis say. It is therefore hand not to justify the sampling of teeth for this purpose.

However, as the specimens become more important and better preserved (and rarer) it becomes harder to justify. It’s no surprise that the first destructive work ever done on Archaeopteryx was only published last year, though it’s still more impressive that several specimens were sampled. Similarly, although there are various feathered dinosaurs, it was hard to justify the destructive sampling necessary to look at the colour of Anchiornis until the method had been well established and it was likely good results would be obtained, and that there were several specimens known so that the loss of information on one does not mean that our only record of this is gone for good.

It might be tempting to argue that anything that possibly damages any fossil (or any scientific specimen) irreparably should not be carried out. After all, technology always increases in scope and accuracy and it is only a matter of time before we could put a whole T.rex under and SEM or put a 5 ton block into synchotron to see what is inside. Science is a steam-roller of a methodology – it takes forever with constant checks, rechecks, corrections, restarts and revisions. A few years or decades will not make so much difference, then will it?

Well, that might be true to a degree, but the obvious counterargument to this approach is that this ensures nothing will ever be done. There will always be another method that’s less invasive, or faster, or cheaper, or provides greater detail coming around the corner and if you wait for one, you’ll wait for the next and the next and the next and no research will ever be performed. In palaeontology we don’t have the luxury of infinite resources or to a degree, such time. We have to get some work done, and if a few specimens have to suffer a little damage to produce a great deal of information, that’s probably no great loss (indeed, on average it’s a gain). So while destructive sampling is hardly the first choice for any specimen, and certainly not ever the choice for some of exceptional historical or scientific importance, it’s a necessary tool in our arsenal and one that is used with care, when appropriate.

Osteological correlates

I’ve now passed the 500 odd post mark (if you include all the old stuff on DinoBase) and frankly it’s getting hard to remember what I have and have not said before. While I don’t think this post is a real repeat of anything I’ve said before I’ll be surprised if I’ve not mentioned it at least in passing and may well have gone into some detail. Since I try to avoid covering ‘new’ things to do with archosaurs, and focus on the basics palaeontology and the mechanics of research on archosaurs I don’t really have the luxury of always ‘moving forwards’. As such it’s really only a matter of time before I end up completely repeating myself in a post or two (or three).

However, I’m working under the assumption that this is unlikely to be a problem. New readers will not necessarily have read my whole back catalogue (though I would ask, if not, why not? It’s all great, honest.) and regular readers won’t necessarily remember what I said two years ago (since I can’t, I doubt they can). Should this end up repetitive then consider it like revision – something rarely stays in the mind permanently after one round, so a little brush up, or re-examination of an old topic is hardly a disaster. With that in mind, onto the largely (I think) uncovered world of osteological correlates and their place in palaeontology.

Continue reading ‘Osteological correlates’

Pterosaur trabeculae

Time for another obscure word in the annals of vertebrate palaeontology and here is one that ties together birds and pterosaurs, if only in a nomenclatural sense. For those that do not know, both pterosaurs and birds have hollowed out, pneumatic bones which in life were filled with air sacs that were extensions of the lungs. However, this obviously could potentially weaken the bones and make them vulnerable to being broken and given the kinds of high forces that many of them would have to deal with (like the bones of the wing or legs for flight and landing respectively) you want to keep them strong.

IMGP2213Evolution has evolved an elegant way around the conflict here – keeping things hollow (and thus light) but strong with some biological scaffolding. The trabeculae are therefore the various small and often intricate little webs and buttresses and spars of bones that populate the insides of various bird and pterosaur bones, providing strength and support to the bone with the minimum of extra mass. These naturally tend to be denser in number and more complex in the ends of bones such as the one pictured here or those with higher stresses and strains, but they can be quite sparse in others.

Inevitably they are little discussed in the literature since in a well preserved bone you can’t see them and even in those that are broken open they are not always visible. Even if they are visible are themselves broken, or as shown here, so complex as to be beyond description. As a result they receive little attention though they are potentially very important as they may help show which bones are taking which stresses where and even in what orientation. As such there may be much functional anatomy hidden in the trabeculae and we have yet to investigate them properly, though with modern scanning methods and further interest beginning this may not be the case for too many more years.

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Bone splinters

While fossils can be preserved as immaculate and perfect pieces of transformed bone (or other organic materials) free from distortion, breaks, damage or really changes of any kind, these are of course the exception. You can also get hideously broken and deformed and ruined specimens. Here is a photo of what happened to an apparently well preserved piece of bone (if nothing else look at how dazzlingly white it is) that crumbled at the slightest touch with, as you can see, devastating results. There are quite a few bones preserved like this at Bayan Mandahu and they look fantastic but are incredibly hard to extract. Even if you apply lots of glue to them they then just stick to the surrounding matrix and while are then less likely to fall apart, they are also incredibly hard to extract from the matrix they are now glued to. Just another small irritation that occurs during fieldwork when you have finally found something that actually is bone and then it falls apart instantly before you can collect it.

IMG_4545

More on things that look like bone and aren’t

gyp1My post last year on “things that look like bone but aren’t” went down well, but certainly suffered from a lack of illustrations. This time out I had a camera handy and was able to take a couple of snaps of a few bits of gypsum on the surface (above) and weathering out of the rock (below) both of which have a great bone-like appearance thanks to the fine grain of the crystals that look very like the texture of bone and the white-ish colours.
gyp-2

If I see a few more examples of ‘not bone’ I’ll keep them coming.

More on bone degradation and disintegration

I recently wrote about scavenging and the odd effects it can have on corpses , and of course how that can affect what you might find as a palaeontologist. While I could always see how odd bones and body parts (like a whole hand) could go missing, one thing that had puzzled me was how you could find parts of skulls with others missing. Of course erosion can lead to pieces being worn away before the specimen is found, and perhaps not all of the cranium was buried originally and thus not fossilised. Some skulls of course also get smashed or broken, so that is another possible explanation, but these were not always in evidence, so what else could it be? Given how (in adult animals at least) the skull is often a tough piece and the sutures of the individual bones are all nicely sealed, it still struck me as odd that sometimes you could find several disparate parts of the skull apparently well preserved, and even in association with other parts of the skeleton but with the rest missing. What had happened to the rest? How had it broken along suture lines without damaging the individual parts? If it had taken a beating then why where the pieces in such good shape and where were the others since the rest of the skeleton was there?

p9196270

Well one explanation at least came up with this skull (another from the Mexican equid graveyard). As you can see it has simply been out in the sun a long time and while the bones are still in great condition, the sutures have all split and the skull is literally coming apart at the seams. I rather suspect this is as a result of alternating rain and sun, since the skulls I saw in the Chinese desert did not split like this, no matter how old and decrepit they were. It is only a partial explanation for the phenomenon of course, I am sure there are plenty of others out there, but it certainly appears to be one and interesting enough in it’s on right as a result.

Edit: not sure why some of the text went walk-about, I hope this has fixed it.

Scavenger Effects

Fossils only rarely intact (i.e. complete and articulated) and can be a collection of all kinds of odd bones that you would not necessarily expect to find together. Many pieces will be retained in close association (e.g. the vertebral column) but others will drift or be destroyed in quite unpredictable ways. I’ll be writing more on this subject later, just wanted to put up this nice picture that demonstrates the point really quite well.

p9196271

Continue reading ‘Scavenger Effects’

Biggest bones?

I’ll be keeping this one short as there is really not much to say, however the photo is a really nice example of how extreme some bits of soem organisms get. While obviously there are some huge bones out there in various organisms (typically revolving around whale and ceratopsian skulls and the odd sauropod humerus) there are also some less likely candidates for biggest (well, OK, longest) bone of the vertebrate world – step forward the cervical rib.

Mamenchisaurus cervical rib This particular one is on display at the IVPP in Beijing and is to my knowldge the best and most complete of its kind. It comes from a specimen of Mamenchisaurs and is a staggering, wait for it, 3.2 m long! Thats right, over three metres and close on 11 feet. For a rib. That fits in the neck.

Not surprisingly things like this are not the easiest to find and preserve badly, you can’t see it in the photo, but there is a huge amount of glue holding it together (though it is definitely one piece) as it was essentially shattered when found. Still, it is a real demonstration of pushing simple bones to extremes and raises some interesting questions about the most basic mechanics of these animals. Mamenchisaurs has one of the most extreme necks of sauropods as it is, and support is an obvious function for a rib of this kind (you can see how straight it is, and that it would be held alongside the neck, and presumeably would overlap with the ribs of other cervicals). Still, it begs the question, how on earth did the neck flex with that buried in it, and if the neck did bend, was the rib pliable enough to bend itself? It is a complex question associated with a single simple rod of bone – science can be damned frustrating at times, but half the fun is finding out.

Incidentally, the feet in the frame are those of Mamenchisaurs, not the same animal but a reconstruction of one that was probably similar in size, which gives you a feel for just how big that thing is.


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