Archive for February, 2010



LAGs

One area I have steered clear of on the Musings (among quite a few others to be honest) is dinosaur physiology. It’s just something I’m not that into and have not read too much about and it’s an extremely complex and tortuous subject to write on. However, while writing another piece I referred to LAGs and realised that I’d not mentioned them before, so it seemed like time to dust them off and get them out of the way.

We have before dealt with determining the age of a vertebrate animal, at least in general terms, by the patterns in which bones fuse up and change during ontogeny. LINK However, in addition to just being able to say if an animal is young, maturing, and adult or perhaps an old individual, it is possible to (tentatively) get an actual date on the specimen – in other words, tell you how old, in years, it was when it died.

First off of course, I should as ever note that this method certainly has a few caveats and while I’d hardly say the results are ever wrong as such, some caution needs to be exercised with this and not everything can be taken at face value. The short version is that as bones grow they expand outwards fairly steadily, but any sudden change in the metabolism of the animal can mean the lay down a layer of rather denser bone that leaves a characteristic trace behind, a ‘line of arrested growth’ (or LAG). Since the only thing that is likely to cause a fairly regular change in metabolism is a change of season, then it follows that these are likely to be annual and so each LAG represents the passing of one year. Each time winter comes around, there weather gets colder, food is more scarce, growth slows up and a LAG is formed. In other words, cut a long bone in half (like a femur or radius as opposed to say a rib) and count the rings to get the age of the dinosaur. Simple, right?

Too simple of course, hence the caveats. First off, as animals get bigger and older their bones remodel themselves so that LAGs, even if laid down, might later be lost. Some younger animals don’t seem to have them at all, and in some cases the number of LAGs can vary between different bones of the same animal (so LAGs counted in the femur might be a different number to those in the tibia). LAGs also vary in living organisms too and of course, while even in the modern tropics there is still seasonality, an animal going though an especially good patch might not leave any LAGs at all, or one with stunted growth might be getting older while not laying down any new ones if the metabolism is low. LAGs are also largely un-recordable in some animals – the hollow bones of pterosaurs (and couple with their generally flattened preservation) make them pretty unsuitable subjects.

Even allowing for all of this, increasing work both on the patterns of LAGs in dinosaurs and how they are laid down in living taxa make this an increasingly accurate science. The lack of LAGs in some young animals and the loss of some in older ones means that a LAG count should often be taken as a minimum, but as a more detailed measure of age than just juvenile-subadult-adult they are useful. There is of course more to this that I am covering here, but these are the bare essentials and should give you a good start the next time you are left with a broken theropod bone and asked how old the animal was.

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Dealing with breaks – best practice

Something a bit more practical this time out, what to do when you break a bone. Breakages are pretty much a matter of course – no matter how careful you are and how robust the bone, things will break. I don’t know of a single professional who has not broken something, and while I’m not exactly proud of the record, I can think of perhaps a dozen specimens that have breaks in them now that didn’t before I was working on them. You will also come across specimens that are broken too, either where old glue has lost its bonding powers or the specimen has simply broken under its own weight (or of course where someone else broke it and didn’t realise or didn’t tell you). Still, for all the frequency that this happens, I’ve yet to see anyone lay out what you should do afterwards so here’s my attempt.

First off, don’t just reach for the glue to fix it as many will be tempted to do. Try not to move or disturb things – there are often small bits that have hung on and will break or come off if you touch them. So be careful and put the thing down as best you can to avoid making anything worse.

If there are a number of larger pieces, try and lay them out such that it’s clear how the thing should be put back together. This will make life a lot easier for whoever has to repair the specimen. If there are any very small pieces, try and collect them – don’t let any bits go to waste (even if these can’t be glue back, they could be used later for SEM work or isotope analysis, and it will save people having to take a sample if there are broken bits already available).

Next, take some photos and notes on the specimens. Write down what broke, where and how and do a little sketch if necessary. Again, this will really help make sure the repairs are done correctly. Photographs are especially important as often for the integrity of the whole piece the specimen will be glued back together so this is perhaps the one and only opportunity to get good images of the internal structure of the bones or see the cross-sectional shape of the broken part. Include a scale bar and try to take good photos, you may want to publish these later.

Obviously you should tell the curator what has happened and let them decide how to proceed. They may want to repair the specimen immediately, or it might be better to wait until all your work is done, but it’s their specimen so they should decide how to proceed. If it’s your specimen, or you are asked to do the repair work yourself, take time to assess it. Pick a good glue – preferably a commercially available one that is easily soluble so it can be taken off later if necessary. Try to be consistent as well such that the glues used on the specimen are all of one type (if they are mixed, then using one type of solvent might free one glue but cause a bad reaction with another). Any pieces that cannot be fitted should be put in a box with the original specimen with the specimen number on it and note as to where they came from.

In addition to taking notes for yourself, write a short note to go with the specimen itself. Put the date, your name, the specimen number / bone on it and then just a few words to explain what broke where and how it was repaired (a print out with photos is even better). That way, anyone coming to the specimen in future will therefore know that the specimen has a weak point to watch out for, how it was glued back, and that there are notes and photos available from you if necessary.

That should cover it and give you more than a few pointers on the way forward. Hopefully this will help keep our specimens in the best condition possible for as long as possible. Accidents will happen, but we can intervene to make them as painless as possible, both to the specimens and the curators who look after them and the researchers that follow us into the collections.

Microraptor and the feathered dinosaurs are not fakes

Whether by accident or design it’s hard to say, but the Musings has largely been free of creationist madness and incompetence over the (already) years (OK, only two) I’ve been writing. I tend not to delve into that side of things simply because more people do it better than I could, and I have no interest in engaging with people who don’t understand, or want to learn, the first thing about science. Even so, making the odd statement or correcting the more egregious public errors are hardly out of my realm and obviously the title of this post is rather relevant. Both the new UV paper and other recent papers on feather colour add to the general pattern of observations that Microraptor and other Lianoning feathered dinos are not fake so it is perhaps worth collating a few of them here.

Most obviously, these things look exactly like feathers and they appear in places we’d expect feathers to be and arrayed in the same way. This is no chance association. It would be easy to scoff and say that a good faker would go for this pattern, but that’s not actually necessarily true. The presence of different feather types in phylogenetically consistent and meaningful patterns is not the kid of thing one could fake easily, if at all without huge coordination of all those farmers and fossil dealers collecting and selling specimens. Not to mention you know, the actual researchers who go out and collect fossils firsthand themselves. We’re getting into ‘evolution ninja’ levels of conspiracy here to account for protofeathers being found only in earlier taxa and then more specialised and more derived feathers in more derived taxa, so best move on.

Secondly, the feathers are pretty much indistinguishable between the various birds and the feathered dinosaurs. If the dinosaurs truly are faked, then how come the feathers are apparently identical to the supposedly non-faked birds. The feathers are also pretty much identical to the apparently uncontroversial feathers preserved in the Solnhofen of Germany and the Crato of Brazil. And actually, more recent feathers that don’t date from the Mesozoic look the same too, again confounding the supposed difference between bird and dinosaur feathers.

Incidentally, none of these feathers form any of these formations look fake. Stick them under a microscope and they are (in most cases, obviously not all of them are perfectly preserved) very highly detailed (down to the sub-millimeter scale) and could hardly have been painted on. Of course, go a fair bit further with an SEM kit and we can see that these are indeed preserved in incredibly detail. They have the structure of composition of feathers (right down to identifiable melanosomes of different kinds) and are not fakes, the remains of bacteria, or for that matter, degraded collagen fibres.

Finally of course (though less critical than several of these points, but hell, it’s my research) we also see that under UV there is still so signs of fakery or other shenanigans, and of course there are now more feathers (or more accurately more bits of feathers) that could not seen before. Few people would go to the trouble of faking things that cannot be seen or even perhaps even detected using a technology they don’t even know about. These are not faked and there is no possible evidence or reason to suggest that they are or even could be or how on Earth this could be done.

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Microraptor in UV, wider implications

Microraptor gui holotype legs feathers under UV light. Modified from Hone et al., 2010.

So having covered the basics of the new Microraptor paper, it’s time to move beyond a single specimen of a single dromaeosaur and talk about the wider implications of the paper. For all the attention that feathers have had in the last few weeks (and there has been quite a bit, and fully deserved at that, and with more to come too) it’s worth remembering that at the core of these papers, new methods tell us new things about old (or in the case of Microraptor, not quite so old) specimens.

Researchers have been using UV light to look at fossils for decades, but a lack of powerful lights and limited interest meant that few people saw much and if they did, didn’t write about it or explain what they did in any detail. UV work has kept going and that have long been proponents out there and people making use of UV light to find new features, or just improve the contrast been bones and matrix. However, it is also probably not unfair to note that my colleague Helmut Tischlinger is largely responsible for bringing the science of UV light work on fossil vertebrates forward in enormous leaps and bounds, and that his work has been highly significant. However, Helmut also works most on pterosaurs which simply don’t get much attention (let’s face it) and also publishing primarily in the German language in small German journals was never likely to reach a huge audience. That is a problem given the importance that this method can have for interpreting fossils and finding new information on them. This lack of awareness is certainly starting to change with UV work slowly gaining attention and prominence but I hope that this paper will accelerate that process. PLoS1 is, after all, an open access journal and UV stuff is not especially hard to do. Now there is extensive documentation of the methods in a very well distributed format, and that can only be a good thing bearing in mind the results that UV can bring.

For example, while we can now say fairly confidently that the feathers of Microraptor are in a genuine position and are present, just not visible in the ‘halo’ we can also transpose this hypothesis at least to other specimens. Given the life-like position of the feathers and the way in which feathers do articulate in living birds, combined with the results of the UV work, we can be fairly confident that other specimens showing the same halo pattern do have their feathers preserved, but just hidden. Obviously we want to test this on a few more specimens with further investigations, but a whole new wave of inferences are possible about a wide range of specimens based on this work. Unless there is obvious disruption to the layout of the feathers, it’s pretty safe to assume that the feathers are present, even when preserved in a halo.

A fossil lizard with a regrown tail under UV light. Modified from Tichlinger & Wild, 2006.

More importantly, this brings forwards the fact that things can be completely hidden in natural light but wonderfully clear in UV. There are far better examples of this that Microraptor in the literature, but again, probably little read. This aspect is particularly important – most fossils go through quite a bit of preparation work before researches study them and this primarily involves stripping off the rock from around any bones or visible bits of soft tissue. The key word being ‘visible’. If things are not visible in natural light, and the perparator is not using UV, then he won’t see things that might be preserved. In other words, huge amounts of fossil information, most notably the normally rarely preserved soft tissues can be lost because the people don’t know they are there.

This is critical really. Places like the Solnhofen and Lainoning yield incredible looking fossils with both stunning and stunningly important preservation of soft tissues. And yet, that soft-tissue information that we value the most might be being destroyed in the search for the bones it surrounds. In short, we really must start using UV light extensively to check specimens from Lagerstaat deposits before and during preparation to make sure we are not stripping out otherwise invisible soft tissues. Based on Helmut’s work in the Solnhofen it has certainly happened in the past and at least one museum now regularly prepares material with UV (as happened with Juravenator for example). Long may it continue, and more importantly, the faster it spreads the more chance we have of being able to write papers like this in the future where we can get new information out of otherwise ‘exhausted’ specimens.

Hone DWE, Tischlinger H, Xu X, Zhang F (2010) The Extent of the Preserved Feathers on the Four-Winged Dinosaur Microraptor gui under Ultraviolet Light. PLoS ONE 5(2): e9223. doi:10.1371/journal.pone.0009223

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Microraptor in UV and feather attachment

Microraptor gui holotype under UV light. Modified from Hone et al., 2010.

Yes, it’s self promotion time again as I have a new paper out in PloS1. The press embargo ends today, hence my posting this up now, but the paper is not officially out till Monday. As ever with PLoS, it’s free online so don’t waste my time or yours asking me for a reprint, download it from here (link should go active on Monday).

The origin of this paper lies with Helmut Tischlinger’s trip to China which involved lots of UV light work. Some of that has already turned up in print via Jeholopterus but constraints in paper length meant we did not get to include everything we would have liked to talk about and that is rectified here, in addition to the new information on the Microraptor holotype. Those keeping up on UV light work and its ability to spot various things (including fakes, on occasion) will know that bones, matrix and especially soft tissues often look very different under UV than under natural light. As a result, with the right techniques and equipment you can find some interesting details and get more information from your fossils.

First off here I will freely admit that the results here are far from Earth shattering, but they are a neat demonstration of a technique that, outside of the pterosaur community, still seems to be very little know. Hopefully this will help make more people aware of what UV can and cannot do and get people using these methods. As hopefully will become clear, this is potentially really quite important.

So, onto Microraptor, or more specifically, the holotype specimen on Microraptor gui. While there are a number of specimens of this and other species, this is probably the best, certainly the most famous and most studied, and thus arguably the most important one. While there are obviously large numbers of well preserved feathers on the slab and that they are both associated with, and structured around, the skeleton something else is also pretty clear: the feathers don’t actually reach the bones. Instead there is a ‘halo’ of space between where the bones are and the feathers start.

Microraptor gui holotype with feathers (white arrows) and 'halo' effect (black arrows). Modified from Hone et al., 2010.

This is actually quite common in Lianoning specimens both in other feathered dinosaurs and also birds, and it’s also problematic. If you look at modern birds, the big flight feathers penetrate deep into the skin and basically reach the bones (hence you get quill knobs, as also now seen even in dromaeosaurs). If the feathers are not replicating this pattern (and they don’t seem to be) then the obvious question is what has happened? In some fossils, the feathers do reach the bones, both in Liaoning stuff and things like Archaeopteryx (and yes, Tianyulong too) so why not here? The obvious answer is that the feathers have moved – they are, after all, preserved next to a corpse and could easily have come free and drifted off from the bones, or perhaps they have not been preserved close in, or were destroyed during preparation or some other reason.

Microraptor gui under UV light with throat feather penetrating the halo under UV (arrows). Modified from Hone et al., 2010.

However, what the UV light study shows is that the feathers were, at least in part, there all along. What has happened is that the soft tissues have decayed and spread out around the specimen. You can see them incredibly clearly under UV where they shine brightly and are very pale. This is likely what is covering the feathers in most cases, but can we be sure? Close in on the legs and it certainly looks it. Several ‘arcs’ of feathers now penetrate the halo and the arc continues into the halo to the bone, though the soft tissues make it hard to see. (I should note here that good though these pictures are, this is of course much clearer when you are looking at the original slides, and better still with the original specimen itself – photos are good, reality is better). Even better are the feathers around the throat / chest where the filaments really are quite clear under UV where they are simply not visible under natural light. But what does this mean for Microraptor?

In short, it means that the feathers as we see them on the slab are very likely in their original and natural positions. They have not decayed, or moved or generally been disturbed: they are simply obscured. Secondly, this means that Microraptor’s feathers are pretty similar to those of birds and other dinosaurs in that they do, in many places, actually reach the bones of the animal. It also means that a number of measurements made of the feathers and associated calculations based on those measurements are likely in error. The feathers are longer than assumed.

All of this is pretty much as expected in a sense. We do have other specimens that suggest the pattern of feathers reaching the bones is normal. We know from modern birds that this is what we might expect. There were a variety of reasons that could plausibly lead to the feathers apparently being absent, but to be able to confirm that they are not and offer an explanation why is quite nice. What is means more generally however is perhaps more important, but you’ll have to wait for the next post for that.

Oh yes, and ReBecca over at Dinochick has an interview with me and a bit more on the methodology and history behind the paper. Edit: further coverage from friends and colleagues at Dracovenator, The Whirlpool of Life, and Dinosaur Tracking. Thanks to all.

Hone DWE, Tischlinger H, Xu X, Zhang F (2010) The Extent of the Preserved Feathers on the Four-Winged Dinosaur Microraptor gui under Ultraviolet Light. PLoS ONE 5(2): e9223. doi:10.1371/journal.pone.0009223

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Gallimimus et al., the ornithomimosaurs

Ornithiomimosaurs (or more commonly, though less correctly, ornithomimids) first came to the attention of the general public with the appearance of Gallimimus in Jurassic Park, when before then they’d been largely overlooked. One can see why – they’re not especially big, lack big teeth, crests, horns or big display structures and they’re probably not predatory either. For a theropod in competition with Allosaurus, Tyrannosaurs, Deinonychus and the rest for a bit of media, or even museum, coverage you can see why they might loose out. Still, like pretty much any living organism (or previously living organism) they have their interesting features once you start to dig down and their share of unresolved mysteries.

Archaeornithomimus

In gross morphology they are quite big by human standards, but pretty small by theropod standards with a typical animal being 3-4 m long and standing about 2 high or so to the top of the head. They are pretty gracile with relatively small bodies, long arms, legs, and a long neck with a small (and usually toothless) head that housed large eyes and a fairly large brain. The legs are, in fact, especially long and the group are justifiably considered likely to be the fastest of dinosaurs.

The hands and arms are also quite big with relatively large claws on the fingers, which is a bit of a surprise (photo is of Shenzhousaurus). If these animals are indeed herbivorous as has been suggested (though filter feeding for some has also been supported) then it’s hard to see why they might need such arms and claws (though the arms do not appear to be especially strong and the claws are far less curved that those of definitively predatory theropods). The idea of herbviory for most, if not all, ornithomimids comes in part from the fact that with a couple of early exceptions, they lack teeth but they also lack any obviously powerful crushing / cutting beak that say many oviraptorosaurs have that could get at eggs, small animals or nuts. They are also known in several cases with gastroliths which as noted before are indicators (though far from absolute ones) of herbivory.

Shenzhousaurus. Courtesy of Steve Brusatte.

The last thing worth mentioning here is the naming of the group. Ornithomimids basically translates as bird mimic and this is kept up throughout almost the entire group with Gallimimus (chicken mimic), Struthiomimus (ostrich mimic), Pelicannimimus (pelican mimic), Anserimimus (goose mimic) and others. This is something I really like from taxonomists as it does help you remember the names and keep things sorted out in your head. It used to be really rather common (rhynchosaurs at least are still pretty much all ‘rhynchus’s or ‘onyx’s) but is dying out as people strive to get more inventive with their names, which is rather ironic given the plethora of unoriginal and unhelpful names that abound these days.

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Windmills, tilting at

Journals again. I’ve reviewed several papers in the last couple of weeks and completed corrections or updates on several more. This has once again brought me into contact with many of the joys of dealing with various journals, editors, online review / submission systems and others. While before now I’ve had a right go at the whole review system and many of the general problems it entails, here are a few more specific criticisms that seem to come up again and again and whose entire existence seems to be based around the concept of wasting time or confusing people unnecessarily. So get your popcorn and enjoy ‘Dave pointlessly whines about certain issues surrounding reviews and submissions which will probably never change’:
Continue reading ‘Windmills, tilting at’

Archosaur Musings 500th post unspectacular

Told you it was unspectacular. Things will improve though – coming soon – Chinese feathered dinosaurs* in UV.

I have however, now managed 500 posts on this version of the Musings, well done me.

*Well, one anyway.

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Zygopophyses in dromaeosaurs

So having covered ornithischian ossified tendons it’s time to switch to the other side of the dinosaurian tree and take a look at the hyper elongate zygopophyses of dromaeosaurs. This is a bizarre feature of dromaeosaur tails where the (normally) little articulation points between vertebrate (the pre and postzygopophyses) are elongated such that they overlap other individual vertebrae rather than just articulating with each other. The postsygos (at the rear) are only mildly elongate compared to the truly mammoth prezygos which can overlap half a dozen or more bones.

Here, several have become disarticulated so that the individual shafts of the zygopophyses stick out free of the tail making them more visible. Just about visible (it’s not the greatest image) is the fact that these are part of the vertebrae and continuous with them and are not separate elements as are the ossified tendons of the ornithischians. A good look under a microscope makes that pretty clear, though of course a bad photo shot through glass in a museum doesn’t always. Also worth noting is the fact that under the tail, the chevron bones are also massively elongated too.

It’s tempting to assume that this makes the tail an incredibly stiff rod-like structure and this has been suggested in the past, but this is not likely to be the case. For a start this specimen is hardly unique in that the bones have separated out from each other even when the rest of the skeleton remains articulated, so clearly if even a fairly mild disturbance after death can move the bones around, then in life there must have been a degree of flexibility. Secondly, other specimens are preserved with the tail flexed to a degree suggesting that things are not that rigid. Finally, it’s pretty unlikely that the whole thing was exceptionally rigid as this would make it prone to breaking – even our own long bones can flex at least a bit when stressed without snapping, and some long and thin bones (like this one for example) pretty much must have had some flexibility or they’d break constantly – bones are not always very rigid (and indeed as an aside, bat bones are incredibly flexible). So while the tail was undoubtably stiffened, it was unlikely the flag-pole that some people think it was.

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Flugsaurier 2010 second circular

This has just arrived from Jungchang Lu. This year’s pterosaur meeting will be held in Beijing with talks, posters, discussions and a fieldtrip to Liaoning. I’m sure I’ll see at least a few of you there. I have left out some details of the registration and payment methods etc. contact JC or Dave Unwin (or me I suppose, since I have a copy of the forms) for details.

The previous version posted had some errors in it. These have now been fixed and this is the full and correct circular.

Continue reading ‘Flugsaurier 2010 second circular’

A good article on science…

in a national newspaper. Makes a nice change, though of course, it is written by a scientist, so perhaps it’s less of a surprise.

Still, this is well worth a read on the subject of scepticism and self-correction in science.



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Shenzhousaurus

The ornithomimosaurs could not have had much less attention on here if I’d tried (Deinocheirus aside), despite the frankly massive bias towards theropods on here. I must confess to not finding them especially exciting, but a good specimen with an interesting feature or two is always worth a quick look. In this case the photos come courtesy of Steve Brusatte (occasional Musings guest poster and research collaborator) as, although the specimen is on exhibit in Beijing, I never got around to taking any photos of it and Steve has a nice set that he was willing to share. Thanks, Steve. (BTW, it’s another boxed in specimen hence the reflections / flash flare).

Shenzhousaurus is known from this single beautifully preserved and excellently prepared skeleton. That on its own makes it worth showing here (as it makes quite a change from either mounted skeletons in exhibition halls, squished flat Liaoning specimens, or isolated teeth) but I suppose I should talk about the group in a bit of detail now I’ve started. I’ll wrap up with just a couple of comments on this taxon and then pick up with a more general post on the clade soon.

Hopefully you can see the small teeth preserved in the front of the jaws (it’s better in the close-up below), something only found in this animal and other basals ornithomimosaurs Pelecanimimus and Harpymimus. All other members of the clade are toothless and presumably had some kind of beak. Also just about visible are a scattering of small stones that are probably gastroliths. These are normally found in a single patch when present, but here it looks like the stomach burst and they escaped and thus are a bit spread out, but still inside the rib cage and there are no other stones like these in the block suggesting they’re genuine gastroliths.

It’s really rather well preserved and an important specimen. I keep meaning to write something on the importance of early members of clades but have never quite got around to it. Even so, hopefully you can appreciate that having an animal with a few small teeth, that descended from a group with lots of big teeth and who is a member of a clade whose later members had no teeth can really help fill in a gap and inform you about their evolution.

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