“Some palaeontologists think…”

This insidious phrase really ought to be banned when people are writing about dinosaurs (though to be fair it seems to be true about pretty much any aspect of science if you just substitute in ‘scientists’). Not only is it a horribly hackneyed and tired cliche, but in my experience it only ever occurs immediately before one of two kinds of follow up statements, both of which are nearly equally misleading. In addition to the problem of ‘think’ being used as a rather inaccurate replacement for ‘have evidence for’, the problem is that ‘some’ is such an indeterminate word and can account from anything from 1-99% of people, though of course most people would use is for a middling or far from overwhelming sum like 30-70%. This is where the problems begin:

Guest post: A brand new brachiosaur

L-R Jeff Wilson, Dan Chure & Brooks Britt. Image courtesy of BYU.

One of the few sauropods I am in anyway familiar with is Giraffatitan (formerly Brachiosaurus) and as a result I have developed more of an interest in the brachiosaurs than other sauropods. I was excited to learn that a new taxon had recently been unearthed and described and, against the odds, there’s good skull material. Lead author on the study, Dan Chure, was gracious enough to put together a guest blog post on the subject and here is it:

The dromaeosaur pubis – ornithischian saurischians

It would of course be silly to say that bird have anything but a bird-like pelvis, but of course birds descended from the saurischian dinosaurs (the lizard hips) and not the ornithischian (bird hipped) dinosaurs. Birds then and their closest relatives are therefore saurischians with an ornithischian condition. The differences between the pelves of the two groups we have covered before but as with much in evolution, it’s not like birds just popped into place with their pubic bones pointing backwards.

Here then are the pubes of (somewhat inevitably) Sinornithosaurus. While the pelvis of this animal are disarticulated, you should be able to see that the ‘arms’ of the bone while mostly straight, then curve posteriorly such that the spoon shaped ends finish under the ischia (the bones that sits behind the pubes). A more typical saurischian pubis would point forwards to a degree, so we can see that this droamaeosaur pubis (or rather pubes, both are there and fused together at the end) is somewhat transitional between a more normal anteriorly facing pubis of other saurischians and the very posteriorly facing one of birds.

Flugsaurier circular update

There were some errors in the recently released Flugsaurier Meeting second circular. These have now been corrected. Follow the link back to the original post where the corrections have been made.

Theropod teeth again

As with the dromaeosaur tails, the teeth of Sinornithosaurus also allow us to revisit a recent post on anatomy – the anatomy of theropod teeth. As before the photo isn’t perfect, but should be well enough to illustrate a few points.

The point where the root ends and the crown starts is quite well demarked. Although the teeth are loose in the sockets and have extruded, the crown is curved where the root is straight and there’s a slight colour difference too. There is also a deep groove on the tooth root and in some cases this extended part-way onto the crown.

Astute readers will be thinking about a recent paper on this very taxon and its tooth a jaw morphology, but I’m not going to comment here on it (that’s what the literature is for, not blogs, or comments as far as I’m concerned). I do think it’s safe and uncontroversial to say that more work is needed in this particular area however.

Dromaeosaur tails again

Since I have all these nice photos of Sinornithosaurus that show off some nice bits of anatomy, I’m trying to make the best of them. A while back I made mention of the enormous zygapophyses of dromaeosaur tails that lead to their rather rod-like appearance. The photo I had to hand to illustrate this was not bad but was far from great. This one is a bit better and shows a block of vertebral centra (lying in the middle) with the various zygapophyeses and chevrons lying wither side extending alongside.

The furcula

For many years one of the arguments against birds being dinosaurs was that birds have a furcula and dinosaurs do not. Now clearly the avian furcula (or wishbone) is a highly specialised bone and it is formed by the fusion of the clavicles (the collar bones) but the absence of a furcual in theropods hardly rules out theropod ancestry. After all, basal theropods don’t have feathers, or beaks, or could fly. One rather key concept of evolution is that things change over time, so an absence of a furcula hardly rules them out of contention – nothing else had a furcula either so unless birds somehow sprang out of the ground fully formed, then the furcula had to have a genesis in one lineage or another.

However, despite this obvious flaw in the argument, there is a rather better argument – the presence of a furcula in numerous theropods. A recent survey of the literature and specimens shows that they are now known in coelophysoids, spinosauroids, allosauroids, tyrannosauroids, compsognathids, oviraptorosaurs, torrdontids and dromaeosaurs. Outside of the theropods, there’s clavicles known in a prosauropod and several in some ornithischians. Dinosaurs have clavicles and furculae.

And just to show off what they look like, here is the furcula of Sinornithosaurus. It’s the boomerang-shaped element in the centre of the picture and is quite typical in morphology, though many of them also have a short spar coming out of the middle.

Sinornithosaurus

There is a significant danger of this turning into Sinornithosaurus week since I now have a nice set of photos I took recently when the holotype went on display at the IVPP. As one of the first described feathered dinosaurs (and certainly on that has much better preserved feathers than Sinosauropteryx) it already has had a lot to say about dinosaur evolution. Although rather squashed and disarticulated the skull is also in pretty good condition and so too are the teeth.

Here’s just a general photo of the whole specimen and a couple of close-ups of the skull and the hand (the former is a bit dodgy owing to some nasty shadows so I had to play around with the image to get it this ‘good’). This animal shows off quite a few nice bits of dinosaur / theropod anatomy so I’ll be going over it in more detail in the next few days. I’m not foolish enough to waste all this material on just one big post! Not when I’m this busy and this short of good images at least.

Pedal unguals

Unguals, as regular readers will know, are the often specialised bones on the end of the digits that support keratin sheaths, or in other words – claws. The unguals I’ve shown on here before have tended to have a classic ‘claw’ shaped, though of course there are more to them than this. Here are the pedal unguals of a hadrosaur which can really only be described as a hoof.

As you can see they are broad and flattened and well rounded towards the tip. There’s also quite a lot of texture to the bone which you don’t see in other phalanges (or other claws usually). That shape is going to give a good solid contact with the ground during locomotion and help spread out the animal’s considerable weight, especially on softer ground. Incidentally, the manual unguals of hadrosaurs and iguanodontids are pretty similar in shape to those of the feet which is a good reason for thinking they were walking on all fours at least a fair amount of time unlike older bipedal-only depictions.

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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.

Helicoprion

Just because I work on archosaurs does not make me immune to the charms of other fossils (well, not quite all of them anyway). Who, after all, could be anything but charmed and intrigued by the lower jaw of Helicoprion? This ancient shark has perhaps the oddest dental arrangement of any vertebrate and probably had the most expensive dental bills.

While we are on aquatic non-tetrapodan vertebrates do also check out the news on the new giant filter-feeding fish that’s just out. Featuring research by the wonderful Jeff Liston and art from Musings buddy Bob Nicholls.

Multiple specimens

This post is, in a way, an excuse to show off this specimen of Anchiornis which I was surprised to see on display at the IVPP. Surprised because I hadn’t seen it before and didn’t know it was in the collections, but even in these times of endless publications, not all specimens get illustrated in the literature. This leads me reasonably onto the area of multiple specimens of taxa, something that does seem to cause confusion for some people, perhaps because it’s simply never discussed.

While the fossil record is famous for being incomplete, and while a great many vertebrate taxa are named from a single and often very incomplete specimen, that does not mean that all fossils species are like that. Predators are, naturally, rather rarer than herbivores but there’s over 30 specimens of Allosaurus known (and probably quite a few more knocking around in various basements) over 15 Tyrannosaurus and who known how many of Coelophysis. Even so, often only the single best specimen of a given species is illustrated in a paper and that one image can be endlessly reproduced in papers or in books and these days online too. That means it can be easy to fall into the trap of thinking these is only one specimen out there when there may be dozens.

Microraptor (yes, that again) serves as a good example – search for images of this genus and you’ll find hundreds of photos of the holotpye of M. gui. You could be forgiven for thinking that this was the only one, but this was the second species to be named in the genus. On top of that, the holotype was one of six specimens listed in the 2003 description that named M.gui. Since then plenty more specimens have been uncovered and are in various museums but few have been described since they don’t contain much more information than is available in the holotype and are unlikely to be anyone’s top priority.

Given the readership of this blog, this is likely stating the obvious, but the short version is that (as noted before) there are a lot of fossils out there, and often far more than you might realise. Certainly there are a lot more specimens of some taxa that you might ever see going by images used by the media, or books, or even in some cases the scientific literature itself. After all, if you want to quickly and effectively communicate what Microraptor looks like, you’d include a photo of the M. gui holotype and not a half incomplete one with no skull and no feathers preserved. However, that won’t stop the others from existing or any information on the genus as a whole being based on multiple specimens, something that seems to bypass at least a few people from time to time.