Archive for the 'Practical Palaeontology' Category

Darren Tanke’s Gorgosaurus preparation 30: turning the block 2

The block is lifted off the table by a large overhead crane (it runs on tracks mounted near the ceiling and can move 4 directions) and lowered onto a pallet jack. Then it was taken to a larger empty work area nearby. The red lifting straps are readjusted so when the block is lifted it now stands vertically, then the whole crane is moved over and simultaneously the cable lowered so the jacket comes to rest “upside-down”. Actually it is now in its original field orientation. The flipped block is put back on the pallet jack, wheeled over to the work desk, the straps readjusted a final time and the block lifted back onto the table. This work is always done with others helping for safety reasons.

Once the block was on my work table I was able to refind the holes I drilled through days ago and “connect the dots” with a red marker pen. Now I  know exactly where the skull is positioned inside. Now the manual labor of pulling the jacket off begins!

Darren Tanke’s Gorgosaurus preparation 29: Turning the block over 1.

The new support jacket was labelled with the specimen number, again several times in case the number accidently gets rubbed off. Strong nylon rachet straps were put around the specimen to hold it all together. Four 1/2″ holes were drilled through the new jacket at each “corner” and down through the old field jacket underneath. I used photographs to ensure I was not drilling through bone. Heavy bolts and washers were inserted into the holes and a nut tightened on underneath. These bolts will ensure everything stays together. Then lifting straps were slid under the block in preparation for lifting and turning the block over.

Darren Tanke’s Gorgosaurus preparation 28: The plastering begins.

A very hard and strong plaster called FGR 95 is mixed up. This is incredibly strong stuff- used alot to make hollywood sets (building frontages) I’ve heard. The damp burlap is lowered into the pan of mixed plaster and dragged through the creamy mix so both sides are liberally coated. The burlap is removed and gently squeezed or wrung out over the pan- usually it is squeezed by being pulled through a hole created by the index finger touching the thumb tip.

The “bandage” is put on the toilet papered specimen and starting at the middle, the bandage pressed down into the specimen, adhering to its contours and any air underneath is pushed out to the edges if necessary. Then another bandage is put next to the first one with a good bit of overlap. Three thick FGR 95 and burlap layers (with heavy overlap) were put on the Gorgosaurus. A final coat of thick FGR 95 was put on top of that and as it cured, it was smoothed out by hand, which was frequently dipped into a pan of clean water. Plaster and burlaping took about 1 hour.

Once done the just made support jacket was allowed to sit, cure and dry. The jacket gets quite warm as the chemical reaction in the plaster occurs. Alowed to sit and dry, much water evaporates out reducing the weight of the specimen. The final picture shows the new support jacket finished; scale bar = 10 cm.

Darren Tanke’s Gorgosaurus preparation 27: burlap additions

All of the exposed bone and rock was then covered up with wet tissue paper. The low spots on the body that were infilled with plaster earlier were in need of a separating layer too – I again used a cut up plastic garbage bag. Then the main support jacket was ready to be made.

A bolt of dry burlap was cut up into various-sized pieces first- enough (and more) for the job that needed to get done next. One always cuts more than needed- you don’t want to run out of cut burlap near the end of a project! The next person doing a plaster/burlap job can always use your cut up pieces. All the cut burlap pieces were put into water and allowed to soak for 15-20 minutes then wrung out. Now we are ready for the plastering phase.

Darren Tanke’s Gorgosaurus preparation 26: numbers

The skull block was numbered again numerous times. Numbers on jackets have a way of fading, getting cut or rubbed off, etc, so it is better to overnumber a jacket. Note how the numbers were written on upside down- this was done so when the block is turned over the numbers will be correctly oriented. Low spots on the body were also covered in wet toilet paper and infilled with plaster, but these infillings were done in sections with care taken that they are not in contact with each other for ease of removal in the future should it ever be necessary.

At this point in time we think no, but some future technician will be grateful if he/she has to turn the specimen over yet again and remove these infillings. Each is outlined in red felt marker so they will know where one section ends and another begins. As some of the low spots on the skeleton are wider at the bottom than the top, these plaster infillings are now “locked” in place and will need careful airscribing to break them up for removal.

The plan is to keep the skull block inside the jacket when it is flipped over, so we will have a “jacket inside a jacket”. Therefore it is necessary to separate the jacket skull from the jacket for the whole specimen (which will be made soon). I used a garbage bag cut in half and covered the skull with that. Then I filled in the areas where I had dug around the skull with old rags and put paper on top of that, thereby filling the void.

Darren Tanke’s Gorgosaurus preparation 25: completing the skull jacket

The skull was then jacketed. A picture of the skull (without separator) shows the bandaging (jacketing) material used. It is a hospital product of cloth impregnated with dry plaster. It is used there to set and hold broken bones in place, but is also ideally in the lab or field for collecting and stabilizing a fossil specimen. [I have few posts on this on the Musings – here, here and here]. You simply soak it in a pan of water for about 5-10 seconds, squeeze out excess water and then apply it to the item being jacketed. It can be cut into pieces as shown or dispensed right off the roll. About 6 layers were used.

The wooden frame was put back on the jacketed skull and more hospital-type bandages used to attach it. I typed up the specimen number in enlarged font, printed it off, then cut the number out and glued it in place with white glue. It looks messy at first but the glue dries clear, sealing the number inside.

Darren Tanke’s Gorgosaurus preparation 24: jacketing the skull

The skull was then readied for jacketing. Prior to doing that, a small woden frame was measured up and assembled with glue and small nails. This frame will be incorporated into the skulls plaster jacket later on and provide both strength and allow the jacket to sit flat on a table, not rock back and forth.

Before the skull was jacketed, several things needed to be done. Any deeper low spots (gaps between teeth mostly) were packed with wet toilet paper, then dry sheets of same were put on the skull and dabbed with a wet paintbrush. This toilet paper layering is done until the brown bone coloration can no longer be seen. The toilet paper acts as a separating layer between the skull and the plaster jacket. If you don’t create a separating layer, you are putting plaster directly on to the bone which will have catastrophic results- it will be hard to remove the set plaster without damaging the fossil.

There were still a couple areas on the skull that were rather deep (antorbital fenestra in particular) so these were carefully filled in with solid plaster of Paris until the depression was flush with the rest of the skull. The plaster is mixed in a rubber cup which is easy to clean when finished- you just squeeze the cup and all the dried plaster cracks and falls out.

Darren Tanke’s Gorgosaurus preparation 23: drilling

When a specimen is flipped over one has to think in reverse regarding where the specimens various parts are then located. Boney processes that pointed one way, now point in the reverse. Bone processes that pointed up are now pointing down. So do I cut or grind away the plaster jacket here? Maybe not, there was a rib or limb bone there. Usually one just guesstimates where everything is but as the incredible Gorgosaurus skull is close to the original field jacket I did not want to do this. So what to do? I tried something different and have never tried before.

First I took a red marker pen and drew a line around the skull, several centimeters away, thereby marking a safe buffer zone. Then using that line as a guide, I drilled a series of spaced holes with a power drill and a long bit. The holes were drilled all the way through the jacket. In curved areas the holes were drilled closer together. When the block is flipped over, these holes will appear and the holes can be reconnected with a red felt pen and thus accurately outline the skull. As the jacket is then pulled and cut apart, the holes will always be there until the very end to remind me where the skull is.

I also spent a couple hours photographing the specimen under various light levels, angles and distances. These pictures will serve as a valuable reference when I prepare the other side and will be useful for future researchers.

Darren Tanke’s Gorgosaurus preparation 22: trenching the skull

Yes as promised, Darren is back with more Gorgosaurus stuff! For those who are new to this a review and links to the first 21(!) parts can be found here.

Much work has resumed on the Gorgosaurus. I was away on fieldwork and extended holidays and a number of other delays means most of the things covered in these new updates happened days to weeks ago. The Gorgosaurus was successfully molded in a high grade rubber material in April. The mold came off OK, then it was time to do a number of things in preparation of flipping the specimen over to prepare the other (top) side. Ideally we would remove the skull now, but we could not get the plaster jacket to really “grip” onto it properly as the original field jacket (now on the bottom) was in the way. So the skull was trenched all the way around with a small hammer and awl, just like it would be done in a field setting and newly exposed bone stabilized and glued. Small scalpels were used for close-in work. The top of the head was uncovered. The disarticulated right postorbital was found long ago, but it is now evident that the right lacrimal bone is missing too and that has yet to be seen.

The curious absence of cervical or neck vertebrae is now also confirmed, though was suspected when we were in the field. The intention with the skull now is to jacket it, then encase that within another jacket that supports the entire specimen. It is an unusual, but correct ploy in this instance- a jacket within a jacket. Future updates will detail all this work required to flip the specimen over.

Taxonomic practice and publications

Thanks to some reviews I have been writing, papers I’m working on, conversations with colleagues and a recent blog post, I’ve been thinking much about the practices of myself and my colleagues when it comes to taxonomy. Obviously I’ve written about the how-s and what-s to a degree in the past, but this is a little more specific.

The main point I’d make (as a referee / editor and recipient of referee reports) is one roughly in the line of Voltaire. I disagree with your taxonomy, but I defend your right to publish it.

Now obviously this has limits. You’re specimen must be genuinely diagnostic. You’ll have to use consistent characters. They must be well defined and not vary ontogenetically or be subject to excessive intraspecific variation (or be so massive as to not make this an issue). Or if you are trying to synonymise a bunch of taxa then you’ll need to show that other diagnoses were flawed or didn’t stick to these rules etc.

However, I may think you are overly splitting or lumping something, but I still think you should be allowed to publish (as indeed, so should I). There really are no hard or fast rules as to exactly what constitutes a genus or species. Exactly how many characters you need for one or the other, or whether some are better than others. Taxonomy really does work by consensus and the starting point of any discussion will be the publication of a new taxon / synonymy of an old one. Not allowing such a paper actively inhibits discussion / research.

A paper that on balance few people agree with will soon fall by the wayside. But it’s mere existence will allow a greater depth of discussion by getting people to examine and evaluate the characters at hand and compare them more thoroughly. So let these be published. The authors get a paper, the journal gets a paper, and the worst thing to happen is that a few people quibble about it, everyone gets some citations and we move on, but with a better understanding of the issues.

Here is something I wrote in a review of a paper that intended to name a new species (and has now been published):

I actually tend towards ‘splitting’ over ‘lumping’ myself, and I would not wish to prevent the author erecting a new taxon here if he feels it is necessary, but I would say that I do not think it is required and in the same position I would not erect one myself…. The author does effectively concede all of these points in his text, and clearly still feels the erection of a new taxon is necessary and appropriate and I am happy for him to make that call from a superior position of knowledge, but I do offer a contrary position.

This is a position I wish far more people would take. Make your points and give your opinion, but let the author make their decision and allow for the fact that they have been putting more time and effort into this that you have and know the material better.

On a similar note, I notice a tendency by some (admittedly often online rather than necessarily with respect to the literature, either published or at the review level) to second guess people working on specimens. Now for sure, people with detailed anatomical knowledge of specimens can see certain errors that others will miss (or that at least need to be verified more carefully) based on photos or drawings or descriptions alone. There is nothing wrong at all with making that clear. But I have seen people in the past second-guess authors based on things that haven’t seen. It is most frustrating to be told by someone 5 thousand miles away that you have got something wrong when you have the material in your hands and have been looking at it for months and all they have is a black and white photo of it. (And on that note, there’s a huge difference between asking someone to recheck and telling them it’s wrong. Ultimately the message is the same but the first is polite and the second isn’t. And of course you risk looking very foolish if you are wrong).

This is something raised by Larry Witmer in his excellent recent blog post about the tiny Tarbosaurus. His team commented extensively on the potential taxonomic issues of their work and explicitly which specimens / taxa this might effect and even how. But they also pointedly didn’t make any revisions. With none of them having looked in detail at any of the key specimens, they felt it unwise (and I would suggest, even impolite, impertinent, or maybe even unprofessional) to have done so. I wholeheartedly agree (as you probably guessed form the contents of those parentheses).

Yes there are exceptions to every rule, but as with the above point, I think you have to be careful before messing around with taxonomy and however much you disagree, respect the interpretations and work of your colleagues. If there are huge and obvious errors, then point them out do. But I’d avoid any kind of formal synonymy without having seen critical material first hand. There is, after all, nothing quite like seeing a fossil.

Where to stop?

One under appreciated feature of almost any paper is the incredibly difficult problem of where to draw line under the work and just stop. Every aspect of science is of course completely interconnected with other things and if you follow every possible tangent or lead everything you write will swell to dozens or even hundreds of papers.

Even something as simple as describing an isolated tooth or bone will have further implications for other branches of work. It could be the first record of something in a formation / time / place, extending the range of a group, or may be in association with another species, or have a pathology with implications for diagnosis of the species or clade or, or, or….. When you’re doing a more complex paper that integrates a number of major lines of evidence then this gets harder and harder as more and more important things have to be cut off somewhere, or at least not followed up to the depth you want.

This means inevitably that the paper will to a certain degree have a truncated feel. If you have an interest in a particular area it’s frustrating to see a paper that leads up to a significant point and then shies away and leaves it unsaid or doesn’t explore things, or give you quite the depth you wanted. Or of course, fails to make the link with something you have said in another paper or work you are very familiar with.

This can on occasion be a real issue with referees on papers. It’s very annoying when they demand you remove what they consider a tangent to the main work, and you consider an important extension of the thesis. It’s even more annoying when they do they opposite and demand you massively expand one section you don’t want to (or can’t if it lies beyond your expertise). Indeed, following up from yesterday’s post and the first half of this paragraph, there are few things more annoying than people complaining that basically you didn’t write the paper they wanted you to write. It’s your paper and you’re probably already compromising on a page length limit from the journal, desires from co-authors, and your own limitations of what you want to write about now and what you have brewing further down the line.

Traditional taxonomic rankings

Everyone on here is probably familiar with the old taxonomic ranks of kingdom, phylum, class, order, family, genus and species that was a mainstay of school biology classes and of course was a fundamental part of taxonomic work for, well, pretty much centuries. However, with the advent of cladistics more and more specific groupings of taxa were possible based on branching nature of phylogenetic trees. While there were sub-ranks of subfamilies, superorders, tribes and the like, these were rarely invoked and I think people shied away from them because they implied a level of detail that couldn’t really be inferred based on how these groups were generally formalised.

However, many of the intermediate ranks are rapidly falling by the wayside because they simply are no longer useful or don’t make sense. Kingdoms and phyla are still useful and major groups of taxa that represent fundamental divisions, and of course genera and species are the basis of all taxonomy, but that stuff in the middle? Doesn’t fit.

To take an excellent example (floated my way by Mike Taylor, despite the fact that it should have been obvious to me) birds are in Class Aves, we now accept that birds are dinosaurs but more specifically that means they sit within the traditional Superorder Dinosauria, Order Saurischia, Suborder Maniraptora and (depending on your favoured phylogeny / family definition) Family Paraves. So a Class ends up sitting in half a dozen groups that are supposed to be subordinate to it. And all the various orders and families of birds also sit in there. Oh.

We are increasingly getting close to building the Tree of Life – a single vast and unified trees that put whole phyla together at the species level in clades that most experts generally agree on. No longer are new or odd species somewhat arbitrarily assigned to families or have new families erected for them because they are special. We simply don’t think of trees and relationships in those terms anymore – not everything has to sit in a family, and it’s no longer the case that just a couple of researchers look at their clade and split up the taxa with no reference to related clades or other, wider patterns. As such, while at a conversational level, it still makes sense to use and discuss things like the ‘cat family’ or ‘dog family’ increasingly these are being abandoned for their formal names (Felidae and Canidae in this case) though the endings of various names betray their origins as the –idea, -inae, -oidea, and so on demonstrate. These now represent successive ranks rather than ‘families’ and ‘tribes’ as once they would.

@Dave_Hone on Twitter

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 553 other followers