What can you do with a fragment?

Having already talked about naming fragments a great many moons ago, it seemed about time I wrote a little more on this subject. Fossil archosaurs of course can be represented by complete articulated skeletons down to just parts of single bones or isolated teeth. As I have discussed before, obviously not of these are equally valuable, or equally valueless, but it might seem obvious that small bits are typically of little use.

The key point here of course is just how diagnostic that ‘fragment’ is (and a fragment here can really be ¾s or more of a large bone). You can probably tell if that distal end of a femur is from a tyrannosaur and that means you must have tyrannosaurs (or for a real example, a pubis). When this might be the only evidence of an entire clade it’s obvious that this is important.

It should therefore be of interest to realise just how diagnostic individual bones, or even parts of bones can be. Chevrons for example all look pretty much alike (or at least there is very significant overlap in morphology over very different taxa) so half of one of them really won’t tell you much, but even there at least some in hadrosaurs for example look rather different to those of theropods or sauropods and can be of some use. Ribs are understandably often of little use, but humeri or maxillae say can be identified to small clades or even species in some cases and so too can little bones like the astragalus and of course neomorphs like pteroids are great.

That mean that while yeah, sure, there are some really rubbish fossils out there that are not really worth collecting, even small bits of small bones can be really important. You may not see much in them, but someone coming through the collection might well be in a position to say “Holy Cow! That can only be left tracularsplanknick bone from a derived pseudomadeupia and they don’t appear in the fossil record for another 50 million years!”. Fragments can be really important.

Applying your time correctly

An exchange of comments on this recent SV-POW! post was in good fun, but it masked an actual issue within research that’s worth making note of. The short version is that you can’t know everything (though some people get quite close!) and you certainly can’t study everything you’d like. Thus you do have to balance your time and efforts to what will yield the best or most productive veins of research. No matter how good your ideas or how much you might like to take on certain projects, it’s often simply not a worthwhile endeavour.

If you want to step well outside your normal field of research into an area you are not familiar with this likely represents a very significant investment of time. You’ll have to dig into the literature and specimens to get up to speed and there’s still a chance you are duplicating someone else’s work or reinventing the wheel. Obviously communication and collaboration can ameliorate this, but then if you are new to a field, there may not be much you can potentially bring to the table with your new potential colleagues.

This is not to denigrate or discourage people from spreading out and diversifying. I think too many researchers are actually too specialised. However, in the incredibly, and increasingly, competitive world of research it is sadly rather normal to feel pressured to produce as much work as possible as fast as possible and as such, to make a significant shift towards another area that will require a significant investment of time and may not yield much in terms of novelty, is not likely to be high on anyone’s agenda.

I don’t have the time to do the work I really do want to do, let alone the random things I’ve thought of that might work if only I had the time and assuming it’s not a half-baked plan that won’t work because I don’t know the material well enough. Jerry Harris once told me his hardest lesson was to learn to say ‘no’ to cool projects he was invited onto. Much as we’d like, we can’t do everything, so you have to pick your battles. Which is a shame, as I’d really like to take a good few months off and serious work on important issues such as “what is the most cool colour / pattern combination for a Styracosaurus frill?”

Taxonomy never stops

It’s hard to tell if this is a misconception about taxonomy as it never seems to even be mentioned conceptually, but I suspect it is one, or at least is never even thought about. Taxonomy quite simply does not stop with the naming of a new species. While this is perhaps the most obvious, and arguably most important, aspect getting a new species named is just the start. Now I’m sure that most readers by now will be familiar with the various arguments about whether or not individual species are valid and genuinely different and the issues caused by different species concepts.

However, the recent post on the problem with undiagnostic types masks a more serious issue. Even the best type specimen and a good solid description and diagnosis is often only the start of a species’ taxonomic identity and work for the taxonomist. Taxonomy never really stops.

We’ll keep things overly simple but imagine we find a new species of a brand new mammalian family. It’s some kind of carnivoran with blue fur and giant fangs. That makes it nice and easy to diagnose – blue, big fangs. Then another new species turns up with is also blue and has no fangs, each is clearly different. But what happens now if we get a light blue one with no fangs and a darker blue one with fangs. These are still different, but our original definitions need to shift to take this new information into account. We can’t just go with ‘blue’ but need ‘light blue’ and ‘medium blue’ and ‘dark blue’. So not only do we need to be careful with the descriptions of our new species, but we also have to revise the definition of the original ones too. So even if they are valid taxa and have good descriptions and types, our definitions need to be corrected in the light of new information. Discovery of alternate colour morphs, tooth variation, other new species etc. will only add the need for more refinements.

And this is why taxonomy never stops. All that new information from ontogeny, variation, new analyses (DNA, interbreeding, behaviour etc.) will help to redefine and refine a species’ identity, and new discoveries of new taxa will complicate this further. All of this must be weaved together correctly and that takes time, skill and a good understanding of the situation. Some surprisingly famous species have poor or out of date or problematic definitions and these only get more complicated as time goes on. Calling something Linheraptor or Limusaurus and everyone agreeing it is new is really the start, not the end.

Darren Tanke’s Gorgosaurus preparation: final roundup

I have been less than brilliant at cross-linking all the various Gorgosaurus posts that have been running now since December and finished yesterday with Darren’s final summary and update. It seemed sensible then to have a final little round-up on here back linking to all the previous posts and giving a central repository for everything up to this point.

I also want to use the opportunity to repost a few of my favourite images from the series which are scattered in below. Of course I also want to give huge thanks to Darren for all his work on this. I’d originally conceived of the series of being little more than some nice pictures shows the rock slowly clearing to reveal the underlying dinosaur with a few notes on what was going on. Darren obviously has gone way beyond this with a huge series of detailed posts and documenting every step of the process and every little trick and tip he has going. My thanks too, to the Royal Tyrell Museum for letting us do all of this and stick this, as yet undescribed, specimen all over the web.

Right, here we go:

Darren Tanke’s Gorgosaurus preparation 21: The end

The Gorgosaurus preparation on this side is now completed. On February 18th, Dr. Philip J. Currie came to examine the specimen and do some research on it. He will likely return and do more once the specimen is flipped over.

The specimen has now acquired a Dinosaur Provincial Park quarry number: the quarry site is now known as quarry 257. The only thing that needs to be done on the Gorgosaurus block now is the addition of a thicker, penetrating glue into all the rock surrounding the bones so it resists the deep penetration of the curing silicone molding compound and hold together when the mold is removed. This gluing will be done on February 22nd and will then be left for a week or so to fully dry while I am engaged in some other work. This means the rock will now be harder on the other side, but recall the glue is acetone-based so I can just use pure acetone to soften the glue as required. Even though the main block is done (on this side), there are still some small blocks that were removed during the initial fieldwork in 2009. These consisted of two blocks, one an epipterygoid (a palate bone) and a long mid-dorsal rib, with another unidentified bone alongside. The epipterygoid (opened jacked shown above)was started today and went quickly. It will be fully prepared out of the rock. A crew was working near the quarry in 2010 and when they revisited the site, they found another bone being exposed by erosion.

Normally we dig 1 metre past the last bone and stop there. This bone was a little beyond that and it was missed, so was collected in 2010. I worked on that bone as well and see now it is an angular- one of the lower jaw bones positioned at mid-length along the bottom edge. It is good to have these skull bones but they tell us the skull will not be as complete on the other (upper) side as the side (bottom) we have been watching on this blog.

Next updates will cover the molding process. I don’t know when this will start as some other Tyrrell staff do that work and they are (or soon will be) experimenting with the silicone rubber that will soon mold the Gorgosaurus.

Dave writes: This is however, the end of the *preparation* series (hence the title) so we are rather drawing a line under this piece given that every practical part of the preparation has now been done and with Phil’s arrival the research phase of this specimen is beginning. While we will add more during he casting process, this is the end for now. We hope you have enjoyed this and any feedback on the series as a whole is most welcome. Thanks!

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

How complete is complete?

Descriptions of fossils generally include an opening line that comments on how complete the specimen is based on how much material is present. Statements like complete / nearly complete / mostly complete / some elements preserved etc. are all common. These are of course reasonable guesstimates based on what is there, in terms of the total numbers of bones that are present.

However, reasonable though this is, it is of course possible to have very significant numbers of bones of the skeleton be missing and still have an effectively complete specimen. Or to be more precise, to have all of the necessary anatomical information. After all, assuming you have one complete and articulated arm, the other one won’t actually tell you anything you don’t already know (even if it does make for a nicer specimen). You don’t therefore really need one hand and arm or leg and foot or for that matter half the pelvis or shoulder girdle. You can get rid of half the ribs and gastralia and, in theory at least, half of the skull too. In fact given that in most taxa the ribs, gastralia and chevrons are pretty uniform you could loose most of them without compromising any information.

I reckon you could easily loose about 30% of the bones and write as full and accurate description as if you had 100%. Obviously this is just a thought experiment, but it (might) show that a ‘nearly complete’ specimen that’s missing the skull, or both feet might not actually have as much information as an ‘only partially complete’ specimen.

A few more words on distortion

I wrote recently about the ways in which bones can be distorted and modified as fossils when compared to their original shape. And here is an example of that, a Pteranodon metacarpal photographed in the Oxford Museum. Two different things are clearly evident here and perhaps a third.

First off you can see the crushing that has taken place by all the little fragments and breaks along the middle of the bone. In particular there seems to be a crack running the whole length of the midline. Since pterosaur bones are generally hollow then the bone would expect to sort of fold in on itself and crack and break down the middle as it caved in under pressure. This certainly appears to be in evidence.

Secondly the bone seems to have twisted a little. The bone is seen at an angle somewhere between lateral and ventral view, but the condyles (the articulating bits at the ends) don’t seem to quite line up right. This could be supported by the fact that towards the ends, the broken parts are more concentrated in the upper right and lower left part of the bone. This has undergone a bit or torsion along the midline.

Finally, this might have been flattened a bit. Sure it’s crushed, but the shape might still be right, but I’m not sure. Based solely on eyeballing it, this looks wider than it should be for its length. This of course can be checked with a few simple measurements and proportions based on a good and uncrushed specimen, but if I was going to describe this bone that’s something I’d be looking to check.

Typical Type Problems

Returning to the theme of Archaeopteryx in its 150^th anniversary it seemed a good opportunity to mention type specimens. I’ve generally steered clear of these in the past since I suspect most readers have a general idea of how things work and what types actually are and because I really didn’t want to sink deep into the depths of lectotypes and so on. However, there is a more common problem that Archaeopteryx can illustrate well so let’s crack on with that.

Type specimens in general are given special recognition in taxonomic work – these are if you like the ‘definitive’ specimens: the ones that stand out as being the recognised ‘identity’ of a species. As discussed in the ‘morphological species concept’ post, species can have several different definitions and there are various ways of defining things. In order to make sure everyone is talking about exactly the same thing, type specimens are erected to provide that literal physical basis of identity. Among types, the holotype is the most important. This single specimen is the one and all references to species identification should ultimately come back to the holotype.

For most of biology this is fine. You go out and find a new bird species say, collect some specimens, sort through them and when you describe it you name a holotype and maybe a few paratypes or whatever. You have the luxury of a whole set of specimens to pick through and can make sure your holotype really is typical and complete and contains every bit of information you think in should.

In palaeontology of course you generally don’t get a choice. Even if you are lucky enough to discover multiple specimens when finding something destined to be a new species, it’s unlikely that you’ll get a single and nice complete adult animal in good condition. Holotypes are almost inevitably incomplete, or crushed, or have key parts not clearly visible or who knows what and of course some are really based on very little material indeed – as little as a single bone. There’s nothing wrong with this really since if that’s all you have, that’s all you have. You can’t assume you’ll ever find another specimen of the same species (and that may not be any better than what you have already) so you have to go with what’s there and if it’s distinct and diagnosable then it should be named.

However, things can be distinct and diagnosable at the time and later loose that title as new discoveries show that what had appeared to be unique turn out to be common. On occasion though things can be pretty much undiagnostic to begin with. Enter Archaeopteryx stage left.

When it was first named, Archaeopteryx was just a feather (photo here on Pick and Scalpel). For all the famous specimens that attract all the attention, the original name was erected for a single bit of integument. Now arguably this was diagnostic in that there were no such things as Mesozoic birds at the time. I’m inclined to disagree with this since a separation of time and space is helpful to help separate out species, but hardly concrete evidence of genuine difference. In any case the rapid discovery of ‘real’ specimens of Archaeopteryx, and other birds, means that the feather is undiagnostic. There’s not really anything there that can be genuinely shown to be different to any other fossil feathers, or indeed those of many living birds. As a side problem, not only is the feather not diagnostic, but it’s also the holotype specimen.

That actually means that in theory at least, we don’t know what Archaeopteryx is. Or to be more specific, we don’t have an official holotype that is diagnostic. In practice of course we have important and complete specimens like those of London and Berlin that everyone accepts are members of this species and are distinct and diagnostic, so while this does need to be sorted out (and indeed the wheels are very much in motion on this) it’s not a huge problem. But it does provide an obvious illustration of these problems. I doubt there’s anyone reading this who doesn’t have a good mental image of what Archy really is, but I doubt that is just a single small feather, though technically, it should be.

My thanks to Paul Barrett for some info and fact checking on the status of the feather as holotype, Paul is part of the petition to get the London specimen designated as the new holotype.

Darren Tanke’s Gorgosaurus preparation 20: fixing undercuts, the final preparation

The last of the Gorgosaurus preparation (on this side) was finished February 10th. In readiness for molding, holes, cracks and undercuts have to be filled and this phase is rapidly reaching the end, too. The plan to mold the edge of the field jacket as well means the edges between the cut part of the plaster jacket and the rock itself needs special treatment.

The plaster jacket was of course made in the field with no advance knowledge that it would be molded in part later on. So these edges need to be fixed. They are rough, full of undercuts and often form vertical faces that are harder to fix to make look like rock. Most of these problematic edge areas are simply glued and crushed sand and silt thrown against the wet glue. Once dry, excess sand/silt is vacuumed off and the process repeated up to three times until the white plaster is hidden by simulated rock. Undercut areas on the edge of the jacket are fixed by using the glue/sand/silt mix which is roughly pressed into the undercut or hole, then sprinkled with dry sand/silt which is then firmly pressed (with the heel of the hand) into the damp glue/sand/silt mix underneath. This is done for any other gentle depressions or undercuts: a series of pictures are given here. Once dry the effect is quite realistic. Also, any remaining cracks are being heavily glued. I try to do heavy gluing jobs on a Friday afternoon- this way it has all weekend to dry without any disturbances from me. Come Monday morning everything has firmly set and the process begins anew until everything is done. Vertebrate paleontologist Philip J. Currie is to visit our museum (and see the Gorgosaurus) for the first time on February 18th so it is important that I be done by then.

I must apologize to readers about the image quality. The specimen, when seen in person, is really quite spectacular- the bones have a beautiful chestnut-brown to orangey-brown (more heavy on the orange) and all with a deep, rich lustre. These color qualities, which really make the specimen all that more amazing I have found very difficult to convey photographically. The overhead lighting near the Gorgosaurus has been changed this week which also has affected image quality.

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

Late edit: Matt van Rooijen has done a colour edit on that last image to try and perk it up a bit:

Not quite body modification

Yesterday I talked about my amazing time traveling research in the journal Geological Curator. As you might imagine this focuses on the ‘behind the scenes’ side of museum work – preparing and storing fossils and minerals and all the accompanying aspects of this. While obviously I spend a fair bit of my time in museums, this is a bit of a departure for me, but the paper was fun to do.

In this case it deals with the modifications made to a pair of pterosaur specimens held in the collections at Dublin. Well, sort of. You might think this means that someone went over them and damaged or destroyed the bones, or tried to mend and improve them. In fact the description is about how the two were mounted for sale. In both cases the surfaces of the specimens appear to have been polished to make them very smooth, plaster has been added to cover up cracks, and screws have been sunk through the matrix of the slabs and into a heavy wooden case.

If all of this sounds horrifying then don’t be too alarmed. For a start this was done in the late 1800s and this kind of thing was hardly uncommon (though the screws thing is new to me). Secondly, despite all of this, in some cases fairly drastic, modification it was done with some care. The fossil dealers responsible have done all of this without really affecting the quality of the material at all and that’s quite impressive. What was done was clearly there with the aim of making the material look nicer, but not at the expense of the information it contained.

Modified Rhamphorhynchus plate and counterplate. From Hone, 2010

Given the ongoing issues with chimeras, faked fossils and the like it’s almost refreshing to see that 120 years ago, commercial dealers were actually careful with the scientific information in their material and presumably understood that researchers were interested in that. It’s a lesson a few people could do with now sadly.

Hone, D.W.E. 2010. A short note on modifications to Nineteenth Century pterosaur specimens held in the National Museum of Ireland – Natural history, Dublin. Geological Curator, 9: 261-265.

Not exactly a guest post: What Should Everyone Know About Paleontology?

My guest posts are generally exclusive but this one’s doing the rounds after Tom Holtz wrote this up on the DML. The title question was recently asked by Roberto Takata on the Dinosaur Mailing List and Tom took up the challenge. :

I think that is a good question. What really are the most important elements of paleontology that the general public should understand? I took a shot at coming up with a list of key concepts, based on experiences with teaching paleontology and historical geology and with less-formally structured outreach to the public. I have offered this list (cross posted at the Sauropod Vertebrae Picture of the Week and Superoceras blogs) as a way for it to reach a wider audience. That this is Darwin Week makes it even more appropriate, as we should use this occasion to encourage a better understanding of the changes of Earth and Life through Time for the public at large.

Much as I might like to think otherwise, the specific details of the hindlimb function of Tyrannosaurus rex or the pneumatic features of brachiosaurid vertebrae really are not the most important elements of the field. Understanding and appreciating the nitty gritty details of the phylogeny and anatomy of any particular branch of the Tree of Life are not really necessary for everyone to know, any more than we would regard detailed knowledge of bacterial biochemistry or the partitioning of minerals in a magma chamber to be significant general knowledge. (Indeed, these latter two items are actually far more critical for human society than any specific aspect of paleontology, and so from a certain point of view really more important for people to know than the History of Life.)

That said, all human societies and many individuals have wondered about where we have come from and how the world came to be the way it is. This is, in my opinion, the greatest contribution of paleontology: it gives us the Story of Earth and Life, and especially our own story.

I have divided this list into two sections. The first is a list of general topics of paleontology, touching on the main elements of geology that someone would need to know for fossils to make any sense. The second is the more specific list of key points in the history of life.

(NOTE: as the idea of this list is that it should be aimed at the general public, I have tried to avoid technical terminology where possible.)

Darren Tanke’s Gorgosaurus preparation 19: preparing to mould

An important meeting was held on February 3rd, regarding the Gorgosaurus and plans to make a mold of it so casts can be made in the future. Much earlier, plans were to latex mold it but that has changed. Because the specimen is so spectacular it will be molded with a slow-setting high-quality silicone rubber. This rubber will be brushed on in a single thick coat of a depth of about .5-1 cm. It takes about 16 hours to cure. Then a rigid plastic support jacket will be made for the mold. The specimen had been prepared with the intention of a standard latex mold being made, so the silicone rubber was unexpected (but pleasant surprise). The silicone mold will be extremely high resolution. Because it takes 16 hours to set, the silicone moves into every nook and cranny. This means I have to be extra diligent now to find and eliminate every tiny crack or hole the silicone may penetrate into and where we don’t want it to go. Such holes and cracks are found visually with ambient light, but it really helps to use a bright light and move the light up and down above and to the side of the specimen. Doing this, one looks for “dark spots”. Is that dark spot a small safe undercut or an unwanted hole that needs to be filled? One walks around the jacket many times doing this, then repeats, but now walking the other direction. These circular walks are done at normal head height and crouched down at various levels. It looks silly and I am sure the museum visitors looking through the preparation lab window must think I am mad, but it needs to be done to find all the unwanted holes and cracks.

At the same meeting it was decided we will likely make a mold of the edges of the plaster field jacket at the same time- it makes for a nice “frame” around the skeleton. One cannot simply paint silicone rubber onto dry plaster. First the plaster jacket was patched. Wet plaster was smoothed into the holes and cracks with a small spatula. Then, once dry, that new plaster was sanded down with coarse drywall sandpaper. Then the fixed areas were vacuumed to remove all dust, and then a couple coats of acryloid glue (medium thickness) was painted onto the exposed plaster. The small brown “dots” that you can see in the last plaster jacket photo is the cross-sections of the individual burlap fibres in the woven sheets used to make the field jacket. None of this plaster fixing work has to look pretty, it just has to last long enough for the mold to be made. At the same meeting one of the scientists wanted the orbit (eye socket) highlighted a bit better. This meant having to undo some of the work I did months ago. This is no big deal and actually welcomed as I was able, by digging down through my prior work, to see how well (or not) my preparation and gluing work has suceeded. All had held together OK, but I discovered a new crack inside the orbit that was not visible previously. This was fixed and restored as per prior updates. Dr. Philip Currie is visiting our museum February 18th and see the Gorgosaurus for the first time- I will have the specimen ready for molding by then. How the mold is made will be shown in future updates.

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