Archive for February, 2011

Typical Type Problems

Returning to the theme of Archaeopteryx in its 150th 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.

Honey, I blew up the pterosaur skull – Shenzhoupterus

While it’s probably a reasonable assumption that we now have all the major groups of dinosaurs and pterosaurs, new ones do on occasion pop up. The alvarezsaurs have only really been around for 20 years and the scansoriopterigids might well turn out to be another one. In the case of the pterosaurs, the azhdarchoids have undergone a huge bloom in recent decades with several clades having been identified and are now represented by multiple species.

Perhaps the most bizarre of these are the tongue-twisting chaoyangopterids which have, for want of a better phrase, blown up heads. Monofenestratan pterosaurs (so that’s pterodactyloids plus things like Darwinopterus) are in part diagnosed by having a single large fenestra in the anterior of the skull that represents a coming together of the naris and the antorbital fenestra. In some cases this can get really big and ‘fill’ a large chunk of the skull meaning that there can be more space than bone. However, in the case of chaoyangopterids, the top of the skull is bowed outwards enormously and all that extra skull volume is filled by the nasoantorbital fenestra giving them a bizzarely shaped head that consists of thin bone struts and a hue amount of nothing.

Here’s one of them, Shenzhoupterus, showing off that truly bizarre cranium. My thanks to Lu Junchang for the opportunity to see this at Flugsaurier 2010 in Beijing.

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:


My thanks to Matt van Roojin for pointing me in this direction and my apologies for not spotting or mentioning it sooner. The folks over at Art Evolved have been running one of their speed-painting competitions based on questions and answers from Ask A Biologist. There’s some fun stuff on there, not least this effort on that most pressing of zoological problems – who would win in a fight between a shark, a bear and an eagle?

Oh, and since I set up this post (but obviously before I posted it) they’ve now done a Musings challenge. Check out things based on this very blog such as ‘What colour was Anchiornis?” and a very dapper looking Darren Tanke Gorogosaurus preparation.

Scelidosaurus returns!

I recently put up a pair of posts with lots of photos of various Scelidosaurus specimens, but particularly of one incredible complete and articulated one. That is, sadly from a research point of view, privately owned but at least it’s available to be seen. And it has been cast too. Recently a donor purchased one and gave it to the St George Museum in Utah. That has now been mounted and thanks to Jerry Harris, here is a photo of it in all it’s glory.

Identifying Middle Jurassic teeth – early deinonychosaurs?

Some parts of skeletons are very easy to identify and can be diagnostic right down to individual genera in some cases. Others are, sadly, far less easy to sort out and even very different species can have very similar features, or the range of variation can be so great that all manner of things can overlap making identification difficult at best. Such is the lot of theropod teeth (as we have seen before) and while there are *some* good characters which seem pretty conservative within groups, in general it can be hard to tell with confidence exactly which groups a given tooth might (or might not) belong to.

However, this doesn’t mean we can’t try and work this out and there are cases where positive (or at least reasonable) identifications can be made. And this can shed real light on the diversity and distribution of certain clades.

Theropod teeth from the Shishugou. From Han et al., 2011.

And so we move to the Shishugou Formation of Middle Jurassic age in China. The name might not be familiar but the theropods will be – Limusaurus, Guanlong, Haplocheirus and Zuolong are all from here and a giant tooth suggests the presence of Sinraptor or something very similar too. That’s already quite a bit of variety (ceratosaurs, tyrannosaurs and alvarezsaurs) but there’s more to come. A number of isolated theropod teeth collected a few years ago were given to one of Xu Xing’s Masters students as part of his thesis work and a paper on this has just been published. I feature in the authorship list in the obviously most important place of ‘last’ though Tom Holtz suggests that I should in fact advertise this as “special guest star”.

Anyway, this is a real challenge. Not only are many theropod teeth not diagnostic or highly variable, but the Middle Jurassic represents perhaps the peak of theropod diversity at least in terms of the clades that were around at the time. The early coelophysoids have died off by then but ceratosaurs, allosaurs, tyrannosaurs, spinosaurs, and every maniraptoran was, or should be, around. Ah. Still, Han Fenglu stepped up the the challenge and the result of his work and the rest of the team has come to fruition.

Possible troodontid teeth. Modified from Han et al., 2011.

Perhaps unsurprisingly given the conditions not all of these teeth could be identified down to any especially narrow set of possibilities but a couple were very good candidates for deinonychosaurs teeth and not much else. For those that don’t know this is the name of the group that consists of dromaeosaurs and troodontids and thus are the closest dinosaurian relatives of birds. While the discovery of Anchiornis has finally pushed back the record of this group to before Archaeopteryx, these teeth predate even that. This marks them out then as (possibly, or dare I say probably) one of the oldest records of the group. Hardly groundbreaking stuff, but quite interesting none the less. Filling in all those gaps in the fossil record is generally a piecemeal and occasional occupation in any case, but any chip away at it should be welcomed.

What’s also interesting is that while many of the teeth could not be assigned to any particular group, many of them could be fairly confidently kept apart from taxa we know are present. You might not know quite what a tooth came from, but you can compare it to Guanlong and the rest and see if it’s a match. If not, you might well have something new there. In this case there were several possible newbies which means that not only might we have early troodontids and dromaeosaurs but there are probably other new theropod taxa waiting to be discovered in the Shishugou as well. Time will tell if all or any of these interpretations are correct, but they are certainly intriguing.

Han, F., Clark, J.M., Xu, X., Sullivan, C., Choiniere, J., & Hone, D.W.E. 2011. Theropod teeth from the Middle-Upper Jurassic Shishugou Formation of northwest Xinjiang, China. Journal of Vertebrate Palaeontology, 31: 111-126.

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.

Time travelling research

On the face of it, most research would seem to appear in only a handful (relatively) of journals. However there are all manner of small, and perhaps even obscure places where papers can appear. A great many museums and universities and small societies have their own journals that publish regularly. You won’t find them online, or even indexed in many or the more obvious places like PubMed, but they are there and in big numbers. True not much ‘great’ research gets into these places, and some of them fall into the category of ‘grey’ literature but they can have some amazing features, like time travel. Sort of.

Even the best produced journals can run late with the odd issue and obviously this is more likely with small and locally produced journals. Obviously I’m building to a case in point and so it obviously is with a small report I’ve written in the ‘Geological Curator‘. I’m working on some pterosaur specimens that are held in Dublin and the curator of the collection is also the editor of the aforementioned journal and he asked me to write a note on the preparation of the material that I was happy to do.

I only submitted this in late January, but between a lightning review by Mark Witton and a bit of delay on the December issue (and having a few pages to fill) it’s come out with a 2010 publication date. PLoS One might think they are fast but I’d like to see them publish a paper *before* it was submitted!

The Eichstaett Archaeopteryx

Yesterday I made mention of Professor Franz Mayr and his relation to the Jura Museum in Eichstaett in southern Germany. And here, thanks to Helmut Tischlinger, is a photo of the man himself with the Eichstaett specimen of Archaeopteryx. The photo is from 1972 (just two years before he died) and was taken to mark the completion of the preparation work on the specimen that was undertaken by Prof. Mayr and Ludwig Meier.

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.)

Continue reading ‘Not exactly a guest post: What Should Everyone Know About Paleontology?’

Celebrating Archaeopteryx

Larry Witmer’s timely post on Archaeopteryx over on ‘Pick and Scalpel’ serves as a timely reminder for me to hurry up and finish several posts I have on this most important of taxa. For those who don’t know, 2011 represents the 150th anniversary of this animal coming to light and it is highly significant.

In his post Larry notes that the German’s are releasing a special commemorative 10 Euro coin to mark the occasion and I’ll certainly be after one. However, I already own a couple of Archaeopteryx medals that have been produced at various times. From the Humboldt Museum in Berlin I have one of the Berlin specimen (something I am told is no longer available) and from Eichstaett I have this one.

As you can see it has an image of the Eichstaett specimen on one side and the building that houses the Jura museum on the other. Also of interest is the inscription on the face “Creatura Clamat Creatorem” which thanks to Helmut Tischlinger I’m told translates as “The creature points to the creator” (or perhaps “calls for a creator”) but more importantly Helmut also offers an explanation for this. The ‘founder’ of the museum was a Catholic priest, Professor Franz Mayr and the museum sits in what was Willibald castle that was taken over by the state of Bavaria from the church in order to found the museum. However Mayr was no creationist but a firm supporter of evolution and (as you might guess from the ‘Professor’ bit) a scientific researcher. This quote of his about Archaeopteryx refers to a position more that such wonders of nature do reveal (to him at least) the glory of god. In short, it is more about the wonder of discovery and the beauty of the fossils, and I can hardly complain about that.

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.

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