April 27, 2013
A few weeks ago I threw this picture into the “Night at the Museum” post and promised to say more later. Later is now.
I started sculpting dinosaur claws because of the coincidental arrival of two things in my life. One was a cast of OMNH 780, the horrifically awesome thumb claw of Jurassic megapredator Saurophaganax maximus, which I blogged about here. (If you’re curious, I’m using it to amaze people at public talks, so it is serving a semi-legit educational purpose.)
The other is this video of Adam Savage’s TED talk on how he got into sculpting two very different birds. I’ve watched it about a zillion times and shown it to loads of friends, because Savage so nicely captures what it’s like to be obsessed by interesting things. We have different objects of desire, and, okay, I don’t have 20 gigs of photos of anything, but when I’m having a lousy day, watching that video reminds me why I do what I do. You should blow off the rest of this post and go watch it right now.
Back so soon? So, I am a little obsessed with theropod claws right now (aesthetically and fanboyishly, not scientifically), and I thought it would be cool to try my hand at making them. Also, I’ve been wanting to do some molding and casting, and I wanted to be able to practice on cool stuff without having any ethical concerns about trading in fossils or replicating someone else’s specimen. More on the molding and casting in a future post.
A final boring note before the actual instructions: I have no idea what I’m doing. Those two claws in the photo above? The little one on the right is the first thing I’ve sculpted out of anything more serious than Play-Doh, and the big one on the left–the subject of this post–is the second. If I can do this, you can do this.
On to the how.
Sculpey isn’t really clay in the traditional sense. It’s slightly oily plastic that polymerizes when baked. When it first comes out of the package, it’s surprisingly brittle and crumbly. You have to knead it for a while before you can do anything useful with it.
Here’s a lump after some kneading. My work surface here is a dinner plate covered with aluminum foil.
At the local hobby store you can buy a set of clay sculpting tools, in plastic for about five bucks or in wood for up to thirty. But unless you’re a professional sculptor you can skip all that folderol and just use your fingers and crap you find around the house.
The main thing I learned during this stage? You can achieve just about any shape you want, depending on how much time you’re willing to invest. I worked iteratively, smoothing and resmoothing and smoothing some more.
Cheap tools in action: using popsicle sticks to smooth the edges of the claw. You can get a bag of 100 of these suckers at the dollar store. If you don’t already have a decent pair of wire cutters, you can get them at the dollar store, too, and you can use the wire cutters to cut all kinds of edges into the popsicle sticks. So that’s like 100 clay tools for a buck or two.
If it seems like I’m hating on fancy clay tools, it’s because IME real artists just get on with making art and don’t get too precious about it. Here’s Zak Smith on painting (warning–nothing bad in that post, but there is some NSFW stuff elsewhere on that site):
the process is as follows: I take a very small paint brush with wet paint on it, put it on the paper, and move my hand around. There is no magic or machinery involved and it is done freehand. Sometimes I look at a real thing or person and paint it, sometimes its a picture i took, and sometimes i just make it up. How to tell? If its a picture with a title like “Lisa” then probably that’s from real life, if it’s, say, a zebra-man with two samurai next to it, then that’s made up.
“What kind of paint?” The cheapest kind they have at whatever store I am at.
So it drives me crazy when I see wannabe artists shelling out thirty bucks for tools they could make or emulate for less than a tenth of that. (If you’re serious enough to have actual fancy tools, holster the angry comments, I don’t think you’re keeping the local Hobby Lobby in business buying the faux-fancy tools.)
Need a clay knife? Floss picks work pretty well. I used this one a LOT. Here I’m angling the articular facet for the next phalanx.
Blood vessel grooves. I think I used the blunt end of a bamboo kabob skewer to install these, with some follow-up shaping with popsicle sticks. I also straightened and shortened the claw tip a bit from the previous photo.
Funny story: a few years ago I was going through the public exhibits at a certain nameless museum and at the “touch a fossil” table an excited young docent started to explain how the “blood groove” was there to let the blood flow out of the wound so the claw wouldn’t get trapped by suction. I tried to explain that it was really there to hold the vessels that nourished the keratin sheath that covered the bony claw in life, but he was unpersuaded. I wished, for the first and only time, that I had a cast Tenontosaurus claw with me so he could explain why herbivores needed “blood grooves” on their claws, too…
Now: detailing. I didn’t want to sculpt the claw as it was in life, I wanted a fossil claw, something that looked like it might have been left out in the rain for 145 million years. The bone I picked up on the beach, and the exposed spongiosa is just perfect for putting a realistic bone texture on stuff. The rock is a rock. I used it for nicks and gouges.
I carve cracks with a straight pin. I carve them fairly deep, a couple of mm, so if I accidentally smudge some clay over a crack I can cut or sand it off, post-baking, and get the crack back. I don’t worry about raised edges along the edges of the cracks–these sand off in a heartbeat after baking. Just carve away.
Right after the above photo was taken, I popped the whole plate in the oven for about 45 minutes at 295 F to bake the Sculpey. There are lots of different kinds of Sculpey and other polymer clays on the market, so read the instructions on the box before you bake. Also, the baking drives off the oils that made the stuff kneadable, so save your baking for a nice day when you can have the windows open. If you’re going to bake a lot of Sculpey, you might want a separate oven for it. The vapors from the baking Sculpey do make me feel a little ill, so I get some good airflow through the house and limit my exposure. Caveat sculptor.
Here’s the claw right after baking. Some areas are smooth and shiny from being in more intimate contact with the foil. If you’re not going to sculpt the other side of something and you want a perfectly flat, smooth surface, watch out for this.
The only point of this photo is to show that the baked Sculpey is not rock-hard. The tip of the claw is drooping under its own weight here. For my first, smaller claw, I carved a groove in the flat side with a Dremel and put in a section of bent hanger wire to help it maintain its shape. For this second one, I figured the other half of the claw would give it sufficient thickness to hold its shape after baking, and I was right.
Here’s the reverse side, sculpted using the same techniques as I used for the first side, but not baked yet. I suppose there might be some kind of Sculpey Einstein out there who can do a whole claw in one go, but I couldn’t figure out how to do both sides without leaving fingerprints everywhere, or how to support the thing while it baked, so I did the two sides sequentially. If you think of a better solution, let me know, although really this is not much extra work–about an hour, max, while I was watching Mythbusters.
Now we gotta talk about asbestos for a while (this is relevant, I promise). Here’s a photomicrograph of a macrophage (a kind of white blood cell) self-impaled on some asbestos fibers, in what started out as attempted consumption of foreign material by the macrophage, and ended up closer to a crucifixion.
Here’s the deal: you have macrophages roaming around in your lungs, and when they find stuff that isn’t supposed to be there–which is pretty much everything other than your own living cells–they eat the offending material. And by “eat” I mean “engulf and try to chemically destroy”, using all kinds of profoundly noxious stuff–hydrochloric acid, hydrogen peroxide, chlorine gas. And if the offending material is extremely resistant to such treatment, as is the case with asbestos, the macrophages just keep unleashing hell. Forever. Which doesn’t dissolve the asbestos, but does eventually dissolve your lungs. Asbestos by itself doesn’t hurt you much–it’s what you do to yourself trying to get rid of it that kills you.
Why am I bringing up this depressing stuff? Partly because you are in command of a human body and you should know something about how it works. And partly because, if you have been following this little how-to, very soon you are going to be sanding your Sculpey dinosaur claw. Which is made out of plastic. Which is going to shed tiny particles of plastic into the air while you sand it. Which you are going to inhale unless you are wearing a mask. Now, I don’t know the actual resilience of baked Sculpey particles under the chemical assault your macrophages are prepared to light them up with, and I don’t recommend that you perform the experiment on yourself. I got a pack of five of these:
for two bucks at the hardware store. If you can afford ten bucks for a block of Sculpey, you can afford to spend two more to save your lungs.
This goes for sanding just about everything, by the way. It’s like germs or radiation, just because you can’t see or feel the damage doesn’t mean that it isn’t happening. Also like germs and radiation, some simple precautions are all you need to avoid the vast majority of the problems. Or you can skip them, and someday someone like me may be using your corpse to teach people about how not to care for a human body. Your pick!
Sanding. I only do one pass, with 220 grit. If you start with 60 grit, you can say goodbye to all the details you put in, because they are going to be gone very quickly. Basically I’m just trying to knock off the most egregious of the rough edges. I’m not trying to get a very smooth surface–that comes next.
I didn’t take any pictures of this, but after the sandpaper I scrubbed the whole claw with 000 steel wool. I had never used this stuff before–I only learned about it from that Adam Savage TED talk–and it is pretty amazing. For one thing, it will give whatever you are sanding a shockingly smooth finish. For another, it actually goes away as you use it. You’ll start out with a full-sized bundle and after sanding for 10 minutes you’ll be down to a half-size bundle. If you’re slouching in front of the TV, it will look like a metal cat shed all over your t-shirt. The chances of actually inhaling a tiny sliver of steel and having it get all the way down into your lungs are probably pretty slim, but I masked up anyway (there are still microscopic Sculpey shards coming off at this stage). Anyway, the steel wool gives a very even appearance to the surface, so you can’t tell what areas got really hit by the sandpaper, and for me it was one of the most satisfying parts of the whole process.
And here’s the final result. On the right the tip is a little blackened from over-baking, since the right side went through the oven twice, but it’s not bad. At this point you can paint or do whatever. I haven’t experimented with painting Sculpey yet, and online sources are mixed about what works best. You don’t want to use anything thick for a primer or you’ll lose the fine details. When I do finally get around to painting, I’m going to start with flat black auto primer, just like Adam Savage used on his Maltese Falcon (which I know was resin, not Sculpey, but still), and see if that doesn’t do the trick. If you know of something better, please tell us in a comment.
Next up in this series: molding and casting.
April 26, 2013
Earlier this spring London and I got on a building dinosaurs kick, inspired by this post at Tumblehome Learning. I used a few of these photos as filler in this post, but I haven’t talked much about what we did and what we learned.
Above is my first attempt at a wire skeleton for a papier mache dinosaur. Yes, despite being a dino-geek from the age of three on, I had never made a papier mache dinosaur before this spring. The thicker white wires are from a hanger, and the thin ones are from a reel of wire I found in the hardware section at Wal-Mart. It’s held together with masking tape, and the thick wires running down the legs of the dino are going into holes I drilled in that piece of scrap wood.
Here’s part of the wireframe for my first skull. At this point I was still thinking of Alioramus. Notice the sections of drinking straw, split and popped onto the wires to bulk out the wireframe and give the papier mache more than a 2D plane to bite on.
Here’s that lower jaw with the rest, a skull of some kind of predatory coelurosaur. Fairly early on I abandoned the strict Alioramus plan and followed in the footsteps in Barnas Monteith at Tumblehome Learning (who posted the instructions linked above) in going for a sort of generic critter instead of any particular real-life taxon. Therefore, I was free to freewheel without having to worry too much about accuracy (Robert Frost would have said I was playing tennis with the net down). As you can see here, this is another wire job held together with duck tape, and the lower jaw already has the first layer of papier mache on.
Papier mache is pretty hard to screw up: put some water in a bowl, add flour until it gets thick, stick pieces of torn-up newspaper in the mix and put them on whatever you’re making. Anything more than that, you should learn on your own by experimentation.
Progress on “Rexy” and my skull was going too slow for London, so I knocked out a crude Velociraptor skull in cardboard for him to work on at his own pace. This became “Rapty”.
An early family portrait: “Rapty”, “Rexy”, and my “Uglioramus” skull. You can see the Wedel method for not messing up the dining room table: first, put down a layer of plastic trash bags taped together, then a layer of newspapers taped together. For Rexy, we put down a layer of cling wrap to keep the papier mache drips off the wood base, which was a huge win in the long run. Rapty and Ulgioramus are sitting on foil-covered pizza-baking sheets. Those turned out to be useful for…
…baking skulls. Papier mache dries s l o w l y in cool, wet weather. But if it will fit, you can pop your thing in the oven on low heat for 15-20 minutes and get’er done quickly. This worked for both skulls, but it worked better for Rapty. On Uglioramus, the metal expanded enough to keep poking its way out of the papier mache, so I did a lot of patching. Still probably faster than waiting for the whole thing to air-dry.
Teeth. I went a little nuts with these in terms of size (I know, those teeth won’t fit into that maxilla, but it looks rad if you switch your brain off, kind of like Jurassic Park). They’re made up of flat cardboard from a cheap box (not corrugated) layered together with wood glue to give them some thickness, and coated with more wood glue and papier mache goo to soften the contour lines.
Before painting I sealed the whole thing with a thin layer of Titebond wood glue. That probably wasn’t 100% necessary, given what went on next, but I knew it would get the job done and strengthen the structure.
Back to “Rapty”: he got a set of teeth–one layer of thin cardboard this time–entirely speculative nasal and parietal horns courtesy of London, and a couple of coats of Kilz2 white latex primer left over from a telescope-making project. Then he was off to school for show-and-tell. Since then he’s gotten one thin coat of brown watercolor paint. Some of the holes in the skull just about closed up during papier-macheing, but since the impetus for the project was to have fun, it doesn’t trouble me.
Here’s Uglioramus, also dressed in Kilz, awaiting his first coat of paint in my expensive, professional paint box. Leaving a freshly-painted object without overhead protection in this neighborhood is just asking for it to be hit by falling vegetation.
And here we are after the first coat. I use Krylon because it’s cheap, tough, and dries fast, but with the Kilz on I could probably use just about anything.
And that brings us up to the present. I have some ideas on how to finish Uglioramus to make it look more like a fossil skull and less like some cast-off from a flea market, but those will have to wait for another post.
The upshot of all of this is that I am not an expert on either theropod skulls or papier mache, and if a doofus like me can do this well the first time out, you can probably do as well or better yourself. And it’s cheap, messy fun. Highly recommended.
January 24, 2013
Okay, before some wag makes this point, the gator is missing a good chunk of its tail, so this is more like the left half of the anterior two-thirds of a gator. But that would make a lousy title.
We might have more to say about this in the future, but for now, I’m going to let this 1000-word-equivalent speak for itself.
Many thanks to Elizabeth Rega for the use of the gator.
January 22, 2013
Our friends Tim and Michelle Williams moved into a local house a few months ago. In the garage, they found a jam jar containing the bones of a squirrel and the remains of its rotting flesh, dated 1985: presumably a zoologist lived in that house 28 years ago, began preparing a specimen, and moved out before finishing.
Tim was inexplicably lacking in excitement over this discovery, and passed the jar to me. I cleaned the bones (holding my nose) and am now the proud owner of a plastic tub full of tiny, tiny bones. Among the most interesting are the mandibles, and here’s why. First, I’ll show you the right mandible in medial view, with its incisor sitting in its socket as it would have done in life:
The bones were clean enough that the teeth all came out of their sockets, so here is the same mandible in the same aspect to the same scale, but with the tooth removed:
I know! It’s ridiculous! You wouldn’t think it would ever fit inside the bone of the jaw! But it does — just. Here are the tooth and the jaw juxtaposed:
So there is it: the tooth literally could not be any bigger.
Rodents: they’re not quite as dull as you think.
January 18, 2013
Matt and I have been sniggering at the Lousy Book Covers tumblr (slogan: “Just because you CAN design your own book cover doesn’t mean you SHOULD”). A couple of evenings ago, he wondered whether we could do better. And whether we could do it in half an hour.
In no time at all, a competition was born. Here are the rules:
- You have 30 minutes total to create the cover from scratch.
- When the time starts, generate a batch of six random titles at the kitt.net Random Book Title Generator.
- Choose the one you like most, and make a cover for it.
- Use your own name as the author.
- You may only use copyright-free or CC BY materials, and be prepared to demonstrate that you have done so.
- The cover must be in the correct aspect ratio for a “B Format” paperback (129 x 198 mm) and in a decent resolution — at least one megapixel.
There are probably better random title generators out there, but we just used the first one we found. It gave Matt these six titles: Silken Magic, The Missing Bridges, Theft of Abyss, The Sorceror’s Slaves, The Year of the Beginning and Cloud in the Petals. And it gave me these: Rough Eyes, The Trembling Spirits, Snow of Eye, The Wind’s Flames, The Names of the Name, and Mists in the Servants. Obviously some of these are completely unusable (“The Mists in the Servants” — I mean to say, what?) but you’re pretty much always going to get at least one that works.
Anyway, here’s what Matt came up with, interpreting his chosen title as non-fiction and sneakily inserting a subtitle:
Pretty sweet work, I think — although Matt was unhappy with the vertical spacing, feeling that the author name was too close to the bottom. The baby-turtle image is by John Winkelman, from flickr, and it’s CC BY. (Matt cut the hand and turtle out so that he could drop the contrast a bit on the background, which accounts for the obvious ‘shoppage around the fingers visible at full res.)
I interpreted mine as a Fantasy novel, and I guess I sort of added a subtitle too, in a way. Here it is:
The background image is cropped and modified from Desert sky scene at dusk by Steve Hillebrand of the U.S. Fish and Wildlife Service, which is public domain. The parts that work well, I think, are the different capitalisation, size and colour of the “the”s and “NAME”s; and the translucent star underneath the title. If I could do it again, I would swap the two dark reds, but there you go.
I ran out of time to do the author name nicely, so it’s pretty blunt. If I’d had more time, I would also have put a small but clear single artifact in the middle of the cover — perhaps a sword or lantern, or maybe something a bit more left-field like a scroll or a leather water bottle. But since I ran out of time, this is how it stays.
(One important lesson I learned is that I need to figure out how the get GIMP on my Mac to recognise more fonts — it has a tiny selection, and all the sans-serif ones look like they’re straight out of a PowerPoint presentation.)
So now we challenge you: what can you come up with thirty minutes total? If you have a go at this challenge, upload your images and post a link in a comment. (You can upload easily at sites like imgur.com if you don’t have an account on flickr or similar.)
March 14, 2012
Another picture from the recent ostrich dissection (click for full-size, unlabeled version). Last time we were in the middle of the neck, looking from anterior to posterior. This shot is from closer to the base of the neck, looking from posterior to anterior. A lot of the stuff is the same: the ragged cut from the saw at the meat processing plant where the ostrich was cut up; the spinal cord with the supramedullary airways above it in the neural canal; and the large interspinous ligament with diverticula on either side. We’ll have reason to refer back to some of those things in the not-too-distant future, but right now I want to draw your attention to something else: the tendons of the paired longus colli dorsalis muscles toward the top of the photo.
Here’s a modified version of Wedel and Sander (2002: fig. 2) with the course of the longus colli dorsalis highlighted in red (anterior is to the left). It is a curious aspect of bird necks that the large dorsal muscles do not insert on the neural spines but on the epipophyses (or dorsal tori or dorsal tubercles) above the postzygs. A naive approach based on beam theory would suggest that inserting on the neural spines would give those muscles more leverage, but necks are tricky and often defy such a priori predictions.
Instead of inserting on the neural spines, the longus colli dorsalis muscles originate from them, especially in the posterior part of the neck, and that’s what the photo at the top shows. From the reader’s point of view, the big interspinous ligament runs forward to attach to the posterior side of the neural spine (not visible because it’s buried in gloop, but it’s about a third of the way down from the top). The longus colli dorsalis tendons are running forward from the anterior side of the neural spine.
Here’s the same thing again, also in an ostrich, but in an MRI this time (and with anterior to the right; Wedel et al. 2000: fig. 20). The dark streaks running forward from the neural spines are those longus colli dorsalis tendons. The interspinous ligament also shows up nicely as a series of white bands connecting adjacent neural spines.
- Wedel, M.J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates; pp. 201-228 in Wilson, J.A., and Curry-Rogers, K. (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.
- Wedel, M.J., R.L. Cifelli and R.K. Sanders. 2000. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45(4): 343-388.
March 10, 2012
Those ostrich necks I went to Oro Grande to get last Thursday? Vanessa and I started dissecting them last Friday. The necks came to us pre-cut into segments with two to three vertebrae per segment. The transverse cuts were made without regard for joints so we got a bunch of cross sections at varying points through the vertebrae. This was fortuitous; we got to see a bunch of cool stuff at the cut faces, and those cut faces gave us convenient avenues for picking up structures and dissecting them out further.
In particular, the pneumatic diverticula in the neck of this ostrich were really prominent and not hard at all to see and to follow. The photo above shows most of the external diverticula; click through for the full-resolution, unlabeled version. The only ones that aren’t shown or labeled are the diverticula around the esophagus and trachea (which had already been stripped off the neck segments, so those diverticula were simply gone), those around carotid arteries, which are probably buried in the gloop toward the bottom of the photo, and the intermuscular diverticula, of which we found a few in parting out the dorsal and lateral neck muscles.
There is one final group of diverticula that are shown in the photo but not labeled: the interosseous diverticula that fill the air spaces inside the bone.
We have tons of cool photos from this dissection, so expect more posts on this stuff in the future.
For previous posts showing diverticula in bird neck dissections, see:
Things to Make and Do, part 7b: more fun with rhea necks (admittedly, not the most creative title ever)
November 23, 2011
Here at SV-POW! we are ardently pro-turkey. As the largest extant saurischians that one can find at most butchers and grocery stores, turkeys (Meleagris gallopavo) are an important source of delicious, succulent data. With Thanksgiving upon us and Christmas just around the corner, here’s an SV-POW!-centric roundup of turkey-based geekery.
The picture at the top of the post shows a couple of wild turkeys that frequented our campsite in Big Bend in the winter of 2007. Full story here.
If you’re wondering what to do with your turkey, the answer is GRILL IT. I use the recipe (available on Facebook) of my good friend and colleague, Brian Kraatz, who has fallen to the Dark Side and works on mammals–rabbit tooth homology, even (Kraatz et al. 2010)–but still grills a mean theropod. (In his defense, Kraatz has published on extinct saurischians–see Bibi et al. 2006.) My own adventures in turkey grilling are chronicled in this post, which will show you the steps to attaining enlightenment, or at least a larger circumference.
While you’re cooking and eating, you might as well learn something about muscles. This shot of the fanned-out longus colli dorsalis muscles in a turkey neck was the raison d’etre for this post, and turned up again with different muscles labeled in one of the recent Apatosaurus maquette review posts. Mike and I ate those muscles, by the way.
After the meal, you’ll have most of a turkey skeleton to play with. This diagram is from my other ‘holiday dinosaur’ page, which I put together for the Lawrence Hall of Science and UCMP back in 2005. That page has instructions on how to turn your pile of greasy leftovers into a nice set of clean white bones. Tom Holtz is widely acknowledged as King of the Dino-Geeks, and in kingly fashion he took the above diagram and turned the geek-o-meter up to 11. Steel yourself, gentle reader, before checking out the result here.
Speaking of bones, here’s a turkey cervical from Mike’s magisterial work in this area, which first appeared as a tack-on to a post about the holotype dorsal vertebra of the now-defunct genus Ultrasauros. The huge version of the composite photo has its own page on Mike’s website, where it is available in three different background colors. The lateral view also turned up in one of my rhea neck posts.
From the serving platter to publication: when I was young and dumb, I used a photo of a broken turkey vert to illustrate the small air spaces, or camellae, that are commonly found in the pneumatic bones of birds and some sauropods (Wedel and Cifelli 2005:fig. 11F).
I made a much better version by sanding the end off a cleaned-up vertebra, and used that in Wedel (2007), in this popular article on pneumaticity (which has instructions for making your own), and way back in Tutorial 3–only the 12th ever post on SV-POW!
Finally, it would be remiss of me not to point out that turkeys are not only readily accessible, tasty sources of anatomical information, they are also pretty interesting while they’re still alive. Don’t stare at the disgusting freak in the photo above or you might lose your will to eat. Instead, head over to Tetrapod Zoology v2 for Darren’s musings on caruncles, snoods, and other turkey parts that don’t even sound like words.
That does it for now. If you actually follow all of the links in this post, you might just have enough reading to keep you occupied during that post-holiday-meal interval when getting up and moving around is neither desirable nor physically possible. If you’re in the US, have a happy Thanksgiving; if you’re not, have a happy Thursday; and no matter where you are, take a moment to give thanks for turkeys.
- Bibi, F., Shabel, A.B., Kraatz, B.P., and Stidham, T.A. 2006. New fossil ratite (Aves: Palaeognathae) eggshell discoveries from the Late Miocene Baynunah Formation of the United Arab Emirates, Arabian Peninsula. Palaeontologia Electronica Vol. 9, Issue 1; 2A:13p.
- Kraatz, B.P., Meng, J., Weksler, M., and Li, C. 2010. Evolutionary patterns in the dentition of Duplicidentata (Mammalia) and a novel trend in the molarization of premolars. PLoS ONE 5(9): e12838. doi:10.1371/journal.pone.0012838
- Wedel, M.J. 2007. Aligerando a los gigantes (Lightening the giants). ¡Fundamental! 12:1-84. [in Spanish, with English translation]
- Wedel, M.J., and Cifelli, R.L. 2005. Sauroposeidon: Oklahoma’s Native Giant. Oklahoma Geology Notes 65 (2):40-57.
November 7, 2011
This is the second post on the Wedel lab’s recently acquired skull of Ursus americanus, the American black bear. The first installment covered ended with the disinterred-but-still-filthy skull bits sitting on my dining room table. This post covers putting the teeth back in, and just enough anatomy to justify putting up more cool pictures.
About five minutes after I took the last picture from the last post, I put the cranium and mandible to soak in warm, soapy water and spent the rest of the day doing other things. Last night I got a couple of old toothbrushes and scrubbed off most of the dirt from the external surfaces of the skull. I alternated toothbrush work with running water from the bathtub faucet over and through the skull bits. I also used one of the rubber nasal aspirator bulbs (or “snot suckers”, as new parents in the real world invariably call them)–which make tremendous water guns–to sluice out some of the grimier cavities. It was fun to force water into the mandibular foramen and see it come shooting out the mental foramen, along the canal traveled by the inferior alveolar nerve and vessels.
All of the teeth were loose in their sockets, and the incisors and upper canines were either falling out or could be pulled out without too much trouble. I yanked all of the teeth that I could, figuring that it was better to yank-and-glue rather than leaving them loose. I set the loose teeth on separate plates, one upper, one lower, arranged in the same order they were in the alveoli, and let everything air dry overnight.
Shown above is my setup for replacing the teeth:
- a trash bag for protecting the table
- a dish towel to provide a soft surface
- the bear skull pieces
- loose teeth on their respective plates
- five minute epoxy
- toothpicks for mixing and spreading the epoxy
I had been going to use something less hardcore for the gluing, but fortunately Vicki got home and I was able to draw on her experience from reconstructing loads of human skulls from archaeological and forensic sites. She said just go with epoxy, and so I went.
Here we are about halfway through the process. A few tips, some obvious, some maybe less so:
- Even if you’ve done a perfect job of keeping the teeth in order, test-fit them anyway. If nothing else, this will give you a visceral sense of what the tooth feels like sliding into the socket, and it will help you figure out how much glue to apply. Also, test fit adjacent teeth together so you’ll know if they have to go back in in a particular order; sometimes one tooth is at a subtle angle and blocks the next tooth from coming out or going back in.
- Better to put the glue in the socket than on the tooth. The roots are not much smaller in diameter than the alveoli and the crowns stand out a bit from the bone (although the ‘exposed’ roots would have been covered with gums in life). If you put the glue on the tooth you’re liable to either have it bulldozed off by the alveolar rim as you slide the tooth into the socket, or you’ll put too much on and have a bunch of worthless glue on the exposed portion of the root.
- If the teeth are worn, like the incisors are here, it’s nice to do a bunch at once so you can get all of the wear surfaces lined up as they were in life. Better than having one tooth set up completely and then realizing it was all the way forward/back/in/out and the other teeth can’t match its orientation.
Everything back in. There are a couple of incisors still AWOL, and a few premolars, but the dentition is still reasonably complete (remember that I am used to working on Early Cretaceous North American sauropods, so a little completeness goes a long way). I ran a thin bead of epoxy around the bases of all of the teeth that had not come out of the alveoli, to hopefully rein in any future wanderlust on their parts.
Sweet action. I wish I had something more intellectual to say here, but I really don’t.
Nasal turbinates. Holy crap, were these a pain to get clean. I didn’t get them completely clean, there’s probably enough dirt up in there to germinate something. But I asymptotically approached the point where removing more dirt would have meant damaging the turbinates, which are at least manilla-envelope-thin if not laser-printer-paper-thin.
A closeup of the infraorbital foramen on the right, which transmitted the infraorbital artery and vessels in life. The neurovascular tracks on the external surface of the bone are pretty sweet; you can see them on the left side, in context, two photos up.
In addition to closing our jaws in a hinge-like motion, we can slide them fore and aft and also from side to side. Those kinds of motions are fine when you’ve got comparatively weak jaws like ours, and we still occasionally get into trouble–jawbreakers are so named for a reason. But those non-hinge-like motions would be disastrous for something that can close its jaws with several hundred pounds of force. So most big carnivores have wide, almost cylindrical jaw joints that constrain the motion to being almost purely hinge-like. In mustelids (weasels and kin), which have the strongest bites for their sizes of any mammals, the condyle is so cylindrical and the fossa so deeply enclosing (imagine a Q sitting inside a very slightly larger C–that’s the jaw joint seen from the side) that sometimes you simply can’t get the jaws to disarticulate after death. This ain’t quite that extreme, but it’s closer to the mustelid condition than the human. Not surprising, since weasels are united with bears and seals in the clade Arctoidea.
And here’s why bears need those cylindrical jaw joints: check out the muscle attachment scars on the back of the mandible. These are for the temporalis and masseter muscles, the same muscles you can feel bulging out on the side of your head and the corners of your jaw when you bite down forcefully or grit your teeth. IIRC, the maximum bite force a human can exert is around 180 pounds, and lions can do something like 900 pounds. Not sure where Ursus americanus falls, but definitely on the please-don’t-bite-me end of the scale.
And here’s why those muscle attachment scars are so big. The zygomatic arches are only partly complete here, but you can see how wide is the space between the left arch and the braincase. All of that space–two full inches, mediolaterally–was filled with temporalis muscle that provided most of the power for jaw-closing. This is why pit bulls have such wide, flat-looking heads: they have normal-sized dog brains and huge, thick jaw muscles. See also: my hyena dissection photos.
Looking very dog-like here in anterior view. There are some butchery marks on the skull, most noticeably across the external nares here, and along the mandibles. Not sure what that’s all about, since I can’t reconcile the stated backstory–cop shoots dangerous bear, buries head in backyard–with a need to make repeated cuts across the snout and jaws. And no, they’re not shovel marks. I knew that already, and Vicki confirmed that the marks are peri-mortem (around the time of death, but impossible to confirm as pre- or post-mortem). Anyway, I’m not complaining. Despite the damage, the skull is still an awesome thing, and the cut marks add a touch of mystery. I’ll post more pictures when I get the left temporal region glued back on.
November 6, 2011
After three months as a paleontology grad student, this morning Vanessa I. Graff got to sink a shovel in the service of science. Now, it was a bear skull, deliberately buried in someone’s back yard, so technically today’s exploits fall under the heading of contemporary zooarcheology rather than paleontology, but we’ll take what we can get.
This story has a backstory. The guy on the right here is Hossein Aziz, one of my advisees among the DO students at Western. His landlady’s ex-husband is in law enforcement, and about a year and a half ago he had to shoot a bear that had become a threat to humans. He buried the head in the backyard and separated from his then wife. She found out from Hossein that one of his professors was a paleontologist and offered to donate the skull to science, if only we’d come dig it up. So we did. Involved in the excavation (right to left in the above photo) were Hossein, his girlfriend Lia, my son London, Vanessa, and yours truly.
Additional note: Hossein’s landlady is a British expatriate, and she served us proper English tea. It was the most civilized dig I have been on, which, admittedly, is sort of like being the least worthless Kardashian. Anyway, the tea was great, and we all had a good time.
My wife, Dr. Vicki Wedel, was out of town, but she lent us her archaeological toolkit, so we had nice trowels and kneepads and such. Here Hossein is pretending to advise Vanessa and London on what they should be doing, which is funny because that’s usually my job (pretending, that is).
After about half an hour of digging, we found intact vertebrate remains! And there was much rejoicing.
First out of the ground was the mandible, which is in essentially perfect shape.
Ursus americanus mandible and lower dentition, Homo goofballensis for comparison and scale.
Lia and London clearing dirt from around the cranium, which looks disturbingly hominoid from this angle.
There really aren’t any words for what’s going on here. Just bask a moment in the glory and move on.
We were going for American Gothic here, but Vanessa blew it by smiling. Standard.
Lia and Hossein marveling at what is, after all, a pretty badass critter. Even a small bear has seriously impressive teeth, which you hope to never find embedded in your flesh.
Still, it can be fun to pretend otherwise.
Here’s what we have. The occipital region is just gone. The left temporal region is more intact and has a long crack leading away across the frontals. On the right, everything from the zygomatic process of the maxilla to the occiput is just gone. So I reckon the rifle bullet went in on the left and blew out an exit wound the size of an orange on the right side of the bear’s head.
After a good rinse in the tub, all the bits are now soaking in soapy water. I’ll post more pictures when I get it all cleaned up and presentable. In the meantime, many thanks to Hossein’s landlady for the skull, the tea, and her amused tolerance at having a bunch of dirty people digging in her yard, and to Hossein, Lia, Vanessa, and London for their work. It was a pretty darned good way to start the weekend.