Another nice display from the Museum of Osteology in Oklahoma City (previous MoO posts here and here). Check out the really gnarly ones that are indeed growing right through the bones of the face. That must have sucked.
We’ve covered rodent teeth here a few times before (one, two)–more than is probably right, for a blog ostensibly about sauropod vertebrae. Sherlock Holmes said, “Life is a great chain, the nature of which can be determined by the discovery of a single link.” I’d amend that to, “Life is a great tree, the inherent fascination of which flows through every tiny twig.”
Back when we started SV-POW!, Mike predicted that the technical niche blog was the wave of the future. That prediction does seem to be coming true, albeit more slowly than I thought it would. Nevertheless, if you are susceptible to the inherent fascination of rodent teeth, get yourself over to Ian Corfe’s Tetrapod Teeth & Tales for more geeky goodness.
Now, in a move that will possibly enrage one segment of the audience but hopefully delight another, I am going to forge even further away from the ostensible raison d’être of the blog and talk about monsters. Specifically Cthulhu–in my experience, in the Venn diagram of life, the “interested in paleo” and “interested in Lovecraft” circles overlap almost entirely. Over at my everything-except-paleontology-and-astronomy blog, I’ve been thinking about Lovecraftiana and wrestling with what a Cthulhu idol, such as those described in Lovecraft’s stories, ought to look like. If you’d like to contribute, get on over there and leave a comment. If you send* me a picture (drawing, painting, 3D render, photo of sculpture, whatever) or leave a link, I’ll include it in an upcoming post. Cthulhu fhtagn!
* Send to mathew.wedel@gmail.com, please include Cthulhu in the subject line.
How to overcome Imposter Syndrome
April 18, 2013
I guess pretty much all researchers must suffer from Imposter Syndrome every now and then — the sense of not really belonging, not knowing enough, not getting enough done to justify our position. I particularly remember feeling this after being awarded my Ph.D: the sense that I couldn’t possibly know enough about enough to be worthy of it. Even now, several years down the line, I sometimes look at my papers and think, pfft, there’s nothing to them, anyone could have done that.
I thought of this tonight because of a a tweet I just saw from M. J. Suhonos, Digital Technologies Development Librarian at Ryerson University:
https://twitter.com/mjsuhonos/status/324963845179314177
And the advice I gave in response:
The reason I say this is because a few days ago I did a phone interview for a news piece, and was sort of surprised to find myself talking confidently and fluently, just like someone who knows what he’s talking about. Until I realised that’s what always happens when I do an interview. And that’s because, well, heck, I do know my subject (otherwise why would they even be talking to me?)
And I bet you know your subject, too. You just need to see your own knowledge against the backdrop of what a normal person knows.
—
Meanwhile, as a contribution to John Conway’s superb “grumpy Hypsilophodon” meme, I give you: this.
Hey, look–dinosaurs!
My spouse, Vicki, the other Dr. Wedel, is a physical and forensic anthropologist. And she’s one of a very small number of scientists who have (a) learned something new about the human body, and (b) used it to help identify dead people. And since that process involves the sciences of hard-tissue histology and skeletochronology–not to mention lots of dead folks–I reckon it might be of interest here. Hence this post.
This started about a decade ago, when Vicki was working on her PhD under Alison Galloway at UC Santa Cruz. Vicki worked with Alison on a ton of forensic cases, including some you probably heard of–they analyzed the remains of Laci Peterson and her unborn baby, Connor, for Scott Peterson’s murder trial. I had the unusual privilege of assisting a couple of times, on other cases, once to take some pictures in the lab while Vicki fished the skeleton out of the bag of skin that was all that was left of the body, and once to crawl around on my hands and knees picking human finger bones out of a muddy slough near Santa Cruz. All in all, I’m happy that my usual victims have been dead a lot longer.
CT reconstruction of skull with bullet holes. Courtesy of the National Library of Medicine
Incidentally, the only show with forensic content that Vicki will watch voluntarily is Dexter. She cannot stand CSI, NCIS, or the other “behind the scenes” forensic investigation shows. We’ve tried watching them, but the inaccuracies drive her crazy (paleo people: imagine getting the Clockwork Orange therapy and being forced to watch Clash of the Dinosaurs). Real cases are solved by teams of specialists, not two omnicompetent protagonists; it takes weeks or months, not half an hour; and if the forensics people carry guns, it’s because they know waaaay too much about how some very bad, very organized people dispose of bodies (the short answer is, not thoroughly enough*).
* Once a guy who was threatening to testify against a certain criminal organization was shot in the head, his body burned, and his burnt remains scattered along the side of the road. Vicki and Alison picked the bone shards out of the roadside gravel, identified some of them as bits of skull, and found bevelling diagnostic of ballistics trauma on some of those. The way the bone had shattered showed that the gunshot had been inflicted perimortem–around the time of death–and before the body was burned. Bottom line, whatever plan you have to get rid of the body, it is probably not going to be enough to keep someone like Vicki from figuring out how you did it. That much, the TV shows do get right.
Skull being cleaned by dermestid beetle larvae. Image from Wikipedia.
Not only is hard to really, truly get rid of a human body, it’s also hard to tell exactly when a person died, especially if all you have is a body in the woods. Insects are good–there’s a whole field of forensic entomology, whose practitioners age cadavers based on what insects are present and what stages of their life cycles they’re in. But what if all that is left is a pile of bones in the woods (which happens more often that you might think, and sometimes for completely innocuous reasons)? I’m preaching to the choir here, but bones can survive for a long time, so general wear-and-tear doesn’t tell you much. Rapetosaurus looks like it died last year.
There’s another side to this, which is figuring out how old someone was at the time of death based on their skeleton. Tooth eruption is good, and fusion of the epiphyseal growth plates, but both of those processes are basically done by the time people are in their mid-20s (teeth) to mid-30s (epiphyseal fusion). After that, there are methods based on the morphology of the auricular surface of the ilium and the public symphyses, but these only narrow things down to intervals of 5 to 15 years, and that’s a lot of missing persons reports to sift through. And none of the regular skeletal methods work past the age of 55 or 60. After that, no matter how healthy you are, the primary skeletal changes are attritional (i.e., you’re wearing out), and that process varies so much among individuals and populations that there are basically no predictive guidelines.
All of this was on Vicki’s mind when she was a grad student, so she was alert to anything that might help forensic anthropologists narrow down the possibilities for identifying dead folks. She was teaching in an osteology course and one of her students, Josh Peabody, brought up dental cementum increment analysis (DCIA), which is used in zooarcheology to determine the age and season at death of animal remains found at archaeological sites. Josh wanted to know if the method worked on humans.
Faunal bone from an archaeological dig. Image borrowed from the University of Copenhagen.
At the time–2004–DCIA was being tested for age at death in some historical human populations from archaeological sites, but no-one had tried using it for season at death. So Vicki and Josh set out to see if it would work.
Our teeth, like those of other mammals, are held in their sockets by periodontal ligaments. The periodontal ligament of each tooth attaches via Sharpey’s fibers to the dental cementum on the tooth root(s). Cementum is laid down in annual bands, so you can count the number of bands on a tooth, add the normal age at which that tooth erupts, and get a pretty tight estimate of when the animal died. So much for age at death, which was already being done on humans in a limited way in the early 2000s, albeit in archaeological rather than forensic contexts.
But wait, there’s more. Actually two bands of cementum are laid down every year–a dark band in the winter (roughly October to March) and a light band in the summer (roughly April to September). ‘Dark’ and ‘light’ describe the appearance of the bands under polarized light microscopy. In the summer months, the collagen fibrils that make up the cementum are aligned parallel to the tooth root, so more light comes through. In the winter, the collagen is aligned perpendicular to the root, so less light is transmitted, and the winter bands appear darker by comparison. So not only does the number of pairs of light-and-dark bands tell you the number of years since the tooth erupted, the color of the outermost band tells you in which six-month period the individual died, and the thickness of the outermost band might help you narrow that down even further.
Dental cementum increments in a human tooth, from V. Wedel (2007: figure 1).
At least, that’s how it works in other mammals. Would it hold up in humans? After all, we’re pretty good at adjusting our environments to suit us, rather than vice versa. If the winter-summer banding pattern was present in humans, it would be a huge boon to forensic science. Even people in their 40s and beyond with no very reliable skeletal indicators of age could be aged to within a year or two, and their season at death narrowed down to a 2-3 month window.
To find out, Vicki and Josh had a dentist in Santa Cruz collect 112 teeth pulled from patients over the course of a year (with full IRB approval and informed consent from the dental patients). For their purposes, a tooth pulled from a live person is just as good as one from a cadaver or skeleton–extraction kills the tooth as surely as death of the body. Better, even, in that it was easier to quickly get lots of teeth with very precise extraction data.
Vicki and Josh cut a few teeth together and they found dark and light bands right away. They presented those preliminary results at the American Academy of Forensic Sciences meeting in 2005. After that, Josh got busy with his own research, but Vicki pressed on (while finishing a dissertation on different project, and being a first-time mom).
If this was a movie, this is the part where there would be a montage of inspirational music to get us quickly past a lot of hard, boring work. Each of the 112 teeth had to be embedded in plastic, a section through the root cut out with a saw, that section mounted on a slide and ground down until it was translucent (this process will be familiar to bone histologists of all stripes, paleo or neo). Then Vicki had to go all the way around the perimeter of the each root to find the place where the cementum bands showed the most clearly, and count them. This part is trickier than it sounds, unless you’ve done some histo and know just how butt-ugly some sections can be under the scope.
The results? In the words of the Bloodhound Gang, which Vicki quotes in her DCIA talks, “You and me baby ain’t nothin’ but mammals”. Here’s the payoff graph:
Percent completion of outer cementum increment by month, from V. Wedel (2007: figure 4).
The one out-of-place measurement was probably caused by the dark band not being thick enough to register clearly on the image.
Now that she knew that DCIA could be used to determine season at death in humans, Vicki started applying it in her forensic cases, of which there have been many. The vast majority of the work of forensic anthropologists is invisible to the public: after analyzing a set of remains, a forensic anthropologist writes a case report for whatever law enforcement office (or, much less frequently, law firm or other entity) brought them in, and that’s that. The case reports are almost always confidential, but they have to be written to exacting standards since they may be used as evidence in court. So forensic anthropologists spend a lot of time toiling over papers that hardly anyone gets to read.
However, sometimes a case is written up for journal publication–if it’s sufficiently novel or unusual, and if permission can be secured from all of the relevant parties. In 2008, Vicki was approached by the Merced County sheriff’s office to help try to identify the remains of a young woman who had been murdered in 1971. That’s the 37-year-old cold case mentioned in the title of this post, and rather than tell you about it, I’ll point you to Vicki’s case report (Wedel et al. 2013), published last month in the Journal of Forensic Identification and freely available here.
Vicki with the exhumed skeleton of Jane Doe. Photo by Debbie Noda of the Modesto Bee.
I wasn’t sure whether to post about this or not–as cool as they are, murder cases are not our normal stock in trade on this blog. What decided me was talking with Andy Farke. He read Vicki’s paper as soon as it came out, and he said that he really enjoyed getting to see how forensic anthropologists work in the real world. I sometimes take for granted that, since I am married to a forensic anthropologist, I get to see how this works all the time. But that’s a pretty rare experience–if paleontology is a small field, forensic anthropology is positively tiny. So if you want to see an example of the real science that CSI and the like are based on, here’s your window.
What’s next? Vicki has several validation studies on DCIA in progress, for which she and her collaborators have collected a much larger sample size–over 1000 teeth–to try to answer questions like: what tooth is best to use for DCIA? Should the histological sections be made longitudinally or transversely through the tooth root? Does cementum banding vary with latitude? And since banding patterns are reversed in the Southern Hemisphere, following the flip-flopped season, what happens at the equator? Watch this space, and keep an eye out for Vicki’s future publications–including a book due out next year–at her website, Bodies, Bugs, and Bones.
References
- Wedel, V.L. 2007b. Determination of season at death using dental cementum increment analysis. Journal of Forensic Sciences 52(6): 1334-1337.
- Wedel, V.L., G. Found, and G.L. Nusse. 2013. A 37 year-old cold case identification using novel and collaborative methods. Journal of Forensic Identification 63(1): 5-21.
Trend Micro thinks SV-POW! is malicious
June 23, 2012
Folks, I just got this email from open-access guru Peter Suber (quoted with permission):
I get ominous warnings when I try to visit your blog at https://svpow.com/. The warning in the browser says, “Malicious website blocked”. The warning in a separate pop-up says, “The Web page you are attempting to visit…could potentially harm your computer.”
Both warnings are from Trend Micro, which came factory installed on my Windows-based Dell laptop. I’ve found it reliable in the past.
Has anyone else seen this? Is it something we should be worried about? Does anyone know what we can do to stop it?
(BTW., for what it’s worth I can assure anyone else who’s seeing this warning that it can be ignored. There’s no malware here.)
Always two there are…
October 31, 2011
…a master and an apprentice.
Here’s how the Wedel Lab rolls on Halloween:
Check out that padawan braid. It’s official, I have the world’s coolest grad student. Although Vanessa’s choice of lightsaber is a bit worrying. Great danger I foresee in her training.
Tutorial 12b: Too far may not be far enough
February 17, 2011
(This is sort of a riff on the recent post, Tutorial 12: How to find problems to work on, which you might want to read first if you haven’t already.)
Something that has been much on my mind lately is the idea that if you don’t go too far, you don’t know how far you should have gone.
I first encountered this idea in a quote from concept artist Ian McCraig, in The Art of Star Wars: Episode I (p. 195):
People ask when I know when to stop scribbling, and decide a work is finished. I say you have to go too far and destroy it, because then you know when you should have stopped and can go back. If you don’t, you leave untold riches out there.
I’m sure McCraig wasn’t the first to formulate the idea, he’s just the medium through which I first learned of it, back in 1999.
Scott Aaronson calls brief statements of this sort “Umeshisms“, after his advisor, Umesh Varizani, who said,
If you’ve never missed a flight, you’re spending too much time in airports.
A follow-up post, reporting the results of an Umeshism contest among his readers, also has some gems.
For the sake of completeness, I should note the very economical general formulation of this idea from Tagore Smith, in a comment on Mike’s blog that Mike later promoted into a stand-alone post (the comment, not this excerpt):
I haven’t gone too far yet so I am not sure if I have gone far enough.
Here’s the larger lesson Aaronson drew from his advisor’s airport quip:
In a single sentence, Umesh was communicating an entire philosophy of life: concentrate on the high-order bits. The squash player who runs back and forth to attempt every shot, the student who’s never late with an assignment, the researcher who stalks an unimportant problem like Captain Ahab: all have succumbed to the tyranny of the low-order bit. They need to realize that, as in a randomized algorithm, occasional failures are the inevitable byproduct of a successful strategy. If you always win, then you’re probably doing something wrong.
One of the reasons this is so much on my mind is that I did an editing pass on a manuscript Mike is working on, and he took some of my suggestions, but not all of them. And I realized that that is probably a good thing; if he’d taken all of my suggestions, it would mean that I not edited hard enough. And it occurred to me that the Umeshism philosophy can probably be more effectively implemented by two people than by one. One can’t be an iconoclast all the time and still be productive; you have to settle down sometime. Also, two sets of eyes are going to see more ways to push the edge of the envelope.
“The researcher who stalks an unimportant problem like Captain Ahab” is also worth thinking about–specifically, to wonder which among my many concurrently developing projects are high-order bits, and which are not. Mike and I refer to our lists of works-in-progress as POOP, or Prioritized Ordering Of Projects, but we (or at least I) tend to slip into using “priority” to mean, “what am I working on next”, and not, “what should I be working on next”. I have let many projects slip into limbo while pursuing others, and it would be worthwhile to periodically reassess whether I’ve let the right ones slip. I strongly suspect that it has not always been the case. I just wrote in Tutorial 12 that any productive researcher is going to die with a mountain of intended work left undone. It is probably not too early for any of us to look at our array of projects and ask, “Which among these most needs rescuing from that mountain?”
The long Aaronson quote above also raises the specter of the costs of catching mistakes, which Paul Graham and Mike have both written essays about. Both basically boil down to “safety is expensive”. And that is sort of what I meant in Tutorial 12 when I wrote, “If you’re not feeling stupid, you’re too comfortable, and it might be time to do an audit and see if you’re actually contributing to science at all.” Feeling stupid–in the scientifically productive way–is a symptom of being out of your safety zone, where you are more likely to learn valuable things and have new ideas. I also argued that you have to sift through a lot of facts and ideas to hit on the handful that might meaningfully become part of your research. Most of the stuff you encounter will not be relevant to whatever it is you’re trying to do, but that’s okay. If all of your ideas seem like good ones, either you’re playing it very safe (and therefore the ideas aren’t actually that good), or you’re having delusions of grandeur.
I remember seeing somewhere–irritatingly, at this point I have no idea where–some guy arguing, maybe half-seriously, that any project was plagued both by errors that one knows about and also by other errors or biases of which we are ignorant, and that therefore he always tried to make sure that his known errors were bigger, because that way he was in control (the original was more cleverly and economically phrased).
All of this interests me, because so many forces in our lives conspire to make us afraid of making mistakes, and often even more afraid of admitting to them once they’ve been made. But we all make mistakes, all the time. So what are we going to do about it?
Right now my Gmail sig quote is a line from Clay Shirky:
To put yourself forward as someone good enough to do interesting things is, by definition, to expose yourself to all kinds of negative judgments, and as far as I can tell, the fact that other people get to decide what they think of your behavior leaves only two strategies for not suffering from those judgments: not doing anything, or not caring about the reaction.
The hardest reaction to not care about is your own. Doing good work demands the capacity to take mistakes in stride and keep moving forward. Doing great work might require another level of perspective, in which some kinds of mistakes are just indicators that you’re on the right path.
Seems that SV-POW! is only the second greatest blog in the universe
November 19, 2010
Just noticed this over on ScienceBlogs:
Tetrapod Zoology conquers the world!
SV-POW!sketeer Darren’s Naish’s other blog Tetrapod Zoology has — rightly — often featured strongly in the Readers’ Picks sidebar; but this is the first time I’ve seen it, or indeed any blog, completely monopolise the list.
ScienceBlogs has other blogs that get more hits and more comments than Tet Zoo — mostly because they consist of flamebait — but when you want solid chunks of meaty, scientific nourishment, Tet Zoo now seems to be pretty well established as king of the hill. On the slight chance that any SV-POW! readers aren’t already regulars at Tet Zoo, let me recommend it in the strongest terms: I know of no other blog that does such a good job of presenting hardcore science in a readable, approachable manner.
So congratulations to Darren, and long may it continue!
Tutorial 9: how to get copies of academic papers
November 9, 2010
There’s recently been a rash of requests for PDFs on the VRTPALEO mailing list. Or maybe “plague” would be a better word. What invariably happens is that a new paper comes out, and someone emails the list saying “Please can someone send me a PDF of this?”; then another half-dozen or so people all reply to the list saying “I’d like a copy, too”. (The situation is exacerbated by the VRTPALEO list’s utterly advanced policy of forcing all replies to go to the whole list instead of just to the person being replied to, but that’s a whole nother rant.)
The result is of course that several thousand people get half a dozen spams. Yes, it’s true that it only takes a couple of seconds to recognise and delete such messages. But when two thousand people each take two seconds to delete a message, that’s 4000 seconds of time that could have been used for something useful. In other words, to save yourself a couple of minutes’ work, you’ve wasted more than an hour of other people’s time.
Folks, this has to stop.
So what should you do when you want to get hold of a paper? It’s a simple three-stage process. And before you ask, yes, this is good for hobbyists as well as professionals.
Step 1: Google
Just search for the title of the paper. You’d be surprised how often it just turns up. Sometimes it’s in an open-access journal, such as Acta Palaeontologica Polonica, Palaeontologia Electronica or PLoS ONE. Sometimes the author has posted a copy, as for example I do with all my stuff and Matt does with his. Sometimes, there just happens to be a copy lying around somewhere — for example, because a lecturer made it available to his students.
Often, though, the paper you want is out there, but paywalled. So go on to …
Step 2: ask the author
Nine times out of ten, the abstract pages that the big commercial publishers put up include the author’s email address. So just drop him or her a line asking for a copy.
Dear Dr. Haddockwhittler,
I was interested to see the abstract of your new paper on eroded non-diagnostic ornithopod pedal phalanges in the Journal Of Small Boring Fossils. I would be very grateful if you would send me a PDF. Many thanks.
And you’ll almost always get the PDF back within a day or two. Sometimes authors don’t respond at all — most likely because they’ve not seen the message; and very occasionally they don’t have the PDF themselves. But these are very rare situations. And I have never, ever, known an author to just flatly refuse to send out a PDF.
I’ve had a few people telling me that they’re nervous about cold-contacting an Actual Credentialled Professional, and that they fear getting the brush-off because of their own amateur status. Put this foolish idea out of your mind. Every professional is always delighted when anyone, professional or not, is interested in their work.
SPECIAL BONUS FRINGE BENEFIT: every now and then, you may find that as a by-product of such a request, you strike up a conversation with the author. If you and they are interested in the same stuff, you sometimes find that you each have light to shed on the others’ thoughts. As a matter of fact, this is precisely how I met and became friends with Matt (which in turn is how I became a palaeontologist — a story that I must tell some time in Tutorial 10: how to become a palaeontologist). Usually this won’t happen: you’ll just have a brief, courteous exchange, and move on. But sometimes it might.
But suppose you can’t find the author’s email address? (This is much more common with older papers.) Or suppose it’s a really old one — a classic Janensch paper or something — and the author is dead? Or suppose you send an email, but the author never responds? Then on to …
Step 3: ask a friend
If you know someone who’s at an institution that has good access to subscription resources, drop them a line as ask whether they’d mind pushing a copy your way. If you’re friends already it’s probably because you’re interested in the same stuff, which means that they’ve likely already downloaded the paper in question — or, if not, they’ll be grateful to you for the heads-up. Even if not, you’re only wasting one person’s time instead of two thousand.
And if all else fails …
… then fall back to the original: email the list and ask whether anyone can help. Sure, there’s a place for this: it’s part of what the list is there for, and it can be absolutely invaluable when you’re trying but failing to track down an obscure old paper.
If you do this, then please use a meaningful subject for your email. If you just write “PDF request” than I will delete it without even opening it, and I bet most other people will, too. Do yourself a favour and write something terse but informative, like “Looking for PDF of Haddockwhittler 2010 on ornithopod phalanges”.
Another situation where mailing the list with a PDF request is appropriate: when you don’t know exactly what it is that you’re looking for, and you need expert guidance. For example, I did this when looking for an ostrich osteology: I didn’t know of a good one (and hadn’t been able to discover the existence of one using Google), so I asked. Not a problem.
But, people, this should be the last resort, not the first.
(There are those that say Inter-Library Loan should be on the List Of Things To Do Before Spamming VRTPALEO, but that’s not usually an option for amateurs with no formal affiliation.)
Well, I hope that’s helpful. Now go forth and obtain papers!
—
This post is an expanded version of an email that I have written many, many times to individuals. I got bored of writing it over and over, and figured that it would be quicker and easier to post this, and then be able to point people to it.
The new Miocene sperm whale Leviathan is now Livyatan
August 26, 2010
A bit frightening to realise it’s been more than a month since the last SV-POW! post. We have some excuse for that: I am just back from a fortnight’s holiday with my family, and shortly before that Matt was at a conference in Uruguay. Still, a whole month?
And this post is going to be disappointingly short and off-topic — it’s just a bit of housekeeping really.
Back at the end of June, I pointed out on this blog that the awesome new Miocene sperm whale Leviathan was a junior synonym of Koch’s name Leviathian which he introduced as a more than usually stupid synonym of Mammut, the mastodon. (See the original piece for the gory details.)
I am pleased to note that this has now been resolved: the authors of the new Leviathan paper have published a short corrigendum proposing the replacement name Livyatan, resulting in the new combination Livyatan melvillei. Since the corrigendum is so short, here it is in its entirety:
The genus name Leviathan, proposed in this Letter for a new fossil physeteroid from the Miocene of Peru, is preoccupied by Leviathan Koch, 1841 (ref. 1), a junior subjective synonym of Mammut Blumenbach, 1799 (ref. 2). We propose here a replacement name Livyatan gen. nov. The type species is placed in this genus to form the binomial Livyatan melvillei. The diagnosis and content of the new genus follow our Letter. ‘Livyatan’ is a Hebrew name applied to large marine monsters in popular and mythological stories. We thank M. P. Taylor and D. Yanega for bringing this to our attention.
It’s nice to get a mention, though a shame they weren’t able to include a link to SV-POW!. Probably Nature‘s guidelines don’t allow that — they wouldn’t be alone — and in any case we’ve hardly been a friend to the Nature Publishing Group, so maybe we’d have even less reason to expect any love from them :-)
SV-POW! is, as I’m sure you know, devoted to sauropod vertebrae. But occasionally we look at other stuff… and you might have noticed that, in recent months, we’ve been looking at, well, an awful lot of other stuff. I’m going to continue that theme here and talk about salamanders. Yeah: not sauropods, not sauropodomorphs, not saurischians, and not even dinosaurs or archosaurs. But salamanders. Don’t worry, all will become clear. This all started back in May 2010 when I blogged about amphiumas over at Tet Zoo. Amphiumas are very unusual, long-bodied aquatic salamanders.
A Three-toed amphiuma _Amphiuma tridactylum_. Photo by Brad Moon.
As it happens, amphiuma vertebrae are particularly interesting if you work on saurischians because (drum-roll)… they have laminae. The term lamina is not restricted to structures present only in pneumatic saurischians: I would argue that it should be used for any sheet-like bony process on a vertebra, and I hope everyone agrees with me. Laminae are not common outside of Saurischia, but are present here and there: they’re present in stem-archosaurs (like Erythrosuchus), various crurotarsan archosaurs (including aetosaurs), some neosuchian crocodilians, and silesaurids (Desojo et al. 2002, Parker 2003, Nesbitt 2005, Wedel 2007, Butler et al. 2009). Even weirder, they’re present in Aneides lugubris, the Arboreal salamander of California and Baja California (Wedel 2007). But that’s about it.
Why would a salamander ‘want’ vertebral laminae? The laminae of the Arboreal salamander are presumed to be related to the extensive accessory ossification present in the skeleton of this animal, itself a consequence of adaptation to a peculiar climbing lifestyle. In other words, it’s hypothesised that the function (if I may be so bold as to use that word…) of the salamander’s laminae is nothing like that of the archosaurs that have them.
And now we know that A. lugubris isn’t the only salamander with laminae: amphiumas have them too. They’re clearly figured in the amphiuma literature (Gardner 2003), but (so far as I know) no-one has previously drawn attention to them when discussing archosaur laminae.
A mid-dorsal vertebra of _Amphiuma_, from Gardner (2003).
Gardner (2003) figured schematic amphiuma dorsal vertebrae that were based on a combination of features present in two of the three living amphiuma species (namely, Amphiuma means and A. tridactylum). On the lateral sides of the centra are structures that – if seen in an archosaur – would almost certainly be identified as anterior and posterior centrodiapophyseal laminae (using, as always, the nomenclature proposed by Wilson (1999)) [see the digram above, from Gardner (2003)]. There are also structures on the dorsal surfaces of the postzygapophyses that look something like laminae: they extend from the posterolateral parts of the neural arch and run across the tops of the postzygapophyses, hence recalling spinopostzygapophyseal laminae. Actually, I’ve just realised that similar structures are also sometimes present in anurans (frogs and toads) where they’ve been called paraneural crests or paraneural processes. These structures do have a ‘known’ function: in amphiumas they’re associated with complex dorsalis trunci epaxial muscles. Unlike the spinopostzygapophyseal laminae of saurischians, the structures in the amphibians are low ridges that don’t contact the neural spines, so it could be argued that they aren’t so lamina-like after all.
But what about the structures on the sides of the centra? Why are laminae present in a group of long-bodied aquatic salamanders? Why are laminae present at all? This question has been asked a few times here on SV-POW! (here, for example), and there are two primary hypotheses. One is that the laminae keep the various air sacs separate from each other, perhaps because they persist while much of the bone around them is resorbed during ontogeny, while the other is that they somehow provide mechanical support and are aligned along lines of stress (for more on this subject see the piece on finite element analysis).
An assortment of _Amphiuma_ cervical, dorsal and caudal vertebrae, from Gardner (2003). The 'paraneural crests' (the lamina-like structures on the postzygapophyses) are visible in G and L, and the lateral central laminae are visible in some of the other vertebrae figured here.
The pneumaticity explanation can’t work for amphiumas (given that they’re apneumatic): does the ‘mechanical support’ one apply instead? We don’t know anything about stress distribution in amphiuma vertebrae – in fact, I don’t think we know anything about the mechanics of amphiumas at all – but it’s possible that the laminae might play this role, especially given that amphiumas have to bend, twist and push with their bodies while excavating burrows.
In conclusion, we just don’t really know what’s going on here. In fact, all we can really do at the moment is wave our arms around a bit and say “Hey, amphiumas have vertebral laminae, too”, and that’s pretty much all I’m doing here. It’s also possible that the structures I’m talking about in amphiumas are very different in detail from the vertebral laminae present in archosaurs: I’ve never even seen a single amphiuma skeletal element and am basing all of this on photos and diagrams in the literature. Nevertheless, it’s something definitely worth bringing attention to. As usual, we stand poised at the abyss, straining our eyes to see into the infinite darkness ahead.
References
Butler, R. J., Barrett, P. M. & Gower, D. J. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters 5, 557-60.
Desojo, J. B., Arcucci, A. B. & Marsicano, C. A. 2002. Reassessment of Cuyosuchus huenei, a Middle–Late Triassic archosauriform from the Cuyo Basin, west-central Argentina. Bulletin of the New Mexico Museum of Natural History and Science 21, 143–148.
Gardner, J. D. 2003. The fossil salamander Proamphiuma cretacea Estes (Caudata; Amphiumidae) and relationships within the Amphiumidae. Journal of Vertebrate Paleontology 23, 769-782.
Nesbitt, S. J. 2005. Osteology of the Middle Triassic pseudosuchian archosaur Arizonasaurus babbitti. Historical Biology 17, 19–47.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of northern Arizona. Unpublished MS thesis, Northern Arizona University, Flagstaff, AZ, 312 pp.
Wedel, M. J. 2007. What pneumaticity tells us about ‘prosauropods’, and vice versa. Special Papers in Palaeontology 77, 207-222.
Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19, 639-653.
Sauropod Vertebra Picture of the Week 