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.
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.
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).
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.
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.
April 21, 2010
Here at SV-POW! Towers, we have often lamented that so much dinosaur research is locked up behind the paywalls of big for-profit commercial publishers, and that even work that’s been funded by public money is often not available to the public.
One of the quiet delights of the last couple of years has been watching the hide-research-from-researchers edifice slowly crumbling, and indeed we have a whole section of the site dedicated to that very thing: the Shiny Digital Future. The process is slow, which should surprise nobody given that large, powerful, profit-motivated corporations are trying to prevent it, but it does feel increasingly inevitable.
This week has brought two more steps towards the open-access utopia: one of them specific and immediate, the other more long term but potentially much more far-reaching.
- In the immediate, the New Mexico Museum of Natural History has made all issues of its Bulletin up to 2008 freely available. Although the quality of the articles in these issues is hugely variable, there is a lot of good and important stuff in there, and it’s a boon to the community that they are now open to anyone who wants to read them.
- I just heard today about the Federal Research Public Access Act (HR 5037), brought before Congress six days ago by a bipartisan group of six representatives (four Democrats and two Republicans). If passed it would ensure that all research funded by eleven U.S. federal agencies was made open-access. If you’re American, follow the link to see what you do to help ensure that it’s passed!
As Galadriel said, the world is changing.
Finally: I know that whenever we talk about proprietary publishers, I always tell people to go and read Scott Aaronson’s essay on the subject, but seriously: if you’ve not read it before, go and read it now. It’s brilliant.
Update (22 April 2010)
Thanks to Phil for the clarification below on whether the pictured vertebra is or is not the Nopcsaspondylus holotype (it is). Phil also sent me a scan of Nopcsa’s original figure of this plate, which is rather better than the reduced version that made it into the new paper, so here it is!
April 15, 2010
As often happens here, a comment thread got to be more interesting than the original post and ended up deserving a post of its own. In this case, I’m talking about the thread following the recent Mamenchisaurus tail club post, which got into some interesting territory regarding mass estimates for the largest sauropods. This post was inspired by a couple of comments in particular.
Zach Armstrong wrote:
I don’t trust Mazzetta et al.’s (2004) estimate, because it is based off of logarithmic-based regression analyses of certain bone lengths, which a recent paper by Packard et al. (2009) have shown to overestimate the mass by as much as 100 percent! This would mean the estimate of 73 tonnes given my Mazzetta would be reduced to 36 tonnes.
To which Mike replied:
Zach, Mazzetta et al. used a variety of different techniques in arriving at their Argentinosaurus mass estimate, cross-checked them against each other and tested their lines for quality of fit. I am not saying their work is perfect (whose is?) but I would certainly not write it off as readily as you seem to have.
Weeeeell…Mazzetta et al. did use a variety of measurements to make their mass estimates, but they did it in a way that hardly puts them above criticism. First, their estimates are based on limb-bone allometry, which is known to have fairly low accuracy and precision (like, often off by a factor of 2, as Zach noted in his comment). Second, the “raw data” for their allometric equation consists of volumetric mass estimates. So their primary estimation method was calibrated against…more estimates. Maybe I’m just lazy, but I would have skipped the second step and just used volumetric methods throughout. Still, I can see the logic in it for critters like Argentinosaurus where we have limb bones but no real idea of the overall form or proportions of the entire animal.
Anyway, the accuracy of their allometric estimates is intertwingled with their volumetric results, so if their volumetric estimates are off…. The volumetric estimates used a specific gravity of 0.95, which to me is unrealistically high. Taking into account the skeletal pneumaticity alone would lower that to 0.85 or 0.8, and if the critter had air sacs comparable to those of birds, 0.75 or even 0.7 is not beyond the bounds of possibility (as discussed here and also covered by Zach in his comment).
Now, Mazzetta et al. (2004) were not ignorant of the potential effects of pneumaticity. Here’s what they wrote about density (p. 5):
The values from Christiansen (1997) were recalculated using a slightly higher overall density (950 kg/m^3), as the 900 kg/m^3 used in that paper may be slightly too low. Most neosauropods have extensively pneumatised vertebrae, particularly the cervicals, which would tend to lower overall density. However, these animals are also very large, implying a proportionally greater amount of skeletal tissue (Christiansen, 2002), particularly appendicular skeletal tissue, and consequently, they should have had a higher overall density.
This is pretty interesting: they are arguing that the positive allometry of skeletal mass as a fraction of body mass–which is well documented in extant critters–would offset the mass reduction from pneumaticity in animals as big as sauropods. I haven’t given that enough thought, and I definitely need to. My guess–and it is a guess–is that the effects of skeletal allometry were not enough to undo the lightening imposed by both PSP (~10%) and pulmonary air sacs (another ~10%, separate from the lungs), but I haven’t done any math on this yet. Fodder for another post, I reckon.
Getting back to Mazzetta et al., some of the volumes themselves strike me as too high, like ~41,500 liters for HM SII. That’s a LOT more voluminous than Greg Paul, Don Henderson, or Mike found for the same critter. The 16 metric ton Diplodocus and 20.6 metric ton Apatosaurus used by Mazzetta et al. are also outside the bounds of other recent and careful estimates. Not necessarily wrong, but definitely at the upper end of the current spectrum.
Mazzetta et al. got a mass estimate of 73,000 kg for Argentinosaurus, but (1) they used a density that I think is probably too high even if skeletal allometry is considered, (2) at least some of the volumetric mass estimates that form the “data” for the limb-bone regressions are probably too high, and (3) even if those problems were dealt with, there is still the general untrustworthiness of limb-bone regression as a mass estimation technique. 1 and 2, if fixed to my satisfaction, would tend to push the estimated mass of Argentinosaurus down, perhaps significantly (the effect of 3 is, if not unknowable, at least unknown to me). Given that, Zach’s ~52 metric ton estimate for Argentinosaurus is very defensible. (Probably worth remembering that I am a sparse-wing fanatic, though.)
None of this means that Mazzetta et al. (2004) were sloppy or that their estimate is wrong. Indeed, one of the reasons that we can have such a deep discussion of these points is that every link in their chain is so well documented. And there is room for honest disagreement in areas where the fossils don’t constrain things as much as we’d like. You cannot simply take a skeleton, even a complete one, and get a single whole-body volume. The body masses of wild animals often fluctuate by a third over the course of a single year, which pretty well buries any hope of getting precise estimates based on skeletons alone. And no one knows how dense–or sparse–sauropods were. I haven’t actually done any math to gauge the competing effects of skeletal allometry on one hand and PSP and air sacs on the other–and, AFAIK, no one else has either (Mazzetta et al. were guessing about pneumaticity as much as I’m guessing about skeletal allometry). Finally, Argentinosaurus is known from a handful of vertebrae and a handful of limb bones and that’s all, at least for now. If we can’t get a single body volume even when we have a complete skeleton, we have to get real about how precise we can be in cases where we have far less material.
The upshot is not that Argentinosaurus massed 73 metric tons or 52 or any other specific number. As usual, the two-part take home message is that (1) mass estimates of sauropods are inherently imprecise, so all we can do is make our assumptions as clear as possible, and (2) even the biggest sauropods might have been smaller than you think. ;-)
Mazzetta, G.V., Christiansen, P., and Farina, R.A. 2004. Giants and bizarres: body size of some southern South American Cretaceous dinosaurs. Historical Biology 2004:1-13.
Shunosaurus lii is a basal eusauropod from the Middle Jurassic of China. Outside of palaeontological circles, it’s not at all well known — which is kind of surprising, as it’s one of the best represented of all sauropods. It’s known from numerous complete skeletons, including skulls, and has been described in detail in Zhang’s (1988) monograph: 89 pages and 15 plates. Here’s a skeleton of one individual, as found in the ground:
Apart from being so well represented, Shunosaurus is known mostly for its tail club, which at the time of its discovery was unique among sauropods. Despite recent discoveries of Mamenchisaurus hochuanensis individuals with preserved tail-clubs, and of Spinophorosaurus, the Shunosaurus tail-club is the best developed and best preserved.
But I don’t want to show you that. I want to show you something I’ve been wanting to see for many years, and today finally saw for the first time: a feature of the dorsal vertebrae totally unique to Shunosaurus, known as postparapophyses.
Sadly, these are the only figures in the paper that show the postparapophyses (and as far as I know the only published figures anywhere). So we have them in lateral view only, and lack what would be an informative posterior view. Plate 10, part 1, supposedly shows one of the posterior dorsals in posterior view, but in my PDF at least the reproduction is so poor as to be wholly uninformative.
What makes things even worse is that the extended English-language abstract on pages 86-91 of Zhang (1988) does not mention this feature at all — in fact it occurs only in the list of anatomical abbreviations on page 6. So, to the best of my knowledge, here is the entirety of what has been published in the English language about this feature based on observation of the material:
Wilson and Sereno (1998:14-15) expanded a little on this, but it’s not clear that what they wrote was based on anything more than the figure above. Here it is anyway, for completeness:
Comments–Zhang’s (1988:78-79) diagnosis listed numerous features, only a few of which appear to be autapomorphies of Shunosaurus lii. One of the more striking autapomorphies is an unusual articulation between the ribs and the posterior dorsal vertebrae. The parapophyseal articulation is split between adjacent vertebrae, with a portion of the articulation in its usual position by the prezygapophyses and an anterior extension located near the postzygapophysis on the preceding vertebra (Zhang, 1988:figs. 31, 32; “postparapophysis”).
That’s your lot.
So if we’re to make anything at all of the PPPs, it will have to be on the basis of the figure reproduced above. And I don’t really know how much we can say. The PPPs look sort of like postzygapophyses, havng a distinct ventrally oriented facet. This makes me wonder whether they are in fact lateral extensions of the postzygapohyseal facets, perhaps connected by a lamina that would be visible in posterior view.
The bottom line is, I don’t know, and I would greatly appreciate comments (or better still, photos!) from anyone who has seen the material first-hand.
I leave you with Zheng’s (1988:fig. 57) skeletal reconstruction of this distinctively dumpy-looking sauropod. Note by the way that the plantigrade manus reconstruction is almost certainly wrong: the metacarpals should be held in a more or less vertical arcade as in other sauropods.
- Wilson, Jeffrey A. and Paul C. Sereno. 1998. Early evolution and Higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.
- Zhang Yihong. 1988. The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuam, vol. 1: sauropod dinosaur (I): Shunosaurus. Sichuan Publishing House of Science and Technology, Chengdu, China.
Update (9 March 2010)
Rob Taylor found this nice photograph of what is apparently a skeletal mount of Shunosaurus: the original is here. Any information about this mount will be gratefully received: please comment below if you know anything.
February 19, 2010
Lovers of fine sauropods will be well aware that, along with the inadequately described Indian titanosaur Bruhathkayosarus, the other of the truly super-giant sauropods is Amphicoelias fragillimus. Known only from a single neural arch of a dorsal vertebra, which was figured and briefly described by Cope (1878) and almost immediately either lost or destroyed, it’s the classic “one that got away”, the animal that sauropod aficionados cry into their beer about late at night.
I’m not going to write about A. fragillimus in detail here, because Darren’s so recently covered it in detail over at Tetrapod Zoology — read Part 1 and Part 2 right now if you’ve not already done so. The bottom line is that it was a diplodocoid roughly twice as big as Diplodocus in linear dimension (so about eight times as heavy). That makes it very very roughly 50 m long and 100 tonnes in mass.
But Mike!, you say, Isn’t it terribly naive to go calculating masses and all from a single figure of part of a single bone?
Why, yes! Yes, it is! And that is what this post is about.
As I write, the go-to paper on A. fragillimus is Ken Carpenter’s (2006) re-evaluation, which carefully and tentatively estimated a length of 58 m, and a mass of around 122,400 kg.
As it happens, Matt and a colleague submitted a conference abstract a few days ago, and he ran it past me for comments before finalising. In passing, he’d written “there is no evidence for sauropods larger than 150 metric tons and it is possible that the largest sauropods did not exceed 100 tons”. I replied:
I think that is VERY unlikely. [...] the evidence for Amphicoelias fragillimus looks very convincing, Carpenter’s (2006) mass estimate of 122.4 tonnes is conservative, being extrapolated from Greg Paul’s ultra-light 11.5 tonne Diplodocus.
Carpenter’s estimate is based on a reconstruction of the illustrated vertebra, which when complete he calculated would have been 2.7 m tall. That is 2.2 times the height of the corresponding vertebra in Diplodocus, and the whole animal was considered as it might be if it were like Diplo scaled up by that factor. Here is his reconstruction of the vertebra, based on Cope’s figure of the smaller but better represented species Amphicoelias altus:
Matt’s answer to me was:
First, Paul’s ultra-light 11.5 tonne Dippy is not far off from my 12 tonne version that you frequently cite, and mine should be lighter because it doesn’t include large air sacs (density of 0.8 instead of a more likely 0.7). If my Dippy had an SG of 0.7, it would have massed only 10.25 tonnes. Second, Carpenter skewed [...] in the direction of large size for Amphicoelias. I don’t necessarily think he’s wrong, but his favoured estimate is at the extreme of what the data will support. Let’s say that Amphicoelias was evenly twice as large as Dippy in linear terms; that could still give it a mass as low as 90 tonnes. And that’s not including the near-certainty that Amphicoelias had a much higher ASP than Diplodocus. If Amphicoelias was to Diplodocus as Sauroposeidon was to Brachiosaurus—pneumatic bones about half as dense—then 1/10 of its volume weighed ½ as much as it would if it were vanilla scaled up Dippy, and we might be able to knock off another 5 tonnes.
There’s lots of good stuff here, and there was more back and forth following, which I won’t trouble you with. But what I came away with was the idea that maybe the scale factor was wrong. And the thing to do, I thought, was to make my own sealed-room reconstruction and see how it compared.
So I extracted the A.f. figure from Osborn and Mook, and deleted their dotted reconstruction lines. Then I went and did something else for a while, so that any memory of where those lines might have been had a chance to fade. I was careful not look at Carpenter’s reconstruction, so I could be confident mine would be indepedent. Then I photoshopped the cleaned A. fragillimus figure into a copy the A. altus figure, scaled it to fit the best as I saw it, and measured the results. Here it is:
As you can see, when I measured my scaled-to-the-size-of-A.f. Amphicoelias vertebra, it was “only” 2293 mm tall, compared with 2700 mm in Ken’s reconstruction. In other words, mine is only 85% as tall, which translates to 0.85^3 = 61% as massive. So if this reconstruction is right, the big boy is “only” 1.87 times as long as Diplodocus in linear dimension — maybe 49 meters long — and would likely come in well below the 100-tonne threshhold. Using Matt’s (2005) 12-tonne estimate for Diplodocus, we’d get a mere 78.5 tonnes for Amphicoelias fragillimus. So maybe Matt called that right.
Folks — please remember, the punchline is not “Amphicoelias fragillimus only weighed 78.5 tonnes rather than 122.4 tonnes”. The punchline is “when you extrapolate the mass of an extinct animal of uncertain affinities from a 132-year-old figure of a partial bone which has not been seen in more than a century, you need to recognise that the error-bars are massive and anything resembling certainty is way misplaced.”
- Carpenter, Kenneth. 2006. Biggest of the big: A critical re-evalustion of the mega-sauropod Amphicoelias fragillimus Cope, 1878. pp. 131-137 in J. Foster and S. G. Lucas (eds.), Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36.
- Cope, Edward Drinker. 1878. Geology and Palaeontology: a new species of Amphicoelias. The American Naturalist 12 (8): 563-566.
- Osborn, Henry Fairfield, and Charles C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, n.s. 3:247-387, and plates LX-LXXXV.
February 12, 2010
Since I started taking photographs of sauropod vertebrae back in 2004, I’ve got much, much better at it, and for the last few months I’ve been meaning to write an article about what I’ve learned along the way. A few weeks ago, fellow SV-POW!er Ranger Matt Wedel posted an article on his 10 Minute Astronomy blog on how to photograph the moon through binoculars, and that served as a prod to get back into blogging gear in the post-Christmas season.
Before I launch in, let me be really clear that I am not a proper photographer — not at all. I don’t even know what an F-stop is or what Single Lens Reflex means. Probably I should invest some time into learning some of this, since specimen photographs are so important in the world of sauropod vertebrae. (After all, the specimens are more than a little cumbersome to loan, so photos often have to stand as proxies for the actual specimens.) Nevertheless, what I’ve learned in the last five or six years has got me to the point where I am producing much, much better specimen photographs than when I started, and I hope at least some of you can benefit from what I’ve learned.
First up, get a decent camera. However skilled you are, you can’t take better photos than the hardware allows. Although I am to blame for the composition above and for some of blurriness, the over-exposure, poor definition and artifacts are the fault of the camera. I was using a truly horrible camera back then — some super-cheap list-of-features-on-a-discount-website piece of kit.
The good news is that a “decent” camera doesn’t need to break the bank: for our purposes you don’t need to spend a fortune on professional-photographer standard equipment. I am looking on ebay right now, and it seems you can get my model of camera for £100 in the UK or $150 in the US (second-hand of course) which is a level of investment we really should be prepared to put into one of the most important aspects of descriptive work.
What constitutes a decent camera? Mostly, optics. These days, every camera has more than enough megapixels for most purposes, so you can just forget about that statistic altogether. It’s about the quality of the lens and the size of the CCD — those are the factors that determine how much information the camera can capture, and if it puts out more bits than that, then all it’s doing is wasting disk-space and bandwidth.
Can I justify the claim that all modern cameras have enough megapixels? I think so. Suppose you’re preparing a full-page plate for the Journal of Vertebrate Paleontology. In practice, plates are nearly always composites of several photos, but suppose you want a single shot filling the whole plate. The printable area of a JVP page is 182 x 233 mm, which is 7.2 x 9.2 inches. At 300 dpi, that’s 2161 x 2752 pixels, which is 5947072, or a slice under 6 megapixels. So 6 Mp is enough for a full-page plate. (For what it’s worth, my camera does 2272 x 1704 = 3.8 megapixels, and I have never found myself feeling a need for more resolution.)
For the same reason, you definitely want optical zoom rather than digital zoom, which really amounts to just blowing up the image.
Another big win: get a spare battery, so that one can be recharging while you’re using the other. If you don’t do that, your camera is out of commission half the time.
And get a big enough memory card. What’s “big enough”? For me, that means enough space to hold a whole day’s images so I can do a single dump onto the laptop in the evening, rather than having to keep stopping to transfer. I can take maybe a maximum of 300 photos a day. With 1 Mb images, that means I need a 300 Mb card, which is chickenfeed. You literally can’t buy cards that small any more, so this is not really a factor these days and I might just as well not have mentioned it. (The reason I did mention it is that my camera originally came with a 16 Mb card or something similarly stupid, which meant ten minutes or so of photography before downloading.)
Get the specimen in frame
Shoot from cardinal directions
Don’t put anything in front of the specimen
Use a plain background when possible.
But the good news is that all these problems can be ameliorated if you follow the last and most important rule in this section which is:
Take many shots and keep only the good ones
I remember reading once, long ago, that the single biggest factor in the difference of quality between a professional photographer’s work and an amateur’s is that the pro takes ten times as many shots and throws 90% of them away. In these days of digital cameras with huge memory cards, we can all make like professionals now. When Matt and I were at the Field Museum in Chicago, we took 168 photos of those Brachiosaurus dorsals alone. Of those, maybe a dozen or so are really worth keeping. But at least I have those dozen.
In general, I take every photograph twice. As I’ve got better at taking the photos, I am increasingly finding that both come out well and it’s a toss-up which to keep, but maybe one time in ten or twenty, one of them just doesn’t come out right — something is wrong with the focus, or the camera shakes, or something — and that’s when I’m glad I have the spare.
On the other hand, my camera’s built-in flash is pretty lame. Expensive flash units might do much better.
As with flash, it seems that the only thing to do is try photos with and without external lights, and with the lights in various different positions, and see what comes out best.
So what can you do? Well, there are several levels of compensation.
Simply being aware of remaining still
When I have to hold the camera in my hands and I know it’s going to be a long exposure I find myself going into a sort of zen state — I become aware of my heartbeat and try to time the shutter release so that the camera doesn’t get moved by my pulse. It’s error-prone, but at least being aware of it can help.
Brace against a door-frame or similar
The combination of tripod mounting and shutter delay means that you can get good exposure in almost any light.
… And finally …
From: Carol Brown<email@example.com>
We just posted an article, “100 Best (Free) Science Documentaries Online” (http://www.onlineuniversities.com/blog/2010/01/100-best-free-science-documentaries-online/). I thought I’d drop a quick line and let you know in case you thought it was something you’re audience would be interested in reading. Thanks
January 27, 2010
[Hello to any redditors who have followed a link here. Please scroll down to find the more interesting articles; sorry that your introduction to SV-POW! is a backlink article.]
Excuse the self-promotion, but some SV-POW! readers might be interested to know that I have an Ask Me Anything going over at the social news aggregator site reddit com. I posted a long comment on someone else’s submission on whale size, and a lot of people asked me questions, so I started a separate thread, which you can read here.
I seem to be at the top of the IAMA page:
January 18, 2010
The last time we talked about Alamosaurus, I promised to explain what the arrow in the above image is all about. The image above is a section through the cotyle (the bony socket of a ball-and-socket joint) at the end of one of the presacral vertebra. The external bone surface would have been over on the left; it was either very thin (which happens) or a bit eroded, or both. The arrow is pointing at something weird–a plate of bone inside the vertebra that forms a sort of shadow cotyle deep to the articular surface.
This is weird for a couple of reasons. First, once camellate (small-chambered) vertebrae get above a certain level of complexity, it’s hard to make any sense of the orientation of individual bony struts. Possibly I haven’t seen enough vertebrae, or played with enough 3D models, to figure it out. You would certainly expect that the struts would be oriented to resist biomechanical loads, just like the struts in the long bones of your limbs; the fact that sauropod verts were filled with air whereas your long bones are filled with marrow shouldn’t make any difference. Back in the day, Kent Sanders–who is second author on that super-important paper on unidirectional air flow in croc lungs that you’ve probably heard about (Farmer and Sanders 2010)–speculated to me that the complex of laminae we see in the vertebrae of most sauropods are still there in the inflated-looking vertebrae of titanosaurs and birds, they’re just incarnated in internal struts rather than external laminae. Cool hypothesis for somebody to test.
The other reason that this is weird is that the plate of bone is parallel to the articular surface. One place where I have seen some regularity in terms of strut orientation is in zygapophyses, where in both camerae and camellate vertebrae the internal struts are oriented at right angles to the articular surfaces of the zygs, like beams propping up a wall. In this Alamosaurus section, there are indeed smaller struts that run at right angles to both the cotyle and the internal plate, but I have no idea why they’re so wimpy and the plate is so thick; a priori I would have expected the reverse.
It turns out that this isn’t even the first time that an internal “shadow” of the cotyle has been figured–check out this figure that I redrew from Powell’s (1992:fig. 16) Saltasaurus osteology. But don’t credit me with the discovery. I’d looked at this section a hundred times and even drawn it and never noticed the shadow cotyle, until it was pointed out by Woodward and Lehman (2009)–another reason to read that paper if you haven’t yet. Kudos to Holly Woodward for spotting this and making the connection.
Now that I’ve drawn attention to the weirdness and given credit where it’s due, this is one of those times I’m going to throw up my hands in confusion and open the floor for comments.
- Farmer, C.G., and Sanders, K. 2010. Unidirectional airflow in the lungs of alligators. Science 327:338-340.
- Powell, J.E. 1992. Osteologia de Saltasaurus loricatus (Sauropoda – Titanosauridae) del Cretacico Superior del noroeste Argentino; pp. 165-230 in J.L. Sanz and A.D. Buscalioni (editors), Los Dinosaurios y Su Entorno Biotico: Actas del Segundo Curso de Paleontologia in Cuenca. Institutio Juan de Valdes.
- Woodward, H.N., and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.
January 4, 2010
Last year was good for sauropod pneumaticity. In the past few months we’ve had the publication of the first FEA of pneumatic sauropod vertebrae by Schwarz-Wings et al (2009), as well as a substantial section on pneumaticity in the big Alamosaurus histology paper by Woodward and Lehman (2009). I won’t repeat here everything that Woodward and Lehman have to say about pneumaticity, I just want to draw attention to a little piece of it. Their work is observant, up-to-date, and worth reading, so if you can get access to the paper, read it.
The major brake on the growth of our knowledge and understanding of pneumaticity is sample size. I harped on this in 2005 (Wedel 2005), and Mike just brought it up again in a comment on a previous post. In fact, what he had to say is so relevant that I’m going to just cut and paste it here:
How does degree of pneumatisation vary between individuals? Here are three more: how does it vary along the neck, how does it vary long the length of an individual vertebra, and how does it vary through ontogeny? Then of course there is variation between taxa across the tree. So what we have here is a five-and-half-dimensional space that we want to fill with observations so that we can start to deduce conclusions. Trouble is, there are, so far, 22 published observations (neatly summarised by Wedel 2005:table 7.2), which is not really enough to let us map out 5.5-space! That’s one reason why, at the moment, each observation is valuable — it adds 4% to the total knowledge in the world.
To be fair, there are a few more published observations. Schwarz and Fritsch (2006) published ASPs for cervicals of Giraffatitan and Dicraeosaurus, and I have a gnawing feeling that there are a couple here and there that I’ve seen but not remembered. I’ve got some more of my own data in the as-yet-unpublished fourth chapter of my diss, which I failed to get out as part of the Paleo Paper Challenge. And, getting back to the subject of the post, Woodward and Lehman (2009:819) have some tasty new data to report:
Digital images of sections of vertebrae and ribs were imported into ArcGIS 8.1 (Dangermond, 2001; for methods see Woodward, 2005). A unitless value for the total area of the image was calculated, using the outline of the bone as a perimeter. Subtracted from this was the area value taken up by bone, as determined by color differences (lighter areas are camellate cavities, darker areas are bone). Using this method, longitudinal sections of centra are estimated to be roughly 65% air filled. The amount of open space similarly calculated for the pneumatic proximal and medial rib sections is about 52%, whereas the cancellous spongiosa in distal rib transverse sections yields an average estimate of about 44% of their cross sectional area. Hence, the camellate cavities result in an appreciably lower bone volume compared to spongiosa.
The ASP of 0.65 for centra is right in line with the numbers I’ve gotten for neosauropods, and with the results of Schwarz and Fritsch (2006) for Giraffatitan (Dicraosaurus had a much lower ASP, around 0.2 IIRC). The stuff about the ribs is particularly interesting. Using densities of 0.95 for bone marrow, 1.8 for avian (and sauropod) compact bone, and 1.9 for mammalian compact bone we get the following:
- Pneumatic Alamosaurus vertebrae – ASP of 0.65, density of 0.63 g/cm^3.
- Pneumatic Alamosaurus ribs – ASP of 0.52, density of 0.86 g/cm^3.
- Apneumatic Alamosaurus ribs – MSP (marrow space proportion) of 0.44, density of 1.43 g/cm^3.
- Pneumatic bird long bones – ASP of 0.59, density of 0.74 g/cm^3.
- Apneumatic bird long bones – MSP of 0.42, density of 1.44 g/cm^3.
- Apneumatic mammal long bones – MSP of 0.28, density of 1.63 g/cm^3.
ASPs and MSPs of bird and mammal bones are calculated from K values reported by Cubo and Casinos (2000) for birds and Currey and Alexander (1985) for mammals. I don’t know what the in vivo density of sauropod compact bone was; changing it from the avian value of 1.8 to the mammalian value of 1.9 would have a negligible effect on the outcome.
At least with the data in hand, we can make the following generalizations:
- The apneumatic bones of birds are thinner-walled than those of mammals, on average. (This has been known for a long time.)
- The apneumatic ribs of Alamosaurus were more similar in density to apneumatic bird bones than to apneumatic mammal bones.
- In both birds and Alamosaurus, pneumatization reduces the amount of bone tissue present by 15-30% in the same elements (long bones for birds, ribs for Alamosaurus). Pneumatic bones are light not just because the marrow is replaced by air, but because there is less bone tissue than in apneumatic bones, as bird people have been observing for ages.
There’s loads more work to be done on this sort of thing, so I’m going to stop blogging now and get back to it. Stay tuned!
- Cubo, J., and Casinos, A. 2000. Incidence and mechanical significance of pneumatization in the long bones of birds. Zoological Journal of the Linnean Society 130: 499–510.
- Currey, J. D., and Alexander, R. McN. 1985. The thickness of the walls of tubular bones. Journal of Zoology 206:453–468.
- Schwarz D, and Fritsch G. 2006. Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus. Eclogae Geologicae Helvetiae 99:65–78.
- Schwarz-Wings, D., Meyer, C.A., Frey, E., Manz-Steiner, H.-R., and Schumacher, R. 2009. Mechanical implications of pneumatic neck vertebrae in sauropod dinosaurs. Proceedings of the Royal Society B. doi: 10.1098/rspb.2009.1275
- Wedel, Mathew 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.
- Woodward, H.N., and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.
December 22, 2009
Ever since we started working on Sauroposeidon, Rich Cifelli and I dreamed of seeing the reconstructed neck on display. That vision has come to fruition.
The Oklahoma Museum of Natural History opened a totally new building in 2000. Coincidentally, the opening ceremony for the new digs was held the same week that the paper naming Sauroposeidon came out in JVP. The exhibits in the new building were pretty cool right out of the gate, but the exhibit people have not been idle, and if you haven’t been there in a year or three you will find many things that you have not seen before.
My favorite upgrade is the new orientation gallery, which introduces museum visitors to the functions of the museum and the kinds of work that go on in the research wing, including most of the traditional -ologies. The reconstructed neck and head of Sauroposeidon hang from the ceiling, spanning most of the length of the gallery and extending out into the museum’s great hall.
The beast was reconstructed by Research Casting International. I got to visit their workshop in Ontario, Canada, a little over a year ago to see how things were coming along. The people there were extremely serious about getting things right (how refreshing!). We spent quite a while talking about how Sauroposeidon was different from Giraffatitan (RCI remounted the Humbolt dinos) and sketching out what the missing bits might have looked like, especially the skull.
Of course we don’t have any skull material from Sauroposeidon, but we do have skulls and partial skulls from several other basal titanosauriforms. Together with one of the people working on the Sauroposeidon project, I filled up a couple of pieces of paper with sketches showing what a slender mid-Cretaceous brachiosaur might have looked like. In particular, and in keeping with the gracility of the cervical vertebrae, we narrowed the skull a bit to get rid of the dreaded Giraffatitan Toilet-Bowl Head.
The completed neck and head were already mounted in the OMNH when I visited last Christmas, but the gallery wasn’t open yet so all I got–and all I could pass on to you–was this teaser. The new orientation gallery opened in the middle of this spring, so Sauroposeidon has been hanging out there for a while. This is just the first chance I’ve gotten to go see my baby.
What a fine present. Merry Christmas from the SV-POW!sketeers!
Update from Mike
Here is my Christmas card to you all.