Monthly Archives: January 2010

Things to Make and Do, part 5: anaglyphs (red-and-cyan 3D images)

I hope you have a pair of 3D glasses.  If you do, then check this baby out:

Brachiosauridae incertae sedis NHM R5937, "The Archbishop", damaged cervical vertebra S in right posterolateral view; red-cyan 3D anaglyph. This image and others of the same specimen copyright the NHM since it's their specimen.

(This is of course the same vertebra that we last saw in a multi-view composite figure at the end of the Brachiosaurus coracoid post.)

I’ve started to get into the habit recently of photographing some specimens from two slightly different angles: I couldn’t tell you exactly how much rotation I use, but I would guess it’s something like three to five degrees.  That’s because I’ve found that flipping back and forth between the two images can give a useful sense of depth.  If you don’t believe me, here are two not-quite-identical photos of the Archbishop’s Cervical S: open each of them in a tab, then flick back and forth between them:

Cervical S, first image

Cervical S, second image

It had occurred to me a while back that, just for fun, it would be interesting to composite them into a red-cyan 3D image.  But I was prodded into action by two things.  First, the free Lego marketing magazine that my boys get sent every month arrived, and with it a freebie pair of cheap cardboard red-cyan glasses.  And second, Matt published a steropair of moon images on his blog.  Matt’s friend Jarrod is a professional digital effects artist — in fact he’s won Emmies for stuff like blowing up Los Angeles for 24 — and threw together an anaglyph from the moon pictures.  I got instructions from Jarrod on how to do this, and was gratified how easy it was.  Here you go:

  • Open the two photos as two layers of a single image.
  • Using the Colour Levels dialogue, turn the red channel of one of the photos all the way down to zero (so that it appears in shades of cyan)
  • Using the same dialogue, turn both the blue and green channels of the other photo down to zero (so that it appears in shades of red)
  • Change the Layer Mode of the top layer to Brighten Only

That’s it, you’re done!  Save the resulting composite image as a JPEG and upload it to your sauropod-vertebra blog.  Jarrod uses PhotoShop; I use the Gimp, which is a free more-or-less equivalent program — the same technique works fine with both.

If I was pleasantly surprised at how simple the technique is, I was astounded at the quality of the result.  I’d expected all the colour of the image to be gone, and to see a vague monochrome haze.  Instead, I saw rock-solid 3D in full colour — truly informative images that convey the morphology of complex bones far better than any published figure I’ve ever seen.  Seriously, go get your red-cyan glasses, you won’t regret it.

Here is another anaglyph of the same vertebra, in posterior view close-up, showing in detail what looks suspiciously like a hyposphene below and between the postzygs.  (If this is indeed a hypophene, then I believe it’s unique among sauropods.)

Cervical S, posterior view in close-up, showing possible hyposphene.

Journals have occasionally published stereopair images of palaeo specimens: small images a couple of inches wide, next to each other, which you can supposedly see as a single 3D image if you cross your eyes in just the right light provided the wind is from the southeast — personally, I have never been able to see these things, thought Matt can.  But these big, full-colour 3d images are orders of magnitude more information.

I’ve never seen one in a journal, in part of course because colour printing is such an insanely expensive luxury.  But as Matt says, we all live in the future now, and I hope that’s about to change.  I will be sending the Archbishop description, when it’s done, to PLoS ONE, which because of its electronic-only format can include any number of full-colour figures at no cost.  I plan to send a few anaglyphs among the more conventional figures.  Fingers crossed that they make it into the published version — I guess if I get a traditionalist reviewer, he might think these are frivolous and demand that I remove them.  But they are not frivolous: they may be the most informative figures I have ever prepared.

Finally, I leave you with our old friend the pig skull, from all the way back in Things To Make And Do part 1 — but this time in glorious 3D!

Domestic pig skull in left anterodorsolateral view (3d anaglyph).

Off-topic: I have an Ask Me Anything up at Reddit

[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:

Here is your regularly scheduled sauropod vertebra:

Brachiosauridae incertae sedis NHM R5937 "The Archbishop", dorsal centra 4 and 5. Top to bottom: left lateral; dorsal with anterior to right; posterior, right lateral and anterior. Images copyright the NHM since it's their specimen.

What’s up with the Brachiosaurus coracoid?

In my not-long-quite-so-recent-any-more paper on Brachiosaurus and Giraffatitan, I gave as one of the autapomorphies of Brachiosaurus proper that the glenoid articular surface of its coracoid is laterally deflected.  Although we’ve discussed this a little in comments on SV-POW!, it’s not yet made it into one of our actual articles.  I hestitated to feature it here since it’s so darned appendicular, but in the end I concluded that it was too interesting and potentially important to overlook.

So here it is!

Brachiosaurus altithorax holotype FMNH P25107, left coracoid in lateral, posterior and ventral views (oriented as though the scapular blade were horizontal). Modified and composed from photographs by Phil Mannion; used with permission.

The deflected surface is most apparent in the posterior view at the right of the fiigure, in which it appears deflected about 55 degrees from the horizontal.  That’s misleading, though — partly because the shape is more complex in three dimensions than can be easily visualised from these orthogonal shots, and partly because of course the coracoid was not held perfectly vertical in life.  In fact, the orientation of the coracoid in sauropods, and of the entire shoulder girdle, remains rather controversial.  It’s not an area I’ve got involved in so far, but this Mystery Coracoid Of Weirdness (hereafter MCOW) might just be my gateway into the wacky world of pectoral girdles.

The ventral view at the bottom of the figure is also informative: as you can see from that angle, the articular surface extends a long way laterally (i.e. towards the top of the figure  in this orientation).  Once you’ve got your eye in with those images, it’s easy to see the facet in the lateral-view photo, despite the less than ideal saturated lighting: it’s shaped like a raindrop falling towards bottom left.  (Well, not really: raindrops are actually vertically flattened spheroids rather then raindrop-shaped, but that’s not the point.)

Observations and interpretations on this oddity will be very welcome.

Finally, here is your regularly scheduled sauropod vertebra:

Brachiosauridae incertae sedis NHM R5937 "The Archbishop", cervical S. Top to bottom: left lateral; dorsal with anterior to right; posterior, right lateral and anterior. Images copyright the NHM since it's their specimen.

More on the internal structure of Alamosaurus vertebrae

A section of the cotyle of a presacral vertebra of Alamosaurus (Woodward and Lehman 2009:fig. 6A).

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.

References

  • 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.

‘Angloposeidon’, cover-girl

It isn’t everyday that a sauropod vertebra makes it onto the cover of a technical journal. In fact… this might be the first time that it’s ever happened (please let us know if you know otherwise. So far as I can tell, even Journal of Vertebrate Paleontology has never had a sauropod vertebra on the cover [though it has featured sauropod skeletons in their entirety]). Yes world, I give you the cover of issue 1 of Volume 31 of Cretaceous Research, a journal I do editing work for. We’ve had dinosaurs on the cover before (a Triceratops skull), but when the opportunity arose for new submissions I decided to try my luck. I submitted a nice photo of MIWG.7306 (aka ‘Angloposeidon’) – albeit it only the posterior half – and… here we are. This is a major achievement, it’s open-bar night here at SV-POW!

PS – Mike and I tried to get a sauropod vertebra on a journal cover back in 2007. We failed. Can you guess what that particular sauropod vertebra was?