Sauropod sighting

October 10, 2011

But where? You tell us. All will be revealed shortly.

Why did sauropods have such long necks?

Mamenchisaus hochuanensis skeletal reconstruction (Young and Zhao 1972:fig. 4), based on the holotype

It’s the single most obvious and important question about sauropods, so it’s a bit surprising to think that we’ve never really addressed this question directly.

Maybe sauropod necks are so obvious and familiar that we just take them for granted, and move straight on to questions of how they were able to grow so long and remain workable.

Well, let’s fix that.  Let’s think about why they had such long necks.  What were they for?  What were sauropods doing with their necks that was valuable enough to justify all that investment?

Back in the good old days, everyone assumed that sauropod necks were all about high browsing.  If you have a 9.5m neck, then of course you will use it to browse high up in trees — it’s intuitively obvious.  But of course “intuitively obvious” is not the same thing as “true”.

Then John Martin (1987) proposed that the long necks were used for low browsing — not raised above shoulder level, but swept back and forth to allow food to be gathered across a wide area without all that tedious mucking about with locomotion.  This interpretation was of course endorsed by Stevens and Parrish (1999) in their DinoMorph work.

There has been plenty written about habitual sauropod posture — including by us (Taylor et al. 2009).  But actually the high-browsing and low-browsing explanations of sauropod neck elongation have much in common.  Most crucially, they both relate to enlarging the feeding envelope; more broadly they are both explanations that rely on the neck having a survival benefit.  But Senter (2006) proposed a completely different explanation — that sauropod necks were sexual signals, selected not for survival advantage but for reproductive success.  The idea is that female sauropods, being very shallow, would go for the males with the biggest protuberances.

Are there other candidate explanations that I’ve missed?

Or is it between high browsing, low browsing and sexual selection?

Comments are open!

References

Onward!

February 22, 2011

Sinclair brontosaur, Hennessey, Oklahoma. This one has cement shoes because some ne’er-do-wells ganked the old one in the middle of the night a couple of years ago.

How fat was Camarasaurus?

January 16, 2011

For reasons that will soon become apparent (yes, that’s a teaser), Matt and I wanted to figure out how heavy Camarasaurus was.  This is the story of how I almost completely badgered up part of that problem.  I am publishing it as a cautionary tale because I am very secure and don’t mind everyone knowing that I’m an idiot.

Those who paid close attention to my recent paper on Brachiosaurus and Giraffatitan will remember that when I estimated their mass using Graphic Double Integration (Taylor 2009: 802-804) I listed separately the volumes of the head, neck, forelimbs, hindlimbs, torso and tail of each taxon.  In Giraffatitan, the torso accounted for 71% of the total volume (20588 of 29171 litres), and in Brachiosaurus, 74% (26469 of 35860 litres), so it’s apparent that torso volume hugely dominates that of the whole animal.  In the giant balloon-model Giraffatitan of Gunga et al.’s (1995, 1999) estimates, the torso accounted for 74% of volume (55120 of 74420 litres) so even though their fleshing out of the skeleton was morbidly obese, the relative importance of the torso came out roughly the same.  Finally, Gunga et al’.s (2008) revised, less bloated, model of the same Giraffatitan had the torso contributing 68% of volume (32400 of 47600 litres).  So far as I know, these are all of the published accounts that give the volumes of separate parts of a sauropod body, but if there are any more, please tell me in the comments!   (Odd that they should all be for brachiosaurids.)

3D “slim” version of reconstruction of the “Brachiosaurus” brancai mounted and exhibited at the Museum of Natural History in Berlin (Germany).  A. Side view, upper panel; B. top view, lower panel.  The cross in the figure of upper panel indicates the calculated center of gravity.  (Gunga et al. 2008: figure 2)

So it’s evident that, in brachiosaurs at least, the torso accounts for about 70% total body volume, and therefore for about that much of the total mass.  (The distribution of penumaticity means that it’s denser than the neck and less dense than the limbs, so that its density is probably reasonably close to the average of the whole animal.)

Now here’s the problem.  How fat is the sauropod?  Look at the top-view of Giraffatitan in the Gunga et al. figure above: it’s easy to imagine that the torso could be say 20% narrower from side to side, or 20% broader.  Those changes to breadth would affect volume in direct proportion, which would mean (if the torso is 70% of the whole animal) a change in total body volume of 14% either way.  Significant stuff.

So what do we know about the torso breadth in sauropods?  It obviously dependant primarily on the orientation of the ribs and their articulation to the dorsal vertebrae.  And what do we know about that?

Nothing.

Well, OK, I am over-simplifying a little.  It’s been mentioned in passing in a few papers, but it’s never been discussed in any detail in a published paper that I know of.  (There’s a Masters thesis out there that starts to grapple with the subject, but I don’t know whether I should talk about that while it’s still being prepared for publication, so I won’t say anything more.)  The most important published contribution is more than a century old — Holland’s (1910) smackdown of Tornier’s and Hay’s comical Diplodocus postures, which included the following cross-sections of the torsos of several animals at the seventh dorsal vertebra:

(This figure previously appeared on SV-POW! in Matt’s post, Sauropods were tacos, not corn dogs, which as far as I am aware is the only existing non-technical treatment of sauropod torso-shape.)

Holland unfortunately did not discuss the torso shape that he illustrated, merely asserting it.  Presumably it is based on the mounted skeleton of the Diplodocus carnegii holotype CM 84, which is at the Carnegie Museum in Pittsburgh, where Holland was based.  I have no reason to doubt it; just noting that it wasn’t discussed.

All right then — what about Camarasaurus?  I think it’s fair to say that it’s generally considered to be fairly rotund among sauropods, as for example this skeletal reconstruction by Greg Paul shows:

Camarasaurus lentus skeletal reconstruction, in dorsal and right lateral views. (Paul 2010:197)

Measuring off the height and width of the torso at the seventh dorsal vertebra, using GIMP, I find that they are 341 and 292 pixels respectively, so that the eccentricity is 341/292 = 1.17.  This compares with 1760/916 = 1.92 for Holland’s Diplodocus above, so if both figures are accurate, then Camarasaurus is much fatter than Diplodocus.

But is Paul’s Camarasaurus ribcage right?  To answer that, I went back to my all-time favourite sauropod paper, Osborn and Mook’s (1921) epic descriptive monograph of Camarasaurus (and Cope’s other sauropods).  I knew that this awesomely comprehensive piece of work would include plates illustrating the ribs; and in fact there are four plates that each illustrate a complete set of dorsal ribs (although the associations are doubtful).  Here they all are:

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXVIII)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXIX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXXI)

But hang on a minute — what do you get if you articulate these ribs with the dorsal vertebrae?  Osborn and Mook also provided four plates of sequences of dorsal vertebrae, and the best D7 of the four they illustrate is probably the one from plate  LXX.  And of the four 7th ribs illustrated above, the best preserved is from plate LXXIX.  So I GIMPed them together, rotated the ribs to fit as best I could and …

What on earth?!

I spent a bit of time last night feeling everything from revulsion to excitement about this bizarre vertebra-and-rib combination.  Until I happened to look again Osborn and Mook — earlier on, in the body of the paper, in the section about the ribs.  And here’s what I saw:

(Note that this is the vertebra and ribs at D4, not D7; but that’s close enough that there’s no way there could be a transition across three vertebrae like the change between this and the horrible sight that I presented above.)

What’s going on here?  In the plates above, the ribs do not curve inwards as in this cross-section: they are mostly straight, and in many case seem to curve negatively — away from the torso.  So why do O&M draw the ribs in this position that looks perfectly reasonable?

And figure 70, a few pages earlier, makes things even weirder: it clearly shows a pair of ribs curving medially, as you’d expect them to:

So why do these ribs look so totally different from those in the plates above?

I’ll give you a moment to think about that before I tell you the answer.

Seriously, think about it for yourself.  While you’re turning it over in your mind, here is a picture of the beautiful Lego kit #10198, the Blockade Runner from the original Star Wars movie.  (I deeply admire the photography here: clear as a bell.)

OK, welcome back.

Got it?  I bet most of you have.

The answer was right there in figure 71:

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

And, my word, isn’t it embarrassingly obvious once you see it?  I’d been blithely assuming that the ribs in O&M’s plates were illustrated in anterior view, with the capitula (which articulate with the parapophyses) located more medially, as well as more ventrally, than the tubercula (which articulate with the diapophyses).  But no: as in fact the captions of the plates state perfectly clearly — if I’d only had the wits to read them — the ribs are shown in “external” (i.e. lateral) view.  Although it’s true that the capitula in life would indeed have been more medially positioned than the tubercula, it’s also true that they were more anteriorly positioned, and that’s what the plates show at the rib heads.  And the curvature that I’d been stupidly interpreting as outward, away from the midline, is in fact posteriorly directed: the ribs are “swept back”.  The ventral portions of the ribs also curve medially, away from the viewer and into the page … but of course you can’t see that in the plates.

The important truth — and if you take away nothing else from this post, take this — is that I am dumb bones are complex three-dimensional objects, and it’s impossible to fully understand their shape from single-view illustrations.  It’s for this reason that I make an effort, when I can, to illustrate complex bones from all cardinal directions — in particular, with the Archbishop bones, as for example “Cervical S” in the Brachiosaurus coracoid post.

Because ribs, in particular, are such complex shapes — because their curvature is so unpredictable, and because their articulation with the dorsal vertebrae is via two points which are located differently on successive vertebrae, and because this articulation still allows a degree of freedom of movement — orthogonal views, even from all cardinal directions, are of limited value.  Compositing figures will give misleading results … as demonstrated above.  PhotoShop is no more use here.  Fly, you fools!

Paradoxically, our best source of information on the shapes of saurpod torsos is: mounted skeletons.  I say “paradoxically” because we’ve all grown used to the idea that mounts are not much use to us as scientists, and are really there only as objects of awe.  As Brian Curtice once said, “A mounted skeleton is not science.  It’s art.  Its purpose is to entertain the public, not to be a scientifically accurate specimen”.  In many respects, that’s true — especially in skeletons like that of the “Brontosaurus” holotype, YPM 1980, where the bones are restored with, and in some cases encased in, plaster so you can’t tell what’s what.  But until digital scanning and modelling make some big steps forward, actual mounted skeletons are the best reference we have for the complex articulations of ribs.

Giraffatitan brancai paralectotype HMN SII, composite mounted skeleton, torso in left posteroventrolateral view (photograph by Mike Taylor)

And I finish this very long (sorry!) post with yet another note of caution.  Ribs are long and thin and very prone to damage and distortion.  It’s rare to find complete sauropod ribs (look closely at the O&M plates above for evidence), but even when we do, we shouldn’t be quick to assume that the shape in which they are preserved is necessarily the same as the shape they had in life.  (If you doubt this, take another look at rib #6 in the third of the four O&M plates above.)  And as if that weren’t enough to discourage us, we should also remember that the vertebra-rib joints would have involved a lot of cartilage, and we don’t know its extent or shape.

So bearing in mind the complicated 3D shape of ribs and of dorsal vertebrae, the tendency for both to distort during and after fossilisation, and the complex and imperfectly known nature of the joints between them, I think that maybe I wasn’t too far wrong earlier when I said that what we know about sauropod torso shape is: nothing.

It’s a sobering thought.

References

Bifid Brachiosaurs, Batman!

September 6, 2009

These are the days of miracle and wonder, especially for all you right-minded people out there who are lovers of fine brachiosaurs.  I heard yesterday evening about a new paper in Proceedings of the Royal Society B: You and Li’s (2009, duh) description of a new brachiosaur, the first one known from the Cretaceous of Asia: Qiaowanlong kangxii. Best of all, it’s based primarily on vertebral material:

You and Li (2009:fig. 2)  Cervical vertebrae of Qiaowanlong kangxii holotype FRDC GJ 07-14.

You and Li (2009:fig. 2) Cervical vertebrae of Qiaowanlong kangxii holotype FRDC GJ 07-14. (a) Photograph and (b) interpretative line drawing of C4-C7 in left lateral view; (c) a distal portion of a cervical rib; C9 in (d) cranial, (e) left lateral, (f) caudal, (g) right lateral, (h) dorsal and (i) ventral views. di, diapophysis; f1-f5, fossa 1-fossa 5; pa, parapophysis; poz, postzygapophysis; prz, prezygapophysis; sp, neural spine. Scale bars, 10 cm.

Brachiosaur aficionados will be gazing slack-jawed at parts d, f and h of this figure (the anterior, posterior and dorsal views of C9), which clearly show that the neural spines of the new taxon are bifid (i.e. have two peaks side by side and a trough between them) — just like the cervical neural spines of flagellicaudatans (diplodocids and dicraeosaurs) and camarasaurs.  And mamenchisaurs.  And some titanosaurs.  And Erketu.  Finding this feature yet again — apparently independently evolved in brachiosaurs — makes it about the most plastic character in the matrix.  Very exciting.

That is, it’s exciting if this really is a brachiosaurid.  Now as it happens, Matt was one of the reviewers for this paper (and by the way did an amazingly professional job of not telling me about it until it came out, the git).  He’s told me in email that he’s satisfied that Qiaowanlong really is a brachiosaur, and I hesitate to question that identification given that (A) unlike the authors I’ve never seen the material, and (B) unlike Matt, I’ve spent most of my brachiosaur-presacral quality time with dorsals rather than cervicals.  But, with that caveat, I’m not sure that a compelling case has yet been made for a brachiosaurian identity.

The authors cite three characters in support of a brachiosaurid identity:

  • The most persuasive is the deeply excavated cervical neural spines.
  • Next is a transition in neural spine height: this is quite abrupt in “Brachiosaurusbrancai between cervicals 6 and 7, and also in Sauroposeidon — presumably also between C6 and C7, but that can’t be known for sure, since it’s only the assumption that this is the case that led to the identification of the four preserved Sauroposeidon cervicals as C5-C8 in the first place.  In Qiaowanlong, this transition is “much less pronounced”, with spines increasing in height by only 25% rather then 100% in the other taxa — and occurs between C8 and C9.  All in all, not really very similar to the condition in “B.” brancai.
  • The final character supporting the brachiosaurid identity of Qiaowanlong is the absence of an anterior centrodiapophyseal lamina.  As the authors point out, though, this lamina does exist in “B.” brancai and is absent only in Sauroposeidon; so if this is evidence of anything, it’s a synapomorphy of a clade uniting Qiaowanlong and Sauroposeidon to the absence of other brachiosaurs — something that seems very unlikely given the proportions of the vertebrae.

Putting it all together, there seems to be only one convincing brachiosaur character cited; and that stands against several non-brachiosaur characters, most obviously the bifurcation of the neural spine and the low Elongation Index (centrum length divided by cotyle height) but also by a few other characters that are not discussed in the paper.  For example, Matt has previously noted that in brachiosaur cervicals, the diapophyses are more anteriorly positioned than the parapophyses whereas in diplodocids the opposite is the case: as shown in fig 2(b) above, C6 at least of Qiaowanlong resembles diplodocids in this respect.

To try to get more of a handle on this, I put together a comparative figure of the 8th and 9th cervicals of various sauropods:

8th/9th cervicals vertebrae of various sauropods, scaled to the same centrum length.  "Brachiosaurus" brancai, Sauroposeidon; Qiaowanlong, Diplodocus; Haplocanthosaurus, Camarasaurus

8th/9th cervicals vertebrae of various sauropods, scaled to the same centrum length. From top to bottom and left to right: "Brachiosaurus" brancai, Sauroposeidon; Qiaowanlong, Diplodocus; Haplocanthosaurus, Camarasaurus. Six sauropod vertebrae for the price of one!

Based on overall proportions, I don’t find it intuitively obvious that the Qiaowanlong (middle row, left) more closely resembles the brachiosaurs (top row) than it does the other three.

What does all this mean?  Probably nothing: most likely there are further reasons for the brachiosaurid identification of the new taxon, and lack of space prevented their explanation and illustration.  We can hope that the authors, having placed an initial brief description in Proc. B, will follow it up with a more comprehensive description and analysis in a journal that does not impose such tight length restrictions.  But for now at least, my feeling is that the case for a bifid brachiosaur has yet to be made.

Moving on … Qiaowanlong is also represented by some nice appendicular material: the entire right side of the pelvis (ilium, ischium and pubis).  The ilium certainly looks brachiosaury, so that is another bit of support for the systematic hypothesis, but the proportions of the pelvic bones are very odd:

Right pelvis of "Brachiosaurus" brancai (left), based on composite of Janensch's (1961) figures, and Qiaowanlong (from You and Li 2009: fig. 3a).  Scaled to same ilium length.

Right pelvis of "Brachiosaurus" brancai (left), based on composite of Janensch's (1961) figures, and Qiaowanlong (from You and Li 2009: fig. 3a). Scaled to same ilium length.

You and Li (2009) describe their pelvis as having a “much reduced ischium”, but as is apparent by comparison with the pelvis of “Brachiosaurusbrancai, the ischium is in reasonable proportion to the ilium, and the oddity is more that the pubis is enormous.  So much so that it makes me feel a little ill looking at it, and it makes me wonder how certain it is that all three of these bones are from the same individual — sadly, the paper doesn’t discuss the association of the material.

[Not to flog a dead horse, but this kind of omission shows once more the perils of publishing new taxa in general-interest journals such as Proc. B that impose draconian length limits.  This paper just creeps onto page 7, and I simply don’t believe that it’s possible to do anything like justice to the description of a new taxon in that little space, especially when there is also geography, geology, phylogeny and discussion to be got through.  I don’t want to go all This Is How To Do It, but I can’t help remembering that Darren and I took 18 pages, nearly three times as long, to describe the single partial vertebra that is Xenoposeidon (Taylor and Naish 2007), and it’s not as though that paper wastes a lot of words.  To give You and Li credit, they did squeeze in photos of a representative vertebra from all six cardinal directions, which is great; but only at the cost of the photos being too tiny to be much use.  Please, folks: send your new taxon descriptions to a proper descriptive journal, not to a tabloid!  </hobbyhorse>]

Back on the Dinosaur Mailing List, B tH asked how big Qiaowanlong was.  According to the BBC, the authors say that “the dinosaur would have been a relatively small sauropod about 12m long, 3m high, and weighing perhaps 10 tonnes”.  Can we confirm that?  Well, the excellently comprehensive table of measurements in the paper gives centrum lengths, not counting the condyle, totalling 267 cm for the seven vertebrae C5-C11.  Janensch (1950a:44) gave measurements for the corresponding vertebrae of “Brachiosaurusbrancai HMN SII totalling 577 cm, which is more than twice as long.  If Qiaowanlong was 267/577 = 0.46 times as long as HMN SII, which Janensch (1950b:102) gave as 22.46 m, then it would have been 10.4 m long; it’s not obvious how the authors got the larger figure of 12 m unless they had reason to think the neck was proportionally shorter than in HMN SII.  If Qiaowanlong was isometrically similar to HMN SII, then it was 0.46^3 = 0.99 0.099 times as heavy.  Using my own in-press mass of 23337 kg for HMN SII, this would make Qiaowanlong only 2312 kg in mass — pretty pathetic for a sauropod.

That’s it for now.  I’d be the first to admit that there’s an awful lot of speculation in this post based on relatively little published information.  Hopefully You Hai-Lu will drop by and comment — I’ll be letting him know that I’ve posted this.

References

  • Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3: 27-93.
    Janensch, Werner.  1950.  Die Skelettrekonstruktion von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 97-103.
    Janensch, Werner.  1961.  Die Gliedmaszen und Gliedmaszengurtel der Sauropoden der Tendaguru-Schichten.  Palaeontographica, suppl. 7 (1), teil 3, lief. 4: 177-235.
    Taylor, Michael P. and Darren Naish.  2007.  An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England.  Palaeontology 50 (6): 1547-1564.  doi: 10.1111/j.1475-4983.2007.00728.x
    You, Hai-Lu, and Li, Da-Qing.  2009.  The first well-preserved Early Cretaceous brachiosaurid dinosaur in Asia.  Proceedings of the Royal Society B: Biological Sciences.  doi: 10.1098/rspb.2009.1278.
  • Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3: 27-93.
  • Janensch, Werner.  1950.  Die Skelettrekonstruktion von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 97-103.
  • Janensch, Werner.  1961.  Die Gliedmaszen und Gliedmaszengurtel der Sauropoden der Tendaguru-Schichten.  Palaeontographica, suppl. 7 (1), teil 3, lief. 4: 177-235.
  • Taylor, Michael P. and Darren Naish.  2007.  An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England.  Palaeontology 50 (6): 1547-1564.  doi: 10.1111/j.1475-4983.2007.00728.x
  • You, Hai-Lu, and Li, Da-Qing.  2009.  The first well-preserved Early Cretaceous brachiosaurid dinosaur in Asia.  Proceedings of the Royal Society B: Biological Sciences.  doi: 10.1098/rspb.2009.1278.

And finally … two announcements!

Traumador the Tyrannosaur has asked us to point out that over on ART Evolved (the palaeo-art blog), the next big art gallery is to be sauropod themed.  Details are on the site, so get over there and submit your sauropod art!

And Matt and I will shortly be teaming up with Andy Farke, the open-source paleontologist, on a new project where we plan to actually do some of this Shiny Digital Future that we keep on talking about.  Andy will be announcing the details on Tuesday 8th September.  Mark the date well!  For now, I shall say no more …

I just got word from the History Channel that their documentary “Evolve: Size” will air Saturday, Nov. 8. Kent Sanders, Brooks Britt, and I filmed a long segment for this back in May, covering pneumaticity in sauropods. Hopefully it didn’t all go to the cutting room floor! With any luck, you’ll see the results of this:

sauropods-the-next-generation-4801

Check local listings for showtimes.

UPDATE: IMMEDIATE REACTION

Hey, not bad. Good stuff:

  • I especially liked that they ascribed the evolution of large size in sauropods to several factors–high plant productivity, efficient food gathering (just biting, no chewing), and, yes, pneumaticity. But pneumaticity was at best an accessory adaptation for large size, and not a prime mover. I was worried that its importance would be overstated–“AIR-FILLED bones made these GIANTS into the HUGEST creatures EVAR!!1!” That’s some impressive restraint for a documentary these days.
  • The bit about pneumatic bones being light but also strong is great. I’m glad they worked in the pneumatic horns of bighorn sheep.
  • I’m really happy that they showed the process of CT scanning the vertebra, partly because It’s never been shown before on TV (to my knowledge), and partly for purely selfish reasons: it’s just cool. Too bad they didn’t have time to show Kent Sanders discussing the results of the scan.

Some clarifications:

  • Brooks Britt is not a grad student now, he’s an Associate Professor of geology at BYU. He pioneered the use of CT to study pneumaticity in dinosaurs when he was a grad student at the University of Calgary (Britt 1993). I am glad that they got the bit in about Brooks first suggesting to me that I should CT scan sauropod vertebrae. He got me into this, and it’s nice to have that recognized.
  • At one point the narrator says, “Wedel suspects that the bones were not only light and easy to lift, they also helped get oxygen directly to the muscles, fed by a system of air sacs throughout the neck, similar to birds today.” Woof–I didn’t say that! They got the ventilatory air sacs in the thorax and abdomen–the ones that blow air through the lungs–confused with the pneumatic diverticula up in the neck. There is no evidence that diverticula play any role in gas exchange for the tissues they are adjacent to, and there is strong contrary evidence. Physiologists have measured how much gas exchange goes on in the avian respiratory system, and where that gas exchange occurs. Ninety-five percent of the gas exchange happens in the lungs, and almost all of the remainder happens in the abdominal air sacs, which are immense and fairly convoluted because they enclose the viscera like a nut-shell (thanks to Wetherbee [1951] for that wonderfully accessible image). It’s a fairly minor thing, I guess, it’s just frustrating to spend so much time working on this and then have an obvious mix-up like that sneak in.
  • In the space of about ten minutes, sauropods are described as “freaks of nature” twice! This is a bit irritating–they are only freaks of nature from our limited, human point of view. Big sauropods had appeared by the late Triassic and huge ones by the Early Jurassic, and they stayed huge and successful through the Jurassic and Cretaceous. For all that they were immense and morphologically derived, sauropods were also just critters. They weren’t mutants, they were functioning and apparently successful members of their ecosystems for a long time, like any other organisms. Possibly, though, long exposure has acclimated me to the just-critters aspect of sauropods more than most folks. :-)

It seems churlish to write so much about a segment that was actually pretty great and right on target except for a few, comparatively minor missteps. Overall I’m thrilled that it turned out so well. See it if you get a chance–your own thoughts are welcome, good, bad, or otherwise.

References

  • Britt, B. B. 1993. Pneumatic postcranial bones in dinosaurs and other archosaurs. Ph.D. dissertation, University of Calgary, Calgary, 383 pp.
  • Wetherbee, D. K. 1951. Air-sacs in the English sparrow. Auk 68:242–244.

It is a strange fate that we should suffer so much fear and doubt over so small a thing.

Such a little thing….

Prepare yourselves, true believers. Pleurocoelus is coming!