I recently reread Dubach (1981), “Quantitative analysis of the respiratory system of the house sparrow, budgerigar and violet-eared hummingbird”, and realized that she reported both body masses and volumes in her Table 1. For each of the three species, here are the sample sizes, mean total body masses, and mean total body volumes, along with mean densities I calculated from those values.

  • House sparrow, Passer domesticus, n = 16, mass = 23.56 g, volume = 34.05 mL, density = 0.692 g/mL
  • Budgerigar, Melopsittacus undulatus, n = 19, mass = 38.16 g, volume = 46.08 mL, density = 0.828 g/mL
  • Sparkling violetear,* Colibri coruscans, n = 12, mass = 7.28 g, volume = 9.29 mL, density = 0.784 g/mL

* This is the species examined by Dubach (1981), although not specified in her title; there are four currently-recognized species of violetears. And apparently ‘violetear’ has overtaken ‘violet-eared hummingbird’ as the preferred common name. And as long as we’re technically on a digression,  I’m almost certain those volumes do not include feathers. Every volumetric thing I’ve seen on bird masses assumes plucked birds (read on).

This is pretty darned interesting to me, partly because I’m always interested in how dense animals are, and partly because of how the results compare to other published data on whole-body densities for birds. The other results I am most familiar with are those of Hazlehurst and Rayner (1992) who had this to say:

There are relatively few values for bird density. Welty (1962) cited 0.9 g/mL for a duck, and Alexander (1983) 0.937 g/mL for a domestic goose, but those values may not take account of the air sacs. Paul (1988) noted 0.8 g/mL for unspecified bird(s). To provide more reliable estimates, the density of 25 birds of 12 species was measured by using the volume displacement method. In a dead, plucked bird the air-sac system was reinflated (Saunder and Manton 1979). The average density was 0.73 g/mL, suggesting that the lungs and air sacs occupy some quarter of the body.

That result has cast a long shadow over discussions of sauropod masses, as in this paper and these posts, so it’s nice to see similar results from an independent analysis.  If you’re curious, the weighted mean of the densities calculated from Duchard’s Dubach’s (1981) data is 0.77. I’d love to see the raw data from Hazlehurst and Rayner (1992) to see how much spread they got in their density measurements.  Unfortunately, they did not say which birds they used or give the raw data in the paper (MYDD!), and I have not asked them for it because doing so only just occurred to me as I was writing this post.

There will be more news about hummingbirds here in the hopefully not-too-distant future. Here’s a teaser:

SkeletonFULL

Yes, those are its hyoids wrapped around the back of its head–they go all the way around to just in front of the eyes, as in woodpeckers and other birds that need hyper-long tongue muscles. There are LOADS of other interesting things to talk about here, but it will be faster and more productive if I just go write the paper like I’m supposed to be doing.

Oh, all right, I’ll say a little more. This is a  young adult female Anna’s hummingbird, Calypte anna, who was found by then-fellow-grad-student Chris Clark at a residential address in Berkeley in 2005. She was unable to fly and died of unknown causes just a few minutes after being found. She is now specimen 182041 in the ornithology collection at the Museum of Vertebrate Zoology at Berkeley. Chris Clark and I had her microCTed back in 2005, and that data will finally see the light of day thanks to my current grad student, Chris Michaels, who generated the above model.

This bird’s skull is a hair over an inch long, and she had a body mass of 3.85 grams at the time of her death. For comparison, those little ketchup packets you get at fast-food burger joints each contain 8-9 grams of ketchup, more than twice the mass of this entire bird when it was alive!

References

  • Dubach, M. 1981. Quantitative analysis of the respiratory system of the house sparrow, budgerigar and violet-eared hummingbird. Respiration Physiology 46(1): 43-60.
  • Hazlehurst, G.A., and Rayner, J.M. 1992. Flight characteristics of Triassic and Jurassic Pterosauria: an appraisal based on wing shape. Paleobiology 18(4): 447-463.

If you’ll forgive me a rather self-indulgent post, the neck-anatomy paper that I and Matt recently had published in PeerJ is important to me for three reasons beyond the usual satisfaction of getting a piece of work out in a good journal.

fig4

Taylor and Wedel (1023:figure 4). Extent of soft tissue on ostrich and sauropod necks. 1, ostrich neck in cross section from Wedel (2003, figure 2). Bone is white, air-spaces are black, and soft tissue is grey. 2, hypothetical sauropod neck with similarly proportioned soft-tissue. (Diplodocus vertebra silhouette modified from Paul 1997, figure 4A). The extent of soft tissue depicted greatly exceeds that shown in any published life restoration of a sauropod, and is unrealistic. 3, More realistic sauropod neck. It is not that the soft-tissue is reduced but that the vertebra within is enlarged, and mass is reduced by extensive pneumaticity in both the bone and the soft-tissue.

Three milestones

First, it brings a drought to an end. For one reason and another, I didn’t get a single paper published in 2012 — my last hit was the neck sexual-selection paper in September 2011, and I’d started to feel that I was drifting off into the distance a bit. Good to be back on the horse.

Second, amazing though it may seem, it’s the first Taylor/Wedel paper (in either order). Matt and I have been collaborating in one form or another for more than thirteen years now (even if the first couple of years of that were just me asking dumb questions and him telling me interesting things). Along the way, we’ve shared the authorship of a few papers with other authors (Taylor, Wedel and Naish 2009 on habitual neck posture; Taylor, Wedel and Cifelli 2011 on Brontomerus; and Taylor, Hone, Wedel and Naish 2011 on sexual selection) but of all the many Mike-‘n’-Matt projects we’ve started, this is the first to make it out into the world.

(As it happens — and at the risk of leaving the stadium before the fat lady sings — we should be adding to that tally of one Real Soon Now. Further bulletins as events warrant.)

Third, and most important, it means that my entire Ph.D is now published. Chapter 1 (the sauropod-history review) was in the Geological Society dinosaur-history volume;  chapter 2 (the Brachiosaurus revision) was in JVP; chapter 3 (the Xenoposeidon description) was in Palaeontology; chapter 4 (the Brontomerus description) was in Acta Palaeontologica Polonica, and now chapter 5 (neck anatomy) is in PeerJ. I’m pretty happy with the selection of venues there: I’m pleased to have had papers in JVP and Palaeontology even though I won’t be going back to either until they’re open access.

Figure 1. Necks of long-necked non-sauropods, to scale. The giraffe and Paraceratherium are the longest necked mammals; the ostrich is the longest necked extant bird; Therizinosaurus and Gigantoraptor are the largest representatives of two long-necked theropod clades; Arambourgiania is the longest necked pterosaur; and Tanystropheus has a uniquely long neck relative to torso length. Human head modified from Gray’s Anatomy (1918 edition, fig. 602). Giraffe modified from photograph by Kevin Ryder (CC BY, http://flic.kr/p/cRvCcQ). Ostrich modified from photograph by “kei51” (CC BY, http://flic.kr/p/cowoYW). Paraceratherium modified from Osborn (1923, figure 1). Therizinosaurus modified from Nothronychus reconstruction by Scott Hartman. Gigantoraptor modified from Heyuannia reconstruction by Scott Hartman. Arambourgiania modified from Zhejiangopterus reconstruction by Witton & Naish (2008, figure 1). Tanystropheus modified from reconstruction by David Peters. Alternating blue and pink bars are 1 m tall.

Taylor and Wedel (2013:figure 1). Necks of long-necked non-sauropods, to scale. The giraffe and Paraceratherium are the longest necked mammals; the ostrich is the longest necked extant bird; Therizinosaurus and Gigantoraptor are the largest representatives of two long-necked theropod clades; Arambourgiania is the longest necked pterosaur; and Tanystropheus has a uniquely long neck relative to torso length. Human head modified from Gray’s Anatomy (1918 edition, fig. 602). Giraffe modified from photograph by Kevin Ryder (CC BY, http://flic.kr/p/cRvCcQ). Ostrich modified from photograph by “kei51” (CC BY, http://flic.kr/p/cowoYW). Paraceratherium modified from Osborn (1923, figure 1). Therizinosaurus modified from Nothronychus reconstruction by Scott Hartman. Gigantoraptor modified from Heyuannia reconstruction by Scott Hartman. Arambourgiania modified from Zhejiangopterus reconstruction by Witton & Naish (2008, figure 1). Tanystropheus modified from reconstruction by David Peters. Alternating blue and pink bars are 1 m tall.

Dissertation thoughts

Actually I have strangely conflicted feelings about my Ph.D all being published now. I like the feeling of closure, but I also feel a bit sad that the dissertation itself — by far the most substantial single piece of work I’ve produced in any field — is now wholly obsolete. Really, the only reason anyone would possibly want to read it now would be for the acknowledgements or the laughably incorrect predictions of what I’d be working on next. Happily, I don’t have to lament time wasted on the dissertation: all five chapters were originally written to be papers, and the versions in the dissertation are all formatted as for the journals they were initially submitted to. (Three of them ended up in different venues, having initially been rejected, but that’s another story.)

An oddity of my Ph.D is that all five chapters were side-projects. They’re all things that I worked on when I was supposed to be working on a core project to do with the Archbishop and the mechanics of neck support. Every one of them I thought would be a quick job that I could push out before returning to my main work. And every one of them “grew in the telling” until it was substantial enough to function as a chapter. I am sure there’s a moral to this story, but heck if I can figure out what it is.

For reasons that seemed to make sense to me at the time, I did not post my dissertation on the Internet when it was accepted. I feared scooping myself on the as-yet unpublished material (Brontomerus and neck anatomy). Honestly, I don’t know what I was thinking. If I was doing it today I would certainly make it available from the moment it was okayed. As of just a couple of days ago it is now available — just in time to be of no interest to anyone.

xx

Taylor and Wedel (2013:figure 2). Full skeletal reconstructions of selected long-necked non-sauropods, to scale. 1, Paraceratherium. 2, Therizinosaurus. 3, Gigantoraptor. 4, Elasmosaurus. 5, Tanystropheus. Elasmosaurus modified from Cope (1870, plate II, figure 1). Other image sources as for Fig. 1. Scale bar = 2 m.

Co-authoring dissertation chapters

A final thing worth mentioning: as noted above, three of the chapters of my dissertation (Xenoposeidon, Brontomerus, neck anatomy) were co-authored. I think this is not particularly common, so it’s probably worth commenting on.

How does it work? For one of the papers, the Brontomerus description, I just excised Matt’s and Rich’s contributions, which were quite separate from the core of the paper, and used a sole-authored version as the chapter. For the other two, I put an explicit statement in the front-matter saying who did what:

Chapter 3 (description of Xenoposeidon): I was responsible for the anatomical part of the introduction, the systematic palaeontology section, description, comparisons and interpretation, phylogenetic analysis, length and mass calculations, diversity discussion, references, figures with their captions except figure 2, and both tables. Darren Naish of the University of Portsmouth was responsible for the geological and historical part of the introduction, the historical taxonomy section, and figure 2.

Chapter 5 (evolution of long necks): this chapter was written by me as a consequence of a series of discussions with Mathew J. Wedel. Dr. Wedel also contributed figure 5.

My sense was that the examiners were perfectly happy with this. Arguably it’s a good preparation for functioning as a researcher, since so many papers are co-authored. It’s not really realistic practice to sole-author all your work. That said, I doubt papers where I wasn’t lead author would have been welcomed.

I mention this because co-authoring may be a more widely available option than is recognised. My advice would be simple: check with your own supervisor first!

The gloves are off!

October 12, 2011

A package!  A package has arrived!

What can it be?

All right!  Let’s get down to business?

Now, where did I leave that monitor-lizard neck skeleton?  Ah yes …

That’s what I’m talkin’ about.

Stay tuned for exciting news about turkey zygapophyses.

 

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

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