Another mystery: embossed laminae and “unfossae”

Broadly speaking, pneumatic sauropod vertebrae come in two flavors. In more primitive, camerate vertebrae, modeled here by Haplocanthosaurus, the centrum is a round-ended I-beam and the neural arch is composed of intersecting flat plates of bone called laminae (lam above; fos = fossa, nc = neural canal, ncs = neurocentral suture; Ye Olde Tyme vert pic from Hatcher 1903).

In more derived, camellate vertebrae, the centrum and neural arch are both honeycombed with many small air spaces. This inflated-looking morphology is very similar to that seen in birds, like the turkey we recently discussed. The fossae and foramina on the outside tend to be smaller and more numerous than in camerate vertebrae, as shown here in a titanosauriform axis from India (Figure 3 from Wilson and Mohabey 2006). The green arrows show that the fossae visible on the external surface are excavations or depressions into the honeycombed internal structure of the bone.

External fossae on bones can house many different soft tissues, including muscles, pads of fat or cartilage, and pneumatic diverticula (O’Connor 2006). Pneumatic fossae are often strongly lipped and internally subdivided and may contain pneumatic foramina, which makes them easier to diagnose (but they may also be simple, smooth, and “blind”, which makes them harder to diagnose as pneumatic). But in all of these cases we are usually talking about the same thing: a visible excavation into a corpus of bony tissue, which may have marrow spaces inside if it is apneumatic, or air spaces inside if it is pneumatic (the corpus of bone, not the dent). That’s probably how most of us think about fossae, and it would hardly need to be explained…except that sometimes, something much weirder happens.

Consider this cervical of Brachiosaurus (this is BYU 12866, from Dry Mesa, Colorado). Brachiosaurus and Giraffatitan have an in-between form of vertebral architecture that my colleagues and I have called semicamellate (Wedel et al. 2000); the centrum does have large simple chambers (camerae), but smaller, thin-walled camellae are also variably present, especially along the midline of the vertebra and in the ends of the centrum. As in Haplocanthosaurus, the neural arch is composed of intersecting plates of bone; unlike Haplocanthosaurus, these laminae are not flat or smooth but are instead highly sculpted with lots of small fossae. Janensch (1950) called these “Aussenkaverne”, or accessory cavities, because they are smaller and more variable than the large fossae and foramina that invade the centrum.

And that’s the weird thing. As the red arrows in the above image show, the “Aussenkaverne” are not excavations or depressions into anything, except the space on the other side of the lamina (which in life would have been occupied by another diverticulum). The neural arches of Brachiosaurus and Giraffatitan are not excavated by fossae, they’re embossed, like corporate business cards and fancy napkins.

What’s up with that!? We tend to think of pneumaticity as reducing the mass of the affected elements, but the shortest distance between two vertebral landmarks is a smooth lamina. These embossed laminae actually require slightly more bony material than smooth ones would.

As you can see above, the outer edges of the laminae are thick but the bone everywhere else is very thin. Maybe, like the median septa in pneumatic sauropod vertebrae, the thin bone everywhere except the edges of the laminae was just not loaded very much or very often, and was therefore free to get pushed around by the diverticula on either side, in the sense of being continually and quasi-randomly remodeled into shapes that don’t strike us as being very mechanically efficient. But also like the median septa, the thin parts of the laminae are only rarely perforated (but it does happen), for possible (read: arm-wavy) reasons discussed in the recent FEA post. And maybe the amount of extra bone involved in making embossed laminae versus smooth ones was negligible even by the very light standards of sauropod vertebrae.

Another question: since these thin sheets of bone were sandwiched in between two sets of diverticula, why are the “unfossae” always embossed into them, in the medial or inferior direction? Why don’t any of them pop out laterally or dorsally, looking like domes or bubbles instead of holes, like Mount Fist-of-God from Larry Niven’s Ringworld? Did the developmental program get accustomed to making fossae that went down and into a corpus of bone, and just kept on with business as usual even when there was no corpus of bone to excavate into? I’m only half joking.

I don’t have good answers for any of these questions. I scanned this vert a decade ago and I only noticed how weird the “unfossae” were a few months ago. I’m putting all this here because “Hey, look at this weird thing that I can only wave my arms about” is not a great basis for a peer-reviewed paper, and because I’d like your thoughts on what might be going on.

In Other News

The Discovery Channel’s Clash of the Dinosaurs premiered last night. I would have given you a heads up, except that I didn’t get one myself. I only discovered it was on because of a Facebook posting (thanks, folks!).

COTD is intended to be the replacement, a decade on, for Walking With Dinosaurs. I’m happy to report that one of the featured critters is Sauroposeidon. I grabbed a couple of frames from the clips posted here.

I haven’t seen the series yet, because I don’t have cable. But I’m hoping to catch it at a friend’s place next Sunday night, Dec. 13, when the entire series will be shown again. With any luck, I’ll have more news next week.

Finally, I got to do an interview at Paw-Talk, a forum for all things animal. I’m very happy with how it turned out, so thanks to Ava for making it happen. While you’re over there, have a look around, there’s plenty of good stuff. Brian Switek, whom you hopefully know from this and this, is a contributor; check out his latest here.

References

• Hatcher, J.B. 1903. Osteology of Haplocanthosaurus, with a description of a new species, and remarks on the probable habits of the Sauropoda, and the age and origin of Atlantosaurus beds. Memoirs of the Carnegie Museum 2:1–72.
• Janensch, W.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3:27-93.
• O’Connor, P.M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs. Journal of Morphology 267:1199-1226.
• Wedel, Mathew J., Richard L. Cifelli and R. Kent Sanders.  2000.  Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon.  Acta Palaeontologica Polonica 45(4): 343-388.
• Wilson, J. A. and Mohabey, D. M. 2006. A titanosauriform axis from the Lameta Formation (Upper Cretaceous: Maastrichtian) of central India. Journal of Vertebrate Paleontology 26:471–479.

Finite Element Analysis of sauropod vertebrae

Figure 3 from Schwarz-Wings et al. 2009. A is Diplodocus, B-D are Giraffatitan.

Earlier this month Daniela Schwarz-Wings and colleagues published the first finite element analysis (FEA) of sauropod vertebrae (Schwarz-Wings et al. 2009). Above is one of the figures showing some of their results. Following standard convention, stresses are shown on a gradient with cooler colors indicating lower stresses and hotter colors indicating higher stresses. I’m not going to dwell on the on the nuts-n-bolts of FEA in general or of this study in particular. Instead, I want to talk about how sauropod vertebrae are built.

CT cross sections of BYU 12866, a mid-cervical of Brachiosaurus sp.

In cross-section, sauropod vertebrae often have thick bone at the outer edges of the laminae and in the walls and especially the floor of the centrum, as shown in this Brachiosaurus cervical. The bone everywhere else is pretty thin. If you hit one of these vertebrae with some magical forumula that would dissolve away all the bone thinner than, say, 1 cm, all that would be left would be the various apophyses, the outer margins of the laminae connecting them, and probably the bottom half of the centrum. It would be like the outline of a vertebra constructed from tent poles, or tinkertoys.

This is weird because most pneumatic sauropod vertebrae have at least something approaching an I-beam shape in cross-section. You might think that the median septum would be mechanically important, but it’s usually very thin, sometimes perforated (see Hatcher’s [1901] Diplodocus cervicals, for example), and often asymmetrically deviated to one side or the other. Not what you would expect for a piece of bone that was doing any work.

And indeed, Schwarz-Wings et al. (2009) found that:

Comparative stresses are distributed evenly around the vertebrae and mainly on the bone cortex. Peak stresses occur only at points where the tendons and muscles are inserting because the insertion areas used were small resulting in extreme localized stresses. The interior of both vertebrae is nearly stress free. Almost no stresses occur around the cavities and in their bony walls (figure 3).

This reminds me not of I-beams but of the long bones of the limbs of terrestrial vertebrates. There’s a reason why you’ve got a big honkin’ marrow cavity running through the middle of your femur: the stresses are being borne by the walls of the bone. It makes sense that vertebrae would function similarly, especially sauropod cervicals which sometimes approximate limb bones in their proportions.

So how about that median septum? Why aren’t sauropod vertebrae just hollow tubes? My guess–and it is a guess–is that they got as close to being hollow tubes as their evolutionary and developmental origins allowed. The pneumatic diverticula invaded the centra from either side and pushed in lateral-to-medial, and I think the median septum is just the wimpy little bit of bone left in between the two sets of diverticula when they almost meet up in the middle.

Even if that’s correct, there’s another mystery: why don’t the diverticula just go ahead and erode away the median septum? I can think of two possible reasons. One is that, for reasons I don’t know and I’m not sure if anyone else does either, pneumatic diverticula are good at getting into bones but pretty lousy at getting back out. There are comparatively few cases of diverticula inside bones making foramina to get out into the  surrounding tissue. It does happen–in humans, the mastoid air cells sometimes bust out and make subcutaneous pneumatocoels, basically bubbles of air under the skin (Anorbe et al. 2000)–but it seems to be rare. Maybe median septa fall under the same inscrutable rule.

(Incidentally, this makes the perforate laminae in Giraffatitan all the weirder.)

Another, more mundane possibility is that the median septa (and other oddly thin bits of bone) are not never loaded, just infrequently loaded. Not enough to make them straight, thick, or normal-lookin’, but enough to make sure they don’t get resorbed entirely.

Sauropod vertebrae are just loaded with these growth-and-form-related mysteries. Kudos to Schwarz-Wings et al. for pushing us a little farther down the road toward solving them.

References

• Anorbe, E., Aisa, P. and Saenz de Ormijana, J. 2000. Spontaneous pneumatocele and pneumocephalus associated with mastoid hyperpneumatization. European Journal of Radiology 36:158–160. [abstract only for free]
• Hatcher, J.B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1: 1-63 and plates I-XIII.
• 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

What a 23% longer torso looks like

Just checking: no-one’s bored of brachiosaurs yet, are they?

Thought not.  Right, then, here we go!

Greg Paul’s (1988) study of the two “Brachiosaurus” species — the paper that proposed the subgenus Giraffatitan for the African species — noted that the trunk is proportionally longer in Brachiosaurus than in Giraffatitan due to the greater length of its dorsal centra. Paul (p. 7) stated that the difference is “25%-30%” on the basis of his figure 2.

Having seen the dorsal vertebrae of the type specimens of both species, my gut reaction was that the difference was nowhere near this great, so I recalculated it for myself (Taylor 2009:table 3).  Dorsal column length is the sum of the “functional length” of the centra of the dorsal vertebrae, where functional length is the length of the centrum not counting the condyle (which of course is nestled in the preceding vertebra’s cotyle when the column is articulated).  For Brachiosaurus, Riggs (1904) did not give this measurement, but did give total heights, and using these for scale I was able to measure the functional lengths from his plate LXXII.  For Giraffatitan, Janensch’s (1950:44) superbly comprehensive table supplied measurements for D4 and D8; for D11 and D12 I was able to determine the length by measuring from Janensch’s (1950:fig. 62) figure, knowing the height from his table; and for D5-D7, D9 and D10, I interpolated linearly between the measurements that I had.  Summing the functional lengths of D6-D12, I got 226 cm for Brachiosaurus and 183 cm for Giraffatitan.  So Brachiosaurus is 226/183 = 1.23 times as long as Giraffatitan — in other words, 23% longer, which is pretty much what Greg Paul said.  So I learned something there.

(Yes, brachiosaurs probably had 12 dorsals.)

So: is a 23% longer torso a big deal?  Back when I was trying to answer that question for myself, I figured it would help to take an image of a familiar animal and stretch it — so here is a horse, stolen from here and stretched:

Horse (top); and evil mutant horse with 23% longer torso (bottom).

To me, that second picture is wrong enough to hurt my eyes a little; your mileage may vary, but I suspect those among you who love horses will feel ill when you look at it.  This image was one of the reasons — one of many — that I concluded that generic separation was unavoidable.

But here’s an odd thing: tonight, for this blog post, I did the same thing to a human body, expecting it to seem even more horrible in light of how familiar we are with our own bodies.  Here it is:

Flayed Homo sapiens in orthograde anatomical position, from Vesalius (1543) "Tertia Musculorum Tabula". Modified from Wilson (2006:fig. 1). Left, as drawn; right, with torso elongated by 23%.

To my surprise, the elongated human doesn’t look appallingly wrong to me.  It doesn’t look right, of course, but it seems within the realms of, for example, what might appear as a representation of a human body in the early issues of Fantastic Four.  I am not sure what to make of that fact.  I don’t believe I have a more finely tuned sense of horse anatomy than human anatomy: it might be that I am more used to badly drawn humans than badly drawn horses; or that there is more variation in human proportions than in horse proportions; or maybe weirdness just looks less weird when it’s upright than when it’s horizontal.  I’ll be interested to hear in the comments whether the Long Horse or the Long Human looks most wrong to readers.

(By the way, I casually talk about the type specimens of both “Brachiosaurus” species: while the situation is simple in the case of Brachiosaurus altithorax, whose holotype is FMNH P25107, things are more complex in the case of Giraffatitan brancai.  Janensch nominated “Skelett S” as the holotype of his new species “Brachiosaurus” brancai, but that turned out to be a chimera, composed of the two skeletons which he subsequently designated SI and SII — but Janensch never designated one of these as the type, and so far as I’ve been able to determine, neither has anyone else done so.  SI is represented by cranial elements and the first seven cervicals, but that’s all; SII is a much larger animal and is represented by most of the skeleton, and has been informally treated as though it were the type specimen most of the while, so I formally proposed HMN SII as the lectotype of the species (Taylor 2009:788) — just a bit of housekeeping.)

Here’s our old friend, the 8th cervical vertebra of HMN II, in a rare posterodorsal aspect, showing just how thin and, well, lamina-like the spinopostzygapophyseal laminae are.  All that space in between them?  Filled with diverticula, mostly.  Amazing.

Giraffatitan brancai lectotype HMN SII, 8th cervical vertebra, in posterodorsal view

Meanwhile some good news:

Remember the good news and bad news about the all-dinosaurs special volume of The Anatomical Record?  Well, since we posted that, the entire issue has been made open access!  Fantastic stuff there: details from D. Schachne of the Wiley-Blackwell Communications Team.  It’s not clear why the articles were all paywalled when originally posted, but all’s well that ends well.

And finally …

There’s been a gratifying amount of discussion in the comments on recent articles.  It can be hard to keep track of, but it helped a lot when I found an RSS feed for comments, which is what I now use.  For anyone else who wants it, it’s at http://svpow.wordpress.com/comments/feed/

References

• Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 27-93.
  Paul, Gregory S.  1988.  The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs.  Hunteria 2 (3): 1-14.
  Taylor, Michael P.  2009.  A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914).  Journal of Vertebrate Paleontology 29(3):787-806.
  Vesalius, A.  1543.  Andreae Vesalii Bruxellensis, Scholae medicorum Patauinae professoris, de Humani corporis fabrica Libri septem [facsimile]. Ex Officina Ioannis Oporini, Basel, 659 pp.
  Wilson, Jeffrey A.  2006.  Anatomical nomenclature of fossil vertebrates: standardized terms or “lingua franca”?  Journal of Vertebrate Paleontology 26(3): 511-518.
• Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 27-93.
• Paul, Gregory S.  1988.  The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs.  Hunteria 2 (3): 1-14.
• Taylor, Michael P.  2009.  A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914).  Journal of Vertebrate Paleontology 29(3):787-806.
• Vesalius, A.  1543.  Andreae Vesalii Bruxellensis, Scholae medicorum Patauinae professoris, de Humani corporis fabrica Libri septem [facsimile]. Ex Officina Ioannis Oporini, Basel, 659 pp.
• Wilson, Jeffrey A.  2006.  Anatomical nomenclature of fossil vertebrates: standardized terms or “lingua franca”?  Journal of Vertebrate Paleontology 26(3): 511-518.

To B.b. or not to B.b — or — So what is a “genus” anyway?

Introduction

Back when the Xenoposeidon paper came out, we suggested that Xeno could be the first repesentative of a new sauropod “family”, and then discussed at some length: what is a “family” anyway? Now that the Brachiosaurus paper is out, and I’ve argued that the species “Brachiosaurus” brancai is generically distinct from Brachiosaurus altithorax, it’s time to talk about what a genus is (and so what “generically distinct” means).

In an unnecessarily snarky aside at the end of the last entry, I implied that Randy Irmis would be the one to say that, because my phylogeny recovered “Brachiosaurus” brancai as the sister taxon to Brachiosaurus altithorax, it could and should remain in the genus Brachiosaurus, irrespective of the morphological differences between the genera.  He didn’t quite do that — although Daniel Madzia very nearly did — but Jaime Headden certainly did over on the Dinosaur Mailing List, and even ended up asking: “So my question is this: Why do we need Giraffatitan, and cannot have a Brachiosaurus proteles etc.?”

There are plenty of possible responses to this, but before we plough into that, here is a pretty picture:

Ligament rugosities on the neural spines of Brachiosaurus dorsals

Brachiosaurus altithorax holotype FMNH P25107, presacral vertebrae 5-7, neural spines in right posterolateral view

The more retentive among you SV-POW! veterans might remember way back in the very first month of this blog when I showed you what I said were the last four presacral vertebrae of the Brachiosaurus altithorax holotype FMNH P25107.  Actually, I don’t know what I was thinking — they were presacrals 4-7, not 1-4, but that’s not the point.  The point is that Mike From Ottawa (whatever happened to him?) asked about the very rugose anterior surfaces of the neural spines, and I replied:

What the photo doesn’t show (but if you stay tuned long enough you’ll probably see one that does) is that the posterior faces of the neural spines have very similar rugosities. In life, these would have been the anchor points for epaxial muscles and ligaments. In Brachiosaurus altithorax (but not B. brancai) these have a distinctive inverted-triangle shape. In the most posterior pair of B. brancai dorsals, which are co-ossified, the ligament joining their neural spines is itself ossified. Picture to follow some time, I guess :-)

I am finally following up on the first half of that promise: the picture above shows the three most anterior of those same four presacral vertebrae from the Brachiosaurus altithorax holotype, but this time in right posterolateral view, so you can see the posterior faces of the neural spines.  And you’ll notice that on the back of each spine, as well as on the front, there’s a large and extremely rough inverted triangle.  I’ve yet to see anything at all like that in any other sauropod — Giraffatitan and the Archbishop included.  Very distinctive.

Right then — back to genera!

Rampant genera on the loose!

Here’s a practical reason to reject the idea that if two taxa are sisters, then they should be regarded as congeneric: Jaime wants to retain the species brancai within Brachiosaurus because it is (in the current analysis) the sister to the type species Brachiosaurus altithorax.  He then wants to put the species proteles into Brachiosaurus because the species we all know as Sauroposeidon proteles is (presumably) the sister to the Brachiosaurus-altithorax-and-brancai clade.  But by induction, if we accept Jaime’s policy, whatever is sister to that clade must also be subsumed into Brachiosaurus, so that we end up losing Titanosauria, Camarasauridae, Diplodocoidea, etc. — Diplodocus carnegii becomes a species of Brachiosaurus.  The good side of this scheme is that eventually, we’ll work our way up to the base of Amniota, at which point I become a member of the species Brachiosaurus sapiens.  That, I could get on board with.  But in other respects, this classification would not be so hot.

I’m assuming that no-one really wants this, and so that advocates of the Sister-Taxa-Are-Congeneric school (hereafter STAC) recognise that you have to draw a line somewhere.  But where?  And how do you choose where?  [Only time will tell whether I just coined an AHATWNUABPANTA.]

How to choose between specific and generic separation

At this point, I am reminded of when I used to be on a mailing list for wannabe writers. Lots of dogma on that list — people saying “don’t overdo adverbs” and “make sure you have enough incidental detail” and so.  People trying to nail down an algorithm for good writing.  But the best advice I saw on that list was from Jane MacDonald: ”My personal advice is don’t overdo, or underdo, anything in your writing.  Do it exactly right.”(*)  That’s my attitude to drawing genus boundaries.  It is, frankly, an art; and there are no substitutes for taste, experience, judgement, familiarity with the group in question and all those other touchy-feely qualities that uber-cladists would love to find a way to abolish if they could.  But they can’t.  There is no algorithm for this.  I also think of an observation by computer scientist Bjarne Stroustrup, the inventor of the C++ programming language: “Design and programming are human activities; forget that and all is lost.”  The same is true of palaeontology.  (And of, well, everything.)

Here’s the thing, folks: a genus, just like any other taxon, is there to be useful.  Its purpose is not to conform to a dogma, but to inform and enlighten.  In the new paper, I wrote that “generic separation is warranted since the two species are more different from each other than, for example, Diplodocus and Barosaurus Marsh, 1890″ (Taylor 2009:798).  I stand by that as a great way to figure out when the morphological differences  between two species merit generic separation: it’s all about conveying degrees of difference.  And, yes, of course I know that the morphological extent of a genus in sauropods is completely different from its extent in, say, botany, where the genus Quercus (oaks) has 700 species or something stupid.  Yes, I fully accept that there is no rigorous and absolute standard by which we can determine The Right Place to drop a genus boundary.  Sure.  But that doesn’t let us out from the responsibility of making the best judgements that we can, based on relevant prior art, recognised conventions, congruence with similar decisions and — there it is again — good taste.

(*) Actually, that is only the second best advice I saw on the wannabe writers’ mailing list.  The best advice of all came second-hand, and was passed on by Greg Gunther: “I was on an [email] list with Tom Clancy once.  Mr. Clancy’s contribution to the list was, ‘Write the damn book’.”  Top advice.

Nomenclatural stability

And so finally I come to Randy’s comment.  In response to his question, I guessed that when I put them all in a matrix together, the Archbishop will form a clade with Brachiosaurus, and Sauroposeidon with Giraffatitan.  Like this: ((Brachiosaurus altithorax, “The Archbishop”), (Giraffatitan brancai, Sauroposeidon proteles)).

,–Brachiosaurus altithorax

,<

/  `–”The Archbishop”

<

\  ,–Giraffatitan brancai

`<

`–Sauroposeidon proteles

And Randy said:

For the sake of discussion, if the topology is as you say, then I do support the generic separation of altithorax and brancai. Now, of course, as you might surmise, if the two sub-clades are well-supported, I would also advocate putting altithorax and the NHM Tendaguru taxon in the same genus, and brancai and Sauroposeidon in the same genus.

Now I yield to no man in my respect for Randy, whose work exceeds my own humble output by a truly humiliating factor, and who makes it even worse by being such a nice guy.  But I hope he will not take it the wrong way if I say that here, he is talking the purest arsegravy.  Suppose the topology came out the way I guessed, and we adopted his suggested nomenclature.  Then five minutes later Paul Upchurch comes along with a new analysis that finds the Archbishop closer to Giraffatitan after all: and suddenly Brachiosaurus archbishopus becomes Giraffatitan archbishopus.  Five more minutes pass and Jeff Wilson publishes his new phylogeny, in which “Sauroposeidon” proteles is sister to Brachiosaurus altithorax, and so what was briefly Giraffatitan proteles becomes Brachiosaurus proteles.  Later that afternoon Jerry Harris shows that Cedarosaurus is more closely related to Brachiosaurus altithorax than the species proteles is: at this point, presumably, either Cedarosaurus gets sunk into Brachiosaurus, as B. weiskopfae, or My Big Fat Brachiosaurus Genus gets smashed up and suddenly, woah, proteles needs its own genus after all and Sauroposeidon is back!

Hands up who wants to deal with tracking all that nomenclatural shifting back and forth?  Hmm, thought not.  Folks, when we name a new species of an existing genus we are betting the nomenclature on the phylogenetic hypothesis.  This is just a dumb thing to do in this day and age — especially if you work on dinosaurs which (A) are big and usually very incomplete and so their positions can’t  be known with certainty; (B) are trendy enough to be subject to a stream of new phylogenetic analyses; and (C) are in a field where pretty much everyone seems to be hot for mandatory monophyly of genera.

So I end with a plea: unless you know for certain that your new taxon is super-closely related to the type species of an existing genus, and unless you are sure that this isn’t going to change with subsequent discoveries, please put your new species in its own monospecific genus.  That way, nomenclature is independent from phylogeny, which is surely how we all want it.  A new monospecific genus is essentially a uninomial that happens to be spelled with a space in the middle.  And uninomials are nice: they rescue us from Linnaeus’s dumb mistake in lumbering nomenclature with binomials.

This has been an Unwelcome Education Product.

Acknowledgements

Many thanks to Jim Farlow for suggesting the title of this post, which I have cheerfully stolen.  I have no idea whether he agrees with the arguments presented in this article.

References

• Taylor, Michael P.  2009.  A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914).  Journal of Vertebrate Paleontology 29(3):787-806.

“Brachiosaurus” brancai is not Brachiosaurus

Today sees the publication of the new Journal of Vertebrate Paleontology, and with it my paper on the two best-known brachiosaurs and why they’re not congeneric (Taylor 2009).  This of course is why I have been coyly referring to “Brachiosaurus” brancai in the last few months … I couldn’t bear to make the leap straight to saying Giraffatitan, a name that is going to take me a while to get used to.

But before we go lunging into the details, here is my skeletal reconstruction of Brachiosaurus proper, taken from the paper:

Skeletal reconstruction of Brachiosaurus altithorax, with Homo sapiens and Canis familiaris for scale, from Taylor (2009:fig. 7). White bones represent the elements of the holotype FMNH P 25107. Light grey bones represent material referred to B. altithorax: the Felch Quarry skull USNM 5730, the cervical vertebrae BYU 12866 (C?5) and BYU 12867 (C?10), the "Ultrasauros" scapulocoracoid BYU 9462, the Potter Creek left humerus USNM 21903, left radius and right metacarpal III BYU 4744, and the left metacarpal II OMNH 01138. Dark grey bones modified from Paul's (1988) reconstruction of Giraffatitan brancai. Scale bar equals 2 m.

Those of you familiar with Greg Paul’s classic reconstruction of Giraffatitan brancai will immediately recognise that Real Brachiosaurus is rather differently proportioned, especially in having a longer torso and tail.

This paper has been in the works for some time, and while it was in review and then in press at JVP, it led double life as Chapter 2 of my dissertation.  (For most of its gestation period, the paper’s title was just “Brachiosaurus brancai is not Brachiosaurus“, and the folder where I keep all the project files is still called “bb-is-not-b”).  In the end, I chickened out and went for a longer, more formal, title.

So why are the two species not congeneric?  Well, it’s a long story, and you can read about the detail in the paper, but the bottom line is that virtually every bone that is known from both species differs in significant respects between them.

Of course, I am not the first to suggest that the African brachiosaurid that we know and love isn’t exactly Brachiosaurus.  Credit for that goes to Greg Paul, who more than twenty years ago executed a then-new skeletal reconstruction of that species (the very same reconstruction that is now considered the classic), and in doing so noticed some differences between the American type species Brachiosaurus altithorax and the African referred species “Brachiosaurus” brancai (Paul 1988).  Paul hedged his bets, though: rather than erect a new genus for the African animal, he proposed a subgenus Brachiosaurus (Giraffatitan), so that the full name of the species would become Brachiosaurus (Giraffatitan) brancai; and that of the type species would become Brachiosaurus (Brachiosaurus) altithorax.  Unsurprisingly, this cumbersome nomenclatural scheme did not catch on, and I have not been able to locate a single subsequent reference to these subgenera in the literature.

Second caudal vertebrae of Brachiosaurus altithorax and Brachiosaurus brancai, equally scaled, from Taylor (2009:fig. 3). A, B, B. altithorax holotype FMNH P 25107; C-G, B. brancai referred specimen HMN Aa. A, C, posterior; B, D, F, right lateral; E, G, anterior. A-B modified from Riggs (1904:pl. LXXV); C-E modified from Janensch (1950a:pl. 2), F-G modified from Janensch (1929:fig. 15). Scale bar equals 50 cm.

That didn’t mean the idea was dead, though: three years later, George Olshevsky’s self-published mega-revision of dinosaur taxonomy proposed raising the name Giraffatitan to genus level (Olshevsky 1991).  Although this genus became popular on the Internet (it cropped up, for example, in Mike Keesey’s much-lamented Dinosauricon web-site), it was almost completely ignored in the technical literature, and even Greg Paul himself subsequently seems to have reverted to using the name Brachiosaurus brancai (e.g. Paul 1994:246).

Why was the new name overlooked?  Partly, I suspect, just because it’s so butt ugly — everyone knows and loves Brachiosaurus brancai, and the name itself has a definite poetry to it that Giraffatitan sorely lacks.  But mostly it’s because Paul didn’t really make a case for the separation that he proposed — wrongly stating, for example, that “the caudals, scapula, coracoid, humerus, ilium, and femur of B. altithorax and B. brancai are very similar” (Paul 1988:7).

That’s how things stood a few years back when I started to take a serious interest in Migeod’s Tendaguru brachiosaurid, which lives in the basement of the Natural History Museum in London.  It quickly started to seem to me that it wasn’t the same thing as what everyone means by Brachiosaurus, but to make sense of it all, I needed first to figure out what the Brachiosaurus actually does mean.  That meant visiting the type material of both species, in Chicago and Berlin, and really looking closely.

Well, I don’t want to go on all day — apart from anything, England play Croatia in a World Cup qualifier in just over an hour — so I’ll just show you some of the the differences between the dorsal vertebrae of the two species.  (You’ll have seen the caudals up above — I just threw them in to break up all that text).

Dorsal vertebrae of Brachiosaurus altithorax and Brachiosaurus brancai in posterior and lateral views, equally scaled, from Taylor (2009:fig. 1). A, B, E, F, I, J, M, N, B. altithorax holotype FMNH P 25107, modified from Riggs (1904:pl. LXXII); C, D, G, H, K, L, O, P, B. brancai lectotype HMN SII, modified from Janensch (1950a:figs. 53, 54, 56, 60-62, 64) except H, photograph by author. Neural arch and spine of K sheared to correct for distortion. A, D, E, H, I, L, M, P, posterior; B, F, G, J, N, right lateral; C, K, O, left lateral reflected. A, B, dorsal 6; C, D, dorsal 4; E-H, dorsal 8; I-L, dorsal 10; M, N, P, dorsal 12; O, dorsals 11 and 12. Corresponding vertebrae from each specimen are shown together except that dorsal 4 is not known from B. altithorax so dorsal 6, the most anterior known vertebra, is instead shown next to dorsal 4 of B. brancai. Scale bar equals 50 cm.

Lots and lots of differences here — I will quote from the Systematic Paleontology section on the type species: “Postspinal lamina absent from dorsal vertebrae (character 130); distal ends of transverse processes of dorsal vertebrae transition smoothly onto dorsal surfaces of transverse processes (character 142); spinodiapophyseal and spinopostzygapophyseal laminae on middle and posterior dorsal vertebrae contact each other (character 146); posterior dorsal centra subcircular in cross-section (character 151); posterior dorsal neural spines progressively expand mediolaterally through most of their length (“petal” or “paddle” shaped) (character 155); mid-dorsals about one third longer than posterior dorsals (see Paul, 1988:7); middorsals only about 20% taller than posterior dorsals (see Paul, 1988:8); dorsal centra long (Janensch, 1950a:72) so that dorsal column is over twice humerus length (Paul, 1988:8); transverse processes of dorsal vertebrae oriented horizontally (Paul, 1988:8); dorsal neural spines oriented close to vertical in lateral view; dorsal neural spines triangular in lateral view, diminishing smoothly in anteroposterior width from wide base upwards; deep inverted triangular ligament rugosities on anterior and posterior faces of neural spines” …. *gasp*

So anyway: the upshot of all this is that “Brachiosaurus” brancai differs from Brachiosaurus altithorax more than, say, Barosaurus does from Diplodocus; and so it must be placed in its own genus … and that genus has to be Giraffatitan, because of the ICZN’s principle of priority.  And THAT is why the very end of the paper — the last sentence of the Acknowledgements — reads:

Finally, I beg forgiveness from all brachiosaur lovers, that so beautiful an animal as “Brachiosaurus” brancai now has to be known by so inelegant a name as Giraffatitan.

Anyway, go and read the paper; full-resolution figures are freely available if you want to look more closely than the JVP’s PDF allows.

References

• Olshevsky, George.  1991.  A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia.  Mesozoic Meanderings #2 (1st printing): iv + 196 pp.
• Paul, Gregory S.  1988.  The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs.  Hunteria 2(3):1-14.
• Paul, Gregory S.  1994.  Dinosaur reproduction in the fast lane: implications for size, success and extinction.  pp. 244–255 in: K. Carpenter, K. F. Hirsch, and J. R. Horner (eds.), Dinosaur Eggs and Babies.  Cambridge University Press, Cambridge.
• Taylor, Michael P.  2009.  A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914).  Journal of Vertebrate Paleontology 29(3):787-806.

(And, yes, Randy, I know what your comment is going to say; go ahead and say it anyway, it’ll give me a chance to explain why your approach is wrong :-))

Bifid Brachiosaurs, Batman!

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. (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 “Brachiosaurus” brancai 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. 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.

You and Li (2009) describe their pelvis as having a “much reduced ischium”, but as is apparent by comparison with the pelvis of “Brachiosaurus” brancai, 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 “Brachiosaurus” brancai 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 …

Tutorial 7: the sauropod family tree

We really should have covered this ages ago …  Here we are, blithering on about brachiosaurids and diplodocoids and all, and we’ve never really spelled out what these terms mean.  Sorry!

The family tree of a group of animals (or plants, or fungi, or what have you) is called its phylogeny.  The science of figuring out a phylogeny is called systematics.  And once you’ve got a phylogeny, the business of naming the parts of it (and of course choosing which parts to name) is taxonomy.

For a long time, sauropod systematics was completely up in the air, so that the McIntosh’s (1990) review article on sauropods in The Dinosauria (first edition) said, rather despairingly, that “although recent discoveries are beginning to clarify the problems of sauropod phylogeny, were are still very far from being able to construct a cladogram” (p. 399).  Happily, this changed rapidly thereafter, with the first published numerical phylogenetic analysis appearing in Russell and Zheng’s (1993) description of the new Mamenchisaurus species M. sinocanadorum.  More importantly, in the same year Paul Upchurch submitted his (1993, duh) dissertation on sauropods, and this contained a much larger analysis which was published as Upchurch (1995).  This paper raised the bar significantly, with an analysis of 27 taxa using 174 characters.  Three years later, Upchurch (1998) published a major revision of his own work; in the same year, the other major school of sauropod phylogeny launched with a JVP memoir (Wilson and Sereno 1998), which featured only 10 taxa and 109 characters, but discussed and illustrated them in more detail.  Wilson (2002) followed this up with a much larger analysis of 27 taxa and 234 characters, and Upchurch et al. (2004), in the second editi0n of The Dinosauria, saw his 27×234 and raised him to 41×309.  The good news is that, by this time, the two schools’ phylogenies, having started out rather different, were converging on a consensus topology with only two significant disagreements, which we’ll come to in a minute.

Since then, Jerry Harris (2006) created a union matrix from the character scores in the Wilson (2002) and Upchurch et al. (2004) matrices, and also threw in a few additional characters from other less ambitious phylogenetic analyses.  This analysis came up with a tree that was very similar to Wilson’s, and subsequent work by Wilson and Upchurch (2009) indicates that Upchurch is now also substantially in agreement with this arrangement.

So here it is!

Consensus phylogeny of sauropod, from Harris (2006)

I plucked this from Jerry’s paper, and coloured it in to show two of the more important groups.  Evolution begins at bottom left, so let’s quickly tour the group.

• First of all, note the outgroups. Sauropods’ nearest relatives are the other saurischian dinosaurs, theropods and prosauropods.  (They’re shown the wrong way round here, because in an unrooted tree it makes no difference.  Ignore that.)
• The most basal sauropods include things like Vulcanodon and, it turns out mostly from the work of Adam Yates (e.g. Yates 2007), a whole bunch of things that, if you looked at them you’d probably guess were prosauropods.
• Sauropods as we know them really begin at the boundary of the group Eusauropoda (“true sauropods”), which is roughly speaking everything more derived than Vulcanodon.  (I won’t discuss the naming of nodes and branches in detail in this post, as it would quickly get too long.  Maybe in Tutorial 8.)  This group I have coloured pink in the diagram above.
• Basal eusauropods include quite a few genera, and the order in which the branched off the “main line” leading to the neosauropods is not clear — as the unresolved polytomy above shows.  Cetiosaurus (which for some reason is not shown in this figure) is generally considered quite derived; some of the Chinese sauropods (Mamenchisaurus, Omeisaurus, etc.) may form a group of their own, but that’s not clear.
• Most of the best-known sauropods fall within the great group Neosauropoda (“new sauropods”), which is coloured purple above.  A few genera float around the root of this group, including Haplocanthosaurus and Jobaria, both of which are sometimes considered neosauropods, and sometimes non-neosauropod sauropods (or what I informally call “eosauropods”, or “dawn sauropods”).
• Otherwise the great split within Neosauropoda is between the diplodocoids (on the left) and the macronarians (on the right) — the groups including Diplodocus on one hand, and Saltasaurus on the other.
• The most basal diplodocoids are the rebbachisaurids over on the left.
• Most other diplodocoids fall into the group Flagellicaudata (“whip-tails”), which is itself composed of dicraeosaurids and diplocodids.  (It’s not clear where in that dichotomy, or maybe just outside it, Suuwassea falls.)
• Over in the other half of the Neosauropods, the first macronarians to diverge are the camarasaurids (which currently means, uh, Camarasaurus).
• Most of the other macronarians fall into Titanosauriformes, the group uniting brachiosaurids (yay!) with titanosaurs and their buddies.  Everything closer to titanosaurs falls within Somphospondyli, and that includes Euhelopus — as it turns out.  (Upchurch had found Euhelopus to fall outside Neosauropoda).
• Once you get past Euhelopus, you’re into Titanosauria (though there are various definitions which place the entry point differently).
• And once inside Titanosauria … well, all bets are off at this stage.  There is a rough consensus that things like Malawisaurus and Andesaurus are pretty basal and Saltasaurus is, sort of by definition, derived.  But apart from that, different studies have come up with wildly different phylogenies, with that of Curry Rogers (2005) being particularly left-field.

Without a doubt, Titanosauria is where the action is right now.  As alluded to in the comments of Matt’s Isisaurus post, it’s a big, big group, encompassing many genera and huge morphological range.  It’s also a long-lived group, spanning the whole of the Cretaceous; and it’s where most new genera are being named, as Argentina seems to be packed full of ‘em.

Well, that’s all for now.  Sorry it’s been wordier than usual — probably not much fun to read, but hopefully useful to refer back to in future.

Here’s the famous 8th cervical vertebra of the “Brachiosaurus” brancai lectotype HMN SII, this time in a left-lateral close-up of its left prezygpapophyseal ramus, showing the many pneumatic excavations.  Enjoy!

"Brachiosaurus" brancai lectotype HMN SII, 8th cervical vertebra, left prezygapophyseal ramus in left lateral view.

References

Curry Rogers (2005)

Harris (2006)

McIntosh (1990)

Russell and Zheng (1993)

Upchurch (1993)

Upchurch (1995)

Upchurch (1998)

Upchurch et al. (2004)

Wilson (2002)

Wilson and Sereno (1998)

Wilson and Upchurch (2009)

Yates (2007)

• Curry Rogers, Kristina. 2005. The Evolutionary History of the Titanosauria. pp. 50-103 in: K. Curry Rogers and J. A. Wilson (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.
• Harris, Jerald D. 2006. The significance of Suuwassea emiliae (Dinosauria: Sauropoda) for flagellicaudatan intrarelationships and evolution. Journal of Systematic Palaeontology 4: 185-198.
• McIntosh, John S. 1990. Sauropoda. pp. 345-401 in: D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 1st edition. University of California Press, Berkeley and Los Angeles.
• Russell, Dale A., and Zheng, Zhong. 1993. A large mamenchisaurid from the Junggar Basin, Xinjiang, China. Canadian Journal of Earth Science 30(10/11): 2082-2095.
• Upchurch, Paul. 1993. The Anatomy, Phylogeny and Systematics of the Sauropod Dinosaurs. University of Cambridge, unpublished Ph.D. dissertation. 489 pp.
• Upchurch, Paul. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London Series B, 349: 365-390.
• Upchurch, Paul. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society 124: 43-103.
• Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pp.
• Wilson, Jeffrey A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217-276.
• Wilson, J. A. and Paul C. Sereno. 1998. Early evolution and Higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.
• Wilson, Jeffrey A. and Paul Upchurch. 2009. Redescription and reassessment of the phylogenetic affinities of Euhelopus zdanskyi (Dinosauria – Sauropoda) from the Early Cretaceous of China. Journal of Systematic Palaeontology 7: 199-239. doi:10.1017/S1477201908002691
• Yates, Adam M. 2007. The first complete skull of the Triassic dinosaur Melanorosaurus Haughton (Sauropodomorpha: Anchisauria). pp. 9-55 in: Paul M. Barrett and David J. Batten (eds.), Special Papers in Palaeontology 77: Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs. The Palaeontological Association, U.K.

How tallweird was Sauroposeidon?

In an email, Vladimir Socha drew my attention to the fact that Tom Holtz’s dinosaur encyclopaedia estimates the maximum height of Sauroposeidon as 20 meters plus, and asked whether that was really possible.  Here’s what Tom actually wrote: “Sauroposeidon was one of the largest of all dinosaurs.  At perhaps 98 to 107 feet (30 to 32.5 meters) long and weighing 70 to 80 tons [...] Sauroposeidon would have been the tallest of all dinosaurs. [...] If it could crane its neck up, it might have been able to hold its head 66 to 69 feet (20 to 21 meters) high or more” (Holtz and Rey 2007:207).  Vladimir was understandably skeptical.  But can it be true?

Wedel and Cifelli (2005: fig. 15) shows Matt’s best skeletal reconstruction of Sauroposeidon, with Boring Old Brachiosaurus and a human for scale:

Sauroposeidon with Boring Old Brachiosaurus and human for scale and 20 m height indicated. Lightly modified from Wedel and Cifelli (2005: fig. 15)

Amazingly, those dummies didn’t include an actual scalebar; but apparently the human figure is 1.8 m tall, so by measuring pixels and cross-scaling, I determined that in this image, Sauroposeidon is a mere 13.43 m tall.  I took the liberty of adding in a marker for the 20 m height proposed by Holtz, and as things stand you’d have to say that it doesn’t look probable.

But let’s see what we can do.  We’ll begin with the classic brachiosaur skeleton of Paul (1988), which shows the well represented species Brachioaurus brancai:

Brachiosaurus brancai skeletal reconstruction in left lateral view. From Paul (1988:fig. 1)

(Some other time, we should take a moment to discuss the differences between this and the Wedel brachiosaur reconstruction; but it will not be today.)

This reconstruction is in a nice erect-necked posture which, in light of our own recent paper, is probably not too extreme.  Since all the neural arches and processes are missing from the only known posterior cervicals of this species, we don’t know how much flexibility they allowed, and so in light of how the rest of the animal is built (high shoulders and all) it seems reasonable to allow a lot of extension at the base of the neck.  So let’s assume that the pose offered by Paul is correct.  By measuring my scan of that figure, and I see that the 2.13 m humerus is 306 pixels long.  The entire reconstruction, from tip of cranial crest down to forefoot, is 1999 pixels tall, which is 1999/306 = 6.53 times as long as the humerus, which scales to 6.53*2.13 = 13.91 m — a little taller than Sauroposeidon (not Brachiosaurus) in Matt’s reconstruction, which seems about right if we imgine Matt’s Brachiosaurus raising its neck into a Paul-compliant posture.

Now Paul’s reconstruction is based on the Berlin mounted skeleton HMN S II.  Cervical 8 is very well preserved in that animal, and has a centrum length of 98 cm (Janensch 1950a:44).  By contrast, the centrum of C8 of Sauroposeidon OMNH 53062 (the only known specimen) is 125 cm long (Wedel et al. 2000a: 110). So if Sauroposeidon is merely an elongated Brachiosaurus brancai, then it’s 125/98 = 1.28 times as long and tall, which would be 17.74 m.

But wait: it seems that Sauroposeidon is to Brachiosaurus brancai as Barosaurus is to Diplodocus — similar overall but more elongate.  And it turns out that Barosaurus has at least 16, maybe 17 cervicals (McIntosh 2005:45) compared with Diplodocus’s 15.  So maybe Sauroposeidon also added cervicals from the brachiosaur base-state — in fact, that would hardly be surprising given that Brachiosaurus brancai has so few cervicals for a long-neck: 13, compared with 15 in most diplodocids, 16 or 17 in Barosaurus, and 19 in Mamenchisaurus.  If you reconstruct Sauroposeidon with two more C8-like cervicals in the middle of the neck, that adds 2*125 = 250 cm, which would give us a total height of 17.74+2.5 = 20.24 m.

So I don’t think Tom Holtz’s estimate is completely unrealistic, even for the one Sauroposeidon specimen we have now — and remember that the chances of that individual being the biggest that species got are vanishingly small.

On the other hand, maybe Sauropodseidon’s neck was the only part of it that was elongated in comparison to Brachiosaurus brancai — maybe its forelimbs were no longer than those of its cousin, so that only the neck elongation contributed to greater height.  And maybe it had no additional cervicals, so its neck was “only” 1.28 times as long as that of Brachiosaurus brancai — 1.28*8.5 = 10.88 m, which is 2.38 m longer; so the total height would be 13.91+2.38 = 16.29 m (assuming the additional neck length was vertical).  And maybe the neck couldn’t get very close to vertical, so that the true height was lower still.

All of this just goes to show the perils of reconstructing an animal based only on a sequence of four cervicals.  (Reconstructing on the basis of a single partial mid-to-posterior dorsal, on the other hand, is a much more exact science.)

Finally: Matt’s reconstruction of Sauroposeidon is really rather conservative, and looks very much like a scaled-up vanilla brachiosaur.  Just to see how it looks, I’ve made a reconstruction of the putative (and very possible) elongated, attenuated version of Sauroposeidon, showing the legs and cervicals 28% longer than in B. brancai, and with two additional cervicals.  I made this by subjecting Greg Paul’s 1988 brachiosaur to all sorts of horrible and half-arsed distortions, so apologies to Greg.  But remember, folks: this is just as likely correct as Matt’s version!

A different view of Sauroposeidon, based on elongation of the cervicals and legs of Brachiosaurus brancai and the insertion of two additional cervicals. Heavily and carelessly modified from Paul (1988: fig. 1)

References

• Holtz, Thomas R., Jr., and Luis Rey.  2007.  Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages.  Random House, New York.  428 pages.
• Janensch, Werenr.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 27-93.
• McIntosh, John S.  2005.  The Genus Barosaurus Marsh (Sauropoda, Diplodocidae).  pp. 38-77 in Virginia Tidwell and Ken Carpenter (eds.), Thunder Lizards: the Sauropodomorph Dinosaurs.  Indiana University Press, Bloomington, Indiana.  495 pages.
• Paul, Gregory S.  1988.  The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs.  Hunteria 2 (3): 1-14.
• Wedel, Mathew J., and Richard L. Cifelli.  2005.  Sauroposeidon: Oklahoma’s Native Giant.  Oklahoma Geology Notes 65 (2): 40-57.
• Wedel, Mathew J., Richard L. Cifelli and R. Kent Sanders.  2000a.  Sauroposeidon proteles, a new sauropod from the Early Cretaceous of Oklahoma.  Journal of Vertebrate Paleontology 20(1): 109-114.
• Wedel, Mathew J., Richard L. Cifelli and R. Kent Sanders.  2000b.  Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon.  Acta Palaeontologica Polonica 45(4): 343-388.

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Blog posts, papers, and the brave new digital world: your thoughts are welcome

A new perspective, or the same old thing?

Brachiosaurus and friends from here (hat tip to Ville Sinkkonen).

In an e-mail with explicit permission to quote, our colleague Casey Holliday sent the following thoughts about our new paper and the subsequent ten days of related blogging:

I don’t know guys. I like your blogs, and your papers are fine. And I liked this paper. And I’m a fan.  But it looks to me that you blogged about far more data, in- or not in support of your paper than you actually presented in your paper. So,…wtf? The posts on Dinomorph far exceeded your (or any) published rebuke. Your explanation (and honorable erred parts) of the semicircular canal data also exceeded that actual published part too, with extra photos, description etc. (is that error going to be OA published too?) Also additional pix of necks (e.g., Nigersaurus), and not only from sauropods that would have
potentially bettered the original pub. So what’s fair? Why weren’t
these data also included in the publication? Maybe it’s not my business and was taken up in review…I don’t know. Frankly, none of this blog stuff really counts in the peer-reviewed world of “real” publications. Its not like this blogging and comments all count as Supplementary Data either. But also, I’m obviously here commenting on it, so also crossing into the fray…But who really cares about all this discussion? Its no different than the DML or any other noise in the internet world (or is it). Similar to what Paul Barrett was posting on Tet Zoo…what counts? Why take up arguments here, when they should (maybe?likely?) be taken up more formally and privately.

If you’re going to air all this additional data and unreviewed
opinion, then I think this discussion is important.

I think this phenomenon of the sauropod neck paper is really
interesting. We have 3 scientists that published a paper, and then, thanks to their current blogosphere cred, basically unleashed a hype not seen in this way previously that I can remember. Maybe that’s the interesting part? and kudos. But interestingly…we’re seeing this intersection of traditional publication (OA or not), blogosphere description, and perhaps, almost certainly, excellent self-promotion.

I’m still a fan. I think this paper is generally solid. But I’m
particularly interested in this phenomenon and hope this is a fair
place to raise it.

The comment field is open, and we SV-POW!sketeers are going to refrain from commenting for a couple of days to let the conversation develop unfettered.

We are genuinely curious to know what you think.

Sauropod neck posture: the world responds

[I wrote this in the cafe on the ground floor of the BBC's Millbank studios, where I spent much of yesterday, just before I headed off for Paddington and the train home.  I have lightly edited it since the original composition.]

It’s been a day spent doing publicity for the new SV-POW! paper on sauropod neck posture.

Two sauropod neck postures for the price of one: Diplodocus (foreground, low neck) and Brachiosaurus (background, high neck) at the Humboldt Museum fur Naturkunde, Berlin.

Overall, there’s been a little less interest than we were able to rustle up for Xenoposeidon, but we nevertheless got a live TV interview on Channel 4 News, plus radio interviews on BBC Radio 4’s Today programme, BBC Scotland, BBC Radio Solent (twice) and finally BBC Wales (which turned out to be my favourite).  In the mean time, Darren was being interviewed on BBC Radio 5 Live.  So a very BBC-centric day, with Channel 4 the only independent to take up the story.  (That contrasts with Xeno, when I seemed to spend the whole day doing interviews on the mobile phone for various independent radio stations as I was rushing between studios for the big boys.)

We got pretty good coverage in print, too.  I bought all the national dalies and went through looking for sauropod-neck news.  There was a good third-of-a-page story in Guardian (thanks to their fine science reporter Ian Sample who also did such a good job on Xeno), and smaller spots in the Times and Independent.  The Telegraph, oddly, in included a nice photo of the NHM Diplodocus with an inset of Mark Witton’s artwork, but accompanied it with no text other than a 38-word caption. Go figure.  There were brief mentions in the early editions of the Mirror and Sun, although they dropped out in later editions; I couldn’t find anything in the Mail, the Express or the Star — I think that’s everything.  There was a nice bonus in Metro, London’s free daily, which had half a page on the story including a nice big photo of the Berlin brachiosaur, with me by its elbow for scale.

As I write this, I’ve not been able to check on the net and see what the online coverage has been like, beyond a very quick informal scan this morning before I left the house I was staying at for the first radio interview.  I did find a story in the Times that was considerably more detailed that what made it into the print edition, so the same may have been true of other papers, too.  I’ll see what Google News digs up for me when I get home.  [Update: we're tracking Internet coverage on this page.]

A few themes emerged as the sequence of interviews progressed.  Most predictably, lots of interviewers wondered whether this meant that the NHM would have to remount its Diplodocus skeleton.  Not at all: the pose that it’s in is still a perfectly valid one, which it would have gone through in the transition between drinking and browsing poses; it’s just not what we think would have been the habitual pose.  Paul Barrett was quoted for the counter-view in several of the printed reports, and made that point (though usually it was reported in truncated form).  The BBC web-site’s coverage was unusually good in carefully reporting what we’d actually told everyone, that the mounted pose is one that would have been adopted from time to time, so hopefully no-one at the NHM will come away from thinking we were getting at them.

Another recurring theme was whether Seymour’s blood-pressure argument was good evidence that our proposed habitual posture is wrong.  I didn’t want to say too much about this, because our thoughts on the subject are still in the process of approaching their final form and are not ready to be published, but hopefully I was able to say enough to satisfy the interviewers and listeners without giving it all away.

Another point that I tried to make when given the opportunity is that we don’t see this paper as closing the debate and settling the issue of posture once and for all — as if that could ever happen for any palaeobiological controversy.  What we hope we’ve done is at least to reopen the debate and the end the unchallenged reign of the DinoMorph-compliant hangdog pose.  Needless to say, plenty of work remains to be done on the issue of neck posture, and there are now at least two published arguments in favour of each candidate posture. The time may be ripe for a review article.  For now, though, we confidently expect a published response from Kent “DinoMorph” Stevens, who we’ve discussed our work with at some length, and who has had a preprint for a few weeks now so that he could get working on it!  Ah, the cut and thrust of debate — bring it on!

Update (later the same evening)

I have finally managed to make an MP3 of the last interview — the second one with BBC Radio Solent, with Sasha Twining who was standing in on the Steve Harris Show.

And a plea for help: although the Channel 4 News interview is still available on Channel 4’s own site, I know it won’t last for long — probably no more than a week — so if anyone is able to make an MPEG, AVI, FLV or similar of these, please please do, and send it my way.  Thanks!