Monthly Archives: September 2009

What I did on my holidays

I made brachiosaur sand-sculptures.

Brachiosaurid in sleep hypothetical posture, left anteroventrolateral view. Juvenile Homo sapiens (Daniel Taylor) for scale.

Brachiosaurid in hypothetical sleep posture, left anteroventrolateral view. Juvenile Homo sapiens (Daniel Taylor) for scale.

(And yes, it’s that Daniel Taylor, the author of Taylor 2005 — a copy of which apparently hangs on the wall of the Padian Lab.)

But wait!  Is the brachiosaur truly asleep, as it seems, or is it actually the victim of a mighty hunter?

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Brachiosaurid in hypothetical death pose, left posteroventrolateral view. Mighty hunter (Michael P. Taylor) for scale. Note bemused bystander in middle distance.

No, it turns out it was just asleep after all; and I joined it.

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Brachiosaurid in hypothetical sleep pose after all, left posteroventrolateral view. Brachiosaur's new best friend for scale.

… and finally: your obligatory sauropod-vertebra shot:

Obligatory sauropod vert shot: the Copehagen copy of Mamenchisaurus hochuanensis

Cast of Mamenchisaurus hochuanensis holotype CCG V 20401, in right lateral view. Need I draw your attention to the truly absurd neck? This cast is owned by the Homogea Museum in Trzic, Slovenia, and was on loan in the car-park of the Geological Museum in Copenhagen.

References

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).

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:

Wilson2006-fig1-human-body-torso-and-+23pc-480px

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.

HMN-SII-C8-posterodorsal-480px

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 https://svpow.wordpress.com/comments/feed/

References


Not a brachiosaur, but too good to ignore

I am not usually one for field photographs — I am not a geologist, and one bit of rock looks the same as any other to me.  I suffer from a debilitating condition that renders me unable to see fossils in the ground, and am reliant on other people to dig ’em out, clean ’em up and reposit them before I’m able to make ’em into science.

But this … this blew me away:

Spinophorosaurus nigerensis, holotype skeleton GCP-CV-4229 in situ during excavation in the region of Aderbissinat, Thirozerine Dept., Agadez Region, Republic of Niger (Remes et al. 2009:fig. 1)

Spinophorosaurus nigerensis, holotype skeleton GCP-CV-4229 in situ during excavation in the region of Aderbissinat, Thirozerine Dept., Agadez Region, Republic of Niger. (Remes et al. 2009:fig. 1)

It’s the astonishingly complete and well-preserved type specimen of a new basal sauropod, Spinophorosaurus, that came out today in a paper lead-authored by Kristian Remes, previously best known for his work on Tendaguru diplodocines (Remes 2006, 2007, 2009) and for his work on the awesome remounting of the Berlin brachiosaur.

I’m not going to write the new taxon up in detail, but here are the figures of its vertebrae:

Spinophorosaurus nigerensis GCP-CV-4229 (holotype; C, E-I) and NMB-1698-R (paratype; A, B, D). (A, B)— Mid-cervical vertebra in left lateral (A) and ventral (B) views. (C)— Last dorsal and first sacral vertebrae in left lateral view. (D)— Clavicle in cranial view. (E, F)— Proximal caudal neural spines in lateral (E) and cranial (F) views. (G)— Mid-caudal vertebra in lateral view. (H, I)— Distal caudal vertebrae in left lateral (H) and ventral (I) views. Abbreviations: pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; spol, spinopostzygapophyseal lamina. Scale bars = 10 cm. (Remes et al. 2009:fig. 3)

Spinophorosaurus nigerensis GCP-CV-4229 (holotype; C, E-I) and NMB-1698-R (paratype; A, B, D). (A, B)— Mid-cervical vertebra in left lateral (A) and ventral (B) views. (C)— Last dorsal and first sacral vertebrae in left lateral view. (D)— Clavicle in cranial view. (E, F)— Proximal caudal neural spines in lateral (E) and cranial (F) views. (G)— Mid-caudal vertebra in lateral view. (H, I)— Distal caudal vertebrae in left lateral (H) and ventral (I) views. Abbreviations: pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; spol, spinopostzygapophyseal lamina. Scale bars = 10 cm. (Remes et al. 2009:fig. 3)

(It’s a shame they didn’t figure more of it, especially as the paper was in PLoS ONE which has no length limits and absolutely stellar figure production, but it would be churlish to complain.)

Finally, here is the skeletal reconstruction: as you can see, it’s a decent size for such a basal sauropod.  Note the freaky all-osteoderm tail-club.

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Skeletal reconstruction of Spinophorosaurus nigerensis. Dimensions are based on GCP-CV-4229/NMB-1699-R, elements that are not represented are shaded. Scale bar = 1 m. (Remes et al. 2009:fig. 5)

A truly amazing specimen — I am looking forward to sitting down with the paper and giving it the attention it deserves.

Best of all, you can also sit down with the paper — because, like all PLoS articles, it is freely available to anyone who wants it.  Follow the link below and enjoy!  (Also available from the linked article: super-high resolution images of the figures.)

Timely Discussion From an E-mail Exchange Today

Matt Wedel: That animal is just flat badass.

Zach Miller: It has a goddamn thagomizer!!!

References

Remes, Kristian.  2006.  Revision of the Tendaguru sauropod dinosaur Tornieria africana (Fraas) and its relevance for sauropod paleobiogeography.  Journal of Vertebrate Paleontology 26(3):651-669.
Remes, Kristian.  2007.  A second Gondwanan diplodocoid dinosaur from the Upper Jurassic Tendaguru Beds of Tanzania, East Africa. Paleontology 50(3):653-667.
Remes, Kristian.  2009.  Taxonomy of Late Jurassic diplodocid sauropods from Tendaguru (Tanzania).  Fossil Record 12 (1): 23-46. doi: 10.1002/mmng.200800008
Remes, Kristian, Francisco Ortega, Ignacio Fierro, Ulrich Joger, Ralf Kosma, Jose Manuel Marin Ferrer, for the Project PALDES, for the Niger Project SNHM, Oumarou Amadou Ide, and Abdoulaye Maga.  2009.  A new basal sauropod dinosaur from the Middle Jurassic of Niger and the early evolution of Sauropoda.  PLoS ONE 4(9):e6924. doi:10.1371/journal.pone.0006924

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

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

“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:

Taylor-SVP-Brachiosaurus-fig7-reconstruction-R3-480px

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 a 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.

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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).

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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

(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 :-))