Here’s one of those text-light photo posts that we always aspire to but almost never achieve. In the spring of 2008 I flew to Utah to do some filming for the History Channel series “Evolve”, in particular the episode on size, which aired later that year. I always intended to post some pix from that trip once the show was done and out, and I’m just now getting around to it…a bit belatedly.

Utah 2008 01 mountains from museum door

Here’s the view out the back door of the BYU Earth Sciences Museum in Provo, Utah. Not bad–the mountains actually made me drag my eyes away from sauropod vertebrae for a few seconds here and there.

Utah 2008 02 Brooks driving forklift

Here’s the view in other direction, with Brooks  Britt using a forklift to retrieve the big Supersaurus cervical.

Utah 2008 03 Supes and giraffe

And here is said cervical, with a mid-cervical of a giraffe for scale. You may remember the big cervical from this post (and if you click that link, notice how much nicer the new collections area is than the off-site barn where I first encountered the Cervical of Doom). Sauropods FTW!

Utah 2008 04 taping down Diplo vert

While the film crew were shooting Brooks and picking up some establishing shots, I was ransacking the collections for pretty vertebrae. We took our treasures up to the University of Utah med center in Salt Lake for CT scanning. Here Kent Sanders is helping me tape down a Diplodocus cervical.

Utah 2008 05 Kent in reading room

And here’s Kent in the CT reading room playing with the data. Like old times–I spent most of my Saturdays in 1998 and 1999 scanning verts with Kent when he was at the University of Oklahoma Health Sciences Center.

Utah 2008 06 NAMAL main drag

The next morning we went to the North American Museum of Ancient Life in Lehi. Here’s a view down the main drag, with the mounted Supersaurus on the left, mounted Brachiosaurus in the center, and original Supersaurus sacrum (on loan from BYU) in the case on the right.

Utah 2008 07 Matt in lift

The highlight of my day trip year.

I was back at BYU just a few months ago shooting another documentary, but that story will have to wait for the dramatically appropriate moment. Stay tuned!

MYDD!

April 23, 2009

mydd-480

Here's your new t-shirt/sticker/desktop wallpaper. Tell the world.

OMG! WTF? Was I asleep? Had I slept? Did I miss something? Does paleontological training destroy the part of the brain that knows how to use a freakin’ tape measure? Are paleontologists incapable of imagining that others might want to make meaningful comparisons with their taxa? Has phylotardation reached the point where people think the character taxon matrix contains all relevant information? Somebody throw me a bone here–so I can measure the damn thing!

Way back when, I discussed the question, “How big was Futalognkosaurus?”, which at the time had only been described in one fairly brief publication (Calvo et al. 2007). Nothing wrong with that, lots of dinos get described that way, and little damage is done to science as long as the follow-up descriptions do eventually appear (sometimes they don’t). But Calvo et al. (2008) put out a longer description of Futalognkosaurus the very next year, for which they are to be commended.

futalognkosaurus-measurement

Thar she blows, Cap'n--an actual measurement! (Calvo et al. 2008:fig. 15)

It’s not all roses, though. You’ll recall that one of the problems with the original paper was that it didn’t include many measurements, and the scale bars in the photographs and the skeletal reconstruction disagreed wildly. I was hoping that Calvo et al. (2008) would include a table of measurements; actual measurements of one of the most complete large titanosaurs would be  invaluable for those of us who are interested in body proportions, neck elongation, mass estimation, and all that good stuff. But sadly the second paper contains no table and almost no measurements; again, it’s all done with scale bars, and since many of the figures appear to be identical to those from the first paper, the precision of the scale bars is hard to determine but possibly low.

It blows my damn mind that a century ago people like Charles Whitney Gilmore and John Bell Hatcher could measure a dinosaur to within an inch of its life, and publish all of those measurements in their descriptions, and lots of folks did this and it was just part of being a competent scientist and doing your damn job. And here we are in the 21st century with CT machines, laser surface scanners, ion reflux pronabulators and the like, and using a narf-blappin’ TAPE MEASURE is apparently a lost art. This vast inexplicable deficiency is not limited to any one working group or country or continent or language, either. Nigersaurus is known from multiple specimens and has been the subject of three separate peer-reviewed papers spread out over a friggin’ decade, but good luck trying to figure out the dimensions of the individual bones.

Dammit, people! Tape measures. Tables of measurements. These are dead simple, cost almost nothing, and add measurably to the usefulness* of descriptive work.

* as in citeability, which none of us can afford to ignore

From now on, when people describe sauropods and don’t publish any measurements, said omissions will be trumpeted here and the perpetrators will be savagely mocked.

You’ve been warned.

Disclaimer

With so many offenders, it’s a bit unfair to single out Calvo et al. for scorn. I am glad that they provided a longer description, which is more than I can say for many. And I have to give them mad props because both Futalognkosaurus papers are freely available at Proyecto Dino. But someone had to get the Wonka ticket in the MYDD! lottery, and they won because I’d been so looking forward to the follow-up paper so that I could answer the original question. Someone with a tape measure and a plane ticket to Argentina (or Beijing, or Chicago) could do a crapload of useful science. Sheesh!

References

I had a new paper come out today. Unofficial supplementary info here, PDF here. I would have had all this ready to go sooner, but the paper came out sooner than I expected. In fact, I didn’t even know that it had been published until Andy Farke (aka the Open Source Paleontologist) wrote me for a PDF. Turnabout’s fair play, I suppose, because last year I congratulated Stuart Sumida on his Gerobatrachus paper before he knew it was out. I guess letting the authors find out through the grapevine that their stuff has been published is part of the “value added” that commercial journals provide. ;-)

Anyway, I’m happy the paper is out, finally. It’s the third chapter of my dissertation, but with teaching and traveling to Spain and such I didn’t get it submitted until last January. I had to forcibly bite my tongue during the Aerosteon saga last fall, when such a big deal was made about the absence of pneumatic hiatuses in non-avian dinosaurs. This despite the facts that there are several good reasons to expect pneumatic hiatuses to be rare, and that pneumatic hiatuses are not the Rosetta Stone or magic bullet for air sacs in saurischian dinosaurs. They’re more like the cinderblock that broke the camel’s back, given all the other evidence for air sacs.

In fact, the structure of the new paper is built around the idea that there are several tiers of evidence for bird-like air sacs in saurischians. Those tiers are:

  1. The presence of postcranial pneumaticity at all. Some of the first authors to get interested in the implications of pneumaticity for dinosaurs argued that pneumaticity probably implies an air sac system, and left it at that. Later workers have tended to denigrate this argument as overly simplistic–just because some of the postcranial skeleton is pneumatic does not mean that the animal’s air sac system was necessarily like that of birds–but it’s not actually a bad argument. We can imagine lots of ways to get air into the postcranial skeleton, but for tetrapods the only system that we have any evidence for is diverticula of a lung/air sac system like we see in birds.
  2. The distribution of pneumaticity in the skeletons of most saurischians and pterosaurs is  diagnostic for specific air sacs, namely the cervical, clavicular, and abdominal air sacs that we see in birds. This is what Pat O’Connor and Leon Claessens established so firmly with their work on mapping parts of the respiratory system to skeletal domains in birds.
  3. The evolutionary patterns of pneumatization in sauropods and theropods parallel the development of pneumatization during ontogeny in birds. Or, more economically, ontogeny recapitulates phylogeny in this system. This is more evidence that the observed patterns of pneumaticity in the skeletons of birds and non-avian saurischians are produced by the same underlying process of diverticula developing from different air sacs in a highly conserved order–even if we don’t know why things evolved, and continue to develop, in the order that they do. And it’s better evidence, because it accounts for more observations (points 1 and 2 can be established from single specimens) and ties postcranial pneumaticity in all saurischians, living and extinct, into a more coherent picture.
  4. Pneumatic hiatuses are more evidence that the postcranial skeleton is pneumatized by diverticula from more than one part of the respiratory system. Not the only evidence–we already suspect this quite strongly based on points 2 and 3–but more evidence. It is possible that the diverticula of extinct animals behaved differently than those of all extant birds, and diverticula from a single source could conceivably pneumatize the whole vertebral column. Possible. Conceivably. How likely? Dunno–our n on this is either 1 (if you count all living birds as a batch) or several hundred (if you count each of the species that Pat O’Connor has dissected and injected). Pneumatic hiatuses offer another level of evidence, because they can potentially show that the patterns of pneumaticity in fossil taxa are inconsistent with pneumatization from a single point. That’s how they work in chickens, and that’s how they may work in non-avian dinosaurs, as long as diverticula don’t leapfrog over  some bones without leaving any traces, or at least don’t do that very often.

For the record, I don’t think that pneumatic hiatuses are stronger evidence than point 3; if I was ranking the tiers based on importance I would put 3 at the top. Pneumatic hiatuses ended up being last in the paper because 1-3 were basically review material, and it made sense to group them together before the big  bolus of description.

[UPDATE the next day: also, I just realized that those 4 are not the same as I used in the paper! In the paper I left out 1, advanced 2 and 3, and added a different number 3, which is pneumatization of the pelvic girdle and hindlimb. I tend to forget about that one because the evidence in sauropods is underwhelming so far. And arguably this is just another aspect of 2 (above), or if you like you can think of 5 tiers. They say consistency is the hobgoblin of small minds!]

The importance of pneumatic hiatuses remains to be seen; there might not be enough of them to tell us very much, or we might find that leapfrogging diverticula exist and are common (we’d then need a way to sort hiatuses caused by multiple sources of diverticula from those caused by leapfrogging diverticula). But they’re important to me, for a couple of reasons.

First, they’re probably one of the two or three best ideas that I’ve had in my life. When I realized that pneumatic hiatuses could potentially indicate pneumatization from multiple sources it really was like a light going on in my head. I walked around seeing stars all week.

I got the idea from this figure, from King (1957):

king_57_figs1-2-480On the left King has drawn the vertebral columns of several chickens, and shaded in the pneumatic regions. Blocks of pneumatic verts separated by apneumatic gaps represent pneumatization from different sets of diverticula. I remember very vividly sitting in the Padian lab reading this paper and thinking, “if we found one of those in a dinosaur it would be the money.” Then I suddenly sat up straight, then stood up, then paced around the room a few times to burn off the discovery energy. I had a very profound need to tell someone. I don’t remember who I told, but it was probably Mike.

The other reason that pneumatic hiatuses are important to me: they are now one of those cool little cases that show that paleontology can be a predictive science. If you want to test a hypothesis in the experimental sciences you manipulate the conditions and see what happens. Historical sciences don’t usually give you that option. But you can play What If? As in, “If hypothesis A is true then we ought to see such-and-such evidence.” In 2003, I predicted that if sauropods had abdominal air sacs we ought to see pneumatic hiatuses once in a while. Finding the evidence that validated the prediction was almost as much of a rush as having the idea in the first place.

haplo-skeleton-with-me-for-scale-480The owner of Sauropod Pneumatic Hiatus #1 is Haplocanthosaurus CM 879, which is a cool animal but fairly pathetic as sauropods go. In my dissertation/job talks I would show the above picture and joke that I could probably beat up that animal on a good day. I found out about the pneumatic hiatus by accident, when I was poring over Hatcher (1903). In one of the figures near the end of the paper, Hatcher shows the centra of the fourth and fifth sacral vertebrae. I noticed that sacral 4 had a pneumatic chamber of some sort but sacral 5 did not. Then a few minutes later I had gotten to the plates at the back of the paper, and saw what looked like a pneumatic chamber on the first caudal. Somewhere in the dank, beer-flooded grottoes of my skull, the neuron fired.

haplo-verts-v3-480This is the figure I put together, using images from Hatcher (1903), for a Jurassic Foundation grant to go see the material in the Carnegie Museum in 2005. It worked; they came through with $1500 for that trip and a week at BYU the same fall (to my immense shame, although the Jurassic Foundation is credited for funding on the first page, I see that I forgot to thank them in the acknowledgments. Belatedly: thanks, you guys rock, I suck). The pneumatic cavities are labeled as foramina because that’s what they look like in the drawing, and not having seen them I didn’t know any better. In fact they are fossae, but they are deep, invasive fossae and their morphology is not consistent with anything other than pneumatic invasion. (Pneumatic invasion!? Flee for your lives!!) See the paper for all the excruciating details. Note that the sacrals have unfused neurocentral sutures, so the animal was not fully mature when it died (there is probably a whole post ahead just on the neurocentral weirdness in this animal).

So that’s the story, for now at least. There are more pneumatic hiatuses coming, but those papers are still in the pipe so I can say no more for now. I’m sure when they come out some alert blogger will notice and e-mail me for a PDF, and then you’ll get the news here.

The moral of the story is that you can make real progress by reading lots of old, obscure stuff. Support–and abuse–your local academic library!

References

I’ve mentioned my ardent love for the Big Bone Room at BYU before. One of the cool things that you can find there and nowhere else is BYU 9047, the holotype of Cathetosaurus lewisi, referred in 1996 to Camarasaurus. In referring to the beast as Cathetosaurus in the title I’m not casting aspersions on that referral. I’m just wondering. Other ‘camarasaurids’ have been promised from time to time, but so far none have panned out. So for now it’s just Camarasaurus….but. With all the species floating around out there, Camarasaurus is getting to be a pretty big tent. I wonder if this most common of American dinosaurs will continue to be a single genus forever, or if new discoveries and reanalysis of old material will break it up into several.

Anywho, I spent some quality time with BYU 9047 when I was in Utah in 2006, on my last or next-to-last dissertation data-gathering trip. As always, I was keeping an eye out for pneumaticity and especially for pneumatic hiatuses. And I  got pretty darn excited when I took this photo of the C. lewisi sacrum in right lateral view.

c-lewisi-sacrum-480

As you can see, it has a foramen on the last centrum, but not on any of the preceding centra. Pneumatic hiatus city–lookout Nature, here I come!

I approached with shuffling steps and ‘bated breath. The acolyte of an eldritch cult, I knelt in the dust before the object of reverence, ducked my head beneath the vasty sweep of its sacral yoke, and dared to poke a finger into the holy of holies. Inside it was….smooth.

Like, freakishly smooth. And perfectly tubular.

In Bill, the Galactic Hero: On the Planet of Bottled Brains, Harry Harrison wrote that “Nature cares nothing for equilateralism, and indeed has a hard time drawing a straight line” (oh yeah, I just went there). What is true of straight lines is true in spades of perfect cylinders, especially in the asymmetric osteological playgrounds of sauropod vertebrae.  Like cold fusion and cheap mortgages, the foramen was Too Good To Be True.

c-lewisi-second-pseudoforamen-480

At some point someone must have planned to mount BYU 9047, but AFAIK it was never actually put up. Must have gotten pretty close, though, because they went to the trouble of drilling a long core out of the sacrum, presumably to house a steel support rod. And the coring wasn’t perfect, either–the borehole nicked the right wall of the last centrum, producing the pseudoforamen that got me all hot and bothered for about 180 seconds. The above photo shows the entrance to the tunnel at the front end of the sacrum. You can look down this hole and see light shining in from the pseudoforamen in the last sacral (the hole does not extend all the way out the posterior end of the sacrum). Somehow I had completely missed it while wheeling the sacrum out, sketching, and taking the first round of photos. So much for the vaunted powers of observation.

You know what this is like? Everyone’s first dig, where they’re running to the dig leader every five minutes with a piece of “bone” that is actually leverite (as in, “leave ‘er right there”). This was my dry well, my leverite mine, my fool’s gold.

Real gold came along later, first a trickle, then a flood. But those are tales for other campfires. Stay tuned…

P.S. Check out how the neural spines all lean together so that they cover much less ground, antero-posteriorly, than the centra. I don’t think it’s distortion–the whole sacrum is in pretty good shape, pretty symmetrical, no obvious crushing or shearing. ‘Sup with that?

Pneumatic dorsal vertebrae of Aerosteon (Sereno et al. 2008:fig 7)

Big news this week: Sereno et al. (2008) described a new theropod, aptly named Aerosteon (literally, “air bone”), with pneumaticity out the wazoo: all through the vertebral column, even into the distal tail; in the cervical and dorsal ribs; in the gastralia; in the furcula; and in the ilium. This is huge news, and it’s free to the world at PLoS ONE. Pneumatic vertebrae and ribs are the norm in theropods and most sauropods (hence our interest here), but the axial elements of Aerosteon are extremely pneumatic. A pneumatic furcula was reported in the dromaeosaur Buitreraptor (Makovicky et al. 2005), but Aerosteon appears to be a basal tetanuran so it pushes furcular pneumaticity a good distance down the tree. Most exciting are the pneumatic ilium and gastralia. Ilial pneumaticity has been suspected in some sauropods and non-avian theropods but the evidence has been lacking until now; either the ilial chambers could not be traced to pneumatic foramina, or the suspected pneumatic foramina could not be shown to lead to internal cavities. Pneumatic gastralia are really wacky–according to the paper, it is the first discovery of pneumatized postcranial dermal bone, and I certainly don’t know of any other examples.

Why is this important? In extant birds, the furcula is only pneumatized by diverticula of the interclavicular air sac, and the ilia are only pneumatized by the abdominal air sacs, so the presence of big pneumatic foramina leading to big internal chambers in both the furcula and ilia of Aerosteon is evidence not just for bird-like air sacs, but specifically air sacs from both the cranial and caudal groups within the thorax that are responsible for the flow-through lung ventilation of birds. It’s pretty dynamite stuff.

Right?

Right?

We-ell . . . There is no question that the fossil material is pretty stunning and shows all the morphological features that Sereno et al. claim (and even some that they don’t–stay tuned for Part 2). But there are parts of the paper that I disagree with, and to understand why, I have to tell you a little about recent research on pneumaticity in sauropods and theropods. In this post and the next I’ll be discussing papers by Pat O’Connor and Leon Claessens, as well as my own; all of these are freely available at the links just provided. So, please, if you have a beef with anything I say below, go read all the relevant literature for yourself, weigh the evidence, and make up your own mind.

First, a brief sketch of what we’ve been up to. Except for the occasional weirdo (surveyed on the third page here), the only extant tetrapods with postcranial pneumaticity are birds. In birds, postcranial pneumaticity is the skeletal footprint of the lung/air sac system. So if we find postcranial pneumaticity in dinosaurs–say, sauropods, or Aerosteon–we can use the ‘rules’ from birds to make inferences about the morphology of the respiratory system. We can’t tell which way the air was blowing in the lungs, but we can tell the minimum extent of the pneumatic diverticula, and we can make some inferences about lung structure. All of the logic of this is really nicely and concisely laid out in O’Connor and Claessens (2005), which is only three pages of text, so if you want to know more, just go read it.

The hypothesis that sauropods and theropods had air sacs like that of birds has been opposed in a couple of ways: pneumaticity doesn’t tell us anything, and vertebral pneumaticity only indicates cervical air sacs. Neither of these counterarguments has gotten much traction, probably because they’re so easily falsified. Let’s have a look.

Historical Misconception #1: Pneumaticity Is Completely Uninformative

“Without integrating functional data into the study, the most that can be inferred from post-cranial pneumaticity in extinct animals is that, as pointed out by Owen (1856), the pneumatized bones received parts of the lung in the living animal… Because pneumaticity has no known functional role in ventilation or thermoregulation or metabolic rates, its usefulness as a hard-part correlate for lung structure and metabolism is, unfortunately, questionable.” (Farmer 2006, pp. 91-92)

Farmer does not distinguish here between inferences based on the presence of postcranial pneumaticity and inferences based on the distribution of postcranial pneumaticity. If all we know about a bone is that it is pneumatic, then she is correct in stating that the most we can conclude is that it was connected to the respiratory system in some way. (The thermoregulatory function of pneumaticity discussed by Seeley [1870] has been demonstrated for cranial pneumaticity [Warncke and Stork 1977] but not for postcranial pneumaticity [Witmer 1997, O’Connor 2006]). But the inference of cervical and abdominal air sacs in non-avian dinosaurs does not depend simply on the existence of postcranial pneumaticity. Rather, these inferences are based on patterns of postcranial pneumaticity that are diagnostic for specific air sacs.

Verdict: Fail.

Historical Misconception #2: Vertebral Pneumaticity Only Comes From Cervical Air Sacs

“Pneumatization of the vertebrae and ribs is invariably accomplished by diverticuli [sic] of the cervical air sacs (McLelland 1989a), which are located outside the trunk and contribute little, if anything, to the respiratory air flow (Scheid and Piiper 1989). Presence of pneumatized vertebrae in non-avian dinosaurs therefore only speaks of the possible presence of such nonrespiratory diverticuli [sic], and cannot be regarded as indicative of an extensive, avian-style abdominal air-sac system.” (Ruben et al. 2003, p. 153)

This remarkable statement is repeated pretty much verbatim by Chinsamy and Hillenius (2004) and Hillenius and Ruben (2004). What’s remarkable about it is that is so thoroughly inaccurate. People have known for more than 100 years that the posterior parts of the vertebral column of birds are pneumatized by diverticula of the abdominal air sacs, and said as much in many papers–for example, Muller (1908), Cover (1953), King (1966, 1975), Duncker (1971), Hogg (1984a, b), and Bezuidenhout et al. (1999). Still, if McLelland said that the vertebrae and ribs are “invariably” pneumatized by diverticula of the cervical air sacs, it’s not their bad, right?

Okay, first, McLelland (1989) is a review paper and presents no new data (this will become really important later on, when we get back to Aerosteon). Second, here’s what McLelland actually said:

“What can be stated with certainty is that in birds generally the cervical air sac aerates the cervical and thoracic vertebrae (Fig. 5. 22) and the vertebral ribs; the clavicular air sac aerates the sternum, sternal ribs, pectoral girdle and humerus (Fig. 5. 23); and the abdominal air sac aerates the synsacrum, pelvis and femur.” (pp. 271-272)

By listing the synsacrum and pelvis separately, McLelland clearly meant that the synsacral vertebrae are pneumatized by the abdominal air sac, and this is confirmed by the sources he cited elsewhere: Hogg (1984a, b).

So Ruben et al. (2003)–and those who recycled that text–were relying not on any of their own research, or any primary research at all, but on a single review paper that actually says exactly the opposite of what they claim it does, based on other primary research papers (those by Hogg) that themselves say the same (opposite) thing.

Verdict: EPIC FAIL.

The Brave New Post-2005 World

He said, she said, yadda yadda. There are lots of inaccuracies in the literature, and it’s not like birds are extrasolar planets. If we want to know what is going on inside them, we can just look. That’s what O’Connor and Claessens (2005) did, by injecting and dissecting 200+ birds representing 19 avian orders. Know what they found? The cervical diverticula do not EVER go farther down the vertebral column than the middle of the thorax. NEVER EVER. So if you find pneumatic vertebrae in the posterior dorsals, sacrum, or tail, it’s pretty likely that they were pneumatized by diverticula of the abdominal air sacs.

I say “pretty likely” because it’s always possible that dinosaurian diverticula worked differently, and that the air that got into the posterior part of the vertebral column actually came from the cervical air sacs, or the lungs directly, or from arse gills, or possibly magic rocks. We can imagine lots of ways for air to get into the back half of the vertebral column, but the only one that we’ve ever seen work in a tetrapod* is diverticula of the abdominal air sacs. Dinosaurs may have worked differently, and had wacky cervical diverticula or arse gills or whatever. But those are not the obvious choices, and we don’t have any evidence for them; all the available evidence points to abdominal air sacs.

*Some osteoglossomorph fishes pneumatize the vertebral column from the swimbladder–strange but true!

So, great. The old confusion has been swept away by a blood-dimmed tide of bird carcasses and good science. Pneumatization of the posterior vertebral column implies abdominal air sacs. The combination of pneumaticity in the neck, trunk, sacrum, and even tail of many theropods and sauropods shows that both cervical and abdominal air sacs were present (as in Apatosaurus, above), which means air sacs both anterior and posterior to the lungs, which means that most (maybe all) saurischians had at least some of the gear they would need for flow-through breathing like that of birds (O’Connor and Claessens 2005, O’Connor 2006, Wedel 2007).

And yea, verily, anatomical accuracy and scientific clarity reigned throughout the land . . .

. . . until now.

TO BE CONTINUED.

References

Considering how much time I’ve spent playing around mounted sauropod skeletons, I cannot believe it never occurred to me to do this:

This is the mounted Brachiosaurus skeleton in the United terminal at Chicago O’Hare. It used to be in the main hall of the Field Museum, but they booted it out to make room for some vulgar overstudied theropod (ht to Paul Barrett for that supremely useful phrase). The indoor version was moved to O’Hare, and they made a second, weatherproof cast which is now mounted outside the northwest corner of the Field Museum.

We spend so much time looking at drawings or photos of bones or entire skeletons in lateral view. It is nice to get a kick-in-the-brainpan reminder that sauropods existed in 3D. And it is always rewarding to see something familiar from a new angle.

Lots of good stuff here. Anterior is toward the bottom of the photo; you can see the scapulae arcing back over the anterior ribs, the coracoids sternal plates converging and disappearing out of the bottom of the image, and the humeri angling out to either side. The thing does not really sprawl as much as it might seem from this picture–keep in mind that there is a lot of vertical foreshortening going on. Speaking of, you can see the neck zooming off into space at the bottom center. At the top of the image you can see the sacrum and the preacetabular blades of the ilia flaring out to either side.

The seven posterior dorsals are cast from the holotype of Brachiosaurus altithorax, as are the sacrum, the first couple of caudals, one humerus, one ilium, and one femur. The rest of the mounted skeleton is either mirrored from available elements or subbed in from Brachiosaurus brancai.

I’m posting this because (a) it’s a really cool photo, and (b) it illustrates something peculiar, which is that the dorsal vertebrae of Brachiosaurus are oddly–one might even say freakishly–slender. This is true of both the B. altithorax and B. brancai dorsals. I was recently standing under yet another copy of this skeleton and someone I was with asked if those were even the right vertebrae, because even to non-specialists they look too small.

I WILL have more to say about that one of these days, but for now just dig the austere beauty.

Photo (c) Tristan Savatier – www.loupiote.com – Used by permission.

Othniel Charles Marsh, who was always careful to base all of his hundreds of new taxa on the best, most diagnostic material available (Alert: Sarcasm detected!), named Pleurocoelus nanus based on a handful of junenile sauropod vertebrae centra from the Arundel clays of Maryland (Marsh 1888). Here’s the dorsal. As you can see, it is loaded with unique features like big pneumatic fossae, which at the time were only known in all other sauropods (we have since found some with less pneumaticity in the dorsals, or none at all), and the absence of a neural arch, which is shared with any sufficiently immature vertebrate.

Here’s a cervical, which was not figured by Marsh (1888). These views are after Lull (1911:pl. 15), as modified by Wedel (2003:fig. 10); pfs stands for pneumatic fossa.

And a sacral, again from Marsh (1888).

To be fair, the criteria for “diagnosably distinct” in the 1880s were different than they are now. Wilson and Upchurch (2003) addressed this in their revision of Titanosaurus: as we find and describe more fossil taxa, characters that originally diagnosed small taxonomic groups (like species and genera) are often found to be more broadly distributed. For example, the original diagnosis of Titanosaurus ended up applying to almost everybody in the clade Titanosauria. It is conceivable that in the future we will discover an entire clade of xenoposeidonids with identical weird dorsals and all of their diagnostic characters elsewhere in the skeleton, and the longish list of weird characters that diagnose Xenoposeidon will turn out to be present in all xenoposeidonids. There’s not much we can do about this, other than to keep working, revisit old diagnoses from time to time and see if they need updating, and generally be nice about it.

I am cool with not being nice about Pleurocoelus, though, because of what happened later. But that’s a story for another post.

Note: In 2005 Carpenter and Tidwell sunk Pleurocoelus into Astrodon, which is totally cool by me, and which makes Astrodon the correct name for the poorly-known Arundel titanosauriform, just like Apatosaurus is the correct name for the Morrison diplodocine that is built like a brick outhouse. But in this series I am Telling a Tale about the Days of Yore, past tense, pre-2005, so I’m using Pleurocoelus.

References