In my 2009 brachiosaur paper, I gave rather short shrift to the sacrum of Brachiosaurus — in part because there is no really good sacrum of Giraffatitan to compare it to. Also my own photos of the sacrum, taken back before I figured out how to photograph big bones, are all pretty terrible.

Happily, Phil Mannion took some much better photos and gave us permission to use them. So I prepared this multi-view figure, which we plan to use in a forthcoming paper about another sacrum:

Brachiosaurus altithorax FMNH P25107 sacrum, from photos by Phil Mannion

At the bottom, we have the sacrum in left lateral view; above it, in dorsal view. To the left is the anterior view (with dorsal to the right) and the right is the posterior view (with dorsal to the left). The idea of this composition is that you could print the image out, and cut and fold it into a cuboid.  (In fact I might just do that.)

As usual with these things, click through for the much more impressive full-resolution version (3809 x 3157 pixels).

In the previous post in this series I looked at the some of the easily available raw data on neural spine bifurcation in Morrison sauropods. In this post I’ll explain how serial variation–that is, variation along the vertebral column in one individual–is relevant to the inferences made in the new paper by Woodruff and Fowler (2012). But first, a digression, the relevance of which will quickly become clear.

How do you recognize an adult sauropod?

There are only a handful of criteria that have been used to infer adulthood in sauropods. In rough order from least to most accurate–so far as I can tell!–they are:

  1. sheer size
  2. fusion of the neural arches to the centra
  3. fusion of the sacral vertebrae to each other, and fusion of the sacral ribs to form the sacricostal yoke
  4. fusion of the cervical ribs to the centra and neural arches
  5. fusion of the scapula to the coracoid
  6. presence of an external fundamental system in the cortices of the long bones

I’ll discuss each one in turn. (Please let me know in the comments if I’ve missed any.)

These vertebrae are rather dissimilar in size and form. Click through to find out why.

1. Size alone is pretty useless. The mounted Giraffatitan is a pretty damn big animal by anyone’s standards, but it’s demonstrably smaller than another individual from Tendaguru, and the scap-coracoid joint is unfused. On the other hand, there are things like dicraeosaurids that apparently matured at relatively small sizes (for sauropods). There is definitely some individual or low-level taxonomic variation. Marsh’s “Brontosaurusexcelsus holotype YPM 1980 is an adult but about the same size as the subadult Apatosaurus ajax holotype YPM 1860 that it ended up being generically synonymised with (see the sacra of the two taxa compared below). The giant Oklahoma Apatosaurus is about 1.4 times the size of A. louisae CM 3018 in most linear measures, but some of the neural arches and cervical ribs are unfused (the vertebra in the linked post is only a quarter bigger than the corresponding element in CM 3018, but there are other elements of the Oklahoma Apatosaurus that are proportionally even larger). On the flip side, I have seen some comparatively tiny Diplodocus material at BYU in which all of the neural arches are fused to the centra, despite the vertebrae being about half the size of those in the mounted D. carnegii CM 84/94. So I am very leery of size as a reliable indicator of age in sauropods. It is a bad criterion in general, and especially bad for cervical vertebrae, which can change so much along the column. C15 of D. carnegii CM 84/94 has a cotyle diameter almost four times that of C3 in the same animal.

Sacra of Apatosaurus excelsus YPM 1980 and A. ajax YPM 1860 at the same scale, from Ostrom and McIntosh (1966:plates 27 and 29)

2. People often cite closure of the neurocentral synostoses* as an indicator of adulthood, but again I am skeptical. There’s no doubt that the neurocentral synostoses do eventually close; my skepticism runs the other way, in that there are sauropods with closed neurocentral synostoses that do not appear to have reached full size. The HM SI** individual of Giraffatitan is one example–it’s about 75% of the size of the mounted (SII) individual, and only 66% the size of the giant HM XV2 (by cross-scaling through HM SII; SI and XV2 share no overlapping elements), and yet the neurocentral synostoses are all closed. Same deal with Apatosaurus CM 555, which has open joints as far back as C8 but is between one-half and two-thirds the size of A. louisae CM 3018. If you found a posterior cervical or anterior dorsal of CM 555 by itself, without the open joints on the more anterior vertebrae to guide you, you’d think it was full grown based on arch fusion. So it seems safest to say that neurocentral synostosis closure is a necessary but not sufficient condition for inferring adulthood.

* Hat tip to Jerry Harris, who alerted me that the term ‘sutures’ is reserved for skulls only, and that the joints between neural arches and centra are properly called synostoses. Thanks also to physical anthropologist Vicki Wedel, who confirmed this.

** Yes, I’m using the old Humboldt Museum numbers here, out of convenience, and because HM SII probably means more to more readers than the correct M.B. R. number that only six people have memorized.

3. Coalescence of the sacrum and formation of the sacricostal yoke have intuitive appeal. The sacricostal yokes are banana-shaped bars of bone formed by the union of the sacral ribs that articulate with the ilia–you can see them on either side of the apatosaur sacra in the image above, and in this post on the sacrum of Camarasaurus lewisi. Since the sacricostal yokes are the bony interfaces between the axial skeleton and the hindlimb girdles, we might expect them to be biomechanically important and for their formation to be closely related to the attainment of adult size. But I’m putting them fairly low on the list for reasons both practical and theoretical. On the practical side, fusion of the sacral vertebrae and ribs is hard to assess unless the sacrum has fallen apart. An intact sacrum might be intact because the bones were actually fused together, or because the unfused bits just happened to hang together through the process of fossilization (if that sounds unlikely, just remember that it’s true of almost every articulated fossil skull you’ve ever seen). On the theoretical side, the timing of sacral fusion seems to be variable. A. ajax YPM 1860 has fused neural arches and cervical ribs but a very incompletely fused sacrum, whereas D. carnegii CM 84/94 has the five sacral centra coossified and a sacricostal yoke uniting the ribs of S2-S5*, but some of the cervical ribs are unfused. Yes, I realize that discounting this criterion because it conflicts with other mutually conflicting criteria is a bit wonky, but (1) that’s the essential challenge of doing non-histological skeletochronology on sauropods–none of the signs seem to tell us what we want–and (2) I’m happy to fall back on the practical reason if you find the theoretical one unconvincing. Last item: I have seen both ‘sacricostal’ and ‘sacrocostal’ used in the literature–can anyone make a case for one being more correct than the other? ‘Sacrum’ is from the Latin sacer, ‘sacred’, apparently because the sacra of animals used to be sacrificed to the gods (not sacroficed–maybe there’s my answer?).

*Hatcher (1901) described an 11th dorsal and four sacral vertebrae, but he noted that the 11th dorsal “functions as a sacral” and “is coossified by the centrum with the true sacrals”. The D. carnegii holotype was one of the first nearly complete sauropod skeletons to be monographically described, and it was not yet clear that the typical number of sacrals for the North American diplodocids–and indeed for most other sauropods–is five (some primitve taxa have four, many titanosaurs have six).

4. Cervical rib fusion might be better. Giraffatitan HM SI and Diplodocus CM 84/94 both have their cervical neurocentral synostoses closed, but both have unfused cervical ribs as far back as C5. This suggests that cervical rib fusion proceeded from back to front (in at least those taxa) and that it followed neurocentral fusion. The sole exception that I have seen is a subadult Apatosaurus cervical from Cactus Park in the BYU collections, which has fused ribs but open neurocentral joints.

5. It’s hard to tell if fusion of the scapula to the coracoid is better or worse than cervical rib fusion, because the timing varies among taxa (hence the caveat that these criteria are in rough order). Giraffatitan HM SII has fused neural arches and fused cervical ribs but open scap-coracoid synostoses (yes, again, synostoses rather than sutures) ; Diplodocus CM 84/94 has a fused scap-coracoid but some unfused cervical ribs. This is probably another necessary but not sufficient condition.

6. The gold standard for determining cessation of growth is the formation of an external fundamental system (EFS) in the outer cortex of a bone. Unfortunately that requires destructive sampling (even if only drilling), is time-consuming, and has been done for few individual sauropods.

The upshot of all of the above is that the readily available ways of determining adulthood in sauropods are all inexact and frequently conflict with each other. Neural arch fusion does not indicate full growth–some sauropods appear to have fused their neurocentral joints when they were only two-thirds grown (in linear terms; 30% grown in terms of mass).

For the purposes of this post and the next, I am going to refer to the big mounted skeletons–Apatosaurus louisae CM 3018, Diplodocus carnegii CM 84/94, etc.–and individuals of like size as ‘adults’ to indicate that they had attained adult morphology, without implying that they were done growing or had EFSs, and also not implying that smaller individuals were necessarily subadult. ‘Adult’ here is used a term of convenience, not a biological fact.

Implications of serial changes in bifurcation for isolated elements

From here, this post picks up right where the last one in this series left off, so feel free to refer back to the previous post for any points that are unclear.

In the diplodocids, adults are expected to have unsplit spines as far back as C5, C6 may be only incompletely bifid (e.g., D. carnegii CM 84/94), and the spines in the posterior dorsals are expected to be either very shallowly notched at the tip or completely unsplit. Therefore it is impossible to say that an isolated vertebra belongs to a juvenile individual on the basis of neural spine bifurcation alone. Depending on how one defines “anterior cervical”, one half to one third of anterior cervicals are expected to have unsplit spines even in adults.

Serially comparable dorsal vertebrae in different Camarasaurus species or ontogenetic stages. Left: dorsal vertebra 7 (top) and dorso-sacral (= D11) (bottom) of Camarasaurus supremus AMNH 5760 and 5761 “Dorsal Series II”, both in posterior view, with unsplit neural spines. Modified from Osborn and Mook (1921: plate LXXI). Right: dorsal vertebrae 7-11 of Camarasaurus lewisi holotype BYU 9047 in posterodorsal view, with split spines. From McIntosh, Miller, et al. (1996: plate 5). Scaled so that height of D11 roughly matches that of C. supremus.

In Camarasaurus the picture is less clear. The immense C. supremus AMNH 5761 has unsplit spines in C3-C4 and in the last three or four dorsals, but some of those very posterior dorsals have extremely shallow depressions in the tips of the spines, with little consistency among the four individuals that somewhat confusingly make up that specimen. In the geriatric C. lewisi all of the post-axial presacral neural spines are at least incompletely bifid. Even in the very posterior dorsals there is still a distinct notch in the neural spine, not just a very slightly bilobed tip as in the posterior dorsals of C. supremus. Either this is an interspecific difference or some amount of ontogenetic bifurcation happened well into adulthood; current evidence is insufficient to falsify either hypothesis.  (That’s the trouble with n=1.)

A final thing to note: as I briefly mentioned in the earlier post, it is easier to detect deep bifurcations than shallow ones if the material is broken or incomplete. The neural spine tips are usually narrow, fragile, and easily broken or lost. If a vertebra is missing the top half of its spine but the bottom half is not split, it is usually impossible to say whether it would have been bifid or not. But if the spine is deeply bifurcated, even a small piece of bone from the base of the trough or one of the metapophyses is enough to confirm that it was bifid.

“Primitive” morphology can be an effect of serial position

Even in ‘adult’ sauropods like the big mounted Apatosaurus and Diplodocus skeletons, the anterior cervicals are less complex than the posterior ones. Compared to posterior cervicals, anterior cervicals tend to have simpler pneumatic fossae and foramina, fewer laminae, and unsplit rather than bifid spines. In all of these things the anterior cervicals are similar to those of juveniles of the same taxa, and to those of adults of more basal taxa. This is also true in prosauropods–in Plateosaurus, the full complement of vertebral laminae is not present until about halfway down the neck (see this subsequent post for details).

An important implication of this is that an isolated cervical might look primitive (1) because it comes from a basal taxon, or (2) because it is from a juvenile, or (3) because it is from near the front of the neck.

Woodruff and Fowler (2012:Fig. 2)

In their Figure 2, Woodruff and Fowler (2012) compare an adult Mamenchisaurus cervical, an isolated cervical of a putative juvenile Diplodocus (MOR 790 8-10-96-204), and a cervical of D. carnegii CM 84/94. The point of the figure is to show that the isolated ‘juvenile’ vertebra is more similar in gross form  to the Mamenchisaurus cervical than to the adult D. carnegii cervical.

Unfortunately the figure confuses ontogenetic and serial variation. Based on the proportions of the centrum and the shape of the neural spine, the isolated MOR cervical is probably from a very anterior position in the series. No measurements are given in the paper or supplementary information (grrr), but using the scale bar in the figure I calculate a centrum length of about 28 cm, a cotyle height of 7 cm, and an elongation index (EI, centrum length divided by cotyle diameter) of 4. That EI, combined with the overall shape of the neural spine and the very long overhang of the prezygapophyses, make the vertebra most similar to C4 and C5 of D. carnegii CM 84/94. But the D. carnegii cervical included in the figure is C12. It differs from the isolated cervical in having a forward-leaning, bifurcated neural spine, a much more complicated system of laminae with many accessory laminae, and more complex pneumatic sculpturing. All of these differences are more likely to be caused by serial variation than by ontogeny–the same characters separate C12 from C4 and C5 in the same individual.

Diplodocus carnegii CM 84/94 cervicals 2-15 in right lateral view, from Hatcher (1901:pl. 3)

So here’s how that figure would have looked, had the comparable C5 of CM 84/94 been used instead of C12:

Woodruff and Fowler (2012:Fig. 2), with Diplodocus carnegii CM 84/94 C12 replaced by C5.

It’s now immediately apparent B more closely resembles C than A, in the possession of overhanging prezygapophyses, non-overhanging postzygapophyses, elongation index, anterodorsal inclination of the cotyle margin, lack of anterior deflection of diapophysis, etc. The biggest differences between B and C are the shape of the neural spine and, for want of a better word, the ‘sinuosity’ of the ventral centrum margin in lateral view. Both characters are highly variably serially within an individual, among individuals in a species, and among species in Apatosaurus and Diplodocus, so it is hard to attach much weight to them.

What is MOR 790 8-10-96-204?

It gets more complicated. The isolated MOR vertebra is presented as an example of juvenile morphology. But does it actually belong to a juvenile?

Here’s what we know for certain about the vertebra:

  • it has an EI of 4 (this is a proportion, so it’s still accurate even if the scale bar is off)
  • the cervical ribs are fused to the neural arch and centrum

In addition, the figure appears to show that:

  • it has a centrum length of 28 cm, although this could be off if the scale bar is incorrectly sized (which is why I prefer measurements to scale bars)
  • the neural arch appears to be fused to the centrum. Admittedly, the image in the figure is small and I haven’t seen the specimen in person. But we know this much: the centrum and neural arch stayed together through the process of preservation and preparation, which does not usually happen unless they have at least started coossifying; the photo does not show an obvious line of fusion between the centrum and neural arch; and the cervical ribs are fused, which in almost all sauropod vertebrae happens after closure of the neurocentral synostoses.

Now, as we’ve just seen above, the morphology of MOR 790 8-10-96-204 is indistinguishable from the morphology of an anterior cervical vertebra in an adult, and it compares especially well to C4 and C5 of D. carnegii CM 84/94. The apparent centrum length (measured from the scale bar in the figure) of MOR 790 8-10-96-204 is 28 cm, compared to 29 cm and 37 cm for C4 and C5 of D. carnegii CM 84/94, respectively. So MOR 790 8-10-96-204 is roughly the same size as the adult C4 and about 80% of the size of the adult C5. Furthermore, its neural arch appears to be fused and its cervical ribs are fused to the neural arch and centrum, whereas the cervical ribs of the ‘adult’ D. carnegii CM 84/94 are not yet fused in C2-C5.

In sum, the isolated MOR vertebra shown in Woodruff and Fowler (2012:Fig. 2) is most likely a C4 or C5 of an adult Diplodocus similar in size to D. carnegii CM 84/94, and based on cervical rib fusion it may be from an individual that is actually more mature than CM 84/94. All of the differences between that vertebra and the D. carnegii C12 shown in the same figure are more easily explained as consequences of serial, rather than ontogenetic, variation.

MOR 790 8-10-96-204 and the Mother’s Day Quarry

MOR 790 8-10-96-204 is from the Mother’s Day Quarry (Woodruff and Fowler 2012:Table 1), which is supposed to only contain juvenile and subadult sauropods (Myers and Storrs 2007, Myers and Fiorillo 2009). Myers and Fiorillo (2009:99) wrote:

The quarry has a strikingly low taxonomic diversity, with one sauropod taxon and one theropod taxon present. However, the relative abundance of elements from these taxa is so uneven – diplodocoid sauropod material comprises 99% of the recovered bones – that the quarry is effectively monospecific (Myers and Storrs, 2007). The theropod material consists of isolated teeth only and is probably related to scavenging of the sauropod carcasses. All identifiable sauropod elements belong to either juvenile or subadult individuals (Fig. 2); none is attributable to a fully-adult individual (Myers and Storrs, 2007).

The Figure 2 cited in that excerpt shows two sauropod centra, a dorsal and a caudal, both with unfused neural arches. And yet here is MOR 790 8-10-96-204, similar in size and morphology to D. carnegii CM 84/94, and with at least partially closed neurocentral synostoses and fused cervical ribs. By all appearances, it belongs to an adult or nearly adult animal. It is hard to avoid the conclusion that the Mother’s Day Quarry includes at least one adult or near-adult Diplodocus. The only alternative is that MOR 790 8-10-96-204 is a juvenile in which the neural arch and cervical ribs fused very early.* But if that were the case, what basis would we have for thinking that it belonged to a juvenile, other than that it came from a quarry that only produced juveniles up until now? I trust that the circularity of that logic is clear. It is much more parsimonious to infer that MOR 790 8-10-96-204 is just what it appears to be–an anterior cervical of an adult or near-adult Diplodocus–and that the Mother’s Day Quarry is not exclusively filled with juvenile sauropods.

* Another wrench in the gears: if MOR 790 8-10-96-204 is a juvenile that had freakishly early fusion of its various bits, then clearly its ontogeny has departed from that of Diplodocus, all bets are off about developmental timing, and we shouldn’t be using it to make inferences about the normal ontogeny of diplodocids anyway. It’s damned if you do (it’s an adult), damned if you don’t (it’s a freak).

I’m not criticizing the work of Myers and Storrs (2007) on the taphonomy of the Mother’s Day Quarry or Myers and Fiorillo (2009) on age segregation in sauropod herds, by the way. It’s possible that they never saw MOR 790 8-10-96-204, or that if they did see the specimen they mistook it for a juvenile vertebra based on its size. All it takes is one bone to show that an animal is present in a quarry, and no number of other bones can prove that said animal is absent; if they only saw juveniles, the inference that the quarry only contained juveniles was sound (the operative word is was). If MOR 790 8-10-96-204 is a C5, it’s still only 80% the size of the same vertebra in D. carnegii CM 84/94, so maybe it was the oldest one in the group, or maybe it was an adult slumming with the juveniles, or maybe groups of juvenile sauropods often had one or more adults present to keep an eye on things. Or maybe it happened along earlier or later and just got buried in the same hole. There are a host of possibilities, most of which do not contradict the general conclusions of Myers and Storrs (2007) and Myers and Fiorillo (2009).

Conclusions

Size matters. Size alone is a horrible, horrible criterion for inferring age, especially in a clade (Diplodocoidea) in which adult size is known to vary, and especially with vertebrae. We should expect cervical vertebrae in a single individual to differ in diameter by a factor of 4.

Serial position matters. Not all vertebrae turn out the same. Even in adults, anterior cervicals look very different from posterior cervicals, and have different character states. Anterior cervicals and cervicals of juvenile individuals often look similar. The best way to tell them apart is to rely on articulated series–which is why I went to the trouble of writing the first post in this series.

Skeletochronology matters. The fact that MOR 790 8-10-96-204 has an apparently fused arch and fused cervical ribs should have been huge red flag that maybe it wasn’t actually a juvenile.

I went through that example at length because it shows how serial changes in size and morphology can mimic or suggest ontogenetic changes. In the next post I will examine the rest of the data Woodruff and Fowler (2012) used to support the hypothesis of ontogenetic control of neural spine bifurcation.

The rest of the series

Links to all of the posts in this series:

and the post that started it all:

 References

  • 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.
  • Myers, T.S., and Fiorillo, A.R. 2009. Evidence for gregarious behavior and age segregation in sauropod dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology 274:96-204.
  • Myers, T.S., and Storrs, G.W. 2007. Taphonomy of the Mother’s Day Quarry, Upper Jurassic Morrison Formation, south-central Montana, U.S.A. PALAIOS 22:651–666.
  • McIntosh, J.S., Miller, W.E., Stadtman, K.L., and Gillette, D.D. 1996. The osteology of Camarasaurus lewisi (Jensen, 1988). BYU Geology Studies 41:73-115.
  • Osborn, H.F. and Mook, C.C. 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History 3:247-287.
  • Ostrom, John H., and John S. McIntosh.  1966.  Marsh’s Dinosaurs.  Yale University Press, New Haven and London.  388 pages including 65 absurdly beautiful plates.
  • Woodruff, D.C, and Fowler, D.W. 2012. Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): a critical phylogenetic character. Journal of Morphology, online ahead of print.

Mike gets a shot of a sauropod sacrum in the AMNH basement.

…with sauropod bones!

Lots of basements have them. Some basements have had them for decades, and other basements have been newly constructed to house them. So you can take advantage of that retro chic while taking your basement into the 21st century!

What the heck am I talking about?

Matt ponders the mysteries of evolution in the AMNH basement.

One of the nifty features of WordPress is that you can track the search terms that people are using to find your blog. After Mike put up his “Suboptimal location of Mamenchisaurus” post, we noticed that one of the top search terms bringing people to SV-POW! was ‘basement’. Yeah, that’s right, ‘basement’. In fact, ‘basement’ is the 5th highest search term of all time that has brought people to SV-POW! And that’s not unusual–in fact, of the top 5 search terms bringing people here, only one is sauropod-related (Brachiosaurus, at number 2).

As of this posting, here are the Top 10 non-sauropod search terms of all time that have led people to SV-POW!, listed by rank, and including the number of hits in parentheses:

1. rabbit (18,235)

3. leopard seal (12,797) — this explains why “Sorting out Cetiosaurus nomenclature”, which even Mike admits is the most boring topic we’ve ever covered here, is the 11th most popular post of all time on this blog!

4. flamingo (10,974)

5. basement (9743)

12. twinkie (3434)

14. flamingos (3102) — double dipping for the “Necks lie” post!

20. pig skull (2099)

21. savannah monitor (2078)

22. varanus exanthematicus (1936) — double dipping for “Four complete, articulated, extant sauropod skeletons–yes, really!”

24. shish kebab (1660) — double dipping for “Sauropods were corn-on-the-cob, not shish kebabs”.

Mike and Darren discover a new dwarf sauropod in the basement at Oxford.

We’re apparently getting a lot of hits from people who want to remodel their basements. I’m all for that (the remodeling, and the extra hits), so I’m embracing it. You want basements, we got ’em. We’ll drown you in pictures of sauropod vertebrae in basements. Did I say basement? Basement, basement, basement!

(Why am I pushing basement and not rabbit, flamingo, or leopard seal? Partly because basement used to be our number 1 search term and I want to see its fortunes rise again. Partly because those other things are at least biological, and it cracks me up to have a common architectural term bringing people to the blog. And partly because I want to upstage John and his freezers.)

Basement Renovation Instructions

This short guide will help you with your project.

Is your basement in a museum?

If YES, then:

1. Fill it with sauropod vertebrae.

2. Call us.

If NO, then:

1. Fill it with anything you like except sauropod vertebrae.

2. Support your local museum.

Don’t forget: basement!

It’s been a little quiet around here lately. Mike has been slammed with day-job work, Darren is terminally busy as always, and I’m in my fall teaching block so I’ve been too busy to think. But life rolls on and there are announcements that need making. To wit:

– My post on the long nerves of sauropods was chosen as one of ten blog posts for the Science Writer Tip Jar at Not Exactly Rocket Science, back in May. Ed Yong, the NERS mastermind, has this to say:

Throughout the blogosphere, people produce fantastic writing for free. That’s great, but I believe that good writers should get paid for good work. To set an example, I choose ten pieces every month that were written for free and I donate £3 to the author. There are no formal criteria other than I found them unusually interesting, enjoyable and/or important.

It was an honor to be chosen; Ed’s a damn fine writer and has a knack for finding good stuff and pointing people to it. So why am I just blogging about this now, in August? I didn’t cover it at the time because the Science Writer Tip Jar runs on reader donations and I thought it would be a little gross to solicit money for myself. And I didn’t cover it right after because Ed’s been busy, too, and it sorta slipped off the radar for both of us. But at the end of last month he sent me a nice donation by PayPal, and I’m finally making good with the blogging about it.

What will I do with the dough? Inevitably, it will be spent on an epic meal of sushi for Mike and I. We don’t get to see each other very often, so when we do we have a sushipocalypse, and it’s pretty common for us to have ideas worth pursuing and publishing at these events. So ultimately the money will be plowed back into science, albeit indirectly. Thanks, Ed, and keep up the stellar work at NERS.

– Speaking of money, if you’d like to win a pile of it–4500 Euros, in fact–for the paleo paper you published in 2010, and get a nice trip to Spain in the bargain, I suggest you submit to Paleonturology 11, sponsored by Fundacion Dinopolis in Teruel, Spain. I know about this awesomeness because one of my papers won back in 2006, and I got a free trip to Spain in December, 2007 (story here). Winners have included papers by grad students and emeritus professors, on everything from trilobite eyes and bivalve shells to Pliocene hominids and dinosaur gastralia. The entrance form is super-simple and the whole process takes about as much time as it does to read this post. So if you published a paleo paper in the calendar year 2010 and you don’t enter, you’re just being silly. The deadline isn’t until November 15, but there’s no reason not to just sit down and do it right now. The form is somewhere on the Dinopolis website, but if your Spanish is as nonexistent as mine, you may find this PDF handy:  Paleonturology 11 entrance form

– This Friday, August 19, I’ll be on Jurassic CSI, talking about big sauropods. Details, showtimes, and some photos are here. The photo up top, of me with an Apatosaurus pelvis at BYU, is borrowed from there.

That’s all for now; further bulletins as events warrant.

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.