When I visited Dinosaur National Monument in October with Brian Engh and Yara Haridy, we spent a decent amount of time checking out DNM 28, a skull and associated bits of Camarasaurus. In particular, I got some shots of the axis (the second cervical vertebra behind the head), and it got me thinking about pneumaticity in this unusual element. Why I failed to get a full set of orthogonal shots is quite beyond my capacity, but we can roll with what I have. Before we go on, you might want to revisit Tutorial 36 to brush up on the general parts of the atlas-axis complex.


Here’s the axis in left lateral view (so, anterior to the left).

And a labeled version of the same. A few things to note:

  • One oddity of sauropod axes (and of axes of most critters) is that not only are the articular facets of the prezygapophyses not set forward of the neural arch, they’re set backward, well behind the forward point of the arch.
  • The dens epistrophei or odontoid process is sticking out immediately below the neural canal. This is the tongue of bone that articulated with the atlas (first cervical vertebra) in life.
  • Check out the prominent epipophysis above the postzygapophysis, which anchored the long dorsal neck muscles. (For more on epipophyses, see these posts, and especially this one.)
  • The diapophysis and parapophysis articulated with a cervical rib, which is not shown here. In fact, I don’t remember seeing it in the drawer that this vert came from. The atlantal and axial cervical ribs are small, apparently fused late in life if they fused at all, and are easily lost through taphonomic processes.
  • At least three pneumatic features are visible in this lateral view: the lateral fossa on the centrum, which is referred to as the “pleurocoel” in a lot of older literature; a ventral fossa that lies between the parapophysis and the midline ventral keel; and a fossa on the neural arch, behind the postzygodiapophyseal lamina. In the nomenclature of Wilson et al. (2011), this is the postzygocentrodiapophyseal fossa.

“Postzygocentrodiapophyseal fossa” is a mouthful, but I think it’s the only way to go. To be unambiguous, anatomical terminology needs to references specific landmarks, and the schemes proposed by Wilson (1999) for vertebral laminae and Wilson et al. (2011) for vertebral fossae are the bee’s knees in my book.

Nomenclatural issues aside, how do we know that these fossae were all pneumatic? Well, they’re invasive, there’s no other soft-tissue system that makes invasive fossae like that in archosaur vertebrae (although crocs sometimes have shallow fossae that are filled with cartilage or fat), and the same fossae sometimes have unambiguous pneumatic foramina in other vertebrae or in other sauropods.

Most of the features labeled above are also visible on the right side of the vertebra, although the ventral fossa is a little less well-defined in this view, and I can’t make out the prezyg facet. Admittedly, some of the uncertainty here is because of my dumb shadow falling across the vertebra. Specimen photography fail!

The paired ventral fossae are more prominent in this ventral view, on either side of the midline ventral keel (anterior is to the top).

And here’s a labeled version of the same ventral view.

Finally, here’s the posterior view. It’s apparent now that the neural spine is a proportionally huge slab of bone, like a broad, tilted shield between the postzygapophyses (which are also quite large for the size of this vertebra). The back side of the neural spine is deeply excavated by a complex fossa with several subfossae (kudos again to Jeff Wilson [1999] for that eminently useful term).

Here’s the same shot with some features of interest labeled. If I’ve read Wilson et al. (2011) correctly, the whole space on the back side of the neural spine and above the postzygs could be considered the spinopostzygapophyseal fossa, but here I’ve left the interspinous ligament scar (ILS) unshaded, on the expectation that the pneumatic diverticula that created that fossa were separated on the midline by the interspinous ligament. I might have drawn the ILS too conservatively, conceivably the whole space between the large deeply-shadowed subfossae was occupied by the interspinous ligament.

I’m particularly interested in those three paired subfossae, which for convenience I’m simply calling A, B, and C. Subfossa A may just be the leftover space between the spinopostzgyapophyseal laminae laterally and the interspinous ligament medially. I think subfossa B is invading the ramus of bone that goes to the epipophysis and postzygapophysis, but I didn’t think to check and see how far it goes (that might require CT anyway).

Subfossa C is the most intriguing. Together, those paired fossae form a couple of shallow pits, just on either side of the midline, and aimed straight forward. They can’t be centropostzygapophyseal fossae, which used to be called peduncular fossae, because they’re not in the peduncles on either side of the neural canal, they’re up above the lamina that connects the two postzygapophyses. Could they be ligament attachments? Maybe, but I’m skeptical for at least four reasons:

  1. Although interspinous ligament attachments often manifest as pits in the cervical vertebrae of birds, in sauropods they usually form rugosities or even spikes of bone that stick out, not inward. Furthermore, these pits are smooth, not rough like the interspinous ligament scars of birds.
  2. The interspinous ligament in tetrapods is typically a single, midline structure, and these pits are paired.
  3. Similar pits in front of the neural spine are present in some sauropod caudals, and they appear to be pneumatic (see Wedel 2009: p. 11 and figure 9).
  4. Pits at the base of the neural spine seem to be fairly uncommon in sauropod vertebrae. If they were attachment scars from the universally-present interspinous ligaments, we should expect them to be more prominent and more widespread.

But if these paired pits are not ligament scars, what are they? Why are they present, and why are they so distinct? Sometimes (often?) subfossae and accessory laminae look like the outcome of pneumatic diverticulum and bone reacting to each other (I almost wrote ‘playing together’), in what looks like a haphazard process of adaptation to local loading. But the symmetry of these pits argues against them being incidental or random. They don’t seem to be going anywhere, so maaaybe they are the first hoofbeats of the embossed laminae and “unfossae” that we see in the vertebrae of more derived sauropods (for which see this post), but again, their symmetry in size and placement isn’t really consistent with the “developmental program gone wild” appearance of “unfossae”. I really don’t know what to make of them, but if you have ideas, arguments, or observations to bring to bear, the comment field is open.

In summary, sauropod axes are more interesting than I thought, even in a derpasaurus like Cam. I’ll have to pay more attention to them going forward.

References

 

The Man Himself, taking notes on what look like Giraffatitan caudals.

Here’s how I got my start in research. Through a mentorship program, I started volunteering at the Oklahoma Museum of Natural History in the spring of 1992, when I was a junior in high school. I’d been dinosaur-obsessed from the age of three, but I’d never had an anatomy course and didn’t really know what I was doing. Which is natural! I had no way of knowing what I was doing because I lacked training. Fortunately for me, Rich Cifelli took me under his wing and showed me the ropes. I started going out on digs, learned the basics of curatorial work, how to mold and cast fossils, how to screenwash matrix and then pick microfossils out of the concentrate under a dissecting microscope, and—perhaps most importantly—how to make a rough ID of an unidentified bone by going through the comparative element collection until I found the closest match.

All set, right? Ignition, liftoff, straight path from there to here, my destiny unrolling before me like a red carpet.

No.

It could have gone that way, but it didn’t. I had no discipline. I was a high-achieving high school student, but it was all to satisfy my parents. When I got to college, I didn’t have them around to push me anymore, and I’d never learned to push myself. I went off the rails pretty quickly. Never quite managed to lose my scholarships, without which I could not have afforded to be in college, period, but I skimmed just above the threshold of disaster and racked up a slate of mediocre grades in courses from calculus to chemistry. I even managed to earn a C in comparative anatomy, a fact which I am now so good at blocking out that I can go years at a time without consciously recalling it.

After three years of this, I had the most important conversation of my life. Because I was a zoology major I’d been assigned a random Zoology Dept. faculty member as an undergrad advisor. I was given to Trish Schwagmeyer, not because we got on well (we did, but that was beside the point) or had similar scientific interests, just luck of the draw. And it was lucky for me, because in the spring of 1996 Trish looked at my grades from the previous semester, looked me in the eye, and said, “You’re blowing it.” She then spent the next five minutes explaining in honest and excruciating detail just how badly I was wrecking my future prospects. I’ve told this story before, in this post, but it bears repeating, because that short, direct, brutal-but-effective intervention became the fulcrum for my entire intellectual life and future career.

The holotype specimen of Sauroposeidon coming out of the ground in 1994.

Roughly an hour later I had the second most important conversation of my life, with Rich Cifelli. While I’d been lost in the wilderness my museum volunteering had petered out to zero, and Rich would have been completely justified in telling me to get lost. Not only did he not do that, he welcomed me back into the fold, in a terrifyingly precise recapitulation of the Biblical parable of the prodigal son. When I asked Rich if I could do an independent study with him in the next semester, he thought for a minute and said, “Well, we have these big dinosaur vertebrae from the Antlers Formation that need to be identified.” Which is how, at the age of 21, with a rubble pile of an academic transcript and no real accomplishments to stand on, I got assigned to work on OMNH 53062, the future holotype of Sauroposeidon proteles.

I was fortunate in four important ways beyond the forgiveness, patience, and generosity of Richard Lawrence Cifelli:

  • OMNH 53062 was woefully incomplete, just three and a half middle cervical vertebrae, which meant that the project was small enough in concept to be tractable as an independent study for an undergrad. Rich and I both figured that I’d work on the vertebrae for one semester, come up with a family-level identification, and maybe we’d write a two-pager for Oklahoma Geology Notes documenting the first occurrence of Brachiosauridae (or whatever it might turn out to be) in the vertebrate fauna of the Antlers Formation.
  • Because the specimen was so incomplete, no-one suspected that it might be a new taxon, otherwise there’s no way such an important project would have been assigned to an undergrad with a spotty-to-nonexistent track record.
  • Despite the incompleteness, because the specimen consisted of sauropod vertebrae, it held enough characters to be identifiable–and eventually, diagnosable. Neither of those facts were known to me at the time.
  • All of Rich’s graduate students were already busy with their own projects, and nobody else was about to blow months of time and effort on what looked like an unpromising specimen.

NB: this guy is not a prodigy.

There is a risk here, in that I come off looking like some kind of kid genius for grasping the importance of OMNH 53062, and Rich’s other students look like fools for not seeing it themselves. It ain’t like that. The whole point is that nobody grasped the importance of the specimen back then. It would take Rich and me a whole semester of concentrated study just to come to the realization that OMNH 53062 might be distinct enough to be diagnosable as a new taxon, and a further three years of descriptive and comparative work to turn that ‘maybe’ into a paper. People with established research programs can’t afford to shut down everything else and invest six months of study into every incomplete, garbage-looking specimen that comes down the pike, on the off chance that it might be something new. Having the good judgment to not pour your time down a rat-hole is a prerequisite for being a productive researcher. But coming up with a tentative ID of an incomplete, garbage-looking specimen is a pretty good goal for a student project: the student learns some basic comparative anatomy and research skills, the specimen gets identified, no existing projects get derailed, and no-one established wastes their time on what is most likely nothing special. If the specimen does turn out to be important, that’s gravy.

So there’s me at the start of the fall of 1996: with a specimen to identify and juuuust enough museum experience, from my high school mentorship, to not be completely useless. I knew that one identified a fossil by comparing it to known things and looking for characters in common, but I didn’t know anything about sauropods or their vertebrae. Rich got me started with a few things from his academic library, I found a lot more in OU’s geology library, and what I couldn’t find on campus I could usually get through interlibrary loan. I spent a lot of time that fall standing at a photocopier, making copies of the classic sauropod monographs by Osborn, Hatcher, Gilmore, Janensch, and others, assembling the raw material to teach myself sauropod anatomy.

The sauropod monographs live within arm’s reach of my office chair to this day.

In addition to studying sauropods, I also started going to class, religiously, and my grades rose accordingly. At first I was only keeping up with my courses so that I would be allowed to continue doing research; research was the carrot that compelled me to become a better student. There was nothing immediate or miraculous about my recovery, and Rich would have to give me a few well-deserved figurative ass-kickings over the next few years when I’d occasionally wander off course again. But the point was that I had a course. After a few months I learned—or remembered—to take pride in my coursework. I realized that I had never stopped defining myself in part by my performance, and that when I’d been adrift academically I’d also been depressed. It felt like crawling out of a hole.

(Aside: I realize that for many people, depression is the cause of academic difficulty, not the reverse, and that no amount of “just working harder” can offset the genuine biochemical imbalances that underlie clinical depression. I sympathize, and I wish we lived in a world where everyone could get the evaluation and care that they need without fear, stigma, crushing financial penalties, or all of the above. I’m also not describing any case here other than my own.)

What fresh hell is this? (Apatosaur dorsal from Gilmore 1936)

Out of one hole, into another. The biggest problem I faced back then is that if you are unfamiliar with sauropod vertebrae they can be forbiddingly complex. The papers I was struggling through referred to a pandemonium of laminae, an ascending catalog of horrors that ran from horizontal laminae and prespinal laminae through infraprezygapophyseal laminae and spinopostzygapophyseal laminae. Often these features were not labeled in the plates and figures, the authors had just assumed that any idiot would know what a postcentrodiapophyseal lamina was because, duh, it’s right there in the name. But that was the whole problem: I didn’t know how to decode the names. I had no map. SV-POW! tutorials didn’t exist. Jeff Wilson’s excellent and still-eminently-useful 1999 paper codifying the terminology for sauropod vertebral laminae was still years in the future.

Then I found this, on page 35 of Werner Janensch’s 1950 monograph on the vertebrae of what was then called Brachiosaurus brancai (now Giraffatitan):

It was in German, but it was a map! I redrew it by hand in my very first research notebook, and as I was copying down the names of the features the lightbulb switched on over my head. “Diapophyse” meant “diapophysis”, and it was the more dorsal of the two rib attachments. “Präzygapophyse” was “prezygapophysis”, and it was one of the paired articular bits sticking out the front of the neural arch. And, crucially, “Präzygodiapophysealleiste” had to be the prezygodiapophyseal lamina, which connected the two. And so on, for all of the weird bits that make up a sauropod vertebra.

It’s been 22 years and I still remember that moment of discovery, my pencil flying across the page as I made my own English translations of the German anatomical terms, my mind buzzing with the realization that I was now on the other side. Initiated. Empowered. I felt like I had pulled the sword from the stone, found Archimedes’ lever that could move the world. In the following weeks I’d go back through all of my photocopied sauropod monographs with my notebook open to the side, reading the descriptions of the vertebrae for the second or third times but understanding them for the first time, drawing the vertebrae over and over again until I could call up their basic outlines from memory. This process spilled over from the fall of 1996 into the spring of 1997, as Rich and I realized that OMNH 53062 would require more than one semester of investigation.

Interlude with a left femur of the Oklahoma apatosaurine (but not the largest individual).

My memories of those early days of my sauropod research are strongly shaped by the places and circumstances in which I was doing the work. Vicki and I had gotten married in the summer of 1996 and moved into a two-bedroom duplex apartment on the north side of Norman. The upstairs had a long, narrow bathroom with two sinks which opened at either end onto the two upstairs bedrooms, the one in which we slept and the one we used as a home office. In the mornings I could get showered and dressed in no time, and while Vicki was getting ready for work or school I’d go into the office to read sauropod papers and take notes. Vicki has always preferred to have music on while she completes her morning rituals, so I listened to a lot of Top 40 hits floating in from the other upstairs rooms while I puzzled out the fine details of sauropod vertebral anatomy.

Two songs in particular could always be counted on to play in any given hour of pop radio in the early spring of 1997: Wannabe by the Spice Girls, and Lovefool by the Cardigans. I am surely the only human in history to have this particular Pavlovian reaction, but to this day when I hear either song I am transported back to that little bedroom office where I spent many a morning poring over sauropod monographs, with my working space illuminated by the light of the morning sun pouring through the window, and my mind illuminated by Werner Janensch, who had the foresight and good grace to give his readers a map.

Figure 5 from my undergraduate thesis: OMNH 53062 in right lateral view.

If you want to know what I thought about OMNH 53062 back in 1997, you can read my undergraduate thesis—it’s a free download here. Looking back now, the most surprising thing to me about that thesis is how few mentions there are of pneumaticity. I met Brooks Britt in the summer of 1997 and had another epochal conversation, in which he suggested that I CT scan OMNH 53062 to look at the air spaces inside the vertebrae. I filed my undergrad thesis in December of 1997, and the first session CT scanning OMNH 53062 took place in January, 1998. So in late 1997 I was still a pneumaticity n00b, with no idea of the voyage I was about to embark upon.

In 2010, after I was settled in as an anatomist at Western University of Health Sciences, I wrote a long thank-you to Trish Schwagmeyer. It had been 14 years since that pivotal conversation, but when she wrote back to wish me well, she still remembered that I’d gotten a C in comparative anatomy. I’d have a chance to make amends for that glaringly anomalous grade later the same year. At ICVM in Punta del Este, Uruguay, I caught up with Edie Marsh-Matthews, who had taught my comparative anatomy course back when. I apologized for having squandered the opportunity to learn from her, and she graciously (and to my relief) shifted the conversation to actual comparative anatomy, the common thread that connected us in the past and the present.

If the story has a moral, it’s that I owe my career in large part to people who went out of their way to help me when I was floundering. And, perhaps, that the gentle approach is not always the best one. I needed to have my head thumped a few times, verbally, to get my ass in gear, when less confrontational tactics had failed. I slid easily through the classrooms of dozens of professors who watched me get subpar grades and didn’t try to stop me (counterpoint: professors are too overworked to invest in every academic disaster that comes through the door, just like paleontologists can’t study every garbage specimen). If Trish Schwagmeyer and Rich Cifelli had not decided that I was worth salvaging, and if they not had the grit to call me out on my BS, I wouldn’t be here. As an educator myself now, that thought haunts me. I hope that I will be perceptive enough to know when a student is struggling not because of a lack of ability but through a lack of application, wise enough to know when to deploy the “you’re blowing it” speech, and strong enough to follow through.

References

  • Gilmore Charles W. 1936. Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175–300 and plates XXI–XXXIV.
  • Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3: 27-93.
  • Wedel, M.J. 1997. A new sauropod from the Early Cretaceous of Oklahoma. Undergraduate honor thesis, Department of Zoology, University of Oklahoma, Norman, OK. 43pp.
  • Wilson, J.A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19: 639-653.

Matt with big Apato dorsal 2000

Final bonus image so when I post this to Facebook, it won’t grab the next image in line and crop it horribly to make a preview. This is me with OMNH 1670, in 2003 or 2004, photo by Andrew Lee.

Spotted this beauty in the collections at Dinosaur Journey this past summer. With the front end of the centrum blown off, taphonomy once again proves to be the poor man’s CT machine, giving us a great look at the pneumatic spaces inside the vertebra.

EDIT, Oct. 13, 2019 — WHOOPS! That ain’t a cervical. Based on the plates in Madsen (1976), it’s a dead ringer for the second dorsal vertebra.

Allosaurus fragilis cervicodorsal transition - Madsen 1976 plates 14-16

Vertebrae C7 through D3 of Allosaurus fragilis in anterior view, from plates 14-16 in Madsen (1976). Abbreviations: dp, diapophysis; li, interspinous ligament scar; nc, neural canal; ns, neural spine; pp, parapophysis; pr, prezygapophysis.

Reference

Madsen, Jr., J.H. 1976. Allosaurus fragilis: a revised osteology. Utah Geological and Mining Survey Bulletin 109: 1-163.

This awesome photo was taken in the SVPCA 2019 exhibit area by Dean Lomax (L). On the right, Jessie Atterholt, me, and Mike are checking out some Isle of Wight rebbachisaurid vertebrae prepped by Mick Green, who is juuuust visible behind Dean. Jessie’s holding a biggish (as rebbachisaurids go) dorsal or caudal centrum and partial arch, me a lovely little cervical, and Mike an astonishingly delicate and beautiful dorsal. You can see behind us more tables full of awesome fossils, and there were more still across the way, behind Dean and Mick. I was going to throw this photo into the last post to illustrate the exhibit area, but by the time the caption had hit three lines long, I realized it needed a post of its own.

Photo courtesy of Dean, and used with permission. Mark your calendars: on Sunday, Oct. 13, Dean will be speaking at TEDx Doncaster, with a talk titled, “My unorthodox path to success: how my passion for the past shaped my future”. You can follow the rest of Dean’s gradual conquest of the paleosphere through his website, http://www.deanrlomax.co.uk/.

My talk (Taylor and Wedel 2019) from this year’s SVPCA is up!

The talks were not recorded live (at least, if they were, it’s a closely guarded secret). But while it was fresh in my mind, I did a screencast of my own, and posted it on YouTube (CC By). I had to learn how to do this for my 1PVC presentation on vertebral orientation, and it’s surprisingly straightforward on a Mac, so I’ve struck while the iron is hot.

For the conference, I spoke very quickly and omitted some details to squeeze the talk into a 20-minute slot. In this version, I go a bit slower and make some effort to ensure it’s intelligible to an intelligent layman. That’s why it runs closer to half an hour. I hope you’ll find it worth your time.

References

And so the series continues: part 9, part 10 and part 11 were not numbered as such, but that’s what they were, so I am picking up the numbering here with #12.

If you’ve been following along, you’ll remember that Matt and I are convinced that BYU 9024, the big cervical vertebra that has been referred to Supersaurus, actually belongs to a giant Barosaurus. If we’re right about, then it means one of two things: either Supersaurus synonymous with Barosaurus, or there are two diplodocids mixed up together.

Jensen (1987:figure 8c). A rare — maybe unique? — photograph of the right side of the big “Supersaurus” cervical vertebra BYU 9024. We assume this was taken before the jacket was flipped and the presently visible side prepped out. We’d love to find a better reproduction of this image.

Which is it? Well, seventeen years ago Curtice and Stadtman (2002:39) concluded that “all exceptionally large sauropod elements from the Dry Mesa Quarry can be referred to one of two individuals, one a Supersaurus and one a Brachiosaurus […] further strengthening the suggestion that all of the large diplodocid elements belong to a single individual.” It is certainly suggestive that, of all the material that has been referred to Supersaurus, there are no duplicate elements, but there are nice left-right pairs of scapulocoracoids and ischia.

But do all those elements actually belong to the same animal? One way to address that question is to look at their relative sizes and ask whether they fit together.

Sadly, when Matt and I were at BYU we didn’t get to spend time with most of these bones, but there are published and other measurements for a few of them. Jensen (1985:701) gives the total lengths of the two scapulocoracoids BYU 9025 and BYU 12962 as 2440 and 2700 mm respectively. Curtice et al. (1996:94) give the total height of the last dorsal BYU 9044 as 1330 mm. We have measured the big cervical BYU 9024 (probably C9) ourselves and found it to measure 1370 mm in total length. Finally, while there is no published measurement for the right ischium BYU 12949 (BYU 5503 of Jensen’s usage), we can calculate it from the scalebar accompanying Jensen’s illustration (with all the usual caveats) as being 1235 mm long.

Jensen (1985:figure 7a). BYU 12946 (BYU 5503 of his usage), the right ischium assigned to Supersaurus. By measuring the bone and the scalebar, we can calculate the length as 1235 mm.

Do these measurements go together? Since we’re considering the possibility of Supersaurus being a big Barosaurus, the best way to test this is to compare the sizes of the elements with the corresponding measurements for AMNH 6341, the best known Barosaurus specimen.

For this specimen, McIntosh (2005) gives 685 mm total length for C9, 901 mm total height for D9 (the last dorsal) and 873 mm for the ischia (he only provides one measurement which I assume covers both left and right elements). The scapulocoracoids are more complex: McIntosh gives 1300 mm along the curve for the scapulae, and 297 mm for the length of the coracoids. Assuming we can add them in a straight line, that gives 1597 mm for the full scapulocoracoid.

I’ve given separate measurements, and calculated separate ratios, for the left and right Supersaurus scapulocoracoids. So here’s how it all works out:

Specimen Element Size (mm) Baro (mm) Ratio Relative
9024 Mid-cervical vertebra 1370 685 2.00 124%
9044 Last dorsal vertebra 1330 901 1.48 92%
9025 Left scapulocoracoid 2440 1597 1.53 95%
12962 Right scapulocoracoid 2700 1597 1.69 105%
12946 Right ischium 1235 873 1.41 88%

The first five columns should be self-explanatory. The sixth, “proportion”, is a little subtler. The geometric mean of the size ratios (i.e. the fifth root of their product) is 1.6091, so in some sense the Dry Mesa diplodocid — if it’s a single animal — is 1.6 times as big in linear dimension as the AMNH 6341 Barosaurus. The last column shows each element’s size ratio divided by that average ratio, expressed as a percentage: so it shows how big each element is relative to a hypothetical isometrically upsized AMNH Barosaurus.

As you can see, the cervical is big: nearly a quarter bigger than it should be in an upscaled Barosaurus. The two scaps straddle the expected size, one 5% bigger and the other 5% smaller. And the dorsal and ischium are both about 10% smaller than we’d expect.

Can these elements belong to the same animal? Maaaybe. We would expect the neck to grow with positive allometry (Parrish 2006), so it would be proportionally longer in a large individual — but 25% is a stretch (literally!). And it also seems as though the back end of the animal (as represented by the last dorsal and ischium) is growing with negative allometry.

A nice simple explanation would be that that all the elements are Supersaurus and that’s just what Supersaurus is like: super-long neck, forequarters proportionally larger than hindquarters, perhaps in a slightly more convergent-on-brachiosaurs way. That would work just fine were it were not that we’re convinced that big cervical is Barosaurus.

Here’s how that would look, if the BYU Supersaurus is a large Barosaurus with different proportions due to allometry. First, Scott Hartman’s Barosaurus reconstruction as he created it:

And here’s my crudely tweaked version with the neck enlarged 24% and the hindquarters (from mid-torso back) reduced 10%:

Does this look credible? Hmm. I’m not sure. Probably not.

So: what if we’re wrong?

We have to consider the possibility that Matt and I misinterpreted the serial position of BYU 9024. If instead of being C9 it were C14 (the longest cervical in Barosaurus) then the AMNH analogue would be 865 mm rather than 685 mm. That would make it “only” 1.58 times as long as the corresponding AMNH vertebra, which is only 3% longer than we’d expect based on a recalculated geometric mean scale of 1.5358 — easily within the bounds of allometry. We really really really don’t think BYU 9024 is a C14 — but it’s not impossible that its true position lies somewhere posterior of C9, which would mean that the allometric interpretation would become more tenable, and we could conclude that all these bones do belong to a single animal after all.

Of course, that would still leave the question of why the Supersaurus scapulocoracoids are 10% bigger than we’d expect relative to the last dorsal vertebra and the ischium. One possible explanation would be to do with preparation. As Dale McInnes explained, there’s some interpretation involved in preparing scaps: the thin, fragile distal ends shade into the cartilaginous suprascapula, and it’s at least possible that whoever prepped the AMNH 6341 scaps drew the line in a different place from Dale and his colleagues, so that the Barosaurus scaps as prepared are artificially short.

Putting it all together: it might easily be the case that all the elements really do belong to a single big diplodocid individual, provided that the big cervicals is more posterior than we thought and the AMNH scaps were over-enthusiastically prepped.

References

Since the previous installment of this epic, we’ve taken two brief digressions on how little importance we should attach the colours of bones in our photographs when trying to determine whether they’re from the same individual: cameras do lie, and in any case different bones of the same individual can age differently. Since then — newsflash! — a third reason has become apparent in the case of the two Supersaurus scaps: the object we discussed as Scap A turns out to be a cast. A really good one, sure, but still: its colour tells us little about the colour of the actual bone.

If you doubt that, consider the scapulocoracoid referred to Ultrasauros (which we’ll be meeting again in the next post). Here is the real bone, at the North American Museum of Ancient Life (NAMAL), with me for scale:

BYU 9462, the scapulocoracoid referred by Jensen to Ultrasauros. Mike Taylor for scale, doing a Jensen. The signage reads: Brachiosaurus scapula and coracoid. Originally believed to belong to the genus Ultrasaurus (now invalid), this shoulder blade is from the giant herbivorous dinosaur Brachiosaurus, a replica of which is mounted in this room. The dinosaur that owned this scapula was over 65 feet long and could tower 45 feet above the ground. When collected by Jim Jensen at Dry Mesa Quarry (Colorado) in 1989, the scapula was believed to represent the largest dinosaur ever found. Note how many separate pieces are within the specimen. A tremendous amount of work is required to complete a fossil of this size. Specimen on loan from Brigham Young University’s Earth Science Museum. Late Jurassic/Early Cretaceous (about 144 million years ago)

And here’s Matt with the cast of the same bone that resides in the BYU collections:

As you can see, the cast has been prepared in a darker and browner colour than the pale greenish grey of the real bone (though don’t forget that cameras lie about colours, so we shouldn’t over-interpret this difference).

Aaanyway …

We finished up last time with the observation that the holotype scapulocoracoid of Supersaurus, BYU 9025, is not obviously diagnostic; and that since the cervical BYU 9024 that has been referred to it actually belongs to Barosaurus, we can’t trust any of the other referrals of big Dry Mesa diplodocid bones to Supersaurus; and that the name must therefore be considered a nomen dubium, resting as it does on non-diagnostic material.

Can the name Supersaurus survive? I think it can, and I see four possible routes to that happening.

Method 0: Everyone ignores these blog posts

This is only a blog, after all. No-one is obliged to pay any attention to anything we say here.

That said, Matt and I do have previous in transforming series of blog posts in to actual papers. Having invested so much effort into writing these posts, I do hope that I’ll be able to do the same thing in this case, so at some stage the ideas from this series should become part of the formal scientific record. (I make no promises about how long that will take.)

So assuming that we can’t all just walk away and pretend that none of this ever happened, are there better ways to save the name Supersaurus?

Method 1. Someone finds autapomophies

Matt and I are of course primarily vertebra jockies. We are not above studying the occasional taxon based on appendicular material, but our expertise lies in the domain of the axial. It’s perfectly possible that someone who understands sauropod appendicular anatomy better than we do could isolate some autapomorphies in the holotype scap BYU 9025, and Supersaurus would then be firmly founded on a diagnostic type specimen.

Can we find hope for this outcome in the results of phylogenetic analyses?

In Whitlock’s (2011) diplodocoid analysis, Supersaurus emerges with but a single autapomophy: “Anterior caudal neural spine height less than 150% centrum height” (page 44). Based, as it is, on a referred element, that doesn’t help us much here. (Although it’s worth noting that Whitlock scored this character as 0 for Supersaurus and 1 for Barosaurus, which does very slightly suggest that the referred caudal is not Barosaurus and therefore might belong to the same individual as the Supersaurus holotype. Yes, this is weak sauce.)

Tschopp et al.’s (2015) unnumbered supplementary file Apomorphies recovered by TNT under implied weighting is difficult to interpret: for example, a heading on the first page says simply “R_iw” and its counterpart on page 8 is simply “P_iw“. But the Supersaurus-relevant entries are the same under both headings. In both cases, they read:

Supersaurus vivianae BYU
Char. 258: 1 –> 0
Char. 274: 1 –> 0
WDC DMJ-021
Char. 165: 1 –> 2
Char. 172: 0 –> 1
Char. 174: 0 –> 1
Char. 257: 1 –> 2

Node 137 (Supersaurus vivianae)
Char. 183: 1 –> 2

I read this as meaning that the two OTUs have autapomorphies as listed, and the node uniting them has a single synapomorphy. But all of these characters related to the presacral vertebrae (C165-C183 in the cervicals, C257-C274 in the dorsals). So again, there is nothing here to help us diagnose Supersaurus on the basis of the holotype scapulocoracoid.

Of course, that doesn’t prove that there there aren’t any diagnostic characters. Someone with a good eye for sauropod scapulocoracoids might find details missed by these phylogenetic analyses, whose remits were much broader. But the news so far is not good.

Method 2. Nominate a neotype from the BYU material

If we accept that there are probably no more than two big diplodocoids in the Dry Mesa quarry, and that one of them is Barosaurus (based in the big cervical BYU 9024), and that the “Dystylosaurus” vertebra BYU 4503 is not Barosaurus, then it must follow that it belongs to Supersaurus. Unlike the type scapulocoracoid BYU 9025, that vertebra probably is diagnostic (it’s an anterior diplodocid dorsal, yet its spine is unsplit) so perhaps Supersaurus could survive by being diagnosed on that basis.

How would this work nomenclaturally? I think it would be difficult. If I have properly understood Article 75 of the ICZN, you can only go ahead and designate a neotype “when no name-bearing type specimen (i.e. holotype, lectotype, syntype or prior neotype) is believed to be extant”. But the holotype scapulocoracoid exists (so far as we know, though we’re not sure where it is).

All is not necessarily lost, though. Paragraph 75.5 (Replacement of unidentifiable name-bearing type by a neotype) says “When an author considers that the taxonomic identity of a nominal species-group taxon cannot be determined from its existing name-bearing type (i.e. its name is a nomen dubium), and stability or universality are threatened thereby, the author may request the Commission to set aside under its plenary power [Art. 81] the existing name-bearing type and designate a neotype.” But that means writing an ICZN petition, and I’m not sure anyone wants to do that. The process is technical, picky and prolonged, and its outcome is subject to the whim of the committee. It’s quite possible someone might go to all the trouble of writing a petition, then wait five years, only to have it rejected.

The irony here is that when Curtice and Stadtman (2001) referred the “Dystylosaurus” dorsal BYU 4503 to Supersaurus, they were at liberty to sink Supersaurus into Dystylosaurus rather than vice versa. Then the unique dorsal vertebra would have become the holotype, and the surviving genus would have been nicely diagnosable. Curtice and Stadtman (2001) did not discuss this possibility; nor did Curtice et al. (1996) discuss the possibility of folding Supersaurus into Ultrasauros when determining that the holotype vertebra of the latter belongs to the same taxon as the former.

Curtice and his collaborators were likely following the principle of “page priority”: preferring Supersaurus over the other two genera as it was the first one named in Jensen’s (1985) article that named all three. However, page priority does not exist at all in the present version of the Code (see Article 24, Precedence between simultaneously published names, spellings or acts), and even in earlier versions was only a non-binding recommendation. So it was really Curtice’s and his friends’ choice which genus to retain.

But that ship has now sailed. According to the principle of first reviser (Section 24.2.1), the pubished actions of Curtice and colleagues established a new status quo, and their choice of genus stands.

Method 3. Nominate Jimbo as a neotype

We might conceivably give up on the mixed-up Dry Mesa material as too uncertain to base anything on, and nominate WDC DM-021 (“Jimbo”) as the neotype specimen instead. It may have less material in total than has been referred to Supersaurus from the Dry Mesa quarry, but the association is somewhat more solid (Lovelace et al. 2008:528).

In some ways this might be the most satisfactory conclusion: it would give us a more solid basis on which to judge whether or not subsequent specimens can be said to belong to Supersaurus. But as with method 2, it could only be done via a petition to the ICZN, and I suspect the chances of such a petition succeeding would be low because clause 75.3.6 of the Code says that neotype designation should include “evidence that the neotype came as nearly as practicable from the original type locality [of] the original name-bearing type”.

So I don’t think this is likely to work, but I mention it for completeness. (Also, I am not 100% sure how solid the association of the Jimbo elements is, as the wording in Lovelace et al. (2008:528) does hedge a little.)

In conclusion …

I think the best hope for the survival of the name Supersaurus would be the recognition of unambiguously diagnostic characters in the holotype scapulocoracoid BYU 9025. In comments on the last post, John D’Angelo has started to think about what characters might work here. We’ll see how that thread pans out.

On the other hand, do we even particularly want the name Supersaurus to survive? It’s a pretty dumb name. Maybe we should just let it die peacefully.

Next time — in what really, really, really will be the last post in this series — we’ll consider what all this means for the other two names in Jensen’s trio, Dystylosaurus and Ultrasauros.

References

  • Curtice, Brian D. and Kenneth L. Stadtman. 2001. The demise of Dystylosaurus edwini and a revision of Supersaurus vivianae. Western Association of Vertebrate Paleontologists and Mesa Southwest Museum and Southwest Paleontologists Symposium, Bulletin 8:33-40.
  • Curtice, Brian D., Kenneth L. Stadtman and Linda J. Curtice. 1996. A reassessment of Ultrasauros macintoshi (Jensen, 1985). M. Morales (ed.), “The continental Jurassic”. Museum of Northern Arizona Bulletin 60:87–95.
  • Jensen, James A. 1985. Three new sauropod dinosaurs from the Upper Jurassic of Colorado. Great Basin Naturalist 45(4):697–709.
  • Lovelace, David M., Scott A. Hartman and William R. Wahl. 2008. Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos do Museu Nacional, Rio de Janeiro 65(4):527–544.
  • Tschopp, Emanuel, Octávio Mateus and Roger B. J. Benson. 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 2:e857. doi:10.7717/peerj.857
  • Whitlock, John A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161(4):872-915. doi:10.1111/j.1096-3642.2010.00665.x