February 2, 2015
Matt’s last post contained a nice overview of the occurrence of epipophyses in sauropodomorphs: that is, bony insertion points for epaxial ligaments and muscles above the postzygapophyseal facets. What we’ve not mentioned so far is that these structures are not limited to sauropods. Back when we were preparing one of the earlier drafts of the paper that eventually became Why sauropods had long necks; and why giraffes have short necks (Taylor and Wedel 2013a), I explored their occurrence in related groups. But that section never got written up for the manuscript, and now seems as good a time as any to fix that.
Theropods (including birds)
Most obviously, epipophyses occur in theropods, the sister group of sauropodomorphs.
In this figure from the 2013 paper, the rightmost images show cervical vertebrae of Majungasaurus (an abelisaurid theropod) and a turkey, both in posterior view. The red arrows indicate epaxial musculature pulling on the epipophyses. They are particularly prominent in Majungasaurus, rising almost a full centrum’s height above the postzygapophyseal facets.
The epipophyses are very prominent in the anterior cervicals of Tyrannosaurus, but much less so in its posterior cervicals — presumably because its flesh-tearing moves involved pulling upwards more strongly on the anterior part of the neck. Here’s a photo of the AMNH mount, from our post T. rex‘s neck is pathetic:
You can see something similar in the neck of Allosaurus, and the trend generally seems to be widespread among theropods.
Note the very prominent epipophyses protruding above the postzygs in the anterior cervicals of this Heterodontosaurus in the AMNH public gallery:
Here’s the hadrosaur Corythosaurus:
The prominent vertebra is C2: note that is has both a modest blade-like neural spine and prominent epipophyses — but that already by C3 the epipophyses are gone. Here is that C2 postzyg/epipophyses complex is close-up, clearly showing anteroposteriorly directed striations on the epipophysis, presumably representing the orientation of the attaching ligaments and muscles:
Here’s a close-up of the neck of the boring ornithopod Tenontosaurus, also in the AMNH gallery. (I’m not sure of the specimen number — if anyone can clarify, please leave a comment).
The interesting thing here is that it its axis (C2) seems to lack epipophyses (unlike C3), and to have a tall blade-like neural spine, as seen in mammals. We don’t really see C2 spines this big in other dinosaurs — compare with the much more modest spine in Corythosaurus, above. The texture of this part of the Tenontosaurus specimen looks suspicious, and I wonder whether that neural spine is a fabrication, created back in the day by AMNH staff who were so used to mammals that they “knew” what a C2 should look like? Anyway, the epipophysis above the postzyg of C3 is very distinct and definitely real bone.
Things get much more difficult with pterosaurs, because their cervicals are so fragile and easily crushed (like the rest of their skeleton, to be fair). While it’s easy to find nice, well-preserved ornithischian necks on display, you don’t ever really see anything similar for pterosaurs.
As a result, we have to rely on specimen photographs from collections, or more often on interpretive drawings. Even high-resolution photos, such as the one in Frey and Tischlinger (2012: fig 2) tend not to show the kind of detail we need. Usually, the only usable information comes from drawings made by people who have worked on the specimens.
Here, for example, is Rhamphorhynchus, well known as the most difficult pterosaur to spell, in figure 7 from Bonde and Christiansen’s (2003) paper on its axial pneumaticity:
It’s not the main point of the illustration, but you can make out clear epipophyses extending posteriorly past the postzygapophyseal facets in at least C3 and C5 — in C4, the relevant area is obscured by a rib. (Note that the vertebrae are upside down in this illustration, so you need to be looking towards the bottom of the picture.)
I’m pretty sure I’ve seen a better illustration of Rhamphorhynchus epipophyses, but as I get older my memory for Rhamphorhynchus epipophyses is no longer what it used to be and I can’t remember where. Can anyone help?
But also of interest is the azhdarchid pterosaur Phosphatodraco, here illustrated by Pereda Suberbiola et al. (2003):
The cervicals of Phosphatodraco seem to have no epipophyses. So they were not ubiquitous in pterosaurs.
What does it all mean? This post has become a bit of a monster already so I’ll save the conclusion for another time. Stay tuned for more hot epipophyseal action!
- Bonde, Niels and Per Christiansen. 2003. The detailed anatomy of Rhamphorhynchus: axial pneumaticity and its implications. pp 217-232 in: E. Buffetaut and J-M Mazin (eds), Evolution and Palaeobiology of Pterosaurs. Geological Society, London, Special Publications 217. doi:10.1144/GSL.SP.2003.217.01.13
- Frey Eberhard and Helmut Tischlinger. 2012. The Late Jurassic Pterosaur Rhamphorhynchus, a Frequent Victim of the Ganoid Fish Aspidorhynchus? PLoS ONE 7(3):e31945. doi:10.1371/journal.pone.0031945
- Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica, Supplement 7 3:27-93.
- O’Connor Patrick M. 2007. The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. pp 127-162 in: S. D. Sampson., D. W. Krause (eds), Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8.
- Osborn, Henry F., and Charles C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, New Series 3:247-387.
- Pereda Suberbiola, Xabier, Nathalie Bardet, Stéphane Jouve, Mohamed Iarochène, Baadi Bouya and Mbarek Amaghzaz. 2003. A new azhdarchid pterosaur from the Late Cretaceous phosphates of Morocco. pp 79-90 in: E. Buffetaut and J-M Mazin (eds), Evolution and Palaeobiology of Pterosaurs. Geological Society, London, Special Publications 217. doi:10.1144/GSL.SP.2003.217.01.08
- Taylor, Michael P., and Mathew J. Wedel. 2013. Why sauropods had long necks; and why giraffes have short necks. PeerJ 1:e36 doi:10.7717/peerj.36
February 6, 2014
Recently I had the opportunity to give a talk on photographing specimens and preparing illustrations in Jim Parham‘s phylogenetics course at Cal State Fullerton. Jim is having each student (1) write a description of a specimen, (2) run a phylogenetic analysis, and (3) do some kind of calibration on their tree. I think that’s rad.
Anyway, it was fun talk and I wanted to put it up for everyone, but Mike had the idea of posting a batch of slides at a time, to hopefully fire some discussion on different aspects of photography and illustration. So if you’re impatient to see the whole thing, blame him! I will post the whole talk at the end of the post series, and you can find all of the talk posts here.
And now, on with the show.
March 11, 2013
For a paper that I and Matt are preparing, we needed to measure the centrum length of a bunch of turkey cervicals. That turns out to be harder than you’d think, because of the curious negative curvature of the articular surfaces.
Above is a C7 from a turkey: anterior view on the left; dorsal, left lateral and ventral views in the middle row; and posterior on the right. As you can see from the anterior, dorsal and ventral views, the anterior articular surface is convex dorsoventrally but concave transversely; and as you can see from the lateral view, the posterior face is concave dorsoventrally and convex transversely.
This means you can’t just put calipers around the vertebra. If you approach the vertebra from the top or bottom, then the upper or lower lip of the posterior articular surface will protrude past the centre of the saddle, and give you too long a length. If you approach from the side, the same will happen with the left and right lips of the anterior articular surface.
What are we trying to measure anyway?
But this raises the question of what it is we’re trying to measure. I said “we needed to measure the centrum length of a bunch of turkey cervicals”, but what exactly is centrum length? Why shouldn’t the upper and lower lips of the posterior articular surface count towards it?
What does centrum length mean?
The problem doesn’t only arise with bird cervicals. The same issue arises in measuring more sensible and elegant vertebrae, such as our old friend HMN SII:C8, or MB.R.2181:C8 as we must now learn to call it.
Although the back of the vertebra is nice and simple here — it’s obvious what line we’re measuring to at the back — we have three choices of where the “front” of the vertebra is, and a case can be made for any of them as being “the length of the vertebra”.
The longest measurement (here marked “T” for “total length”) goes to the front of the prezygapophyseal rami. The next one (“C” for “centrum length”) goes to the anteriormost point of the condyle. The distinction is important: as noted recently, the longest vertebra in the world belongs to Sauroposeidon if we use total length, but to Supersaurus if we use centrum length.
But in life, most of the condyle would be buried in the cotyle of the preceding vertebra. So should it count towards the length of the vertebra? If you consider a string of articulated vertebrae, the buried condyles don’t contribute to the overall length of the neck. So Matt and I call the length from the posterior margin of the condyle to the posterior margin of the cotyle the functional length (marked “F” above), which I believe is a new term.
Another way to think of the functional length is the distance from a given point on a vertebra (in this case the posterior margin of the cotyle) to the same point on the adjacent vertebra:
For our current project, Matt and I are interested in how the lengths of individual vertebrae contribute to total neck length, so for our purposes, functional length is definitely what we want.
By the way, Janensch is the only author I know of to have even recognised the importance of functional length. The measurement tables on pages 39 and 44 have columns for “Gesamtlänge des Wirbels ab Vorderende per Präzygapophyse”, “Gesamtlänge der Wirbel-Körpers in 1/2 Höhe” and “Länge der Wirbel-körpers ohne Condylus in 1/2 Höhe” — that is, “Total length of the vertebra from the anterior end of the prezygapophysis”, “Total length of the centrum measured at mid-height” and “Length of the centrum minus condyle at mid-height”. This is typical of his careful and methodical approach. Kudos!
Hey! I thought this was about turkeys
And so it is. Here is the functional length measurement for a turkey cervical:
It’s the shortest anteroposterior distance between the two articular surfaces.
Measuring functional length
Matt and I chatted about this at some length, and I am ashamed to say that we thought through all sorts of complicated solution involving subtracting measurements from known scaffold length and suchlike.
It took us a stupidly long to to arrive at the very obvious solution, which is just to modify the calipers to have a “tooth” that can protrude into the concavity of the anterior articulation between its left and right lips. Easily done with a flat-ended screw and a blob of wood glue:
With the measurements of all the vertebrae in my series, I can now fairly confidently expect that the sum of the individual lengths will come out at about the length of the complete neck.
You know, unless intervertebral cartilage turns out to be important or something.
- Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.
1. Matt and I are so used to opisthocoelous sauropod presacrals that when we’re talking about vertebrae — any vertebrae — we tend to say “condyle” and “cotyle” for the anterior and posterior articular surfaces, no matter what their morphology. When talking about crocodile cervicals or titanosaur caudals, we’re even likely to say ridiculous things like “the condyle is concave and the cotyle is convex”. Nonsense, of course: condyle means “A rounded prominence at the end of a bone, most often for articulation with another bone.” What we should say is “the condyle is at the back and the cotyle is in front”.
January 10, 2013
I’ve measured a few necks in my time, including the neck of a baby giraffe. I can tell you from experience that necks are awkward things to measure, even if they have been conveniently divested of their heads and torsos. They have a tendency to curl up, which impedes attempts to find the straight-line length. Even when you manage to hold them straight, you want them maximally compressed end-to-end rather than stretched out, which is hard to achieve without buckling them out of the straight line. And then you need to measure between perpendiculars in a straight line.
Tonight, I needed to measure the mass and length of seven turkey necks. (Never mind why, all will become clear in time.) And I found a way to do it that works much better than anything I’ve done before.
Here’s the equipment:
You will need:
- Kitchen scales (for weighing the necks)
- Small numbered labels (for the sandwich bags that the necks will go into for the freezer once they’ve been measured)
- Pen and paper to take down the measurements
- Translucent ruler
- Saucepan full of turkey necks
- Slightly less than one half of a birthday cake decorated like a map of Middle-earth [optional]
- A Duplo baseboard (double-sized Lego) and about fifteen 4×2 bricks
Use the bricks to build an L-shaped bracket on the board — about half way back, so that can rest your hand in front of it.
Now you can push the neck into the angle of the bracket. By keeping it pressed firmly against the back wall (yellow in my construction), you can keep it straight. I find the best way to get the neck exactly abutting the left (red) wall is to start with the neck in its natural position, with the anterior and posterior ends curving towards you, then sort of unroll it against the back wall, and finally push the posterior end into place with your little finger (see below). There is a satisfying moment– almost a click — as the back end pops into place and the neck slides along a little to right as necessary to accommodate the added length.
Now use another brick (blue in this photo) as a bracket: slide it along the back wall from right to left until it’s solidly abutting the anteriormost vertebra. If you do this right, there is very little travel: the entire series of vertebrae is lined up and solidly abutted, with bone pushing against the left wall and your new brick. I find there’s less than half a millimeter of variation between the length under gentle-but-firm pressure (which is what I measured) and under the very strongest force you can exert without buckling the neck.
Once you have found the blue brick’s correct position, you need to hold it firmly in place and measure its position relative the the left wall. (It doesn’t matter if you let the neck re-curl at this point, so long as the blue brick doesn’t shift.)
You need a translucent ruler so that you can lay it across the neck and see where blue brick falls under the scale. (My ruler’s zero is, rather annoyingly, 5 mm from the end; so I needed to subtract 5 mm from the lengths I measured.)
Finally, I bagged up each neck in its own sandwich bag, ready for the freezer. Each neck is labelled with a number so that when I take it out for dissection, I will be able to relate the measurements and observations that I make back to these initial measurements.
For the record, here are the measurements:
- Neck 1: 154 g, 179.5 mm.
- Neck 2: 122 g, 151 mm.
- Neck 3: 154 g, 199.5 mm.
- Neck 4: 133 g, 162.5 mm.
- Neck 5: 142 g, 169 mm.
- Neck 6: 80 g, 167 mm.
- Neck 7: 70 g, 169 mm.
As expected, there is some correlation between neck mass and length; but not as much as you might expect. Naively (i.e. assuming isometric similarity) mass should be proportional to length cubed, but there is a lot of scatter about that line. I don’t know whether that is due to individual variation, or merely because the various necks — all of them incomplete — are different sections of the full neck. Hopefully I will be able to confirm or rule out that possibility when I’ve dissected down to naked vertebrae.
November 23, 2011
Here at SV-POW! we are ardently pro-turkey. As the largest extant saurischians that one can find at most butchers and grocery stores, turkeys (Meleagris gallopavo) are an important source of delicious, succulent data. With Thanksgiving upon us and Christmas just around the corner, here’s an SV-POW!-centric roundup of turkey-based geekery.
The picture at the top of the post shows a couple of wild turkeys that frequented our campsite in Big Bend in the winter of 2007. Full story here.
If you’re wondering what to do with your turkey, the answer is GRILL IT. I use the recipe (available on Facebook) of my good friend and colleague, Brian Kraatz, who has fallen to the Dark Side and works on mammals–rabbit tooth homology, even (Kraatz et al. 2010)–but still grills a mean theropod. (In his defense, Kraatz has published on extinct saurischians–see Bibi et al. 2006.) My own adventures in turkey grilling are chronicled in this post, which will show you the steps to attaining enlightenment, or at least a larger circumference.
While you’re cooking and eating, you might as well learn something about muscles. This shot of the fanned-out longus colli dorsalis muscles in a turkey neck was the raison d’etre for this post, and turned up again with different muscles labeled in one of the recent Apatosaurus maquette review posts. Mike and I ate those muscles, by the way.
After the meal, you’ll have most of a turkey skeleton to play with. This diagram is from my other ‘holiday dinosaur’ page, which I put together for the Lawrence Hall of Science and UCMP back in 2005. That page has instructions on how to turn your pile of greasy leftovers into a nice set of clean white bones. Tom Holtz is widely acknowledged as King of the Dino-Geeks, and in kingly fashion he took the above diagram and turned the geek-o-meter up to 11. Steel yourself, gentle reader, before checking out the result here.
Speaking of bones, here’s a turkey cervical from Mike’s magisterial work in this area, which first appeared as a tack-on to a post about the holotype dorsal vertebra of the now-defunct genus Ultrasauros. The huge version of the composite photo has its own page on Mike’s website, where it is available in three different background colors. The lateral view also turned up in one of my rhea neck posts.
From the serving platter to publication: when I was young and dumb, I used a photo of a broken turkey vert to illustrate the small air spaces, or camellae, that are commonly found in the pneumatic bones of birds and some sauropods (Wedel and Cifelli 2005:fig. 11F).
I made a much better version by sanding the end off a cleaned-up vertebra, and used that in Wedel (2007), in this popular article on pneumaticity (which has instructions for making your own), and way back in Tutorial 3–only the 12th ever post on SV-POW!
Finally, it would be remiss of me not to point out that turkeys are not only readily accessible, tasty sources of anatomical information, they are also pretty interesting while they’re still alive. Don’t stare at the disgusting freak in the photo above or you might lose your will to eat. Instead, head over to Tetrapod Zoology v2 for Darren’s musings on caruncles, snoods, and other turkey parts that don’t even sound like words.
That does it for now. If you actually follow all of the links in this post, you might just have enough reading to keep you occupied during that post-holiday-meal interval when getting up and moving around is neither desirable nor physically possible. If you’re in the US, have a happy Thanksgiving; if you’re not, have a happy Thursday; and no matter where you are, take a moment to give thanks for turkeys.
- Bibi, F., Shabel, A.B., Kraatz, B.P., and Stidham, T.A. 2006. New fossil ratite (Aves: Palaeognathae) eggshell discoveries from the Late Miocene Baynunah Formation of the United Arab Emirates, Arabian Peninsula. Palaeontologia Electronica Vol. 9, Issue 1; 2A:13p.
- Kraatz, B.P., Meng, J., Weksler, M., and Li, C. 2010. Evolutionary patterns in the dentition of Duplicidentata (Mammalia) and a novel trend in the molarization of premolars. PLoS ONE 5(9): e12838. doi:10.1371/journal.pone.0012838
- Wedel, M.J. 2007. Aligerando a los gigantes (Lightening the giants). ¡Fundamental! 12:1-84. [in Spanish, with English translation]
- Wedel, M.J., and Cifelli, R.L. 2005. Sauroposeidon: Oklahoma’s Native Giant. Oklahoma Geology Notes 65 (2):40-57.
November 18, 2011
- Part 1: introduction
- Part 2: the head
- Part 4: body, tail, limbs, base, and skull
- Part 5: posture
- Part 6: texture and color
- Part 7: verdict
It is probably no surprise, given my proclivities, that I have more to say about the neck than about anything else. So unless I develop an abnormal curiosity about and mastery of, say, sauropod foot anatomy in the next few days, this will be the longest post in the series.
As with the head, the neck of the Apatosaurus maquette illustrates a lot of interesting anatomy. Some of this is unique to Apatosaurus and some of it is characteristic of sauropods in general. I’ll start with the general and move toward the specific.
As we’ve discussed before, the necks of most sauropods were not round in cross section (see here and here). The cervical ribs stuck out far enough ventrolaterally that even with a lot of muscle, the neck would have been fairly flat across the ventral surface, and in many taxa it would have been wider ventrally than dorsally.
The non-circular cross section would have been exaggerated in Apatosaurus, which had simply ridiculous cervical ribs (photo above is from this post). The widely bifurcated neural spines would also have created a broad and probably flattish surface on the dorsal aspect of the neck. The extreme width of the vertebrae and the cervical ribs created a very broad neck base. As in Camarasaurus, the base of the neck was a substantial fraction of the width of the thorax (discussed here). Consequently, the cervico-thoracic junction probably appeared more abrupt in narrow-necked taxa like Diplodocus and Giraffatitan, and more smoothly blended in Apatosaurus and Camarasaurus.
All of these features–the non-circular cross-section, the flattish dorsal and ventral surfaces, the wide neck base blending smoothly into the thorax–are captured in the Apatosaurus maquette.
The ventrolateral ‘corners’ of the neck have a ribbed appearance created by, well, ribs. Cervical ribs, that is, and big ones. In contrast to most other sauropods, which had long, overlapping cervical ribs, diplodocoids had short cervical ribs that did not overlap. But in Apatosaurus they were immense, proportionally larger than in any other sauropod and probably larger than in any other tetrapod. What Apatosaurus was doing with those immense ribs is beyond me. Some people have suggested combat, akin to the necking behavior of giraffes, and although I haven’t seen any evidence to support that hypothesis over others, neither does it strike me as far-fetched (an important nuance: giraffes use their heads as clubs, clearly not an option for the small-headed and fragile-skulled sauropods). Whatever the reason, the cervical ribs of Apatosaurus were amazingly large, and may well have been visible from the outside.
Mounted skeleton of Apatosaurus louisae in the Carnegie Museum, from Wikipedia.
Now this brings me to a something that, although not universal, has at least become fairly common in paleoart. This is the tendency by some artists to render (in 2D, 3D, or virtually) sauropods with dished-in areas along the neck, between the bony loops where the cervical ribs fuse to the centra. I am going to be as diplomatic as I can, since some of the people who have used this style of restoration are good friends of mine. But it’s a fine example of shrink-wrapped dinosaur syndrome, and it simply cannot be correct.
Adjacent cervical ribs loops in sauropods would have been spanned by intertransversarii muscles, as they are in all extant tetrapods. And outside of those single-segment muscles were long belts of flexor colli lateralis and cervicalis ascendens, which are also anchored by the cervical rib loops. All of these muscles are present in birds, and only vary in their degree of development in different parts of the neck and in different taxa. The spaces between adjacent cervical rib loops are not only not dished-in, they actually bulge outward, as in the turkey neck above.
And we’re still not done; running up through the cervical rib loops, underneath all of those muscles, were pneumatic diverticula. Not just any diverticula, but the big lateral diverticula that carried the air up the neck from the cervical air sacs at the base of the neck to the vertebrae near the head end (diverticula are reconstructed here in a cervical vertebra of Brachiosaurus, from Wedel 2005: fig. 7.2). Now, it’s unlikely that the diverticula exerted any outward pressure on the lateral neck muscles, but they were still there, occupying space (except when the muscles bulged inward and impinged on them during contraction), and with the muscles they would have prevented the neck from having visible indentations between the cervical rib loops of adjacent vertebrae.
Okay, so sauropod necks shouldn’t be dished in. But might the cervical ribs have stuck out? It might seem like the same question, only seen from the other side, but it’s not. We’ve established that adjacent cervical rib loops supported bands of single-segment muscles that spanned from one vertebra to the next, and longer, multi-segment muscles that crossed many vertebrae. But could the bony eminences of the cervical ribs have projected outward, through the muscle, and made bumps visible through the skin? The idea has some precedent in the literature; in his 1988 paper on Giraffatitan, Greg Paul (p. 9) argued that,
The intensely pneumatic and very bird-like neck vertebrae of sauropods were much lighter in life than they look as mineralized fossils, and the skulls they supported were small. This suggests that the cervical musculature was also light and rather bird-like, just sufficient to properly operate the head-neck system. The bulge of each neck vertebra was probably visible in life, as is the case in large ground birds, camels, and giraffes.
Paul has illustrated this in various iterations of his Tendaguru Giraffatitan scene; the one below is from The Princeton Field Guide to Dinosaurs (Paul 2010) and is borrowed from the Princeton University Press blog.
There is much to discuss here. First, I have no qualms about being able to see individual vertebrae in the necks of camels and giraffes, and it’s not hard to find photos that show these. It makes sense: these are stinkin’ mammals with the usual seven cervical vertebrae, so the verts have to be longer, proportionally, and bend farther at each joint than in other long-necked animals. I’m more skeptical about the claim that individual vertebrae can be seen in the necks of large ground birds. I’ve dissected the necks of an ostrich, an emu, and a rhea, and it seems to me that the neck muscles are just too thick to allow the individual vertebrae to be picked out. In a flamingo, certainly–see the sharp bends in the cranial half of the neck in the photo below–but flamingos have freakishly skinny necks even for birds, and their cervicals are proportionally much longer, relative to their width, than those of even ostriches.
What about sauropods? As discussed in this post, sauropod cervicals were almost certainly proportionally closer to the surface of the neck than in birds, which would tend to make them more likely to be visible as bulges. However, the long bony rods of the cervical ribs in most sauropods would have kept the ventral profile of the neck fairly smooth. The ossified cervical ribs of sauropods ran in bundles, just like the unossified hypaxial tendons in birds (that’s Vanessa Graff dissecting the neck of Rhea americana below), and whereas the latter are free to bend sharply around the ventral prominences of each vertebra, the former were probably not.
All of which applies to sauropods with long, overlapping cervical ribs, which is most of them. But as mentioned above, diplodocoids had short cervical ribs. Presumably they had long hypaxial tendons that looked very much like the cervical ribs of sauropods but just weren’t ossified. Whether the vertebrae could have bent enough at each segment to create bulges, and whether the overlying muscles were thin enough to allow those bends to be seen, are difficult questions. No-one actually knows how much muscle there was on sauropod necks, not even within a factor of two. There has been no realistic attempt, even, to publish on this. Published works on sauropod neck muscles (Wedel and Sanders 2002, Schwarz et al. 2007) have focused on their topology, not their cross-sectional area or bulk.
But then there’s Apatosaurus (AMNH mount shown here). If any sauropod had a chance of having its cervical vertebrae visible from the outside, surely it was Apatosaurus. And in fact I am not opposed to the idea. The cervical ribs of Apatosaurus are unusual not only in being large and robust, but also in curving dorsally toward their tips. If one accepts that the cervical ribs of sauropods are ossified hypaxial tendons–which seems almost unarguable, given that the cervical ribs in both crocs and birds anchor converging V-shaped wedges of muscle–then the ossified portion of each cervical rib must point back along the direction taken by the unossified portion of the tendon. In which case, the upwardly-curving cervical ribs in Apatosaurus suggest that the muscles inserting on them were doing so at least partially from above. So maybe the most ventrolateral portion of each rib did stick out enough to make an externally visible bulge.
Maybe. Many Apatosaurus cervical ribs also have bony bumps at their ventrolateral margins–the ‘ventrolateral processes’ or VLPs illustrated by Wedel and Sander (2002: fig. 3). If these processes anchored neck muscles, as seems likely, then even the immense cervical ribs of Apatosaurus might have been jacketed in enough muscle to prevent them from showing through on the outside.
Still. It’s Apatosaurus. It’s simply a ridiculous animal–a sauropod among sauropods. If this were a model of Mamenchisaurus and it had visible bulges for the cervical rib loops, I’d be deeply skeptical. For Apatosaurus, it’s at least plausible.
Because the cervical ribs are visible in the maquette as distinct bulges, it’s possible to count the cervical vertebrae. Apatosaurus has 15 cervicals, and that seems about right for the maquette. The neck bumps reveal 11 cervicals, but they don’t run up all the way to the head. This is realistic: the most anterior cervicals anchored muscles that supported and moved the head, and these overlie the segmental muscles and cervical ribs in extant tetrapods. The most anterior part of the neck in the maquette, with no cervical rib bumps, looks about the right length to contain C1-C3. Plus the 11 vertebrae visible from their bumps, that makes 14 cervicals, and the 15th was probably buried in the anterior body wall.
One last thing: because the cervical ribs are huge, the neck of Apatosaurus was fat. To the point that the head looks almost comically tiny, even though it’s about the right size for a sauropod head. I first got a visceral appreciation for this when I was making my own skeletal reconstruction of Apatosaurus, for a project that eventually evaporated into limbo. Once you draw an outline of flesh around the vertebrae, the weirdness of the massive neck of Apatosaurus is thrown into stark relief. Apatosaurus is robust all over, but even on such a massive animal the neck seems anomalous. I don’t know what Apatosaurus was doing with its neck, but it’s hard not to think that it must have been doing something. Anyway, I bring this up because the maquette captures the neck-fatness very well. So much so that when I sit back from the computer and my eyes roam around the office and fall on the maquette, I can’t help thinking, for the thousandth time, “Damn, that’s weird.”
In sum, the neck of the Sideshow Apatosaurus maquette gets the non-circular cross-section right, appears to have the correct number of cervical vertebrae, and looks weirdly fat, which turns out to be just right for Apatosaurus. The bumps for the individual vertebrae are plausible, and the maquette correctly avoids the dished-in, emaciated appearance–cocaine chic for sauropods–that has become popular in recent years. It manages to be eye-catching and even mildly disturbing, even for a jaded sauropodologist like yours truly, in that it confronts me with the essential weirdness of sauropods in general, and of Apatosaurus in particular. These are all very good things.
Next time: as much of the rest of the body as I can fit into one post (all of it, it turned out).
- Paul, G.S. 1988. The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs. Hunteria 2(3):1-14.
- Paul, G.S. 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press, 320 pp.
- Schwarz, D., Frey, E., and Meyer, C.A. 2007. Pneumaticity and soft−tissue reconstructions in the neck of diplodocid anddicraeosaurid sauropods. Acta Palaeontologica Polonica 52(1):167–188.
- Wedel, M.J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates; pp. 201-228 in Wilson, J.A., and Curry-Rogers, K. (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.
- Wedel, M.J., and Sanders, R.K. 2002. Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus. PaleoBios 22(3):1-6.