Introduction and Background

2005-09-27 CM 555 c6 480

An epipophysis in a neural arch of a juvenile Apatosaurus, CM 555. From this post.

I have three goals with this post:

  1. To document the range of variation in epipophyses in the cervical vertebrae of sauropods.
  2. To show that the “finger-like processes” overhanging the cervical postzygapophyses in the newly described Qijianglong are not novel or mysterious structures, just very well developed epipophyses.
  3. Finally, to show that similar long, overhanging epipophyses are present in other mamenchisaurids, although as far as I can tell no-one has noted them previously.

Epipophyses are muscle attachment points dorsal to the postzygapophyses, for the insertion of long, multi-segment epaxial (dorsal) neck muscles in birds and other dinosaurs. I know that they turn up occasionally in non-dinosaurian archosaurs, and possibly in other amniotes, but for the purposes of this post I’m only considering their distribution in sauropods. For some quick background info on epipophyses and the muscles that attach to them, see the second half of this post, and see Wedel and Sanders (2002) and Taylor and Wedel (2013a) for further discussion and more pictures.

OMNH emu vert 480

Before we start with the pictures, a fiddly nomenclatural point: this muscle attachment point dorsal to the postzyg has traded under at least six names to date.

  1. The ‘Owenian’ term, used by virtually all non-avian theropod workers, by Sereno et al. (1999) for Jobaria, and probably by loads of other sauropod workers (including myself, lately) is epipophysis.
  2. Beddard (1898) referred to this feature in birds as the hyperapophysis; this term seems to have fallen completely out of use.
  3. Boas (1929), again referring to birds, called it the processus dorsalis. Zweers et al. (1987: page 138 and table 1) followed this terminology, which is how I learned of it when I was an undergrad at OU.
  4. Baumel and Witmer (1993) called this feature in birds the torus dorsalis (note 125 on page 87), which some authors have informalized to dorsal torus (e.g., Harris 2004: page 1243 and fig. 1). Baumel and Witmer (1993: page 87) note that, “the use of ‘Torus’ is preferable since it avoids confusion with the spinous [dorsal] process of the neural arch”.
  5. In my own early papers (e.g., Wedel et al. 2000b) and blog posts I called this feature the dorsal tubercle, which was my own attempt at an informal term matching ‘processus dorsalis’ or ‘torus dorsalis’. That was unfortunate, since there are already several other anatomical features in vertebrates that go by the same name, including the dorsal-facing bump on the dorsal arch of the atlas in many vertebrates, and a bump on the humerus in birds and some other taxa. In more recent papers (e.g., Taylor and Wedel 2013a) I’ve switched over to ‘epipophysis’.
  6. In the last post, Mike coined the term parapostzygapophysis for this feature in Qijianglong. [Note: he now regrets this.]

As usual, if you know of more terms for this feature, or additional history on the ones listed above, please let us know in the comments.

Now, on to the survey.

Prosauropods

Leonerasaurus_cervical_vertebrae - Pol et al 2011 fig 5

I haven’t seen very many prominent epipophyses in basal sauropodomorphs. Probably the best are these in the near-sauropod Leonerasaurus, which is very sauropod-like in other ways as well. Modifed from Pol et al. (2011: fig. 5).

This combination of photograph and interpretive drawing neatly shows why it’s often difficult to spot epipophyses in photos: unless you can make out the postzygapophyseal facet, which is often located more anteriorly than you might guess, you can’t tell when the epipophysis projects further posteriorly, as in the last of these vertebrae. In this case you can make it out, but only because the interpretive drawing shows the facet much more clearly than the photo.

Basal sauropods

Tazoudasaurus cervical - Allain and Aquesbi 2008 fig 9i-j

The most basal sauropod in which I have seen clear evidence of epipophyses is Tazoudasaurus. They’re not very apparent in lateral view, but in posterior view the epipophyses are clearly visible as bumps in the spinopostzygapophyeal laminae (SPOLs). Modified from Allain and Aquesbi (2008: fig. 9).

Jobaria epipophyes

In addition to Qijianglong, some other basal eusauropods have prominent epipophyses. Probably the best known is Jobaria; Sereno et al. (1999: fig. 3) figured and labeled the epipophysis in one of the cervical vertebrae. The vertebra image in that figure is tiny (nice work, glam-magz!), so here are some sketches of Jobaria mid-cervicals (from two different individuals) that I made back in the day when I was doing the research for Gary Staab’s Jobaria neck sculpture (see Sanders et al. 2000 for our SVP abstract about that project).

Turiasaurus also has prominent, overhanging epipophyses in at least some of its cervical vertebrae. You can just make one out as a tiny spike a few pixels long in Royo-Torres et al. (2006: fig. 1K). I have seen that cervical firsthand and I can confirm that the epipophyses in Turiasaurus are virtually identical to those in Jobaria.

Other mamenchisaurids

It’s not air-tight, but there is suggestive evidence of projecting epipophyses in some other mamenchisaurids besides Qijianglong.

Mamenchisaurus epipophyses - lateral view

If you’re really hardcore, you may remember that back in 2005, Mike got to go up on a lift at the Field Museum of Natural History to get acquainted with a cast skeleton of Mamenchisaurus hochuanensis that was mounted there temporarily. During that adventure he took some photos that seem to show projecting epipophyses in at least two of the mid-cervicals. At least, if they’re not epipophyses, I don’t know what they might be.

Mamenchisaurus epipophyses - medial view

Here they are again in medial view. My only reservation is that these vertebrae were distorted to begin with, and some features of the cast are very difficult to interpret. So, probably epipophyses, but it would be nice to check the original material at some point.

Mamenchisaurus youngi epipophyses

Something similar may be present in some posterior cervical vertebrae of Mamenchisaurus youngi. Here’s Figure 17 from Ouyang and Ye (2002). The “poz” label does not not seem to be pointing to the articular facet of the postzygapophysis, which looks to be a little more anterior and ventral, below the margin of the PODL. If that’s the case, then C15 has long, overhanging epipophyses like those of Jobaria. C16 has a more conservative bump, which is to be expected – the epipophyses typically disappear through the cervico-dorsal transition.

Omeisaurus epipophysis

Finally, here’s a cervical vertebra of Omeisaurus junghsiensis from Young (1939: fig. 2). I don’t want to hang very much on just a few pixels, but my best guess at the extent of the postzygapophyseal articular facet is shown in the interpretation above. If that’s correct, then this specimen of Omeisaurus had really long epipophyses, rivaling those of Qijianglong. Unfortunately that’s impossible to check, because this specimen has been lost (pers. comm. from Dave Hone, cited in Taylor and Wedel 2013).

Diplodocoidea

Haplocanthosaurus epipophyses - Hatcher 1903

Haplocanthosaurus nicely shows that the epipophyses can be large in terms of potential muscle attachment area without projecting beyond the posterior margins of the postzygapophyses. Here is C14 of H. priscus, CM 572, in posterior and lateral views, modified from Hatcher (1903: plate 1).

diplodocid epipophyses

Epipophyses that actually overhang the postzygapophyses are not common in Diplodocidae but they do occasionally occur. Here are prominent, spike-like epipophyses in Diplodocus (upper left, from Hatcher 1901: plate 3), Barosaurus (upper right), Kaatedocus (lower left, Tschopp and Mateus 2012: fig. 10), and Leinkupal (lower right, Gallina et al. 2014: fig. 1).

NIgersaurus cervical - Sereno et al 2007 fig 3

Of course, the champion epiphysis-bearer among diplodocoids is the weird little rebbachisaurid Nigersaurus. Here’s a Nigersaurus mid-cervical, from Sereno et al. (2007: fig. 3). Note that the projecting portions of the epipophysis is roughly as long as the articular surface of the postzygapophysis.

Macronaria

Australodocus epipophysis

The epipophysis in this cervical of Australodocus just barely projects beyond the posterior margin of the postzygapophysis.

Giraffatitan c8 epipophyses

In Giraffatitan, epipophyses are absent or small in anterior cervicals but they are prominent in C6-C8. Here’s a posterolateral view of C8, showing very large epipophyses that are elevated several centimeters above the postzygapophyses. You can also see clearly in this view that the spinopostzygapophyseal lamina (SPOL) and postzygodiapophyseal lamina (PODL) converge at the epipophysis, not the postzygapophysis itself.

Sauroposeidon epipophyses

The holotype of Sauroposeidon, OMNH 53062, is similar to Giraffatitan in that the two anterior cervical vertebrae (possibly C5 and C6) have no visible epipophyses, but epipophyses are prominent in the two more posterior vertebrae (possibly C7 and C8). Click to enlarge – I traced the articular facet of the postzygapophysis in ?C8 to more clearly separate it from the epipophysis. For a high resolution photograph of that same vertebra that clearly shows the postzyg facet and the epipophysis dorsal to it, see this post.

Oddly enough, I’ve never seen prominent epipophyses in a titanosaur. In Malawisaurus, Trigonosaurus, Futalognkosaurus, Rapetosaurus, Alamosaurus, and Saltasaurus, the SPOLs (such as they are – inflated-looking titanosaur cervicals do not have the same crisply-defined laminae seen in most other sauropods) merge into the postzygapophyseal rami and there are no bumps sticking up above or out beyond the articular facets of the postzygs. I don’t know what to make of that, except to note that several of the animals just mentioned have mediolaterally wide, almost balloon-shaped cervical neural spines. In our 2013 PeerJ paper, Mike and I argued that the combination of tall neural spines and tall epipophyses in the cervical vertebrae of sauropods made them functionally intermediate between crocs (huge neural spines, no epipophyses) and birds (small or nearly nonexistent neural spines, big epipophyses). Perhaps most titanosaurs reverted to a more croc-like arrangement with most of the long epaxial neck muscles inserting on the neural spine instead of the postzygapophyseal ramus. I’ve never seen that possibility discussed anywhere, nor the apparent absence of epipophyses in most titanosaurs. As usual, if you know otherwise, please let me know in the comments!

malawisaurus-cervicals

Cervical vertebrae of Malawisaurus from Gomani (2005: fig. 9): not an epipophysis in sight. But check out the spike-like neural spines – these are so wide from side to side that from the front they look like party balloons.

And as long as we’re discussing the phylogenetic distribution of epipophyses, it is interesting that long, overhanging epipophyses are so broadly but sporadically distributed. They turn up in some non-neosauropods (Jobaria, Turiasaurus, Omeisaurus) and some diplodocoids (Nigersaurus, the occasional vertebra in Diplodocus and Leinkupal), but not in all members of either assemblage, and they seem to be absent in Macronaria (although many non-titanosaurs have shorter epipophyses that don’t overhang the postzygs). I strongly suspect that a lot of this is actually individual variation that we’re not perceiving as such because our sample sizes of almost all sauropods are tiny, usually just one individual. Epipophyses are definitely muscle attachment sites in birds and no better hypothesis has been advanced to explain their presence in other archosaurs. Muscle attachment scars are notoriously variable in terms of their relative development and expression among individuals, and it would be odd if epipophyses were somehow exempt from that inherent variability.

It also seems more than likely that ontogeny plays a role: progressive ossification of tendons attached at the epipophyses would have the effect of elongating the preserved projection. And since for some aspects of sauropod vertebral morphology, serial position recapitulates ontogeny (Wedel and Taylor 2013b), it shouldn’t be surprising that we see differences in the prominence of the epipophyses along the neck.

Back to Qijianglong

By now it should be clear that the “finger-like processes” in Qijianglong are indeed epipophyses, and although they are quite long, they aren’t fundamentally different from what we see in many other sauropods. I haven’t gone to the trouble, but one could line up all of the vertebrae figured above in terms of epipophysis size or length, and Qijianglong would sit comfortably at one end with Omeisaurus and Mamenchisaurus, just beyond Nigersaurus and Jobaria.

FIGURE 11. Anterior cervical series of Qijianglong guokr (QJGPM 1001) in left lateral views unless otherwise noted. A, axis; B, cervical vertebra 3; C, cervical vertebra 4; D, cervical vertebrae 5 and 6; E, cervical vertebra 7 and anterior half of cervical vertebra 8 (horizontally inverted; showing right side); F, posterior half of cervical vertebra 8 and cervical vertebra 9; G, cervical vertebra 10; H, cervical vertebra 11; I, close-up of the prezygapophy- sis-postzygapophysis contact between cervical vertebrae 3 and 4 in dorsolateral view, showing finger-like process lateral to postzygapophysis; J, close- up of the postzygapophysis of cervical vertebra 5 in dorsal view, showing finger-like process lateral to postzygapophysis. Arrow with number indicates a character diagnostic to this taxon (number refers to the list of characters in the Diagnosis). All scale bars equal 5 cm. Abbreviations: acdl, anterior centrodiapophyseal lamina; cdf, centrodiapophyseal fossa; plc, pleurocoel; pocdl, postcentrodiapophyseal lamina; poz, postzygapophysis; pozcdf, post- zygapophyseal centrodiapophyseal fossa; pozdl, postzygodiapophyseal lamina; ppoz, finger-like process lateral to postzygapophysis; ppozc, groove for contact with finger-like process; przdl, prezygodiapophyseal lamina; sdf, spinodiapophyseal fossa.

Cervical vertebrae of Qijianglong (Xing et al. 2015: fig. 11)

The strangest thing about the epipophyses in Qijianglong is that they seem to be bent or broken downward in two of the vertebrae (B and H in the figure above). I assume that’s just taphonomic distortion – the cervical shown in H wouldn’t even be able to articulate with the vertebra behind it if the epipophysis really drooped down like that. The epipophyses in Qijianglong seem to mostly manifest as thin spikes of bone (or maybe plates, as shown in B and I), so it’s not surprising that they would get distorted – most of the vertebrae shown above have cervical ribs that are incomplete or missing as well.

One more noodle-y thought about big epipophyses. I wrote in the last section that I’ve never seen them in titanosaurs, possibly because titanosaurs have big neural spines for their epaxial muscles to attach to. Maybe long, overhanging epipophyses are so common in mamenchisaurids because their neural spines are so small and low. Although we tend to think of them as a basal group somewhat removed from the “big show” in sauropod evolution – the neosauropods – mamenchisaurids did a lot of weird stuff. At least in terms of their neck muscles, they may have been the most birdlike of all sauropods. Food for thought.

References

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There’s a new mamenchisaurid in town! It’s called Qijianglong (“dragon of Qijiang”), and it’s the work of Xing et al. (2015).

Life restoration of Qijianglong, apparently by lead author Xing Lidar.

Life restoration of Qijianglong, by Cheung Chungtat.

As far as I can make out, the life restoration is also due to Xing Lida: at least, every instance of the picture I’ve seen says “Credit: Xing Lida”. If that’s right, it’s an amazing display of dual expertise to produce both the science and the art! We could quibble with details, but it’s a hundred times better than I could ever do. [Update: no, it’s by Cheung Chungtat, but being uniformly mis-attributed in the media. Thanks to Kevin for the correction in the comment below.]

There’s a mounted skeleton of this new beast in the museum local to where it was found, though I don’t know how much of the material is real, or cast from the real material. Here it is:

A reconstructed skeleton of Qijianglong now on display in Qijiang Museum

A reconstructed skeleton of Qijianglong now on display in Qijiang Museum

A new sauropod is always great news, of course, and it’s a source of shame to us that we cover so few of them here on SV-POW!. (Just think of some of the ones we’ve missed recently … Leikupal, for example.)

But as is so often the case, the most interesting thing about this new member of the club is its vertebrae — specifically the cervicals. Here they are:

FIGURE 11. Anterior cervical series of Qijianglong guokr (QJGPM 1001) in left lateral views unless otherwise noted. A, axis; B, cervical vertebra 3; C, cervical vertebra 4; D, cervical vertebrae 5 and 6; E, cervical vertebra 7 and anterior half of cervical vertebra 8 (horizontally inverted; showing right side); F, posterior half of cervical vertebra 8 and cervical vertebra 9; G, cervical vertebra 10; H, cervical vertebra 11; I, close-up of the prezygapophy- sis-postzygapophysis contact between cervical vertebrae 3 and 4 in dorsolateral view, showing finger-like process lateral to postzygapophysis; J, close- up of the postzygapophysis of cervical vertebra 5 in dorsal view, showing finger-like process lateral to postzygapophysis. Arrow with number indicates a character diagnostic to this taxon (number refers to the list of characters in the Diagnosis). All scale bars equal 5 cm. Abbreviations: acdl, anterior centrodiapophyseal lamina; cdf, centrodiapophyseal fossa; plc, pleurocoel; pocdl, postcentrodiapophyseal lamina; poz, postzygapophysis; pozcdf, post- zygapophyseal centrodiapophyseal fossa; pozdl, postzygodiapophyseal lamina; ppoz, finger-like process lateral to postzygapophysis; ppozc, groove for contact with finger-like process; przdl, prezygodiapophyseal lamina; sdf, spinodiapophyseal fossa.

Xing et al. (2015), FIGURE 11. Anterior cervical series of Qijianglong guokr (QJGPM 1001) in left lateral views unless otherwise noted. A, axis; B, cervical vertebra 3; C, cervical vertebra 4; D, cervical vertebrae 5 and 6; E, cervical vertebra 7 and anterior half of cervical vertebra 8 (horizontally inverted; showing right side); F, posterior half of cervical vertebra 8 and cervical vertebra 9; G, cervical vertebra 10; H, cervical vertebra 11; I, close-up of the prezygapophy- sis-postzygapophysis contact between cervical vertebrae 3 and 4 in dorsolateral view, showing finger-like process lateral to postzygapophysis; J, close- up of the postzygapophysis of cervical vertebra 5 in dorsal view, showing finger-like process lateral to postzygapophysis. Arrow with number indicates a character diagnostic to this taxon (number refers to the list of characters in the Diagnosis). All scale bars equal 5 cm. Abbreviations: acdl, anterior centrodiapophyseal lamina; cdf, centrodiapophyseal fossa; plc, pleurocoel; pocdl, postcentrodiapophyseal lamina; poz, postzygapophysis; pozcdf, post- zygapophyseal centrodiapophyseal fossa; pozdl, postzygodiapophyseal lamina; ppoz, finger-like process lateral to postzygapophysis; ppozc, groove for contact with finger-like process; przdl, prezygodiapophyseal lamina; sdf, spinodiapophyseal fossa.

(At first, I couldn’t figure out what this pocdl abbreviation meant. Then I realised it was a vanilla posterior centrodiapophyseal lamina. Come on, folks. That element has had a standard abbreviation since 1999. Let’s use our standards!)

The hot news in these cervicals is the presence of what the authors call “a distinct finger-like process extending from the postzygapophyseal process beside a zygapophyseal contact”. They don’t give a name to these things, but I’m going to call them parapostzygapophyses since they’re next to the postzygapophyses. [Update: see the comment from Matt below.]

You can get some sense of this morphology from the figure above — although it doesn’t help that we’re looking at tiny greyscale images which really don’t convey 3d structure at all. The best illustration is part J of the figure:

XingEtA2015-qijianglong-fig11J

What are these things? The paper itself says disappointingly little about them. I quote from page 9:

From the axis to at least the 14th cervical vertebra, a finger- like process extends posteriorly above the postzygapophysis and overlaps onto the dorsolateral surface of the prezygapophysis of the next vertebra (Fig. 11I, J). These processes are unique to Qijianglong, unlike all previously known mamenchisaurids that are preserved with cervical vertebrae (e.g., Chuanjiesaurus, Mamenchisaurus spp., Omeisaurus spp., Tonganosaurus). Therefore, the neck of Qijianglong presumably had a range of motion restricted in sideways.

That’s it.

So what are these things? The authors — who after all have seen the actual fossils, not just the rather inadequate pictures — seem to assume that they are a stiffening adaptation, but don’t discuss their reasoning. My guess — and it’s only a guess — it that they assumed that this is what was going on with these processes because it’s what people have assumed about extra processes on xenarthrous vertebrae. But as best as I can determine, that’s not been demonstrated either, only assumed. Funny how these things seem to get a pass.

Armadillo lumbar vertebrae in posterior, anterior and right lateral views.

Armadillo lumbar vertebrae in posterior, anterior and right lateral views.

So what are these processes? It’s hard to say for sure without having seen the fossils, or at least some better multi-view photos, but the obvious guess is that they are our old friends epipophyses, in extreme form. That is, they are probably enlarged attachment points for posteriorly directed dorsal muscles, just as the cervical ribs are attachment points for posteriorly directly ventral muscles.

It’s a shame that Xing et al. didn’t discuss this (and not only because it would probably have meant citing our paper!) Their new beast seems to have some genuinely new and interesting morphology which is worthy of a bit more attention than they gave it, and whose mechanical implications could have been discussed in more detail. Until more is written about these fossils (or better photographs published) I think I am going to have to suspend judgement on the as-yet unjustified assumption that the parapostzygs were there to make the neck rigid against transverse bending.

A final thought: doesn’t JVP seem terribly old-fashioned now? It’s not just the paywall — apologies to those many of you who won’t be able to read the paper. The greyscaling of the figures is part of it — something that makes no sense at all in 2015. The small size and number of the illustrations is also a consequence of the limited page-count of a printed journal — it compares poorly with, for example, the glorious high-resolution colour multiview illustrations in Farke et al.’s (2013) hadrosaur description in PeerJ. Seems to me that, these days, all the action is over at the OA journals with infinite space — at least when it comes to descriptive papers.

References

  • Farke, Andrew A., Derek J. Chok, Annisa Herrero, Brandon Scolieri and Sarah Werning. (2013) Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids. PeerJ 1:e182. doi:10.7717/peerj.182
  • Xing Lida, Tetsuto Miyashita, Jianping Zhang, Daqing Li, Yong Ye, Toru Sekiya, Fengping Wang & Philip J. Currie. 2015. A new sauropod dinosaur from the Late Jurassic of China and the diversity, distribution, and relationships of mamenchisaurids. Journal of Vertebrate Paleontology. doi:10.1080/02724634.2014.889701

 

LACM dino camp 3 - Mamenchisaurus and Triceratops 1

Last night London and I spent the night in the Natural History Museum of Los Angeles County (LACM), as part of the Camp Dino overnight adventure. So we got lots of time to roam the exhibit halls when they were–very atypically–almost empty. Above are the museum’s mounted Triceratops–or one of them, anyway–and mounted cast of the Mamenchisaurus hochuanensis holotype, presented in glorious not-stygian-darkness (if you went through the old dino hall, pre-renovation, you know what I mean).

LACM dino camp 1 - dueling dinos

We got there early and had time to roam around the museum grounds in Exposition Park. The darned-near-life-size bronze dinos out front are a minor LA landmark.

LACM dino camp 2 - fountain

The rose garden was already closed, but we walked by anyway, and caught this rainbow in the big fountain.

LACM dino camp 4  - Mamenchisaurus and Triceratops 2After we checked in we had a little time to roam the museum on our own. I’ve been meaning to blog about how much I love the renovated dinosaur halls. The bases are cleverly designed to prohibit people touching the skeletons without putting railings or more than minimal glass in the way, and you can walk all the way around the mounted skeletons and look down on them from the mezzanine–none of that People’s Gloriously Efficient Cattle Chute of Compulsory Dinosaur Appreciation business. Signage is discreet and informative, and so are the handful of interactive gizmos. London and I spent a few minutes using a big touch-screen with a slider that controlled continental drift from the Triassic to the present–a nice example of using technology to add value to an exhibit without taking away from the real stuff that’s on display. There are even a few places to sit and just take it all in. That’s pretty much everything I want in a dinosaur hall.

Also, check out the jumbotron on the left in the above photo. It was running a (blessedly) narration-free video on how fossils are found, collected, prepared, mounted, and studied, on about a five-minute loop. Lots of pretty pictures. Including this next one.

LACM dino camp 5 - big ilium photo

There are a couple of levels of perspective distortion going on here, both in the original photo and in my photo of that photo projected on the jumbotron. Still, I feel confident positing that that is one goldurned big ilium. I’m not going to claim it’s the biggest bone I’ve ever seen–that rarely ends well–but sheesh, it’s gotta be pretty freakin’ big. And apparently a brachiosaurid, or close to it. Never mind, it’s almost certainly an upside-down Triceratops skull. Thanks to Adam Yates for the catch. I will now diminish, and go into the West.

LACM dino camp 6 - ceratopsian skulls

Triceratops, Styracosaurus, and Einiosaurus–collect the whole set!

LACM dino camp 7 - tyrants

Of course, the centerpiece of the second dinosaur hall–and how great is it that there are two!?–is the T. rex trio: baby, juvenile (out of frame to the right), and subadult. Yes, subadult: the “big” one is not as big as the really big rexes, and from the second floor you can see unfused neural arches in some of the caudal vertebrae (many thanks to Ashley Fragomeni for pointing those out to me on a previous visit).

LACM dino camp 8 - baby rex

Awwwww! C’mere, little fella!

LACM dino camp 9 - pneumatic diplodocid caudals

Still, this ain’t Vulgar Overstudied Theropod Picture of the Week. Here are some sweet pneumatic diplodocid caudals in the big wall o’ fossils (visible behind Mamenchisaurus in the overhead photo above). The greenish color is legit–in the Dino Lab on the second floor, they’re prepping a bunch of sauropod elements that look like they were carved out of jade.

Sculpey allosaur claws

Sudden violent topic shift, the reason for which will be become clear shortly: London and I have been sculpting weapons of mass predation in our spare time. In some of the photos you may be able to see his necklace, which has a shark tooth he sculpted himself. Here are a couple of allosaur claws I made–more on those another time.

LACM dino camp 10  - molding and casting

The point is, enthusiasm for DIY fossils is running very high at Casa Wedel, so London’s favorite activity of the evening was molding and casting. Everyone got to make a press mold using a small theropod tooth, a trilobite, or a Velociraptor claw. Most of the kids I overheard opted for the tooth, but London went straight for the claw.

LACM dino camp 11 - raptor claw mold

Ready for plaster! Everyone got to pick up their cast at breakfast this morning, with instructions to let them cure until this evening. All went well, so I’ll spare you a photo of this same shape in reverse.

LACM dino camp 12 - Camp Wedel in the African bush

We were split into three tribes of maybe 30-40 people each, and each tribe bedded down in a different hall. The T. rex and Raptor tribes got the North American wildlife halls, but our Triceratops tribe got the African wildlife hall, which as a place to sleep is about 900 times cooler. Someone had already claimed the lions when we got there, so London picked hyenas as our totem animals.

LACM dino camp 13 - London with ammonite

Lights out was at 10:30 PM, and the lights came back on at 7:00 this morning. Breakfast was out from 7:15 to 8:00, and then we had the museum to ourselves until the public came in at 9:30. So I got a lot of uncluttered photos of stuff I don’t usually get to photograph, like this ammonite. Everyone should have one of these.

LACM dino camp 14 - Wedel boys with Carnotaurus

London’s favorite dino in the museum is Carnotaurus. It’s sufficiently weird that I can respect that choice.

LACM dino camp 15 - London with rexes

Not that there’s anything wrong with the old standards, especially when they’re presented as cleanly and innovatively as they are here.

LACM dino camp 16 - Matt with Argentinosaurus

Finally, the LACM has a no tripod policy, and if they see you trying to carry one in they will make you take it back to your car. At least during normal business hours. But no one searched my backpack when we went in last night, and I put that sucker to some good use. Including getting my first non-bigfoot picture of the cast Argentinosaurus dorsal. It was a little deja-vu-ey after just spending so much time with the giant Oklahoma Apatosaurus–elements of the two animals really are very comparable in size.

If you’re in the LA area and interested in spending a night at the museum–or at the tar pits!–check out the “Overnight Adventures” page on the museum’s website. Cost is $50 per person for members or $55 for non-members, and worth every penny IMHO. It’s one of those things I wish we’d done years ago.

Posting palaeo papers on arXiv

September 28, 2012

Over on Facebook, where Darren posted a note about our new paper, most of the discussion has not been about its content but about where it was published. We’re not too surprised by that, even though we’d love to be talking about the science. We did choose arXiv with our eyes open, knowing that there’s no tradition of palaeontology being published there, and wanting to start a new tradition of palaeontology being routinely published there. Having now made the step for the first time, I see no reason ever to not post a paper on arXiv, as soon as it’s ready, before — or maybe even instead of — submitting it to a journal.

(Instead of? Maybe. We’ll discuss that below.)

The key issue is this: science isn’t really science until it’s out there where it can be used. We wrote the bulk of the neck-anatomy paper back in 2008 — the year that we first submitted it to a journal. In the four years since then, all the observations and deductions that it contains have been unavailable to the world. And that is stupid. The work might just as well never have been done. Now that it’s on arXiv, that’s over. I was delighted to get an email less than 24 hours after the paper was published, from an author working on a related issue, thanking us for posting the paper, saying that he will now revise his own in-prep manucript in light of its findings, and cite our paper. Which of course is the whole point: to get our science out there where it can do some damage.

Because the alternative is horrible, really. Horribly wasteful, horribly dispiriting, horribly retarding for science. For example, a couple of weeks ago in his SVPCA talk, David Norman was lamenting again that he never got around to publishing the iguanodont systematic work that was in his dissertation, I-don’t-know-how-many-years-ago. The result of that interminable delay is that others have done other, conflicting iguanodont systematic work, and Norman is now trying belatedly to undo that and bring his own perspective. A terrible an unnecessary slowing of ornithopod science, and a waste of duplicated effort. (Thankfully it’s only ornithopods.)

And of course David Norman is very far from being alone. Pretty much any palaeontologist you talk to will tell you of a handful of papers — many more in some cases — that were finished many years previously but have never seen the light of day. (I still have a couple myself, but there is no point in resurrecting them now because progress has overtaken them.) I wonder what proportion of all Ph.D work ever sees the light of day? Half? Less? It’s crazy.

Figure 8. Sauropod cervical vertebrae showing anteriorly and posteriorly directed spurs projecting from neurapophyses. 1, cervical 5 of Sauroposeidon holotype OMNH 53062 in right lateral view, photograph by MJW. 2, cervical 9 of Mamenchisaurus hochuanensis holotype CCG V 20401 in left lateral view, reversed, from photograph by MPT. 3, cervical 7 or 8 of Omeisaurus junghsiensisYoung, 1939 holotype in right lateral view, after Young (1939, figure 2). (No specimen number was assigned to this material, which has since been lost. D. W. E. Hone personal communication, 2008.)

Publish now, publish later

So, please folks: we all need to be posting our work on preprint servers as soon as we consider it finished. It doesn’t mean that the posted versions can’t subsequently be obsoleted by improved versions that have gone through peer-review and been published in conventional journals. But it does mean that the world can know about the work, and build on it, and get the benefit of it, as soon as it’s done.

You see, we have a very fundamental problem in academia: publishing fulfils two completely separate roles. Its primary role (or at least the role that should be primary) is to make work available to the community; the secondary role is to provide a means of keeping score — something that can be used when making decisions about who to appoint to jobs, when to promote, who gets grants, who gets tenure and so on. I am not going to argue that the latter shouldn’t happen at all — clearly a functioning community needs some way to infer the standing of its participants. But I do think it’s ridiculous when the bean-counting function of publication trumps the actual publication role of publication. Yet we’ve all been in a position where we have essentially complete work that could easily go on a blog, or in the PalAss newsletter, or in a minor journal, or somewhere — but we hang onto it because we want to get it into a Big Journal.

Let me say again that I do realise how unusual and privileged my own position is: that a lot of my colleagues do need to play the Publication Prestige game for career reasons (though it terrifies my how much time some colleagues waste squeezing their papers into two-and-a-half-page format in the futile hope of rolling three sixes on the Science ‘n’ Nature 3D6). Let’s admit right now that most palaeontologists do need to try to get their work into Proc B, or Paleobiology, or what have you. Fair enough. They should feel free. But the crucial point is this: that is no reason not to post pre-prints so we can all get on with actually benefitting from your work in the mean time.

Actually, I feel pretty stupid that it’s taken me this long to realise that all my work should go up on arXiv.

Figure 11. Archosaur cervical vertebrae in posterior view, Showing muscle attachment points in phylogenetic context. Blue arrows indicate epaxial muscles attaching to neural spines, red arrows indicate epaxial muscles attaching to epipophyses, and green arrows indicate hypaxial muscles attaching to cervical ribs. While hypaxial musculature anchors consistently on the cervical ribs, the principle epaxial muscle migrate from the neural spine in crocodilians to the epipophyses in non-avial theropods and modern birds, with either or both sets of muscles being significant in sauropods. 1, fifth cervical vertebra of Alligator mississippiensis, MCZ 81457, traced from 3D scans by Leon Claessens, courtesy of MCZ. Epipophyses are absent. 2, eighth cervical vertebra ofGiraffatitan brancai paralectotype HMN SII, traced from Janensch (1950, figures 43 and 46). 3, eleventh cervical vertebra of Camarasaurus supremus, reconstruction within AMNH 5761/X, “cervical series I”, modified from Osborn and Mook (1921, plate LXVII). 4, fifth cervical vertebra of the abelisaurid theropod Majungasaurus crenatissimus,UA 8678, traced from O’Connor (2007, figures 8 and 20). 5, seventh cervical vertebra of a turkey, Meleagris gallopavo, traced from photographs by MPT.

Exceptions?

So are there any special cases? Any kinds of papers that we should keep dry until they make it into actual journals? I can think of two classes that you could argue for — one of them convincingly, the other not.

First, the unconvincing one. When I discussed this with Matt (and half the fun of doing that is that usually neither of us really knows what we think about this stuff until we’re done arguing it through), he suggested to me that we couldn’t have put the Brontomerus paper on arXiv, because that would have leaked the name, creating a nomen nudum. My initial reaction was to agree with him that this is an exception. But when I thought about it a bit more, I realised there’s actually no compelling reason not to post such a paper on arXiv. So you create a nomen nudum? So what? Really: what is the negative consequence of that? I can’t think of one. OK, the name will appear on Wikipedia and mailing lists before the ICZN recognises it — but who does that hurt? No-one that I can think of. The only real argument against posting is that it could invite scooping. But is that a real threat? I doubt it. I can’t think of anyone who would be barefaced enough to scoop a taxon that had already been published on arXiv — and if they did, the whole world would know unambiguously exactly what had happened.

So what is the one real reason not to post a preprint? I think that might be a legitimate choice when publicity needs to be co-ordinated. So while nomenclatural issues should not have stopped us from arXiving the Brontomerus paper, publicity should. In preparation for that paper’s publication day, we did a lot of careful work with the UCL publicity team: writing non-specialist summaries, press-releases and FAQs, soliciting and preparing illustrations and videos, circulating materials under embargo, and so on. In general, mainsteam media are only interested in a story if it’s news, and that means you need to make sure it’s new when they first hear about it. Posting the article in advance on a publicly accessible archive would mess that up, and probably damage the work’s coverage in the press, TV and radio.

Publication venues are a continuum

It’s become apparent to us only gradually that there’s really no clear cut-off where a paper becomes “properly published”. There’s a continuum that runs from least to most formal and exclusive:

SV-POW! — arXiv — PLOS ONE — JVP — Nature

1. On SV-POW!, we write what we want and publish it when we want. We can promise you that it won’t go away, but you only have our word for it. But some of what we write here is still science, and has been cited in papers published in more formal venues — though, as far as I know, only by Matt and me so far.

2. On arXiv, there is a bit more of a barrier to clear: you have to get an existing arXiv user to endorse your membership application, and each article you submit is given a cursory check by staff to ensure that it really is a piece of scientific research rather than a diary entry, movie review or spam. Once it’s posted, the paper is guaranteed to remain at the same URL, unchanged, so long as arXiv endures (and it’s supported by Cornell). Crucially, the maths, physics and computer science communities that use arXiv uncontroversially consider this degree of filtering and permanence sufficient to constitute a published, citeable source.

3. At PLOS ONE, your paper only gets published if it’s been through peer-review — but the reviewing criteria pertain only to scientific soundness and do not attempt to evaluate likely impact or importance.

4. At JVP and other conventional journals, your paper has to make it through a two-pronged peer-review process: it has to be judged both sound scientifically (as at PLOS ONE) and also sufficiently on-topic and important to merit appearing in the journal.

5. Finally, at Nature and Science, your paper has to be sound and be judged sexy — someone has to guess that it’s going to prove important and popular.

Where along this continuum does the formal scientific record begin? We could make a case that all of it counts, provided that measures are taken to make the SV-POW! posts permanent and immutable. (This can be done submitting them to WebCite or to a service such as Nature Precedings used to provide.) But whether or not you accept that, it seems clear that arXiv and upwards is permanent, scientific and citeable.

This raises an interesting question: do we actually need to go ahead and publish our neck-anatomy paper in a more conventional venue? I’m honestly not sure at the moment, and I’d be interested to hear arguments in either direction. In terms of the progress of science, probably not: our actual work is out there, now, for the world to use as it sees fit. But from a career perspective, it’s probably still worth our while to get it into a journal, just so it can sit more neatly on our publication lists and help Matt’s tenure case more. And yet I don’t honestly expect any eventual journal-published version to be better in any meaningful way than the one on arXiv. After all, it’s already benefitted from two rounds of peer-review, three if you count the comments of my dissertation examiners. More likely, a journal will be less useful, as we have to cut length, eliminate illustrations, and so on.

So it seems to me that we have a hard choice ahead of us now. Call that paper done and more onto making more science? Or spend more time and effort on re-publishing it in exchange for prestige? I really don’t know.

For what it’s worth, it seems that standard practice in maths, physics and computer science is to republish arXiv articles in journals. But there are some scientists who routinely do not do this, instead allowing the arXiv version to stand as the only version of record. Perhaps that is a route best left to tenured greybeards rather than bright young things like Matt.

Figure 5. Simplified myology of that sauropod neck, in left lateral view, based primarily on homology with birds, modified from Wedel and Sanders (2002, figure 2). Dashed arrows indicate muscle passing medially behind bone. A, B. Muscles inserting on the epipophyses, shown in red. C, D, E. Muscles inserting on the cervical ribs, shown in green. F, G. Muscles inserting on the neural spine, shown in blue. H. Muscles inserting on the ansa costotransversaria (“cervical rib loop”), shown in brown. Specifically: A. M. longus colli dorsalis. B. M. cervicalis ascendens. C. M. flexor colli lateralis. D. M. flexor colli medialis. E. M. longus colli ventralis. In birds, this muscle originates from the processes carotici, which are absent in the vertebrae of sauropods. F. Mm. intercristales. G. Mm. interspinales. H. Mm. intertransversarii. Vertebrae modified from Gilmore (1936, plate 24).

Citing papers in arXiv

Finally, a practicality: since it’ll likely be a year or more before any journal-published version of our neck-anatomy paper comes out, people wanting to use it in their own work will need to know how to cite a paper in arXiv. Standard procedure seems to be just to use authors, year, title and arXiv ID. But in a conventional-journal citation, I like the way that the page-range gives you a sense of how long the paper is. So I think it’s worth appending page-count to the citations. And while you’re at it, you may as well throw in the figure and table counts, too, yielding the version that we’ve been using:

  • Taylor, Michael P., and Mathew J. Wedel. 2012. Why sauropods had long necks; and why giraffes have short necks. arXiv:1209.5439. 39 pages, 11 figures, 3 tables.

Friday evening I was in a pub with Mike, Darren, John Conway, and Emma Lawlor. We were killing time waiting for the Pink Giraffe Chinese restaurant down the street to open. I was chatting with John about “All Todays”, his speculative presentation with Cevdet Kosemen (a.k.a. Nemo Ramjet) on how future sentients might reconstruct Holocene animals if they were known only from fossils. Like his “All Yesterdays” presentation last year, John’s flights of scientific fancy had fired my imagination and gotten me thinking about how paleontology forms sort of a skin or membrane between the bubble of what we know and the surrounding ocean of what we don’t. I decided that we should pass a pad around and each sketch a speculative sauropod.

My own entry is based on the holotype of Mamenchisaurus hochuanensis, which was found almost complete except for the skull (naturally) and forelimbs. I have often joked that diplodocids were basically bipeds whose forelimbs happened to reach the ground. Mamenchisaurs were probably not that back-heavy, but their presacral vertebrae were extremely pneumatic and if our hypothetical future paleontologists had no other sauropod material to work with, I think it’s possible that they would reconstruct the M. hochuanensis holotype as a biped.

I’m not sure there’s much to say about Mike’s brachiosaur, beyond the Ebert-like observation that if a brachiosaur dressed up in a coat and top hat and went cruising for dames, this, I am forced to conclude, is more or less how it would look.

John Conway also drew a mamenchisaur, this time Mamenchisaurus youngi with its bizarrely bent-back sacrum. John’s explanation for the weird sacrum brings to mind ground sloths and–for those who saw “All Yesterdays” at SVPCA 2011–a certain black-feathered therizinosaur. I’d also like to note that he knocked this out in about 5 minutes, thus demonstrating the difference between a professional artist and a mere doodler like myself.

Darren’s hindlimb-less sauropod complements my bipedal Mamenchisaurus. Here the animal, evidently known from only the front half of the skeleton, has been restored as a giant bird. Dig the giant thumb claws and spreading metapodials. Surely, you say, future paleontologists of any species or machine culture would know a pectoral girdle when they saw one. But I’ll bet a sauropod scapulocoracoid could pass for an ilium, if said future paleontologists were still in the early stages of understanding the morphology and diversity of vertebrates. Remember that Seeley described the sauropod Ornithopsis as “a gigantic animal of the pterodactyle kind” based on its pneumatic vertebrae. There is also a long and honorable (?) tradition of mistaking sauropods for hadrosaurs (Sonorasaurus), theropods (Bruhathkayosaurus), and tree trunks (Sauroposeidon), so don’t be too quick to rule this out.

What I want to see next is a skeletal reconstruction of Darren’s sauro-bird, using only elements from the front half of a sauropod skeleton. Anyone want to give it a shot?

Our penultimate entry is Emma’s rendering of an evil bastard snake devouring an innocent baby sauropod. Tragically this one is not speculative–we have very good fossil evidence that the scene shown here really happened, probably a lot. She tried to make it up to us with a smiley face on the next page, but it was too late. We were so depressed after this that we could barely choke down four courses of excellent Chinese food.

One more for the road: a totally new depiction of the enigmatic sauropod Xenoposeidon by yours truly. I expect to see this incorporated into future talks and papers dealing with European sauropod diversity in the Early Cretaceous. Just credit me as you normally would.

That’s all, folks. I hope that speculative sauropod sketches get to be a Thing, and that we see lots more of them from future conferences.

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.

Although I’m on record of being no fan of the tabloids, there’s no doubt that they are hugely influential.  So it has to be good news to find that in the last few hours, both Nature and Science have publicly come out against the Research Works Act.

The Nature Publishing Group (with publishes Nature), writing jointly with Digital Science, published this statement:

Nature Publishing Group (NPG) and Digital Science note the concern amongst the scientific and library communities about the Research Works Act (H.R. 3699), currently under consideration by the U.S. federal government, and wish to clarify our position.

NPG and Digital Science do not support the Research Works Act.

And within the last couple of hours, the American Association for the Advancement of Science (which publishes Science), has followed suit with its own statement:

The nonprofit American Association for the Advancement of Science (AAAS), the world’s largest general scientific society and publisher of the journal Science, today reaffirmed its support for the current public access policy of the U.S. National Institutes of Health (NIH).

Contrary to recent news reports, AAAS does not endorse the Research Works Act, which would prevent the NIH from requiring its grantees to make biomedical research findings freely available via the National Library of Medicine’s Web site.

This is excellent and very welcome news.  I have written to the NPG and AAAS to express my thanks for their statements.

I hope and expect to see other publishers following their example: this page on the Harvard cyber-law site is maintaining a list of AAP-member publishers who have done so.

Line drawing and photograph of the axis and third cervical vertebra of Chuanjiesaurus anaensis (LCD9701-I). Bar = 10 cm. From Sekiya 2011:fig. 6. Note the absurdly elongated postzygapophysis.

And remember — it’s not too late for you to make a difference to the RWA’s success or failure.  See the Alliance for Taxpayer Action’s page, Call to action: Oppose H.R. 3699, a bill to block public access to publicly funded research.