Hi folks,

It’s been a while since I posted here. I haven’t gone off SV-POW! or anything, just going through one of my periodic doldrums (read: super-busy with Other Stuff). I’m writing now to draw your attention to two books that I’m pretty darned excited about.

The first is All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals, by John Conway, Memo Kosemen, and Darren Naish, with skeletal diagrams by Scott Hartman (lulu, Amazon). This is sort of an SV-POW! love-fest, in that Darren is One Of Us, John and Scott let us use their art a lot–even the goofy stuff–and get a shout-out now and then, and I’ve been awed by the work of Memo–a.k.a. Nemo Ramjet–for longer than SV-POW! has existed (he also created Brontosapiens!). But wait–there’s more! One of the first people to review the book is Emily Willoughby, who was also as far as we know the first person after Paco Gasco to illustrate Brontomerus–that image is still Bronto‘s flagship portrait on Wikipedia.

But enough navel-gazing. The book is based around the mind-blowing presentations “All Yesterdays” and “All Todays” at SVPCA 2011 and 2012, both delivered by John Conway. True story: “All Yesterdays” was the intro to the icebreaker/mixer thing at Lyme Regis, so right after the talk people jumped up to grab pints and socialize. Sometime in the next few minutes, John was separately approached by three different paleontologists who thought that “All Yesterdays” should be a book, and wanted to help write it. Those three hopefuls were Darren, Mike, and me. I’m extremely happy that Darren is the one on the book. Mike and I can wrangle sauropods and we’re both “All [Some]days” fanboys, but the book really needed someone approaching tetrapod omniscience, and that’s obviously Darren.

Whoops, that was actually just another paragraph of navel-gazing. Anywho, I knew after this year’s SVPCA that there would be a book, but I had no idea it would be out so soon. I can’t tell you much about the book itself, for two reasons. First, my dead-tree copy is still en route from lulu.com. Second, I wouldn’t tell you much about the book if I could, because you should see it for yourself. It’s firmly in the tradition of speculative zoology but also has a serious point to make about the memes that drive a lot of paleoart. That’s all you need to know–get the book and prepare to be surprised, amused, amazed, and moved to wonder.

The other new book I’m all het up about is Zombie Tits, Astronaut Fish, and Other Weird Animals, by Becky Crew (Amazon, New South Books). My mutual admiration pact with Bec goes back to 2009. She blogged about one of my posts, I blogged about how indescribably wonderful her blog was, she published something I wrote–my first paying gig as a writer, I think. Now she’s blogging at SciAm, which is great, because although she’s smart, irreverent, and freakin’ hilarious, she’s also mortal, and we need to get as much of that good stuff out of her head and into general circulation as possible while she’s still around. (She’s not sick or anything, she’s just going to die sometime in the next century, and if you read her blog I think you’ll agree that that’s too damn soon.) Zombie Tits does not seem to be available stateside yet, but I will keep a weather eye on things and post an update when that changes.

I’ll probably review both books here in due time, if by “review” one means “alternately drool over and hyperbolically gush about with no attempt at objectivity whatsoever”. And I do mean precisely that.

It’s been a while since we’ve served you up a sauropod, so, finally and fittingly, here’s John Conway’s playful Camarasaurus taking a mud bath. Or maybe just trying to hide its hideousness; as the authors of All Yesterdays note, “Camarasaurus [...] is considered by some experts to be among the ugliest of all sauropods”.

Thanks to the wonder of Osborn and Mook (1921), we have already seen multiview illustrations of the pubis and ischium of Camarasaurus. Now we bring you their Camarasaurus sacrum.

This is the sacrum of Camarasaurus supremus AMNH 5761. Top row: dorsal view, with anterior to left. Middle row, from left to right: anterior, left lateral and posterior views. Bottom row: ventral view, with anterior to left. Modified from Ostrom and Mook (1921:figs. 43-44).

It’s instructive to compare with the “Apatosaurusminimus sacrum. Direct comparison is somewhat hindered for two reasons: first, the ilia are fused to that sacrum but not to this; and second, different views are available, so I put the composites together differently. We can’t do anything about the ilia. But to facilitate comparison, here is a reworked version of the “Apatosaurusminimus illustration with the right-lateral view discarded, a ventral-view silhouette added, and the composition mirroring that of Osborn and Mook’s Camarasaurus:

One thing is for sure: whatever else “Apatosaurus” minimus might be, it ain’t Camarasaurus.

References

More goodness from Osborn and Mook’s (1921) gargantuan Camarasaurus monograph, again prepared largely for comparison with “Apatosaurusminimus. Last time, I showed you one of O&M’s pubis illustrations. Now an ischium:

This shows the left ischium AMNH 576o’/Is.4. Left column: proximal aspect. Middle column, from top to bottom: medial, lateral, posterior (no dorsal view was provided). Right column: distal. Heavily modified from Osborn and Mook (1921: fig. 101) — cleaned up, lettering and lines removed, recomposed in a more informative layout, views rescaled to better match each other, and tweaked for colour.

As usual, click through for full resolution (only 989 x 978 this time).

It’s interesting to compare this with the similarly composed illustration of the “Apatosaurusminimus ischium from last week.

References

(First of all, for anyone who’s not familiar with the plural of “pubis”, it’s spelled “pubes” but pronounced “pyoo-bees”. Stop sniggering at the back.)

As Matt and I struggle to figure out the partial pubis that is one of the elements of the Apatosaurusminimus specimen AMNH 675, one of the most helpful references is Osborn and Mook’s (1921) epic monograph on Camarasaurus. It’s not that 675 particularly resembles Cam — it doesn’t. It’s just that Osborn and Mook is very lavishly illustrated, so that it is (as far as I know) the only published paper in the history of sauropod studies to have shown a sauropod pubis in more than one aspect.

Here is one of the two pubes that they illustrated in the six cardinal aspects:

This shows the left pubis AMNH 5761/Pb.2. Top row: proximal aspect, with anterior to left. Middle row, from left to right: anterior, lateral, posterior, medial. Bottom row: distal, with anterior to left. Heavily modified from Osborn and Mook (1921: fig. 102) — cleaned up, lettering and lines removed, recomposed in a more informative layout, views rescaled to better match each other, and tweaked for colour.

As usual, click through for full resolution (only 1159 x 940 this time).

As you can see, the pubis is a very strangely shaped bone, twisted and with odd rugosities everywhere. If you’re very lucky, we’ll discuss these in more detail later. For now, the take-home message is that sauropod pubes are very weird and confusing, and the simple lateral view that’s typically all you ever see is terribly misleading.

References

Probably everyone who reads SV-POW! already knows that the manus, or forefoot, or sauropods was very distinctive.  The metacarpal bones, rather than being splayed out horizontally as in the forefeet of most animals, were arranged more or less vertically in a horseshoe shape, hence the characteristic shape of sauropod manus prints.

This was first recognised by Osborn (1904), a paper which contains the greatest single sentence in any scientific paper:

My previous figures and descriptions of the manus are all incorrect.

Here is the rather beautiful illustration from that paper (fig. 1):

It depicts the right manus, in anterior view,  of AMNH 965, “Morosaurus” sp.  As described by Osborn and Mook (1921:376-377), that genus was subsequently synonymised with Camarasaurus by Mook (1914), following the earlier suggestion of Osborn (1898), and this synonymy is universally accepted — for now, at least.

If anything, trackway evidence suggests that this illustration shows the metacarpals insufficiently vertical, resulting in the manus being too splayed out.

I have nothing more to say about that; just wanted to post the illustration because it’s beautiful and out of copyright (so feel free to use it however you want!)

References

  • Mook, Charles C.  1914.  Notes on Camarasaurus Cope.  Annals of the New York Academy of Science 24:19-22.
  • Osborn, Henry F.  1898.  Additional characters of the great herbivorous dinosaur Camarasaurus.  Bulletin of the American Museum of Natural History 10: 219-233.
  • Osborn, Henry F.  1904.  Manus, sacrum and caudals of Sauropoda.  Bulletin of the American Museum of Natural History 20:181-190.
  • Osborn, Henry Fairfield, and Charles C. Mook.  1921.  Camarasaurus, Amphicoelias and other sauropods of Cope.  Memoirs of the American Museum of Natural History, n.s. 3:247-387, and plates LX-LXXXV.

Last time, we saw why Haplocanthosaurus couldn’t be a juvenile of Apatosaurus or Diplodocus, based on osteology alone.  But there’s more:

Ontogenetic status of Haplocanthosaurus

Here is where is gets really surreal.  Woodruff and Fowler (2012) blithely assume that Haplocanthosaurus is a juvenile of something, but the type specimen of the type species — H. priscus CM 572 — is an adult.  As Hatcher (1903:3) explains:

The type No. 572 of the present genus consists of the two posterior cervicals, ten dorsals, five sacrals, nineteen caudals, both ilia, ischia and pubes, two chevrons, a femur and a nearly complete series of ribs, all in an excellent state of preservation and pertaining to an individual fully adult as is shown by the coössified neural spines and centra.

So far as I can see, Woodruff and Fowler are confused because the second species that Hatcher describes, H. utterbacki, is based on the subadult specimen CM 879.  Where possible in the previous post, I have used illustrations of the adult H. priscus, so that the comparisons are of adult with adult.  The exceptions are the two anterior cervicals and the first dorsal, which are known only from H. utterbacki.  And sure enough, if you look closely at the illustrations, you can see that in these vertebrae and only these vertebrae, Hatcher had the neurocentral junction illustrated — because it wasn’t yet fused.

Haplocanthosaurus posterior, mid and anterior cervical vertebrae, C14, C9 and C4, in right lateral view. C14 of adult H. priscus (from Hatcher 1903:plate I); C9 and C4 of H. utterbacki (from plate II). Red ellipses highlight neurocentral sutures.

As it happens, the difference in ontogenetic status between these two specimens is nicely illustrated by Wedel (2009), although he was only in it for the pneumaticity:

Neurocentral fusion in Haplocanthosaurus. A, B. Posterior cervical vertebra C?12 of sub-adult H. utterbacki holotype CM 879: A, X-ray in right lateral view; B, coronal CT slice showing separate ossificaton of centrum and neural arch. C, D. Mid-dorsal vertebra D6 of adult H. priscus holotype CM 572: X-rays in (A) right lateral and (B) anterior view, showing fully fused neural arch. Wedel (2009:fig. 6)

So H. utterbacki CM 879 certainly is an immature form of something; and that something is Haplocanthosaurus, most likely H. priscus.  (The characters which Hatcher used to separate the two species are not particularly convincing.)

With that out the way, we can move on to …

Phylogenetic analysis

A simple way to evaluate the parsimony or otherwise of a synonymy is to use a phylogenetic analysis. In their abstract, Woodruff and Fowler claim that “On the basis of shallow bifurcation of its cervical and dorsal neural spines, the small diplodocid Suuwassea is more parsimoniously interpreted as an immature specimen of an already recognized diplodocid taxon”.  Without getting into the subject of Suuwassea again — Matt pretty much wrapped that up in part 4 — the point here is that the word “parsimony” has a particular meaning in studies of evolution: it refers to minimising the number of character-state changes.  And we have tools for measuring those.

So let’s use parsimony to evaluate the hypothesis that Haplocanthosaurus is one of the previously known diplodocids.  Pretending for the moment that Haplocanthosaurus really was known only from subadults, how many additional steps would we need to account for if ontogeny were to change its position to make it group with one of the diplodocids?

You don’t need to be a cladistics wizard to do this.  (Which is handy, since I am not one.)  Here’s the method:

  • Start with an existing matrix, add constraints, re-run it, and see how the tree-length changes.  Since I am familiar with it, I started with the matrix from my 2009 paper on brachiosaurs.
  • Re-run the matrix to verify that you get the same result as in the published paper based on it.  This gives you confidence that you’re running it right.  In this case, I got a minimum tree length of 791 steps, just as in Taylor (2009).
  • Add extra instructions to the run-script defining and imposing constraints.  Note that you do not have to mess with the characters, taxa or codings to do this.
  • Run the matrix again, with the constraint in place, and see how the tree-length changes.
  • Repeat as needed with other constraints to evaluate other phylogenetric hypotheses.

(This is how we produced the part of the Brontomerus paper (Taylor et al. 2011:89) where we said “One further step is sufficient to place Brontomerus as a brachiosaurid, a basal (non−camarasauromorph) macronarian, a basal (non−diplodocid) diplodocoid or even a non−neosauropod. Three further steps are required for Brontomerus to be recovered as a saltasaurid, specifically an opisthocoelicaudiine”.  And that’s why we weren’t at all dogmatic about its position.)

Anyway, going through this exercise with Haplocanthosaurus constrained in turn to be the sister taxon to Apatosaurus, Diplodocus, etc., yielded the following results:

  • (no constraint) –  791 steps
  • Apatosaurus — 817 (26 extra)
  • Diplodocus — 825 (34 extra)
  • Barosaurus — 815 (24 extra)
  • Camarasaurus — 793 (2 extra)
  • Brachiosaurus — 797 (6 extra)

(I threw in the other well-known Morrisson-Formation sauropods Camarasaurus and Brachiosaurus, even though Woodruff and Fowler don’t mention them, just because it was easy to do and I was interested to see what would happen.  And when I say Brachiosaurus, I mean B. altithorax, not Giraffatitan.)

I hope you’re as shocked as I am to see that for Haplocanthosaurus to emerge as the sister taxon of any diplodocid needs a minimum of 24 additional steps — or an incredible 34 for it to be sister to Diplodocus.  In other words, the hypothesis is grossly unparsimonious.  Of course, that doesn’t in itself mean that it’s false: but it does render it an extraordinary claim, which means that it needs extraordinary evidence.  And while “the simple spines of Haplocanthosaurus might bifurcate when it grows up” is extraordinary evidence, it’s not in the way that Carl Sagan meant it.

In short, running this simple exercise — it took me about a hour, mostly to remember how to do constraints in PAUP* — would have given Woodruff and Fowler pause for thought before dragging Haplocanthosaurus into their paper.

Oh, and it’s ironic that placing Haplo as sister to Brachiosaurus requires only a quarter as many steps as the closest diplodocid, and as sister to Camarasaurus requires only two steps.  If you really want to synonymise Haplocanthosaurus, Camarasaurus is the place to start.  (But don’t get excited, it’s not Camarasaurus either.  It’s Haplocanthosaurus.)

[By the way, anyone who'd like to replicate this experiment for themselves is welcome: all the files are available on my web-site.  You only really need the .nex file, which you can feed to PAUP*, but I threw in the log-file, the generated tree files and the summary file, too.  Extra Credit: run this same exercise to evaluate the parsimony of Suuwassea as a subadult of one of these other genera.  Report back here when you're done to earn SV-POW! points.]

Conclusion

It’s a truism that we stand on the shoulders of giants.  In the case of sauropod studies, those giants are people like J. B. Hatcher, Charles Gilmore, Osborn and Mook and — bringing it up to date — John McIntosh, Paul Upchurch, Jeff Wilson and Jerry Harris.  When Hatcher described Haplocanthosaurus as a new genus rather than a subadult Diplodocus, he wasn’t naive.  He recognised the effects of ontogeny, and he was aware that one of his two specimens was adult and the other subadult.  He was also probably more familiar with Diplodocus osteology than anyone else has ever been before or since, having written the definitive monograph on that animal just two years previously (Hatcher 1901).

By the same token, people like Upchurch and Wilson have done us all a huge favour by making the hard yards in sauropod phylogenetics.  If we’re going to go challenging the standard consensus phylogeny, it’s just good sense to go back to their work (or the more recent work of others, such as Whitlock 2011), re-run the analyses with our pet hypotheses encoded as constraints, and see what they tell us.

So in the end, my point is this: let’s not waste our giants.  Let’s take the time to get up on their shoulders and survey the landscape from up there, rather than staying down at ground level and seeing how high we can jump from a standing start.

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.
  • Hatcher, J.B. 1903. Osteology of Haplocanthosaurus with description of a new species, and remarks on the probable habits of the Sauropoda and the age and origin of the Atlantosaurus beds; additional remarks on Diplodocus. Memoirs of the Carnegie Museum 2:1-75.
  • Taylor, M.P. 2009. A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914). Journal of Vertebrate Paleontology 29(3):787-806.
  • Taylor, M.P., Wedel, M.J. and Cifelli, R.L. 2011. A new sauropod dinosaur from the Lower Cretaceous Cedar Mountain Formation, Utah, USA. Acta Palaeontologica Polonica 56(1):75-98. doi:10.4202/app.2010.0073
  • Wedel, M.J. 2009. Evidence for bird-like air sacs in saurischian dinosaurs. Journal of Experimental Zoology 311A:611-628.
  • Whitlock, J.A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161(4):872-915. doi: 10.1111/j.1096-3642.2010.00665.x
  • 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.

This is the third post in a series on neural spine bifurcation in sauropods, inspired by Woodruff and Fowler (2012). In the first post, I looked at neural spine bifurcation in Morrison sauropod genera based on the classic monographic descriptions. In the second post, I showed that size is an unreliable criterion for assessing age and that serial variation can mimic ontogenetic change in sauropod cervicals. In this post I look at the evidence for ontogenetic changes in neural spine bifurcation presented by Woodruff and Fowler (2012). This posts builds on the last two, so please refer back to them as needed.

Another opening digression, on the OMNH baby sauropod material this time

Nearly all of the Morrison Formation material in the OMNH collections comes from Black Mesa in the Oklahoma panhandle. It was collected in the 1930s by WPA crews working under the direction of J. Willis Stovall. Adequate tools and training for fossil preparation were in short supply. A lot of the prep was done by unskilled laborers using hammers, chisels, pen-knives, and sandpaper (apologies if you have experience with fossil preparation and are now feeling a bit ill). Uncommonly for the Morrison, the bones are very similar in color to the rock matrix, and the prep guys sometimes didn’t realize that they were sanding through bone until they got through the cortex and  into the trabeculae. Consequently, a lot of interesting morphology on the OMNH Morrison material has been sanded right off, especially some of the more delicate processes on the vertebrae. This will become important later on.

Do the ‘ontogenetic’ series in Woodruff and Fowler (2012) actually show increasing bifurcation through development?

In the Materials and Methods, Woodruff and Fowler (2012:2) stated:

Study specimens comprise 38 cervical, eight dorsal, and two caudal vertebrae from 18 immature and one adult diplodocid (Diplodocus sp., Apatosaurus sp., and Barosaurus sp.), and two immature macronarians (both Camarasaurus sp.).

However, their Table 1 and Supplementary Information list only 15 specimens, not 18. Of the 15, one is probably not a diplodocid (SMA 0009 ‘Baby Toni’) — a fact that, oddly, the authors knew, as stated in the Supplementary Information.  Of the remaining 14 specimens, 11 are isolated vertebrae, so only three represent reasonably complete probably-diplodocoid series (MOR 592, AMNH 7535, and CM 555). From CM 555 they discuss only one vertebra, the C6; and AMNH 7535 is not mentioned at all outside of Table 1 and a passing mention the Supplementary Information, so the subadult data actually used in the paper consist of isolated vertebrae and one articulated series, MOR 592. (For the sake of comparison, in the first post on this topic I looked up 10 articulated series, only two of which–Diplodocus carnegii CM 84/94 and Camarasaurus lentus CM 11338–are even mentioned in Woodruff and Fowler [2012].)

In light of the previous post, on serial variation, the dangers of using isolated vertebrae should by now be apparent. Recall that even adult diplodocids are expected to have completely unsplit spines as far back as C5 (Apatosaurus) or C8 (Barosaurus) and as far forward as D7 (Apatosaurus) or D6 (Barosaurus), and only partially split spines in the adjacent positions. Furthermore, size is a notoriously unreliable criterion of age; MOR 790 8-10-96-204 from Figure 2 in Woodruff and Fowler (2012) also appears in their Figure 3 as the second-smallest vertebra in this ‘ontogenetic’ series, despite most likely coming from a well-fused adult approximately the same size as the D. carnegii individual that represents the end of the series. So without any evidence other than sheer size (if that size overlaps with the adult size range) and degree of neural spine bifurcation (which cannot help but overlap with the adult range, since the adult range encompasses all possible states), simply picking small vertebrae with unsplit spines and calling them juvenile is at best circular and at worst completely wrong–as in the case of MOR 790 8-10-96-204 examined in the last post.

Unfortunately it is not possible to tell what criteria Woodruff and Fowler (2012) used to infer age in their specimens, because they don’t say. Neural arch fusion is discussed in general terms in the Supplementary Information, but in the text and in the figures everything is discussed simply in terms of size. For example:

In the next largest specimen (MOR 790 7-26-96-89, vertebral arch 9.9 cm high), the neural spine is relatively longer still and widens at the apex…

The Supplementary Information provides more evidence that Woodruff and Fowler (2012) did not consider the confounding effects of size, serial position, and ontogenetic stage. In the section on the Mother’s Day Quarry in the Supplementary Information, they wrote:

Because of this size distribution it is not surprising that there are also different ontogenetic stages present which result in cervical centrum lengths varying between 12 and 30 cm.

Now, there may be different ontogenetic stages present in the quarry, and the cervicals in the quarry may vary in length by a factor of 2.5, but the latter does not demonstrate the former. In D. carnegii CM 84/94 the longest postaxial cervical (C14, 642 mm) is 2.6 times the length of the shortest (C3, 243 mm; data from Hatcher 1901). The size range reported as evidence of multiple ontogenetic stages by Woodruff and Fowler (2012) turns out to be slightly less than that expected in a single individual.

With that in mind, let’s look at each of the putative ontogenetic sequences in Woodruff and Fowler (2012):

Anterior cervical vertebrae

Woodruff and Fowler (2012:fig. 3)

The proposed ontogenetic series used by Woodruff and Fowler (2012) for anterior cervical vertebrae consists of:

  • CMC VP7944, an isolated ?Diplodocus vertebra from the Mother’s Day site, which is described in the text but not pictured;
  • MOR 790 7-30-96-132, an isolated vertebra from the same site;
  • MOR 790 8-10-96-204, another isolated vertebra from the same site;
  • MOR 592, from a partial cervical series of a subadult Diplodocus but with the serial position unspecified;
  • ANS 21122, C6 of Suuwassea (included in Fig. 3, but not discussed as evidence in the accompanying text)
  • CM 555, C6 of a nearly complete (C2-C14) cervical series of a subadult Apatosaurus;
  • CM 84/94, C7 of Diplodocus carnegii

CMC VP7944 is not pictured, but from the description in the text it’s perfectly possible that it represents a C3, C4, or C5, all of which have undivided spines even in adult diplodocids. It therefore contributes no information: the hypothesis that the spine is undivided because of ontogeny is not yet demonstrated, and the hypothesis that the spine is undivided because of serial position is not yet falsified.

MOR 790 7-30-96-132 is shown only from the front, so the centrum proportions and the shape of the neural spine cannot be assessed. The neural arch appears to be fused, but the cervical ribs are not. Again, we cannot rule out the possibility that it comes from an very anterior cervical and therefore its undivided spine could be an artifact of its serial position. It therefore contributes no information on possible ontogenetic changes in neural spine bifurcation.

As shown in the previous post, MOR 790 8-10-96-204 is probably a C4 or C5 of an adult or near-adult Diplodocus about the same size as or only slightly smaller than D. carnegii CM 84/94. It is small and has an undivded spine because it is an anterior cervical, not because it is from a juvenile. It therefore contributes no support to the ontogenetic bifurcation hypothesis.

The pictured vertebra of MOR 592 has a shallow notch in the tip of the spine, which is expected in C6 in Apatosaurus and Diplodocus and in C9 and C10 in Barosaurus. The serial position of the vertebra is not stated in the paper, but about half of the anterior cervicals even in an adult diplodocid are expected to have unsplit or shallowly split spines based on serial position alone. Based on the evidence presented, we cannot rule out the possibility that the shallow cleft in the pictured vertebra is an artifact of serial position rather than ontogeny. It therefore contributes no support to the ontogenetic bifurcation hypothesis.

ANS 21122 has an incompletely divided neural spine, which is in fact expected for the sixth cervical in adult diplodocids as shown by A. parvus CM 563/UWGM (in which C6 is missing but C5 has an unsplit spine and C7 a deeply bifid spine) and D. carnegii CM 84/94 (in which C6 is also shallowly bifid). A. ajax NMST-PV 20375 has a wider split in the spine of C6, but the exact point of splitting appears to vary by a position or two among diplodocids. The hypothesis that the spine of ANS 21122 C6 is already as split as it would ever have gotten cannot be falsified on the basis of the available evidence.

CM 555 C6: see the previous paragraph. Note that in ANS 21122 the neural arch and cervical ribs are fused in C6, and in C6 of CM 555 they are not.

CM 84/94 C7 has a deeply split spine, but this expected at that position. C6 of the same series has a much more shallow cleft, and C5 would be predicted to have no cleft at all (recall from the first post that the neural spines of C3-C5 of this specimen are sculptures). So any trend toward increasing bifurcation is highly dependent on serial position; if serial position cannot be specified then it is not possible to say anything useful about the degree of bifurcation in a given vertebra.

Summary. CMC VP7944 and MOR 790 7-30-96-132 could be very anterior vertebrae, C3-C5, in which bifurcation is not expected even in adults. Since they are isolated elements, that hypothesis is very difficult to falsify. MOR 790 8-10-96-204 is almost certainly a C4 or C5 of an adult or near-adult Diplodocus. ANS 21122 and CM 555 C6 are incompletely divided, as expected for vertebrae in that position even in adults. CM 84/94 has a shallowly divided spine in C6 and more deeply bifid spines from C7 onward, just like CM 555.

Verdict: no ontogenetic change has been demonstrated.

Posterior cervical vertebrae

Woodruff and Fowler (2012:Fig. 4A)

The proposed ontogenetic series includes:

  • OMNH 1267 and 1270
  • MOR 790 7-26-96-89
  • MOR 592
  • CM 84/94

OMNH 1267 and 1270 are isolated neural arches of baby sauropods from the Black Mesa quarries. OMNH 1267 does not appear to be bifurcated, but it has a very low neural spine and it was probably sanded during preparation, so who knows what might have been lost. OMNH 1270 actually shows a bifurcation–Woodruff and Fowler (2012:3) describe it as having “a small excavated area”–but again it is not clear that the spines are as intact now as they were in life. More seriously,  since these are isolated elements (you can all join in with the refrain) their serial position cannot be determined with any accuracy, and therefore they are not much use in determining ontogenetic change. Although they are anteroposteriorly short, that does not necessarily make them posterior cervicals. The cervical vertebrae of all sauropods start out proportionally shorter and broader than they end up (Wedel et al. 2000:368-369), and the possibility that these are actually from anterior cervicals–not all of which are expected to have bifurcations–is difficult to rule out.

The other three vertebrae in the series have deeply bifurcated spines. In the text, Woodruff and Fowler (2012:3) make the case that the bifurcation in MOR 592 is deeper than in the preceding vertebra, MOR 790 7-26-96-89. However, the proportions of the two vertebrae are very different, suggesting that they are from different serial positions, and the centrum of MOR 790 7-26-96-89 is actually larger in diameter than that of the representative vertebra from MOR 592. So unless centrum size decreased through ontogeny, these vertebrae are not comparable. As usual, we don’t know where in the neck the isolated MOR 790 vertebra belongs, and we only see it in anterior view. Nothing presented in the paper rules out possibility that is actually an anterior cervical, and in fact the very low neural spines suggest that that is the case.

Allowing for lateral crushing, the vertebra from MOR 592 (again, we are not told which one it is) looks very similar to the D. carnegii CM 84/94 vertebra (C15–again, I had to look it up in Hatcher), and is probably from a similar position in the neck. In comparing the two, Woodruff and Fowler (2012:4) say that in CM 84/94, “the bifurcated area has broadened considerably”, but this clearly an illusion caused by the lateral compression of the MOR 592 vertebra — its centrum is also only half as wide proportionally as in the CM 84/94 vertebra.

Summary. The OMNH vertebrae are of unknown serial position and probably lost at least some  surface bone during preparation, so their original degree of bifurcation is hard to determine. The other three vertebrae in the series all have deeply bifid spines, but they are out of order by centrum size, MOR 790 7-26-96-89 might be an anterior cervical based on its low neural spines, and the “broadening” of the trough between MOR 792 and CM 84/94 is an artifact of crushing.

Verdict: no ontogenetic change has been demonstrated.

Anterior dorsal vertebrae

Woodruff and Fowler (2012:Fig. 5A)

The ontogenetic series here consists of:

  • MOR 790 7-17-96-45
  • MOR 592
  • CM 84/94

As usual, the serial positions of the MOR 592 and CM 84/94 vertebrae are presumably known but not stated in the paper. The D. carnegii CM 84/94 vertebra is D4. Comparisons to the MOR 592 vertebra are not helped by the fact that it is shown in oblique posterior view. Nevertheless, the two vertebrae are very similar and, based on the plates in Hatcher (1901), the MOR 592 vertebra is most likely a D4 or D5 of Diplodocus. The spines in the larger two vertebrae are equally bifurcated, so the inference of ontogenetic increase in bifurcation rests on the smallest of the three vertebrae, MOR 790 7-17-96-45.

MOR 790 7-17-96-45 is an isolated unfused neural arch, clearly from a juvenile. Its serial position is hard to determine, but it is probably not from as far back as D4 or D5 because it appears to lack a hypantrum and shows no sign of the parapophyses, which migrate up onto the neural arch through the cervico-dorsal transition. The element is only figured in anterior view, so it is hard to tell how long it is proportionally. Still, based on the single photo in the paper (which is helpfully shown at larger scale in Fig. 5B), it seems to be reasonably long, with the prezygapophyses, transverse processes, neural spines, and postzygapophyses well separated from anterior to posterior. In fact, I see no strong evidence that it is a dorsal neural arch at all–the arch of a posterior cervical would look the same in anterior view.

Given that MOR 7-17-96-45 lacks a hypantrum and parapophyses, it is not directly comparable to the two larger vertebrae. Although we cannot determine its position in the presacral series, its spine is shallowly bifurcated, to about half the distince from the metapophyses to the postzygapophyses. In Apatosaurus louisae CM 3018, the notch in D3 is about equally deep, and in C15 it is only slightly deeper, still ending above the level of postzygapophyses. So there is some variation in the depth of the bifurcation in the posterior cervicals and anterior dorsals in the North American diplodocids. Without knowing the precise serial position of MOR 7-17-96-45, it is difficult to derive inferences about the ontogeny of neural spine bifurcation.

Diplodocid anterior dorsal vertebrae. Left and right, dorsal vertebrae 3 and 4 of adult Apatosaurus louisae holotype CM 3018, from Gilmore (1936: plate XXV). Center, juvenile neural arch MOR 7-17-96-45, modified from Woodruff and Fowler (2012: fig. 5B), corrected for shearing and scaled up.

What this element does conclusively demonstrate is that the neural arches of posterior cervicals or anterior dorsals in even small, unfused juvenile diplodocids were in fact bifurcated to to a degree intermediate between  D3 and D4 in the large adult Apatosaurus louisae CM3018 — in fact, so far as neural cleft depth is concerned, it makes rather a nice intermediate between them.  (It differs in other respects, most notable that it is proportionally broad, lacks a hypantrum and parapophyses, etc.)

Summary. The two larger specimens in the ‘ontogenetic series’ are from similar serial positions and show the same degree of bifurcation. MOR 7-17-96-45 is from a more anterior position, based on its lack of hypantrum and parapophyses.  Although it is a juvenile, its degree of bifurcation is similar to that of anterior dorsal vertebrae in adult Apatosaurus (and that of C15 in A. louisae CM 3018, if MOR 7-17-96-45 is, in fact, a cervical).

Verdict: no ontogenetic change has been demonstrated.

Posterior dorsal vertebrae

Woodruff and Fowler (2012:Fig. 6A)

The ontogenetic series consists of:

  • OMNH 1261
  • MOR 592
  • CM 84/94

The D. carnegii CM 84/94 vertebra is D6, and based on its almost identical morphology the MOR 592 vertebra is probably from the same serial position. They show equivalent degrees of bifurcation.

OMNH 1261 is another isolated juvenile neural arch. The portion of the spine that remains is unbifurcated. However, the spine is very short and it is possible that some material is missing from the tip. More importantly, the last 3-4 dorsals in Apatosaurus, Diplodocus, and Barosaurus typically have extremely shallow notches in the neural spines or no notches at all. If OMNH 1261 is a very posterior dorsal, it would not be expected to show a notch even when fully mature.

Verdict: no ontogenetic change has been demonstrated.

Woodruff and Fowler (2012:Fig. 7)

Caudal vertebrae

The ontogenetic series here consists of:

  • MOR 592
  • CM 84/94

The first thing to note is that the ‘bifurcation’ in MOR 592 is at right angles to that in the proximal caudals of D. carnegiiCM 84/94, so the one can hardly be antecedent to the other.

More importantly, antero-posterior ‘bifurcations’ like that in MOR 592 are occasionally seen in the caudal vertebrae of adult sauropods. Below are two examples, caudals 7 and 8 of A. parvus CM 563/UWGM 15556. In other words, in this character MOR 592 already displays adult morphology.

Verdict: no ontogenetic change has been demonstrated.

A. parvus CM 563/UWGM 15556 caudals 8 and 7 in right lateral view, from Gilmore (1936:pl.. 33)

Camarasaurus

The ontogenetic series here consists of:

  • OMNH 1417
  • AMNH 5761

OMNH 1417 is an isolated cervical neural spine, and the pictured vertebra of Camarasaurus supremus AMNH 5761 is a posterior cervical. In C. grandis and C. lewisi, all of the cervical vertebrae eventually develop at least a shallow notch in the tip of the neural spine, but as shown in the previous post there seems to be some variation between Camarasaurus species, and, likely, between individuals. In the absence of information about its serial position and the species to which it belonged, the lack of bifurcation in OMNH 1417 is uninformative; it could belong to an anterior cervical of C. supremus that would not be expected to develop a bifurcation.

Verdict: no ontogenetic change has been demonstrated. There is evidence that neural spine bifurcation developed ontogenetically in Camarasaurus, but it comes from the juvenile C. lentus CM 11338, described by Gilmore (1925), and the geriatric C. lewisi, described by McIntosh, Miller et al. (1996)–see the first post in this series for discussion.

Conclusions

The ‘ontogenetic’ series of Woodruff and Fowler (2012) are not really ontogenetic series. In all of the diplodocid presacral vertebrae and in Camarasaurus, the smallest elements in the series are isolated vertebrae or neural arches for which the serial position is almost impossible to determine (and for the reader, completely impossible given the limited information in the paper) and even the taxonomic identifications are suspect (e.g., the OMNH material–how one reliably distinguishes the Apatosaurus and Camarasaurus neural arches is beyond me). The larger vertebrae in the presacral series are all compromised in various ways: one includes an adult masquerading as a juvenile (MOR 790 8-10-96-204 in the anterior cervicals), one is out of order by centrum size (MOR 790 7-26-96-89 and MOR 592 in the posterior cervicals), and two show no change in degree of bifurcation from the middle of the series to the upper end (MOR 592 and CM 84/94 in the anterior and posterior dorsals). The shallow longitudinal bifurcation in the MOR 592 caudal vertebra is similar to those found in caudal vertebrae of adult diplodocids, and is not antecedent to the transverse bifurcations discussed in the rest of the paper.

Crucially, when information on size and serial position is taken into account, none of the ‘ontogenetic series’ in the paper show any convincing evidence that neural spine bifurcation increases over ontogeny. The best evidence that bifurcation does increase over ontogeny comes from Camarasaurus, specifically the juvenile C. lentus CM 11338 described by Gilmore (1925) and geriatric C. lewisi BYU 9047 described by McIntosh et al. (1996), it was already recognized prior to Woodruff and Fowler (2012), and it has not caused any taxonomic confusion.

There is an asymmetry of interference here. To call into question the conclusions of Woodruff and Fowler (2012), all one has to do is show that the evidence could be explained by serial, intraspecific, or interspecific variation, taphonomy, damage during preparation, and so on. But to demonstrate that bifurcation develops over ontogeny, one has to falsify all of the competing hypotheses. I know of only one way to do that: find a presacral vertebral column that is (1) articulated, (2) from an individual that is clearly juvenile based on criteria other than size and degree of bifurcation, which (3) can be confidently referred to one of the known genera, and then show that it has unbifurcated spines in the same serial positions where adult vertebrae have bifurcated spines. Isolated vertebrae are not enough, bones from non-juveniles are not enough, and juvenile bones that might pertain to new taxa are not enough. It may be that this is not yet possible because the necessary fossils just haven’t been found yet. I am not suggesting that we stop doing science, or that the ontogenetic hypothesis of neural spine bifurcation is unreasonable. It’s perfectly possible that it’s true (though MOR 7-17-96-45 ironically suggests otherwise). But it’s not yet been demonstrated, at least for diplodocids, and to the extent that the taxonomic hypotheses of Woodruff and Fowler (2012) rely on an ontogenetic increase in bifurcation in diplodocids, they are suspect. That will be the subject of the next post.

The rest of the series

Links to all of the posts in this series:

and the post that started it all:

References

  • Gilmore, C.W. 1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument. Memoirs of the Carnegie Museum 10:347-384.
  • Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175-300.
  • 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.
  • 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.
  • Wedel, M.J., Cifelli, R.L., and Sanders, R.K. 2000. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45(4):343-388.
  • 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.

The discussion over the new paper by Woodruff and Fowler (2012)–see this post and the unusually energetic comment thread that follows–made me want to go back to the literature and see what was known or could be inferred about neural spine bifurcation in the Morrison sauropods before the recent paper was published.

In this post I’m mostly going to stick with the “classic” specimens–those that are reasonably complete and have been monographed.  So this is the stuff that anyone could easily have figured out for themselves–I am just gathering it here so that it’s conveniently in one place.

Cervical vertebrae

Apatosaurus louisae, CM 3018, and A. parvus, CM 563/UWGM 15556

Apatosaurus parvus CM 563/UWGM 15556 cervicals 7, 5, 4 and 3 in anterior and right lateral views, from Gilmore (1936:pl. 31)

CM 3018 is the mounted Apatosaurus at the Carnegie Museum in Pittsburgh, which was exhaustively described by Gilmore in his 1936 monograph. In that paper Gilmore also described CM 563, which is now mounted at the University of Wyoming Geological Museum and cataloged as UWGM 15556. Gilmore referred CM 563 to A. excelsus, but in a specimen-level phylogenetic analysis Upchurch et al. (2005) found CM 563/UWGM 15556 to belong to A. parvus–hat tip to alert reader LeeB. for catching the revised specific referral. On the subject of neural spine bifurcation, Gilmore wrote (1936:195):

Unfortunately the type of A. louisae lacks most of the spine tops, only  those of cervicals eight, ten and twelve being complete; thus the point of change from single to bifid spines cannot be determined in this specimen. In specimen No. 563, C.M., identified by Hatcher as pertaining to Brontosaurus, an identification with which I concur [Apatosaurus louisae and Brontosaurus excelsus were then considered by some to be separate genera], there are nine cervical vertebrae preserved, three of which I regard as cervicals, three, four, and five. These show the spines to be single as far posteriorly as the fifth vertebra. Since C. 7 shows a well defined notch between the metapophyses, it seems to be a fair conclusion that C. 6 in Apatosaurus is the first vertebra to show a notch on the summit of the spine.

In Camarasaurus supremus Osborn and Mook make the observation that, “In C. 5, the spine has a very slight median notch.” In C. lentus [Gilmore 1925:369], however, the first notched spine is that of C. 7. From C. 6 to C. 9 inclusive, the spinal notch increases steadily in depth. From C. 9 to C. 15 inclusive the spine is completely divided into two metapophyses.  [An odd statement, since Gilmore (1925:351) says that there are twelve cervicals in C. lentus. By "C. 15" he must mean the 15th vertebra, i.e. D3.]

In CM 3018 the spine of C7 appears to be split, based on Gilmore’s Plate 24 (note that for a deeply notched spine, it is not necessary to have the spine tips preserved; the base of the trough will do), and the spine of C6 might be. Gilmore doesn’t mention it in the text, but the plate seems to show C6 with broken metapophyses (at least in posterior view, there are break lines across the metapophyses at mid-height) but with a preserved trough in the middle, which if accurate is enough to confirm that the spine of C6 was also at least partially bifid.

In CM 563/UWGM 15556, there is little doubt: C3, C4, and C5 all have single spines, and the spine of C7 is deeply split. I am happy with Gilmore’s estimates of serial position, by the way. I don’t think the putative C3 could be further back, given how small and short it is, and it’s the wrong shape for an axis. C4 and C5 fall into line in both size and morphology. There is clearly at least one missing vertebra between C5 and C7. The C7 might just possibly be a C8 but I really don’t think it could be any farther back than that, and I agree with Gilmore that it makes more sense as a C7.

The mounted apatosaurs at the Yale Peabody Museum, the AMNH, and the Field Museum are not much help.* The cervical series of all three are heavily reconstructed, and at least for the YPM and AMNH specimens it is quite difficult to tell where the bone ends and the plaster begins.

* Before some outraged curator, collections manager, docent, or museum-goer gets up in my grill about this, I’m not saying they’re bad mounts, or that the necks are entirely fictional! It’s just a sad fact that the fragile neural spine tips are easily broken off and therefore rarely preserved intact. The museums are not defrauding anyone by sculpting in replacements–but that reconstructive work does make it hard to use those specimens as data if neural spine bifurcation is the character of interest. That’s all I’m saying.

Apatosaurus ajax, NSMT-PV 20375

Apatosaurus ajax NSMT-PV 20375, cervical vertebrae 3, 6 and 7 in anterior and posterior views. Modified from Upchurch et al. (2005: plate 2)

This is the new(ish) A. ajax described by Upchurch et al. (2005). They wrote (pp. 27-28):

The neural spine is unbifurcated in C3, but strongly bifurcated from C6 onwards; this seems to be the typical location for the onset of spine bifurcation in Apatosaurus, since it also occurs in this manner in CM 3018 and UWGM 15556.

Note that the intervening vertebrae are missing from that specimen, so we can’t tell exactly where the bifurcation began, but it is perfectly consistent with CM 563/UWGM 15556.

Diplodocus carnegii, CM 84/94

Diplodocus carnegii cervicals 2-15 in posterior view, from Hatcher (1901:pl. 6). Note that the bifid spines in C3-C5 are sculptures; there is no evidence that these spines were bifurcated when the vertebrae were intact.

Hatcher (1901:20-21; emphasis added):

Cervicals Three, Four, and Five.–All of these vertebrae are more or less injured. The neural spines and transverse processes especially are not well preserved. [...] Commencing with C. 3 the neural spines of these vertebrae have been restored as bifid both anteriorly and posteriorly, each spine consisting of a broad thin plate of bone formed by the union of the pre- and postzygapophyseal laminae of their respective sides. These are made to appear free anteriorly and posteriorly, but united, except at their apices, throughout the inner sides; conditions which prevail in the succeeding cervicals.

Cervicals Six, Seven, Eight, Nine and Ten.–These vertebrae differ so little in their more important characters that they may be very conveniently described together. They are all fairly well preserved and show certain characters which are gradually more emphasized in the succeeding vertebrae of the series. Commencing with C. 6 they  regularly increase in length posteriorly. The neural spines become more completely bifid, resulting in a pair of transversely placed perfectly free spines on the tenth cervical consisting of  triangular plates of bone diverging superiorly and terminating at the summit in a rather blunt, rounded process.

Unfortunately Hatcher’s plates do not show which areas have been reconstructed and which have not–a very common failing in these classic monographs, and one which Upchurch et al. (2005) happily did not duplicate. Hatcher says that certain characters are more emphasized in more posterior vertebrae, and that by C10 the metapophyses are “perfectly free”, which suggests that they might have been less than perfectly free before. The spines of C3-C5 have been reconstructed as bifid, but that was to make them consistent with the succeeding vertebrae. So CM 84/94 is like its neighbor in the Carnegie dinosaur hall, CM 3018, in that in both specimens we know that the spines are bifid by some point but we don’t know what was going on in C3-C5.

Barosaurus lentus, AMNH 6341

A. Barosaurus lentus AMNH 6431 cervical vertebra 8 in anterior, left side, and posterior views. B. Diplodocus carnegii CM 84 cervical 8 in anterior, left side and posterior views (from Hatcher 1901). (McIntosh 2005:fig. 2.2)

This is the mostly-complete skeleton famously mounted in a rearing pose in the AMNH rotunda. McIntosh (2005:47-48):

The neural spine of cervical 8 is flat across the top, and that of 9 shows the first trace of a divided spine (Fig. 2.2A). This division increases gradually in sequential vertebrae, being moderately developed in cervicals 12 and 13, and as a deep V-shape in cervicals 15 and 16. This development is in sharp contrast to Diplodocus, where cervical 3 already shows the first trace of division, and where the division is already quite deep in cervical 7 (Fig. 2.2B). By cervical 11 it is as well developed as cervical 16 of Barosaurus (AMNH 6341; Fig. 2.3A). In the spines, a further difference is that those of the last two cervicals (14 and 15) of Diplodocus project anterodorsally, whereas those of Barosaurus are all directed dorsally (Fig. 2.3B).

(McIntosh’s reference in the text to cervical 7 of Diplodocus carnegii is partly in error; the neural spine cleft is fairly deep in C7 but the vertebra shown in the figure is C8, as correctly noted in the figure caption.)

Suuwassea emilieae, ANS 21122

Suuwassea emilieae C6 in anterior, left lateral, and posterior views, from Harris (2006:Text-fig. 7A-C)

Harris (2006) on C2 (p. 1096, Text-fig. 4):

The spine gradually widens mediolaterally toward the distal end, which is rendered heart-shaped by a 12-mm-deep, sagittal, parabolic notch.

C3 (Text-fig. 5) is missing the end of its spine, enough remains to show that if it was bifid the cleft could not have been very deep.

C4 is missing.

C5 (p. 1099, Text-fig. 6):

The spinous process expands mediolaterally toward its apex, attaining maximal width just proximal to its terminus. A long, narrow crack at the distal end gives the appearance of bifurcation, but the collinear dorsal margin indicates that no true split was present.

C6 (p. 1101, Text-fig. 7, above):

The distal end of the spine is cleft by a parabolic, 11.8-mm-deep intraspinous sulcus, marking the initial stage of bifurcation.

Camarasaurus lewisi, BYU 9047, C. supremus AMNH 5761, C. lentus CM 11338 and YPM 1910

Camarasaurus supremus AMNH 5761, C2-C7 in anterior, left lateral, and poster views, from Osborn and Mook (1921:pl. 67)

McIntosh, Miller, et al. (1996:76) on Camarasaurus (= “Cathetosaurus“) lewisi:

The spines are placed well back on the arches and rise higher than in C. grandis, C. lentus, or C. supremus. The cleft in the bifid spine is much deeper and narrower than in any of those species. The cleft in cervical 3 of C. grandis (YPM 1905) is barely perceptible, very modest in numbers 4 and 5, and distinct in 6.

The metapophyses are transversely broad. If the arrangement portrayed by Osborn and Mook (1921) for the large adult C. supremus (AMNH 5761) is correct, the notch between them first appears in cervical 7, the same position reported by Gilmore (1925) for the juvenile C. lentus (CM 11338). However, a small depression is present in cervical 5 of the holotype (YPM 1910) of the latter species. In C. lewisi (BYU 9047) a narrow, deep, sharp cleft is already present in cervical 3 (Jensen, 1988). The depth continues to increase greatly to cervical 8, the last cervical in which reliable measurements of this feature can be taken, where it appears as a very steep, V-shaped notch. This feature appears to be unique to C. lewisi.

McIntosh’s comments here perfectly match the descriptions provided by Osborn and Mook (1921) and Gilmore (1925) so I have not bothered pasting in the relevant sections of those papers (though I did reread them to make sure everything matched).

Camarasaurus grandis, GMNH-PV 101 (WPL 1995) and YPM 1905

McIntosh, Miles, et al. (1996:11-12):

As in C. grandis YPM 1905, the bifurcation of the spine begins as an incipient notch on cervical 3, but it is not until cervical 5 that one observes the fully developed U-shaped trough, and even then the cleft is not nearly as prominent as in the cervicals of the diplodocids. In this respect GMNH-PV 101 Camarasaurus, and most of the other specimens of the genus, differ from the deep, narrow bifurcation seen in C. lewisi BYU 9047 (see Table C).

However, this description does not match the illustrations. While fig. 25 does show a very subtle notch in C3, fig. 26 shows no bifurcation whatsoever in C4 which has a distinctly convex neurapophysis. Subtle bifurcation returns in C5, and deepens slightly in C6, C7 and C8.

Inferences on bifurcation in cervicals

Remember that here I am not trying to either support or challenge the work of Woodruff and Fowler (2012), I’m just looking at what had been published previously and seeing what inferences could be drawn from that evidence only.

1. There is no evidence in any of the North American diplodocoids of a bifid spine farther forward than C6. The bifid spines in the mounted skeleton of D. carnegii are sculptures; Hatcher was doing his best with imperfect fossils and limited information. The appearance of a split spine in C5 of Suuwassea is caused by a vertical crack and a small amount of missing bone. In the very large AMNH 6341 Barosaurus, the first partially split spine is on C9.

2. Adult sauropods can show unbifurcated spines, partially bifurcated spines, and fully bifurcated spines serially in the same individual. This is true even in very large individuals (e.g., Apatosaurus parvus CM 563/UWGM 15556, Barosaurus lentus AMNH 6341, Camarasaurus supremus AMNH 5761), so it is unlikely to be an artifact of ontogeny. Therefore single spines do not always indicate juveniles, bifid spines do not always indicate adults, and incompletely bifid spines did not always become fully bifid–in all of the specimens listed above, the most anterior bifid spines are only shallowly divided. We should probably describe vertebrae with shallow splits as ‘incompletely’ bifid rather than ‘incipiently’ bifid; the latter term implies that the bifurcation was going to deepen with time, which did not always happen depending on serial position.

3. The evidence from Camarasaurus is consistent with an ontogenetic increase in bifurcation. The juvenile C. lentus described by Gilmore (1925) has the first incipiently bifurcated spine at C7, whereas the larger, presumably adult individual of the same species represented by YPM 1910 has the first split at C5, as do the individuals that make up C. supremus AMNH 5761. In C. lewisi BYU 9047 and C. grandis YPM 1905, and arguably in C. grandis GMNH-PV 101 the first spine to be partially split is C3. It is tempting to interpret the difference between adult C. lentus and C. supremus on one hand (first split at C5) and C. lewisi and C. grandis on the other (first split at C3) as interspecific variation, but it might be individual variation considering that we are dealing with usually just one individual from each species (for neural spine bifurcation in adults; I am aware that there are other individuals not mentioned here).

Dorsal vertebrae

I’m going to report the results here in a more compact form than I did for the cervicals. My convention of convenience will be: spines that are split over more than half the distance from the tips to either the postzygapophyses or transverse processes (whichever are higher) are described as deeply bifid, and those split over less than half that distance, including very shallow dorsal indentations, are described as shallowly bifid. The expected dorsal counts are 10 in Apatosaurus and Diplodocus, 9 in Barosaurus, and 12 in Camarasaurus.

Apatosaurus louisae CM 3018 (Gilmore 1936): Deeply bifid  in D1-D3, shallowly bifid in D4-D6, unsplit in D7-D9, D10 spine missing.

Apatosaurus parvus CM 563/UWGM 15556 (Gilmore 1936): Deeply bifid in D1-D3, shallowly bifid in D4, D5-D10 spines missing.

Apatosaurus ajax NMST-PV 20375 (Upchurch et al. 2005): Deeply bifid in D1-D4, shallowly bifid in D5-D6, unsplit in D7-D10.

Diplodocus carnegii CM 84/94 (Hatcher 1901): Deeply bifid in D1-D5, shallowly bifid in D6-D9, unsplit in D10.

Diplodocus longus USNM 10865 (Gilmore 1932): Deeply bifid in D1-D5, shallowly bifid in D6-D8, unsplit in D9-D10.

Barosaurus lentus YPM 429 (Lull 1919): Deeply bifid in D1, D4, and D5, unsplit in D6-D9 (NB: Lull interpreted the latter as D7-D10 on the expectation of 10 dorsals, based on Diplodocus).

Barosaurus lentus AMNH 6341 (McIntosh 2005): Deeply bifid in D1-D3, shallowly bifid in D4-D8, unsplit in D9.

Camarasaurus lentus CM 11338 (Gilmore 1925): Deeply bifid in D1-D3, shallowly bifid in D4-D6, unsplit in D7-D12.

Camarasaurus supremus AMNH 5761 (Osborn and Mook 1921): Deeply bifid in D1-D6, shallowly bifid in D7-D8, unsplit in D9-D12 (NB: a bit of guesswork here, since Osborn and Mook were working with disarticulated material and interpreted Camarasaurus has having 10 or 11 dorsals).

Camarasaurus lewisi BYU 9047 (McIntosh, Miller, et al. 1996): Deeply bifid in D1-D8, shallowly bifid in D9-D12.

Inferences on bifurcations in dorsals

1. As with the cervicals, most adult sauropods have deeply bifid, shallowly bifid, and unsplit spines in serially adjacent vertebrae. In the diplodocids, the spines of D6-D10 (or D9 in Barosaurus) are always either unsplit or very shallowly indented at the tips.

2. The diplodocid genera show some interesting differences. In Apatosaurus the last four dorsals are always unsplit. In Diplodocus the spines are at least shallowly indented as far back as D8 or D9. Barosaurus goes both ways, with YPM 429 having unsplit spines in the four most posterior dorsals, and AMNH 6341 having an entirely unsplit spine only in the last dorsal.

3. In the diplodocids, deep splits are always confined to the first half of the dorsal series (D1-D5), and these are usually followed by a long run of vertebrae with very shallowly notched spine tips. The exception is Barosaurus YPM 429, which–if the vertebrae are truly consecutive (the series is missing at least two)–has a deep split in D5 and unsplit spines in D6-D9.

4. As with the cervicals, the evidence from Camarasaurus does not rule out an ontogenetic increase in bifurcation. In the juvenile C. lentus CM 11338, the spines are  only bifid as far back as D6; in the adult C. supremus AMNH 5761 to D7; and in the old C. lewisi BYU 9047 to D12. If these differences represent ontogenetic changes rather than interspecific differences (which also cannot be ruled out at this point), it is interesting that there is a bigger difference between the adult C. supremus and the old C. lewisi than between the juvenile C. lentus and the adult C. supremus: in other words, the greatest changes took place after adulthood was attained.

The rest of the series

Links to all of the posts in this series:

and the post that started it all:

References

  • Gilmore, C.W. 1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument. Memoirs of the Carnegie Museum 10:347-384.
  • Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81:1-21.
  • Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175-300.
  • Harris, J.D. 2006. The axial skeleton of the dinosaur Suuwassea emilieae (Sauropoda: Flagellicaudata) from the Upper Jurassic Morrison Formation of Montana, USA. Palaeontology 49:1091-1121.
  • 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.
  • Lull, R.S. 1919. The sauropod dinosaur Barosaurus Marsh. Memoirs of the Connecticut Academy of Arts and Sciences 6:1-42.
  • McIntosh, J.S. 2005. The genus Barosaurus Marsh (Sauropoda, Diplodocidae); pp. 38-77 in Virginia Tidwell and Ken Carpenter (eds.), Thunder Lizards: the Sauropodomorph Dinosaurs. Indiana University Press, Bloomington, Indiana, 495 pp.
  • McIntosh, J.S., Miles, C.A., Cloward, K.C., and Parker, J.R. 1996. A new nearly complete skeleton of Camarasaurus. Bulletin of the Gunma Museum of Natural History 1:1-87.
  • 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.
  • Upchurch, P., Tomida, Y., and Barrett, P.M. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No. 26. Tokyo. ISSN 1342-9574.
  • 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.

Since we’ve been a bit light on sauropods lately, here’s CM 11338, the juvenile Camarasaurus from Dinosaur National Monument, in Plate 15 from Gilmore’s 1925 monograph. It’s probably the nicest single sauropod skeleton ever found, and required only minor restoration and reposing for this wall mount at the Carnegie Museum of Natural History.

The same thing in a fake antique finish suitable for printing at 8×10″ and framing. Yes, I have done this. Make one for the sauropodophile in your life, or the non-sauropodophile you’re trying to convert.

Reference

Gilmore, Charles W.  1925.  A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah.  Memoirs of the Carnegie Museum 10:347-384.

Just  a quick note to let anyone who’s not on the Dinosaur Mailing List know that the DML has spawned a new list dedicated to the history of palaeontology.  It’s hosted at Google Groups, so you have the choice of subscribing to it as a mailing list or reading it as a forum.

Go to the History of Paleontology mailing list.

Osborn and Mook (1921: plate LXXXII). Skeletal reconstruction of Camarasaurus executed in 1877 by Dr. John Ryder. This is the first ever skeletal reconstruction of a sauropod.

References

Osborn, Henry Fairfield, and Charles C. Mook.  1921.  Camarasaurus, Amphicoelias and other sauropods of Cope.  Memoirs of the American Museum of Natural History, n.s. 3:247-387, and plates LX-LXXXV.

 

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