Neural spine bifurcation in sauropods, Part 6: more reasons why Haplocanthosaurus is not a juvenile of a known diplodocid

April 15, 2012

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.
Posted by Mike Taylor
Filed in Apatosaurus, Barosaurus, Brachiosaurus, camarasaurs, Diplodocus, Suuwassea
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Neural spine bifurcation in sauropods, Part 3: the evidence from ontogenetic series

April 10, 2012

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.
Posted by Matt Wedel
Filed in Apatosaurus, camarasaurs, caudal, cervical, diplodocids, Diplodocus, dorsal, juvenile, neural spine
11 Comments »

Neural spine bifurcation in sauropods, Part 1: what we knew a month ago

April 5, 2012

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.
Posted by Matt Wedel
Filed in Apatosaurus, Barosaurus, camarasaurs, cervical, diplodocids, Diplodocus
16 Comments »

A sauropod for you: Gilmore’s baby Cam

February 28, 2012

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.

Posted by Matt Wedel
Filed in Art, camarasaurs, Gratuitously awesome images, juvenile, mounts
2 Comments »

New mailing-list/forum: History of Paleontology

October 3, 2011

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.

 

Posted by Mike Taylor
Filed in camarasaurs, skeletal reconstructions
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Tutorial 15: the bones of the sauropod skeleton

September 7, 2011

We should have done this long ago.  Back in the early tutorials, we covered skeletal details such as regions of the vertebral column, basic vertebral anatomy, pneumaticity and laminae, but we never started out with an overview of the sauropod skeleton.

Time to fix that.  This is numbered as Tutorial 15 but you can think of it as Tutorial Zero if you prefer.  Thanks to the wonder of homology, it doubles as a primer for dinosaur skeletons in general.

Overview

Here is a complete, labelled sauropod skeleton, modified from Erwin S. Christman’s reconstruction of Camarasurus supremus in Ostrom and Mook 1921:plate LXXXIV:

Click through for the full-sized version (2897 by 1280 pixels), which you are welcome to print out and hang on your wall as a handy reference.  (Christman’s original is out of copyright; I hereby make my modified version available under the CC-BY-NC-SA licence.)

Since that’s a lot to take in all at once, we’ll walk through the regions of the skeleton: the head and neck, the rest of the vertebral column, the forelimb and girdle, and the hindlimb and girdle.  But first, a little bit of …

Skeletal nomenclature

Skeletons consist of bones.  The study of skeletons and of bones is called osteology.  There are several ways of dividing up the skeleton into manageable chunks.  One is to consider cranial vs. postcranial bones.  In this division, cranium just means skull (though see below) and postcranium means “everything except the skull”.  Here at SV-POW!, of course, we consider skulls beneath our notice, so this division seems silly to us.  We have been known to refer to the skull as the prepostcranium on occasion.

A more useful division of the skeleton is into axial and appendicular.  The axial skeleton includes the skull, hyoid apparatus (little bones in the neck that anchor tongue and throat muscles), vertebrae, ribs and chevrons (i.e. everything on the midline), and the appendicular bones are those of the limbs and their girdles, i.e. shoulders and hips.  (I learned only very recently that, although they seem to be part of the forelimb girdle, the sternal plates are actually part of the axial skeleton, being related to the ribs rather than the shoulders.)

Head and neck

Let’s start with the head.  Although “cranium” is sometimes used to mean the whole head, as noted above, it more strictly refers to the rigid upper portion of the skull which attaches to the neck and includes the upper jaw.  The lower jar, which moves independently, is called the mandible. Both of these units are made up of many smaller bones.  There is of course much, much more to say about skull anatomy, but that is another tutorial for another day.  For now, we will just pretend that the skull is made of two lumps of bone and move swiftly onwards.

The back of the skull articulates with the neck, which is part of the spine, or vertebral column.  All vertebrates have a spine; and in all tetrapods it’s divided into neck, trunk (or torso), sacrum and tail.  The spine is composed of vertebrae: those in the neck are called cervical vertebrae, or cervicals for short; those in the trunk are called dorsal vertebrae (in crocs and mammals these are further broken down into the thoracic vertebrae, which bear mobile ribs, and the lumbar vertebrae which do not); those in the sacrum are called sacral vertebrae and those in the tail are called caudal vertebrae.  But you already know that if you read Tutorial 1.

In some kinds of tetrapods, including all dinosaurs, the cervical vertebrae have backward-pointing ribs; these are called the cervical ribs.  Birds have these (in reduced form) and so do crocs and mammals, but they are absent in at least some lizards and turtles. Contrary to popular belief, mammals do have bicipital (two-headed) cervical ribs, they are just very short and fused to the vertebrae. Even most human osteology textbooks refer to them as transverse process. But developmentally and functionally they are ribs; they bound the transverse foramina through which the vertebral arteries pass, and they anchor deep neck muscles. The “cervical ribs” that occasionally crop up as a pathology in humans are large, mobile, thoracic-style ribs, and represent segmentation anomalies during early development.

The cervical vertebrae are numbered backwards from the head. Each cervical can be identified by number, so that the tenth is called “cervical 10”, or C10 for short.  Sauropods have between eleven and nineteen cervicals — a lot more than the feeble seven that nearly all mammals have, but well short of the seventy or so that Elasmosaurus could boast.

In most tetrapods, the cervicals from C3 backwards are similar in shape, although they tend to get bigger as they approach the torso; but the first two are distinctive, so they have special names.  C1 is called the atlas — easy to remember as it holds up the head, just as the titan Atlas held up the sky (not the Earth as often thought).  It doesn’t really look like a vertebra at all, being ring-shaped and (in sauropods) tiny.  C2 is called the axis.  It looks much more like a normal vertebra, but has an odd articulation at the front, a distinctive blunt spike that the atlas sits on (it also has small prezygapophyses for the neural arch elements of the atlas–these little bits of bone are often lost in fossil skeletons).  It’s smaller than the succeeding vertebrae — unlike the situation in mammals, in which the axis is ususally the largest cervical — and has a big, blade-like neural spine.

Torso and tail

The vertebral column continues back from the base of the neck, as the torso, which consists of dorsal vertebrae.

In the region of the hips, several vertebrae fuse together: this is true to some extent in most or all tetrapods, but in many groups it’s only two or three vertebrae that fuse, whereas in sauropods (and most dinosaurs) it’s four or more.  This set of fused vertebrae is the sacrum, and the vertebrae that make it up are the sacral vertebrae.

Behind the sacrum is the tail, which is composed of caudal vertebrae.  Hanging beneath these — or, specifically, between the intervertebral joints — are transversely flattened bones called chevrons or haemopophyses.  These exist in most reptiles, but have been lost in most mammals. (They do exist in wallabies, but they are a very different shape.) Developmentally the chevrons mirror the neural arch, and form a canal for the caudal aorta in the same way that the neural arch forms a canal for the spinal cord.

Just as the cervical vertebrae have cervical ribs, so the dorsal vertebrae have dorsal ribs.  These are longer and more vertically oriented than the cervical ribs.  The sacral vertebrae, too, have sacral ribs, but you rarely see them because in lateral view they are obscured by the ilium — as is the case here.  You might, then, wonder whether the caudal vertebrae have caudal ribs, but the answer is not clear.  The first few caudals, at least, do have lateral processes, but surprisingly there is no consensus about what they actually are: ribs that are fused to the vertebrae, or paraphophyses/diapophyses that are fused together.  See the overview in Wilson (1999:642).

How can you tell where the neck ends are the torso begins?  The traditional answer is that the first dorsal vertebrae is the first one with a “free” (i.e. unfused) rib, but it’s not always that clear.  Although cervical ribs generally fuse to their vertebrae and dorsal ribs rarely or never do, there are plenty of exceptions — for example, the last few cervical ribs of the Mamenchisaurus hochuanensis holotype appear unfused.  Also, in specimens where the cervicodorsal transition is well preserved, it’s apparent that the switch from short backward-directed cervical ribs to long downward-directed dorsal ribs may be abrupt, between adjacent vertebrae, or a gradual transition spread out over several vertebrae. Since the shoulder girdle bones don’t articulate with the torso, that clue’s also unavailable, so all in all it can be hard to nail down where the transition was.  You just sort of know it when you see it.

The final axial bones are the sternal plates, which belong somewhere in the breast area.  The exact placement and orientation of these bones is not agreed, and they are rarely if ever preserved in place.

Shoulder and forelimb

The bones of the shoulder are the elongate scapula, or shoulder-blade, on the side of the torso; and the coracoid, lower down wrapping round to the front.  Together, these bones make up the shoulder girdle.  Unlike the pelvis, the shoulder is not fused to the bones of the torso, but would have been bound to it by ligament and muscle.  Because of this, the exact position of the scapula and coracoid are not known, and remain the subject of controversy.  The reconstruction above shows a fairly vertical scapula; some others make it more nearly horizontal.

Where the scapula and coracoid meet, they form a hollow on the underside, called the glenoid.  The head of the humerus fits in here; two parallel bones form the lower limb segment: the ulna and radius.  In sauropods, the ulna is a rounded triangle in cross-section, with a hollow on the front face of the triangle which the radius fits into.

At the bottom of the lower limb segment are the carpals, or wrist bones; then the manus, or hand.  The upper bones of the manus are the metacarpals, which in sauropods are held near-vertical in a semi-circular arcade with the hollow directed backwards and slightly inwards.  Below the metacarpals are the phalanges (singular phalanx); each finger may have multiple phalanges, but sauropods tend to have very few.  When the last phalax of a digit is claw-shaped, it’s called an ungual.

Because both forefeet and hindfeet have phalanges and unguals, we distinguish by saying manual phalanges and manual unguals for the bones of the forelimb, and pedal phalanges and pedal unguals for those of the hindlimb.

Hip and hindlimb

The pelvis, or hip girdle, is made up of three bones on each side: the ilium, on top, is roughly semi-circular; the pubis, at the front, and the ischium, at the back, are more elongate.  Where these three bones meet, they form a circular hole called the acetabulum, or hip socket.  Unlike the shoulder girdle, the pelvis is fused to the torso: specifically, the ilium is fused to the sacrum via the transverse processes of the sacral vertebrae and their sacral ribs.  The pubes and ischia do not fuse.

The femur, or thigh bone, has a head that projects into the acetabulum.  At the knee, it meets two parallel lower-limb bones, the tibia and fibula.  The former is the main weight-bearing bone and is nearest the midline.  The fibula sits to the side of it.  Unlike mammals, most reptiles including non-avian dinosaurs have no kneecap, or patella; but birds do. Sesamoids or “floating” bones like the patella seem to be evolved and lost more readily than the normally-connected bones of the skeleton.

Below these two bones are the tarsals, or ankle bones.  In sauropods there are one or two of these: a large, disc-shaped astragalus beneath the tibia, and sometimes a smaller globular calcaneum below the fibula.  (For some reason, the carpals don’t seem to have names.)  Beneath these is the pes, or hindfoot.  The upper bones of the pes are the elongate metatarsals.  Beyond these are the short pedal phalanges and unguals.

What did we miss?

The bones listed account for nearly all the skeleton.  There are, however, a few extra bones that are rarely recovered or not always present.  Clavicles, or collar bones, have been reported in the limb girdles of some sauropods.  Gastralia, or belly ribs, were probably present in all sauropods, but are fragile and very rarely preserved.  Finally, some sauropods had osteoderms — small, isolated bones embedded in the skin and serving as armour.  None of these are illustrated in Christman’s Camarasaurus.

Comparative osteology

Because the basic tetrapod body-plan is so conservative — many bones change size and shape, but it’s comparatively rare for bones to evolve away or for new ones to evolve — you can look at skeletons of all sorts of animals in a museum and recognise nearly all the bones I’ve listed here.  Birds, the closest living relatives of sauropods, have everything I’ve listed here, though their sternal plates have merged into a single big sternum and their forelimbs are obviously highly modified.  Crocs have everything.  Lizards have everything except cervical ribs.  Even mammals are surprisingly similar, though all the pelvis bones fuse together and the coracoid is lost (the coracoid process of the scapula in humans and other mammals is a different, non-homologous bit of bone).

In particular, you have nearly all the bones in a sauropod skeleton, though of course many of the bones are very different in shape, or fused together, and your tail is contemptible.  You might like to try re-reading this tutorial, finding all the relevant bones in your own body.  You have a few extras as well: most obviously, your kneecaps, but also extra bones in the wrist and ankle.

SEE ALSO: the same thing done for Tyrannosaurus.

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.

Wilson, Jeffrey A.  1999.  A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs.  Journal of Vertebrate Paleontology 19(4): 639-653.  [Wilson used to have a freely available PDF on his site, but he seems to have removed it, and substituted a link to a paywalled PDF.]

Posted by Mike Taylor
Filed in camarasaurs, Nomenclature, skeletal reconstructions, Tutorial
37 Comments »

How long was the neck of Diplodocus?

May 19, 2011

In our recent paper on how the long necks of sauropods did not evolve primarily due to sexual selection (Taylor et al. 2011), one of the ideas we discussed is that sexual dimorphism between the necks of male and female sauropods would be an indicator of sexual selection.  And, rather despairingly, we wrote (page 4):

As Senter himself recognized, available samples of sauropod taxa are unfortunately not large enough to demonstrate bimodal distribution of morphological features within any sauropod species.

But I wonder if we realise just how true this is, and how blind we are flying?  How very far short we are of being able to do any kind of statistical analysis on sauropod necks.

How many complete necks of a given sauropod would we need in order to demonstrate a bimodal distribution of, say, length?  (That is, to show that the necks mostly fall into two separate buckets, a short-necked group and a long-necked group of which one is presumably male and the other female.)  I don’t know enough about stats, but this article at least suggests that you’d need thirty or so before you could be confident that you were seeing something statistically significant.

And how many sauropod species do we have thirty complete necks for?

Correct: none.

All right, then how many do we have ten complete necks for?

Five complete necks?

OK, how about just two necks?

ONE neck?

The answer is: not many species.  Off the top of my head, I think complete necks are known for Camarasaurus lentus (Gilmore 1925, one specimen), Mamenchisaurus hochuanensis (Young and Zhao 1972, one specimen), Shunosaurus lii (e.g. Zhang et al. 1984; probably multiple specimens but the paper is in Chinese so I don’t know for sure) Mamenchisaurus youngi (Ouyang and Ye 2002, one specimen, I think), and Spinophorosaurus nigerensis (Remes et al. 2009, one specimen).

No doubt I have missed some, but the point is that the total number of sauropods for which even one complete neck is known is a tiny, tiny proportion of all the sauropods that have been named.  I have listed five species here, and of those only one is known from more than a single complete neck.  And those multiple specimens have not been described (have they?)  So while in theory it might be possible to determine whether there is a bimodal distribution in the length of Shunosaurus lii necks, the data doesn’t exist to do this work.  (If there really are enough complete necks then someone ought to get out to China and measure those babies.)

So anyway.  We have very, very few complete sauropod necks.

Diplodocus carnegii

“But Mike!”, I hear you cry; “What about Diplodocus carnegii?  We’ve all seen its skeleton in a half-dozen different museums!”

Oh yes.  Here is its “complete” neck, from Hatcher (1901:plate 8):

Let’s, for now, ignore the fact that the scapula seems to articulate with the base of the neck rather than the torso.  We can all see that there are fifteen cervical vertebrae, right?

Right?

Well, let’s see what Uncle J. Bell had to say (Hatcher 1901:4):

[Diplodocus carnegii holotype CM 84] has been entirely freed from the matrix and is found to consist of the right femur and pelvis complete except for the left ilium, which is for the most part wanting, right scapula and coracoid, two sternals, eighteen ribs and forty-one vertebrae divided as follows: fourteen cervicals including the axis, eleven dorsals, four sacrals, and twelve caudals.  These vertebrae are for the most part fairly complete, though unfortunately the sacrals and anterior cervicals are more or less injured.  This series of forty-one vertebrae are believed to pertain to one individual and to form an unbroken series from the axis to the twelfth caudal, although as was shown in a previous paper, there is some evidence that there are perhaps one or more interruptions in the series and that one or more vertebrae are missing.  On the other hand, as will appear later, it is not entirely impossible that at least one vertebra of this supposed series pertains to a second individual belonging perhaps to a distinct genus.

Oh and there’s this, from page 10:

Unfortunately no diagram of the quarry was made, at the time of exhuming the remains, showing the relative position of each of the several vertebrae and other bones as they lay in the rock.  [Plate 1 is a map of the quarry as remembered by W. H. Reed.]

Hey!  That’s not what it said in the brochure!  So, as it turns out, our conclusion is: Diplodocus carnegii had fifteen cervicals, or more, or maybe less.

Giraffatitan brancai

“Well, then, Mike, how about that awesome mounted Giraffatitan skeleton in the Berlin museum?”

Well, the presacral vertebrae of that mount are not real bone, nor even casts, but they are very good sculptures based on real bones.  However, the real bones that they’re based on are those of two specimens — the lectotype SI and paralectotype SII.  The former includes cervicals 2-7, and we can be confident about that because C2 in sauropods is very distinctive, having a completely different anterior articular surface from all the other cervicals; and the latter includes cervicals 3-13 (although many of them are damaged).

But but but.  SI and SII were smushed up and mixed in together, with little articulation.  Any reconstruction — or even assignment of individual vertebrae to one specimen or the other — has to be considered provisional.  Take a look at this quarry map, from Heinrich (1999:fig. 16):

Yeesh, what a mess.  I’ve previously suggested (Taylor 2009:800-801) that the distinctively high-spined dorsal vertebra usually considered the fourth of SII may not actually belong to that specimen, or even that taxon — that it may belong to a more Archbishop-like animal (which may be what SI is).  Janensch (1950:33) says that things are not so bad for the cervical vertebrae, but still not good:

The vertebrae from the 3rd to 15th presacrals [of SII] lay in articulation in a consolidated lime sandstone lens; of them, the 3rd to 5th vertebrae are tolerably complete, the remaining 10 vertebrae were articulated with one another, with one interruption that arose when the 8th presacral vertebra rotated out of the series and was displaced.

So might there have been other displaced cervicals, before and/or after the “8th”, that were not recovered?  And can we be confident that the anteriormost cervical of SII really is C3?  Why?  Because of the overlap with vertebrae of SI?  But we’re not even certain that SI is the same species as SII.  Maybe the anteriormost preserved cervical is really C4?  Maybe some of the “SII” cervicals really belong to SI?

So all in all, our conclusion is: Giraffatitan brancai had thirteen cervicals, or more, or maybe less.

What does it all mean?

Only this: we don’t know as much as we think we do.  We don’t know how many cervical vertebrae Diplodocus and Giraffatitan had, even.  We don’t have complete necks for either of these sauropods, nor for almost any others.  Even those we do have are in some cases badly crushed (e.g. Mamenchisaurus hochuanensis, which I must post about properly some time).  To summarise: we are woefully short of sauropod necks.

We need to get out of the habit of blithely asserting, “oh, Diplodocus had 15 cervicals and Giraffatitan only 13″.  Because we really don’t know this.  We think it’s true: these numbers are certainly the best guesses for the taxa in question.  But they are, in the end, only guesses.

References

Posted by Mike Taylor
Filed in camarasaurs, Diplodocus, Giraffatitan, mamenchisaur, necks
18 Comments »

Sauropods stomping theropods: a much neglected theme in palaeo-art

March 6, 2011

Needless to say, one of the things I love most about Paco’s Brontomerus artwork is that it’s a rare and welcome example of the much neglected Sauropods Stomping Theropods school of palaeo-art.

When I reviewed the examples I know of, I was a bit disappointed to find that they number only five.  Here they are, in chronological order.

First, we have this gorgeous sketch by Mark Hallett, showing Jobaria (here credited as “unnamed camarasaurid”) quite literally stomping on Afrovenator:

To the best of my knowledge, this has never actually been published — I found it on Dave Hone’s Archosaur Musings, in the interview with Hallett.  Mark tells me that this was a concept sketch of possible main art for Paul Sereno’s North African dinosaur article, Africa’s Dinosaur Castaways in the June 1996 issue of National Geographic (Sereno 1996) — three years before Jobaria was described[1] (Sereno et al. 1999); but for some inexplicable reason, it wasn’t used.

It seems incredible to think that there was no published, or even completed but unpublished, sauropod-stomping-theropod art before the mid-1990s, but I’ve not yet found any.  I thought that Bakker might have come up with something in The Dinosaur Heresies (Bakker 1986) or The Bite of the Bronto (Bakker 1994); but I flipped through both and I don’t see anything relevant.  Anyone know of anything earlier?

The next entry on my list is Luis Rey’s striking Astrodon, carrying away a raptor that bit off more than it could chew.

This appeared in Tom Holtz’s outstanding encyclopedia (Holtz 2007), which I highly recommend for every interested layman, including but not limited to bright kids.  The image also turned up, with Luis’s permission, in the publicity for Xenoposeidon — notably in The Sun, one of Britain’s most downmarket, lowest-common-denominator tabloids, where it was a pleasant surprise indeed.

I just love the expression on the raptor’s face.  He’s going HOLY CRAP!, and his buddies are all like, Hey, dude, c’mon, we were only playing!  But Astrodon‘s all, Nuh-uh, you started this, I’m going to finish it.

Next up, and a year, later, we have this moody just-going-about-my-business Camamasaurus, squishing theropod eggs, nests and babies in a casual sort of way, as though he’s saying “Well, you should have got out of my way”:

As it happens, this one was done for me, by Mark Witton.  It was intended as an illustration for a “Fossils Explained” article that I was going to do for Geology Today on the subject of (get ready for a big surprise): sauropods.  In fact, I am still going to do it.  But since it’s been two and a bit years since I got the go-ahead from the editor, I’m hardly in a position to complain that Mark gave the image to Dave Martill and Darren when they suddenly needed artwork to publicise the findings of their Moroccan expedition.  (Since then, the Mail seems to have re-used this picture pretty much every time they have a story about dinosaurs — even when that story is complete and utter crap.)

I don’t mind too much about this Witton original being whisked away from me, because shortly afterwards Mark went on to provide me with a much better piece — the beautifully wistful Diplodocus herd scene that we used in the publicity for our neck-posture paper.

And, amazingly, that brings us up to date.  The next relevant artwork that I know of was Paco’s glorious Brontomerus life restoration, which you’ve already read all about.  Just to vary things a bit, this is the second of the two renders — the one that wasn’t in the paper itself:

So is that the end of the story for now?  Happily, not quite.  Emily Willoughby produced this alternative Brontomerus restoration on the very day the paper came out!

I’m not going to claim that this is close to the quality of the other four pieces in this article, but you have to admire the speed of the work.  Emily wrote most of the initial Wikipedia entry for Brontomerus, and produced this picture to illustrate it.  At first when I saw this, I thought Emily had misunderstood the paper as indicating powerful retractors, so that the drawing had Brontomerus kicking backwards like a horse. But when I looked closely I realised it’s kicking outwards, thanks to the enlarged abductors. Neat.

A question and a challenge

I’d like to end this post with a question and a challenge.  First, the question: what other pieces of palaeoart have I missed that feature sauropods handing theropods their arses?  There have to be others — right?

And the challenge: I’d love it if those of you who are artists were to fix this terrible hole in the fabric of reality?  I’d love to see new and awesome art on the timeless theme of sauropods stomping theropods.  How about it?  If any of you have influence with the Art Evolved people, you might try seeing whether you can get them to join in the challenge.  It would be awesome to see a whole new crop of these pieces!

References

  • Bakker, Robert T.  1986.  The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction.  Morrow, New York.  481 pages.
  • Bakker, Robert T.  1994.  The Bite of the Bronto.  Earth 3 (6): 26-35.
  • Holtz, Thomas R., Jr., and Luis V. Rey.  2007.  Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House, New York.  432 pages.
  • Sereno, Paul C.  1996.  Africa’s dinosaur castaways.  National Geographic 189(6):106-119.
  • Sereno, Paul C., Allison L. Beck, Didier. B. Dutheil, Hans C. E. Larsson, Gabrielle. H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson and Jeffrey A. Wilson.  1999.  Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs.  Science 282:1342-1347.

Footnotes

[1] If you want to call it that.

Posted by Mike Taylor
Filed in Art, Brontomerus, camarasaurs, Jobaria, life restorations, opportunities, Pleurocoelus, stinkin' theropods, ulterior motives
41 Comments »

How weird was the ilium of Brontomerus?

February 26, 2011

Sorry for the very short post. We have some longer stuff planned, but we’ve been too busy to kick it out this week, and I wanted to leave you with something cool to ponder over the weekend. Here’s the ilium of Giraffatitan overlaid on that of Brontomerus, scaled to the same acetabulum diameter (Giraffatitan is HMN J1, left ilium, modified from Janensch 1961: pl. E, fig. 2; Brontomerus is of course OMNH 66430 from Taylor et al. 2011:fig. 2).

And here’s the same thing comparing Rapetosaurus and Brontomerus (Rapetosaurus is holotype FMNH PR 2209, left ilium, modified from Curry Rogers 2009: fig. 39B). This one was tricky to scale because the ilial margin of the acetabulum is so different in the two taxa.

Here is the same trick performed with the ilium of the canonical pretty basal neosauropod Camarasaurus — specifically, Camarasaurus supremus AMNH 5761 Il. 1, left ilium, modified from Osborn and Mook (1921: fig. 87).  In this case, the proportions are so very different that it’s hard to make a meaningful superimposition: we tried to scale to equal acetabulum size, but probably that of the Camarasaurus was proportionally larger than in the other taxa illustrated in this post.  Still, here it is:

Finally, in response to Paul Barrett’s comment on a subsequent article, here is a superimposition of the ilium of Alamosaurus on that of Brontomerus:

(Sorry about the poor quality of this one, but the only figure I could find of a complete Alamosaurus ilium was the line-drawing in Lehman and Coulson (2002:fig. 8) — none of the standard descriptive works seem to illustrate a complete or near-complete ilium.)

We had a figure like these in an early draft of the paper, but we ditched it because we felt that doing a broader comparative figure would be more valuable. But I like the kick in the brainpan that these overlays provide.

References

Posted by Matt Wedel
Filed in Alamosaurus, brachiosaurids, Brontomerus, camarasaurs, Giraffatitan, ilium, Rapetosaurus, stinkin' appendicular elements, titanosaur
12 Comments »

How fat was Camarasaurus?

January 16, 2011

For reasons that will soon become apparent (yes, that’s a teaser), Matt and I wanted to figure out how heavy Camarasaurus was.  This is the story of how I almost completely badgered up part of that problem.  I am publishing it as a cautionary tale because I am very secure and don’t mind everyone knowing that I’m an idiot.

Those who paid close attention to my recent paper on Brachiosaurus and Giraffatitan will remember that when I estimated their mass using Graphic Double Integration (Taylor 2009: 802-804) I listed separately the volumes of the head, neck, forelimbs, hindlimbs, torso and tail of each taxon.  In Giraffatitan, the torso accounted for 71% of the total volume (20588 of 29171 litres), and in Brachiosaurus, 74% (26469 of 35860 litres), so it’s apparent that torso volume hugely dominates that of the whole animal.  In the giant balloon-model Giraffatitan of Gunga et al.’s (1995, 1999) estimates, the torso accounted for 74% of volume (55120 of 74420 litres) so even though their fleshing out of the skeleton was morbidly obese, the relative importance of the torso came out roughly the same.  Finally, Gunga et al’.s (2008) revised, less bloated, model of the same Giraffatitan had the torso contributing 68% of volume (32400 of 47600 litres).  So far as I know, these are all of the published accounts that give the volumes of separate parts of a sauropod body, but if there are any more, please tell me in the comments!   (Odd that they should all be for brachiosaurids.)

3D “slim” version of reconstruction of the “Brachiosaurus” brancai mounted and exhibited at the Museum of Natural History in Berlin (Germany).  A. Side view, upper panel; B. top view, lower panel.  The cross in the figure of upper panel indicates the calculated center of gravity.  (Gunga et al. 2008: figure 2)

So it’s evident that, in brachiosaurs at least, the torso accounts for about 70% total body volume, and therefore for about that much of the total mass.  (The distribution of penumaticity means that it’s denser than the neck and less dense than the limbs, so that its density is probably reasonably close to the average of the whole animal.)

Now here’s the problem.  How fat is the sauropod?  Look at the top-view of Giraffatitan in the Gunga et al. figure above: it’s easy to imagine that the torso could be say 20% narrower from side to side, or 20% broader.  Those changes to breadth would affect volume in direct proportion, which would mean (if the torso is 70% of the whole animal) a change in total body volume of 14% either way.  Significant stuff.

So what do we know about the torso breadth in sauropods?  It obviously dependant primarily on the orientation of the ribs and their articulation to the dorsal vertebrae.  And what do we know about that?

Nothing.

Well, OK, I am over-simplifying a little.  It’s been mentioned in passing in a few papers, but it’s never been discussed in any detail in a published paper that I know of.  (There’s a Masters thesis out there that starts to grapple with the subject, but I don’t know whether I should talk about that while it’s still being prepared for publication, so I won’t say anything more.)  The most important published contribution is more than a century old — Holland’s (1910) smackdown of Tornier’s and Hay’s comical Diplodocus postures, which included the following cross-sections of the torsos of several animals at the seventh dorsal vertebra:

(This figure previously appeared on SV-POW! in Matt’s post, Sauropods were tacos, not corn dogs, which as far as I am aware is the only existing non-technical treatment of sauropod torso-shape.)

Holland unfortunately did not discuss the torso shape that he illustrated, merely asserting it.  Presumably it is based on the mounted skeleton of the Diplodocus carnegii holotype CM 84, which is at the Carnegie Museum in Pittsburgh, where Holland was based.  I have no reason to doubt it; just noting that it wasn’t discussed.

All right then — what about Camarasaurus?  I think it’s fair to say that it’s generally considered to be fairly rotund among sauropods, as for example this skeletal reconstruction by Greg Paul shows:

Camarasaurus lentus skeletal reconstruction, in dorsal and right lateral views. (Paul 2010:197)

Measuring off the height and width of the torso at the seventh dorsal vertebra, using GIMP, I find that they are 341 and 292 pixels respectively, so that the eccentricity is 341/292 = 1.17.  This compares with 1760/916 = 1.92 for Holland’s Diplodocus above, so if both figures are accurate, then Camarasaurus is much fatter than Diplodocus.

But is Paul’s Camarasaurus ribcage right?  To answer that, I went back to my all-time favourite sauropod paper, Osborn and Mook’s (1921) epic descriptive monograph of Camarasaurus (and Cope’s other sauropods).  I knew that this awesomely comprehensive piece of work would include plates illustrating the ribs; and in fact there are four plates that each illustrate a complete set of dorsal ribs (although the associations are doubtful).  Here they all are:

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXVIII)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXIX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXXI)

But hang on a minute — what do you get if you articulate these ribs with the dorsal vertebrae?  Osborn and Mook also provided four plates of sequences of dorsal vertebrae, and the best D7 of the four they illustrate is probably the one from plate  LXX.  And of the four 7th ribs illustrated above, the best preserved is from plate LXXIX.  So I GIMPed them together, rotated the ribs to fit as best I could and …

What on earth?!

I spent a bit of time last night feeling everything from revulsion to excitement about this bizarre vertebra-and-rib combination.  Until I happened to look again Osborn and Mook — earlier on, in the body of the paper, in the section about the ribs.  And here’s what I saw:

(Note that this is the vertebra and ribs at D4, not D7; but that’s close enough that there’s no way there could be a transition across three vertebrae like the change between this and the horrible sight that I presented above.)

What’s going on here?  In the plates above, the ribs do not curve inwards as in this cross-section: they are mostly straight, and in many case seem to curve negatively — away from the torso.  So why do O&M draw the ribs in this position that looks perfectly reasonable?

And figure 70, a few pages earlier, makes things even weirder: it clearly shows a pair of ribs curving medially, as you’d expect them to:

So why do these ribs look so totally different from those in the plates above?

I’ll give you a moment to think about that before I tell you the answer.

Seriously, think about it for yourself.  While you’re turning it over in your mind, here is a picture of the beautiful Lego kit #10198, the Blockade Runner from the original Star Wars movie.  (I deeply admire the photography here: clear as a bell.)

OK, welcome back.

Got it?  I bet most of you have.

The answer was right there in figure 71:

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

And, my word, isn’t it embarrassingly obvious once you see it?  I’d been blithely assuming that the ribs in O&M’s plates were illustrated in anterior view, with the capitula (which articulate with the parapophyses) located more medially, as well as more ventrally, than the tubercula (which articulate with the diapophyses).  But no: as in fact the captions of the plates state perfectly clearly — if I’d only had the wits to read them — the ribs are shown in “external” (i.e. lateral) view.  Although it’s true that the capitula in life would indeed have been more medially positioned than the tubercula, it’s also true that they were more anteriorly positioned, and that’s what the plates show at the rib heads.  And the curvature that I’d been stupidly interpreting as outward, away from the midline, is in fact posteriorly directed: the ribs are “swept back”.  The ventral portions of the ribs also curve medially, away from the viewer and into the page … but of course you can’t see that in the plates.

The important truth — and if you take away nothing else from this post, take this — is that I am dumb bones are complex three-dimensional objects, and it’s impossible to fully understand their shape from single-view illustrations.  It’s for this reason that I make an effort, when I can, to illustrate complex bones from all cardinal directions — in particular, with the Archbishop bones, as for example “Cervical S” in the Brachiosaurus coracoid post.

Because ribs, in particular, are such complex shapes — because their curvature is so unpredictable, and because their articulation with the dorsal vertebrae is via two points which are located differently on successive vertebrae, and because this articulation still allows a degree of freedom of movement — orthogonal views, even from all cardinal directions, are of limited value.  Compositing figures will give misleading results … as demonstrated above.  PhotoShop is no more use here.  Fly, you fools!

Paradoxically, our best source of information on the shapes of saurpod torsos is: mounted skeletons.  I say “paradoxically” because we’ve all grown used to the idea that mounts are not much use to us as scientists, and are really there only as objects of awe.  As Brian Curtice once said, “A mounted skeleton is not science.  It’s art.  Its purpose is to entertain the public, not to be a scientifically accurate specimen”.  In many respects, that’s true — especially in skeletons like that of the “Brontosaurus” holotype, YPM 1980, where the bones are restored with, and in some cases encased in, plaster so you can’t tell what’s what.  But until digital scanning and modelling make some big steps forward, actual mounted skeletons are the best reference we have for the complex articulations of ribs.

Giraffatitan brancai paralectotype HMN SII, composite mounted skeleton, torso in left posteroventrolateral view (photograph by Mike Taylor)

And I finish this very long (sorry!) post with yet another note of caution.  Ribs are long and thin and very prone to damage and distortion.  It’s rare to find complete sauropod ribs (look closely at the O&M plates above for evidence), but even when we do, we shouldn’t be quick to assume that the shape in which they are preserved is necessarily the same as the shape they had in life.  (If you doubt this, take another look at rib #6 in the third of the four O&M plates above.)  And as if that weren’t enough to discourage us, we should also remember that the vertebra-rib joints would have involved a lot of cartilage, and we don’t know its extent or shape.

So bearing in mind the complicated 3D shape of ribs and of dorsal vertebrae, the tendency for both to distort during and after fossilisation, and the complex and imperfectly known nature of the joints between them, I think that maybe I wasn’t too far wrong earlier when I said that what we know about sauropod torso shape is: nothing.

It’s a sobering thought.

References

Posted by Mike Taylor
Filed in camarasaurs, cross sections, Diplodocus, Giraffatitan, I'm stupid, mass estimates, mounts, ribs, size, teaser
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