In the previous post in this series I looked at the some of the easily available raw data on neural spine bifurcation in Morrison sauropods. In this post I’ll explain how serial variation–that is, variation along the vertebral column in one individual–is relevant to the inferences made in the new paper by Woodruff and Fowler (2012). But first, a digression, the relevance of which will quickly become clear.
How do you recognize an adult sauropod?
There are only a handful of criteria that have been used to infer adulthood in sauropods. In rough order from least to most accurate–so far as I can tell!–they are:
- sheer size
- fusion of the neural arches to the centra
- fusion of the sacral vertebrae to each other, and fusion of the sacral ribs to form the sacricostal yoke
- fusion of the cervical ribs to the centra and neural arches
- fusion of the scapula to the coracoid
- presence of an external fundamental system in the cortices of the long bones
I’ll discuss each one in turn. (Please let me know in the comments if I’ve missed any.)
1. Size alone is pretty useless. The mounted Giraffatitan is a pretty damn big animal by anyone’s standards, but it’s demonstrably smaller than another individual from Tendaguru, and the scap-coracoid joint is unfused. On the other hand, there are things like dicraeosaurids that apparently matured at relatively small sizes (for sauropods). There is definitely some individual or low-level taxonomic variation. Marsh’s “Brontosaurus” excelsus holotype YPM 1980 is an adult but about the same size as the subadult Apatosaurus ajax holotype YPM 1860 that it ended up being generically synonymised with (see the sacra of the two taxa compared below). The giant Oklahoma Apatosaurus is about 1.4 times the size of A. louisae CM 3018 in most linear measures, but some of the neural arches and cervical ribs are unfused (the vertebra in the linked post is only a quarter bigger than the corresponding element in CM 3018, but there are other elements of the Oklahoma Apatosaurus that are proportionally even larger). On the flip side, I have seen some comparatively tiny Diplodocus material at BYU in which all of the neural arches are fused to the centra, despite the vertebrae being about half the size of those in the mounted D. carnegii CM 84/94. So I am very leery of size as a reliable indicator of age in sauropods. It is a bad criterion in general, and especially bad for cervical vertebrae, which can change so much along the column. C15 of D. carnegii CM 84/94 has a cotyle diameter almost four times that of C3 in the same animal.
2. People often cite closure of the neurocentral synostoses* as an indicator of adulthood, but again I am skeptical. There’s no doubt that the neurocentral synostoses do eventually close; my skepticism runs the other way, in that there are sauropods with closed neurocentral synostoses that do not appear to have reached full size. The HM SI** individual of Giraffatitan is one example–it’s about 75% of the size of the mounted (SII) individual, and only 66% the size of the giant HM XV2 (by cross-scaling through HM SII; SI and XV2 share no overlapping elements), and yet the neurocentral synostoses are all closed. Same deal with Apatosaurus CM 555, which has open joints as far back as C8 but is between one-half and two-thirds the size of A. louisae CM 3018. If you found a posterior cervical or anterior dorsal of CM 555 by itself, without the open joints on the more anterior vertebrae to guide you, you’d think it was full grown based on arch fusion. So it seems safest to say that neurocentral synostosis closure is a necessary but not sufficient condition for inferring adulthood.
* Hat tip to Jerry Harris, who alerted me that the term ‘sutures’ is reserved for skulls only, and that the joints between neural arches and centra are properly called synostoses. Thanks also to physical anthropologist Vicki Wedel, who confirmed this.
** Yes, I’m using the old Humboldt Museum numbers here, out of convenience, and because HM SII probably means more to more readers than the correct M.B. R. number that only six people have memorized.
3. Coalescence of the sacrum and formation of the sacricostal yoke have intuitive appeal. The sacricostal yokes are banana-shaped bars of bone formed by the union of the sacral ribs that articulate with the ilia–you can see them on either side of the apatosaur sacra in the image above, and in this post on the sacrum of Camarasaurus lewisi. Since the sacricostal yokes are the bony interfaces between the axial skeleton and the hindlimb girdles, we might expect them to be biomechanically important and for their formation to be closely related to the attainment of adult size. But I’m putting them fairly low on the list for reasons both practical and theoretical. On the practical side, fusion of the sacral vertebrae and ribs is hard to assess unless the sacrum has fallen apart. An intact sacrum might be intact because the bones were actually fused together, or because the unfused bits just happened to hang together through the process of fossilization (if that sounds unlikely, just remember that it’s true of almost every articulated fossil skull you’ve ever seen). On the theoretical side, the timing of sacral fusion seems to be variable. A. ajax YPM 1860 has fused neural arches and cervical ribs but a very incompletely fused sacrum, whereas D. carnegii CM 84/94 has the five sacral centra coossified and a sacricostal yoke uniting the ribs of S2-S5*, but some of the cervical ribs are unfused. Yes, I realize that discounting this criterion because it conflicts with other mutually conflicting criteria is a bit wonky, but (1) that’s the essential challenge of doing non-histological skeletochronology on sauropods–none of the signs seem to tell us what we want–and (2) I’m happy to fall back on the practical reason if you find the theoretical one unconvincing. Last item: I have seen both ‘sacricostal’ and ‘sacrocostal’ used in the literature–can anyone make a case for one being more correct than the other? ‘Sacrum’ is from the Latin sacer, ‘sacred’, apparently because the sacra of animals used to be sacrificed to the gods (not sacroficed–maybe there’s my answer?).
*Hatcher (1901) described an 11th dorsal and four sacral vertebrae, but he noted that the 11th dorsal “functions as a sacral” and “is coossified by the centrum with the true sacrals”. The D. carnegii holotype was one of the first nearly complete sauropod skeletons to be monographically described, and it was not yet clear that the typical number of sacrals for the North American diplodocids–and indeed for most other sauropods–is five (some primitve taxa have four, many titanosaurs have six).
4. Cervical rib fusion might be better. Giraffatitan HM SI and Diplodocus CM 84/94 both have their cervical neurocentral synostoses closed, but both have unfused cervical ribs as far back as C5. This suggests that cervical rib fusion proceeded from back to front (in at least those taxa) and that it followed neurocentral fusion. The sole exception that I have seen is a subadult Apatosaurus cervical from Cactus Park in the BYU collections, which has fused ribs but open neurocentral joints.
5. It’s hard to tell if fusion of the scapula to the coracoid is better or worse than cervical rib fusion, because the timing varies among taxa (hence the caveat that these criteria are in rough order). Giraffatitan HM SII has fused neural arches and fused cervical ribs but open scap-coracoid synostoses (yes, again, synostoses rather than sutures) ; Diplodocus CM 84/94 has a fused scap-coracoid but some unfused cervical ribs. This is probably another necessary but not sufficient condition.
6. The gold standard for determining cessation of growth is the formation of an external fundamental system (EFS) in the outer cortex of a bone. Unfortunately that requires destructive sampling (even if only drilling), is time-consuming, and has been done for few individual sauropods.
The upshot of all of the above is that the readily available ways of determining adulthood in sauropods are all inexact and frequently conflict with each other. Neural arch fusion does not indicate full growth–some sauropods appear to have fused their neurocentral joints when they were only two-thirds grown (in linear terms; 30% grown in terms of mass).
For the purposes of this post and the next, I am going to refer to the big mounted skeletons–Apatosaurus louisae CM 3018, Diplodocus carnegii CM 84/94, etc.–and individuals of like size as ‘adults’ to indicate that they had attained adult morphology, without implying that they were done growing or had EFSs, and also not implying that smaller individuals were necessarily subadult. ‘Adult’ here is used a term of convenience, not a biological fact.
Implications of serial changes in bifurcation for isolated elements
From here, this post picks up right where the last one in this series left off, so feel free to refer back to the previous post for any points that are unclear.
In the diplodocids, adults are expected to have unsplit spines as far back as C5, C6 may be only incompletely bifid (e.g., D. carnegii CM 84/94), and the spines in the posterior dorsals are expected to be either very shallowly notched at the tip or completely unsplit. Therefore it is impossible to say that an isolated vertebra belongs to a juvenile individual on the basis of neural spine bifurcation alone. Depending on how one defines “anterior cervical”, one half to one third of anterior cervicals are expected to have unsplit spines even in adults.
In Camarasaurus the picture is less clear. The immense C. supremus AMNH 5761 has unsplit spines in C3-C4 and in the last three or four dorsals, but some of those very posterior dorsals have extremely shallow depressions in the tips of the spines, with little consistency among the four individuals that somewhat confusingly make up that specimen. In the geriatric C. lewisi all of the post-axial presacral neural spines are at least incompletely bifid. Even in the very posterior dorsals there is still a distinct notch in the neural spine, not just a very slightly bilobed tip as in the posterior dorsals of C. supremus. Either this is an interspecific difference or some amount of ontogenetic bifurcation happened well into adulthood; current evidence is insufficient to falsify either hypothesis. (That’s the trouble with n=1.)
A final thing to note: as I briefly mentioned in the earlier post, it is easier to detect deep bifurcations than shallow ones if the material is broken or incomplete. The neural spine tips are usually narrow, fragile, and easily broken or lost. If a vertebra is missing the top half of its spine but the bottom half is not split, it is usually impossible to say whether it would have been bifid or not. But if the spine is deeply bifurcated, even a small piece of bone from the base of the trough or one of the metapophyses is enough to confirm that it was bifid.
“Primitive” morphology can be an effect of serial position
Even in ‘adult’ sauropods like the big mounted Apatosaurus and Diplodocus skeletons, the anterior cervicals are less complex than the posterior ones. Compared to posterior cervicals, anterior cervicals tend to have simpler pneumatic fossae and foramina, fewer laminae, and unsplit rather than bifid spines. In all of these things the anterior cervicals are similar to those of juveniles of the same taxa, and to those of adults of more basal taxa. This is also true in prosauropods–in Plateosaurus, the full complement of vertebral laminae is not present until about halfway down the neck (see this subsequent post for details).
An important implication of this is that an isolated cervical might look primitive (1) because it comes from a basal taxon, or (2) because it is from a juvenile, or (3) because it is from near the front of the neck.
In their Figure 2, Woodruff and Fowler (2012) compare an adult Mamenchisaurus cervical, an isolated cervical of a putative juvenile Diplodocus (MOR 790 8-10-96-204), and a cervical of D. carnegii CM 84/94. The point of the figure is to show that the isolated ‘juvenile’ vertebra is more similar in gross form to the Mamenchisaurus cervical than to the adult D. carnegii cervical.
Unfortunately the figure confuses ontogenetic and serial variation. Based on the proportions of the centrum and the shape of the neural spine, the isolated MOR cervical is probably from a very anterior position in the series. No measurements are given in the paper or supplementary information (grrr), but using the scale bar in the figure I calculate a centrum length of about 28 cm, a cotyle height of 7 cm, and an elongation index (EI, centrum length divided by cotyle diameter) of 4. That EI, combined with the overall shape of the neural spine and the very long overhang of the prezygapophyses, make the vertebra most similar to C4 and C5 of D. carnegii CM 84/94. But the D. carnegii cervical included in the figure is C12. It differs from the isolated cervical in having a forward-leaning, bifurcated neural spine, a much more complicated system of laminae with many accessory laminae, and more complex pneumatic sculpturing. All of these differences are more likely to be caused by serial variation than by ontogeny–the same characters separate C12 from C4 and C5 in the same individual.
So here’s how that figure would have looked, had the comparable C5 of CM 84/94 been used instead of C12:
It’s now immediately apparent B more closely resembles C than A, in the possession of overhanging prezygapophyses, non-overhanging postzygapophyses, elongation index, anterodorsal inclination of the cotyle margin, lack of anterior deflection of diapophysis, etc. The biggest differences between B and C are the shape of the neural spine and, for want of a better word, the ‘sinuosity’ of the ventral centrum margin in lateral view. Both characters are highly variably serially within an individual, among individuals in a species, and among species in Apatosaurus and Diplodocus, so it is hard to attach much weight to them.
What is MOR 790 8-10-96-204?
It gets more complicated. The isolated MOR vertebra is presented as an example of juvenile morphology. But does it actually belong to a juvenile?
Here’s what we know for certain about the vertebra:
- it has an EI of 4 (this is a proportion, so it’s still accurate even if the scale bar is off)
- the cervical ribs are fused to the neural arch and centrum
In addition, the figure appears to show that:
- it has a centrum length of 28 cm, although this could be off if the scale bar is incorrectly sized (which is why I prefer measurements to scale bars)
- the neural arch appears to be fused to the centrum. Admittedly, the image in the figure is small and I haven’t seen the specimen in person. But we know this much: the centrum and neural arch stayed together through the process of preservation and preparation, which does not usually happen unless they have at least started coossifying; the photo does not show an obvious line of fusion between the centrum and neural arch; and the cervical ribs are fused, which in almost all sauropod vertebrae happens after closure of the neurocentral synostoses.
Now, as we’ve just seen above, the morphology of MOR 790 8-10-96-204 is indistinguishable from the morphology of an anterior cervical vertebra in an adult, and it compares especially well to C4 and C5 of D. carnegii CM 84/94. The apparent centrum length (measured from the scale bar in the figure) of MOR 790 8-10-96-204 is 28 cm, compared to 29 cm and 37 cm for C4 and C5 of D. carnegii CM 84/94, respectively. So MOR 790 8-10-96-204 is roughly the same size as the adult C4 and about 80% of the size of the adult C5. Furthermore, its neural arch appears to be fused and its cervical ribs are fused to the neural arch and centrum, whereas the cervical ribs of the ‘adult’ D. carnegii CM 84/94 are not yet fused in C2-C5.
In sum, the isolated MOR vertebra shown in Woodruff and Fowler (2012:Fig. 2) is most likely a C4 or C5 of an adult Diplodocus similar in size to D. carnegii CM 84/94, and based on cervical rib fusion it may be from an individual that is actually more mature than CM 84/94. All of the differences between that vertebra and the D. carnegii C12 shown in the same figure are more easily explained as consequences of serial, rather than ontogenetic, variation.
MOR 790 8-10-96-204 and the Mother’s Day Quarry
MOR 790 8-10-96-204 is from the Mother’s Day Quarry (Woodruff and Fowler 2012:Table 1), which is supposed to only contain juvenile and subadult sauropods (Myers and Storrs 2007, Myers and Fiorillo 2009). Myers and Fiorillo (2009:99) wrote:
The quarry has a strikingly low taxonomic diversity, with one sauropod taxon and one theropod taxon present. However, the relative abundance of elements from these taxa is so uneven – diplodocoid sauropod material comprises 99% of the recovered bones – that the quarry is effectively monospecific (Myers and Storrs, 2007). The theropod material consists of isolated teeth only and is probably related to scavenging of the sauropod carcasses. All identifiable sauropod elements belong to either juvenile or subadult individuals (Fig. 2); none is attributable to a fully-adult individual (Myers and Storrs, 2007).
The Figure 2 cited in that excerpt shows two sauropod centra, a dorsal and a caudal, both with unfused neural arches. And yet here is MOR 790 8-10-96-204, similar in size and morphology to D. carnegii CM 84/94, and with at least partially closed neurocentral synostoses and fused cervical ribs. By all appearances, it belongs to an adult or nearly adult animal. It is hard to avoid the conclusion that the Mother’s Day Quarry includes at least one adult or near-adult Diplodocus. The only alternative is that MOR 790 8-10-96-204 is a juvenile in which the neural arch and cervical ribs fused very early.* But if that were the case, what basis would we have for thinking that it belonged to a juvenile, other than that it came from a quarry that only produced juveniles up until now? I trust that the circularity of that logic is clear. It is much more parsimonious to infer that MOR 790 8-10-96-204 is just what it appears to be–an anterior cervical of an adult or near-adult Diplodocus–and that the Mother’s Day Quarry is not exclusively filled with juvenile sauropods.
* Another wrench in the gears: if MOR 790 8-10-96-204 is a juvenile that had freakishly early fusion of its various bits, then clearly its ontogeny has departed from that of Diplodocus, all bets are off about developmental timing, and we shouldn’t be using it to make inferences about the normal ontogeny of diplodocids anyway. It’s damned if you do (it’s an adult), damned if you don’t (it’s a freak).
I’m not criticizing the work of Myers and Storrs (2007) on the taphonomy of the Mother’s Day Quarry or Myers and Fiorillo (2009) on age segregation in sauropod herds, by the way. It’s possible that they never saw MOR 790 8-10-96-204, or that if they did see the specimen they mistook it for a juvenile vertebra based on its size. All it takes is one bone to show that an animal is present in a quarry, and no number of other bones can prove that said animal is absent; if they only saw juveniles, the inference that the quarry only contained juveniles was sound (the operative word is was). If MOR 790 8-10-96-204 is a C5, it’s still only 80% the size of the same vertebra in D. carnegii CM 84/94, so maybe it was the oldest one in the group, or maybe it was an adult slumming with the juveniles, or maybe groups of juvenile sauropods often had one or more adults present to keep an eye on things. Or maybe it happened along earlier or later and just got buried in the same hole. There are a host of possibilities, most of which do not contradict the general conclusions of Myers and Storrs (2007) and Myers and Fiorillo (2009).
Size matters. Size alone is a horrible, horrible criterion for inferring age, especially in a clade (Diplodocoidea) in which adult size is known to vary, and especially with vertebrae. We should expect cervical vertebrae in a single individual to differ in diameter by a factor of 4.
Serial position matters. Not all vertebrae turn out the same. Even in adults, anterior cervicals look very different from posterior cervicals, and have different character states. Anterior cervicals and cervicals of juvenile individuals often look similar. The best way to tell them apart is to rely on articulated series–which is why I went to the trouble of writing the first post in this series.
Skeletochronology matters. The fact that MOR 790 8-10-96-204 has an apparently fused arch and fused cervical ribs should have been huge red flag that maybe it wasn’t actually a juvenile.
I went through that example at length because it shows how serial changes in size and morphology can mimic or suggest ontogenetic changes. In the next post I will examine the rest of the data Woodruff and Fowler (2012) used to support the hypothesis of ontogenetic control of neural spine bifurcation.
The rest of the series
Links to all of the posts in this series:
- Part 1: what we knew a month ago
- Part 2: why serial position matters
- Part 3: the evidence from ontogenetic series
- Part 4: is Suuwassea a juvenile of a known diplodocid?
- Part 5: is Haplocanthosaurus a juvenile of a known diplodocid?
- Part 6: more reasons why Haplocanthosaurus is not a juvenile of a known diplodocid
and the post that started it all:
- Hatcher, J.B. 1901. Diplodocus (Marsh): its osteology, taxonomy, and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63.
- Myers, T.S., and Fiorillo, A.R. 2009. Evidence for gregarious behavior and age segregation in sauropod dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology 274:96-204.
- Myers, T.S., and Storrs, G.W. 2007. Taphonomy of the Mother’s Day Quarry, Upper Jurassic Morrison Formation, south-central Montana, U.S.A. PALAIOS 22:651–666.
- McIntosh, J.S., Miller, W.E., Stadtman, K.L., and Gillette, D.D. 1996. The osteology of Camarasaurus lewisi (Jensen, 1988). BYU Geology Studies 41:73-115.
- Osborn, H.F. and Mook, C.C. 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History 3:247-287.
- Ostrom, John H., and John S. McIntosh. 1966. Marsh’s Dinosaurs. Yale University Press, New Haven and London. 388 pages including 65 absurdly beautiful plates.
- Woodruff, D.C, and Fowler, D.W. 2012. Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): a critical phylogenetic character. Journal of Morphology, online ahead of print.
March 22, 2012
…with sauropod bones!
Lots of basements have them. Some basements have had them for decades, and other basements have been newly constructed to house them. So you can take advantage of that retro chic while taking your basement into the 21st century!
What the heck am I talking about?
One of the nifty features of WordPress is that you can track the search terms that people are using to find your blog. After Mike put up his “Suboptimal location of Mamenchisaurus” post, we noticed that one of the top search terms bringing people to SV-POW! was ‘basement’. Yeah, that’s right, ‘basement’. In fact, ‘basement’ is the 5th highest search term of all time that has brought people to SV-POW! And that’s not unusual–in fact, of the top 5 search terms bringing people here, only one is sauropod-related (Brachiosaurus, at number 2).
As of this posting, here are the Top 10 non-sauropod search terms of all time that have led people to SV-POW!, listed by rank, and including the number of hits in parentheses:
1. rabbit (18,235)
3. leopard seal (12,797) — this explains why “Sorting out Cetiosaurus nomenclature”, which even Mike admits is the most boring topic we’ve ever covered here, is the 11th most popular post of all time on this blog!
4. flamingo (10,974)
5. basement (9743)
12. twinkie (3434)
14. flamingos (3102) — double dipping for the “Necks lie” post!
20. pig skull (2099)
21. savannah monitor (2078)
22. varanus exanthematicus (1936) — double dipping for “Four complete, articulated, extant sauropod skeletons–yes, really!”
24. shish kebab (1660) — double dipping for “Sauropods were corn-on-the-cob, not shish kebabs”.
We’re apparently getting a lot of hits from people who want to remodel their basements. I’m all for that (the remodeling, and the extra hits), so I’m embracing it. You want basements, we got ‘em. We’ll drown you in pictures of sauropod vertebrae in basements. Did I say basement? Basement, basement, basement!
(Why am I pushing basement and not rabbit, flamingo, or leopard seal? Partly because basement used to be our number 1 search term and I want to see its fortunes rise again. Partly because those other things are at least biological, and it cracks me up to have a common architectural term bringing people to the blog. And partly because I want to upstage John and his freezers.)
Basement Renovation Instructions
This short guide will help you with your project.
Is your basement in a museum?
If YES, then:
1. Fill it with sauropod vertebrae.
2. Call us.
If NO, then:
1. Fill it with anything you like except sauropod vertebrae.
2. Support your local museum.
Don’t forget: basement!
December 23, 2011
December 16, 2011
Hot on the heels of PLoS ONE-like open-access megajournals such as BMJ Open, Nature’s Scientific Reports, the Royal Society’s Open Biology and SAGE’s SAGE Open, now the king of evil predatory price-gouging publishers-whose-business-model-is-to-prevent-papers-being-read Elsevier are — you won’t believe this — launching their own PLoS ONE clone, FEBS Open Bio.
So please join me in giving a hearty “meh”.
I don’t see how this can work. Surely the only reason people ever send their work to Elsevier journals rather than somewhere truly open is because of the reputation that individual Elsevier-owned journals have accumulated over the years? No-one sends to Cretaceous Research because it’s published by Elsevier, do they? In which case I don’t see who is going to submit to a brand new Elsevier journal just because it’s Elsevier’s when PLoS ONE already has the momentum and (increasingly) the prestige.
So I am not predicting a bright future for FEBS Open Bio.
And that suits me fine. Success should go to people who went open because it was the right thing to do, not to for-profit publishers who are belatedly realising that the world has changed and scrabbling to make the best they can of it.
Oh, and by the way: a little bit of searching shows that FEBS Open Bio not actually Open Access. Its User Rights page says that “articles are protected by copyright and may be used for non-commercial purposes”, and goes on to give a long list of things that you’re not allowed to do with FEBS Open Bio articles. As Peter Murray-Rust points out, it’s not Open Access if it has the “non-commercial” clause, which has all sorts of undesirable consequences.
December 5, 2011
This week the SV-POW!sketeers are off to Bonn, Germany, for the Second International Workshop on Sauropod Biology and Gigantism. All three of us will be there, plus SV-POW! guest blogger Heinrich Mallison, plus Wedel Lab grad student Vanessa Graff, plus about 50 other awesome scientists from around the world. So we’ll have a ton of fun, but we probably won’t get much posted.
In the meantime, enjoy this cool encounter from the bone cellar at the Humboldt Museum in Berlin, where Mike and I fetched up at the end of the last IWSBG back in 2008. It’s a transversely-sectioned dorsal centrum of Giraffatitan, one that Janensch illustrated in his 1950 monograph on the vertebrae of Giraffatitan. Mike and I were very familiar with the cross-section image from the paper, so it was cool and a bit unreal to find the actual item.
Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.
November 21, 2011
- Part 1: intro
- Part 2: the head
- Part 3: the neck
- Part 5: posture
- Part 6: texture and color
- Part 7: verdict
A long-running theme here at SV-POW! is that the torsos of most sauropods were not just deep and slab-sided, they were unusually deep and slab-sided, more so than in most other tetrapods (see this and this, and for a more pessimistic take, this). This is something that is easy to get wrong; we are used to seeing round mammalian torsos and a lot of toy sauropods have nearly circular cross-sections. A lot of sculptors of collectible dinos do get the torso cross-section right, though, and the folks who made this Apatosaurus are no exception.
Next item: there’s an upward kink at the base of the tail, as there should be. Gilmore was the first to point this out, in his 1932 paper on the mounting of the Smithsonian Diplodocus (that’s plate 6 from that paper above; the skeleton on the bottom is the more correct one). This came up in the comment thread of the first post in this series, and since I haven’t had any deeper thoughts on the issue in the past week, I’m just going to copy and paste what I wrote then:
The upkink at the base of the tail is unavoidable; the sacrum is shaped like an inverted keystone and there’s no way to get the proximal caudals to do anything but angle upward without disarticulating them…. The reverse keystoning of sauropod sacra is weird. And it’s in every sauropod sacrum I can remember seeing with my own eyes, including Brachiosaurus altithorax. And yet the only authors I can think of off the top of my head who have discussed it seriously are Gilmore (1932), Greg Paul (2010, maybe a magazine article or two I haven’t seen), maybe Jim Jensen (1988), and IIRC Salgado et al. (1997). If there are more, please let me know–this is something I’m very curious about.
The back is gently arched, with the highest point about midway between the shoulder and hip joints. Where the highest point in the back falls depends on a host of factors, including the relative lengths of the forelimb and hindlimb bones, the amount of cartilage on the ends of those bones, the position and angle of the scapula on the ribcage, and the intrinsic curvature, if any, of the articulated series of dorsal vertebrae, which were themselves separated by an unknown amount of cartilage. Opinions are all over the map on most of these issues, particularly scapular orientation. As a scientist, I am agnostic on most of these points; I don’t think that they’re beyond being sorted out, but there’s a lot of work in progress right now and I haven’t seen evidence that would definitely convince me one way or another. So in lieu of saying that Apatosaurus must have had this scapular orientation and that dorsal curvature and so on, I’ll just note that the maquette has been a dominant feature in my office for a few weeks now and nothing about the body profile, shoulder position, or limb length has ever struck me as odd or worthy of comment. It looks like Apatosaurus to me. Moving on…
In the last post I talked about the visible bulges in the neck that allow one to count the cervical vertebrae. The maquette also has low bumps along the back that mark the neural spines of the dorsal vertebrae. This doesn’t strike me as unreasonable. Attachment scars for interspinous ligaments run all the way up to the tips of the neural spines in most sauropods, so the entire height of one neural spine was often webbed to the next by a continuous ligamentous sheet, as Janensch (1929: plate 4) drew for Dicraeosaurus in the illustration above (isp.L). I don’t think those ligaments would have prevented the bony tips of the vertebrae from being visible, necessarily, and the epaxial muscles should have been on either side of the interspinous ligaments and in the triangular spaces between the spine tips and the transverse processes.
What might have smoothed out the dorsal body profile are supraspinous ligaments (ssp.L in the plate above). These are present in crocs (Frey 1988: figs. 14, 16, 17) but apparently absent in most birds; at least, I haven’t seen any myself, and the Nomina Anatomica Avium does not mention any (Baumel et al. 1993: 156-157). So on phylogenetic grounds their presence in sauropods is equivocal. That said, the tips of the neural spines in most sauropods are fairly rugose. Does that mean that they were webbed one to the next by interspinous ligaments only, or that they were embedded in supraspinous ligaments as well? I don’t know the answer, and I don’t know if anyone else does, either. The whole issue of intervertebral ligaments in sauropods has received too little attention to date. In the absence of better data, I’ll just say that although I wouldn’t put any money on the proposition that the spines made externally visible bumps in life, neither does it offend me.
There is one fairly nit-picky point that I am honor-bound to mention. Because the dorsal neural spines make bumps, it is possible to count the dorsals, just like the cervicals last time. And this count doesn’t work out quite as well. Apatosaurus should have 10 dorsal vertebrae, but try as I might I can’t see more than 8 bumps along the back, and that’s generously assuming that c14’s spine is pretty well ahead of its rib. Is this pathologically anal to complain about? Quite possibly. On the other hand, by sculpting in those details the artists were basically begging geeks like me to come along and count vertebrae just because we could.
The tail is pretty cool. It is appropriately massive where it leaves the body, and has a visible bulge for the caudofemoralis muscle, which originated in the tail and inserted on the fourth trochanter of the femur. The caudofemoralis is the major femur retractor in lizards and crocs and in most non-avian dinosaurs, and rather than go on about it I’ll just point you to Heinrich Mallison’s awesome post about dinosaur butts. The tail of the maquette also has an awesome whiplash. I could say a ton more about the hypothesized uses of whiplash tails in diplodocids and other sauropods, but I don’t feel like climbing that hill just now. Suffice it to say that the maquette’s whiplash is pretty sweet, and avoids the “scale is too small so I just stuck in a piece of wire” mode of making whiplashes that I’ve seen in other, smaller diplodocid sculpts.
The tail has a row of little spines running down the dorsal midline, which have been de rigeur for life restorations of diplodocids and many other sauropods (ahem) since they were first reported by Czerkas (1993). AFAIK, such spines have only been found preserved in the tail region of diplodocids. That’s not to say that they weren’t present in the neck or the back of diplodocids, or in other sauropod taxa, just that the only good fossil traces of them to date have been from the tails of diplodocids, and maybe just one or two tails. So the presence of little spines in the tail of the maquette and not the back or the neck is perfectly–one might even say slavishly–consistent with the fossil evidence. I’ll discuss the flamboyancy or lack thereof in the maquette in another post, so I’ll say no more about this design choice for now.
The limbs are mostly good. The muscles under the skin look plausible, with one exception. As noted before in this series, Apatosaurus was a freakishly robust critter, and the limbs look appropriately sturdy and well-muscled, except where the thigh meets the hip. There is a visible bulge for the ilium, and the anterior margin of the thigh should converge with the most forward point on the ilium. That’s what the preacetabular blade of the ilium is for: to anchor thigh muscles (discussed here, and also nicely illustrated here). Unless the animal had some kind of wasting disease, there was no bone sticking out beyond the muscle, and so the anterior-most point of the ilium has to be the start of the anterior margin of the thigh.
On the positive side, there’s a little ridge running down from the anterior arm onto the forearm for the biceps tendon, which is a nice touch. The manus shows the short, solid arc of metacarpals typical for diplodocids, and an inward-curving thumb claw. The hind feet have the big laterally-curving claws on the first three digits that one expects.
In a way that is difficult to describe in words, the feet really look they are bearing a lot of weight, and this impression of solidity helps to ground the whole maquette. It doesn’t look like a sauropod-shaped balloon that just happens to be poling itself along with limbs that barely touch the ground–an impression that I have gotten occasionally from some other sculptures with overly skinny limbs and too-small feet. This critter looks big, heavy, and powerful, and those are exactly the adjectives one wants to come to mind when looking at Apatosaurus. (I do wonder if doing a Diplodocus in the same scale would be more difficult. How do you convey ‘multi-ton animal’ and ‘gracile’ at the same time?)
To sum up, in the trunk, tail, and limbs I find much to like and little to criticize. The only noteworthy problems are the insufficient dorsal count and the mismatch between the ilium and anterior thigh profile. On one hand these are puzzling goofs, given the overall attention to detail and the numerous points at which the sculpt is not just good but surprisingly good. On the other hand, I didn’t notice the dorsal thing until I bothered to count, and I didn’t notice the thigh thing until the other day when I was writing the first draft of this post, so both problems went unnoticed for weeks and are probably below the threshold of perception for the vast majority of people. The accuracy of the sculpt is so high that my approach to its problems has not been, “Where do I begin?” but rather, “What is keeping this thing from being perfect?” And the answer is, not very much.
The base is nice. It’s not just a generic slab of earth, it’s a muddy surface marked with the tracks of other dinosaurs, including a couple of theropods. The base sits nice and flat, and the Apatosaurus sits nice and flat on it, with no rocking at either point of contact. Not only do the feet of the Apatosaurus fit neatly into the sculpted footprints, one of the hindfeet has a little metal rod that slots into a socket in one of the hindfoot prints, to keep the maquette firmly on the base. That means that if you want to display the maquette off the base, you’ll have to either cut off the rod or make sure that your alternative surface will accommodate it.
The skull is…less satisfying. It’s a nice enough rendition of an Apatosaurus skull, and if it had come by itself I would have been very happy with it. The trouble is that the maquette is considerably more detailed, so when the skull sits next to the maquette it suffers by comparison. But what else are you going to do with it? Make a separate shrine to Apatosaurus somewhere else?
The difference in sculpt quality between the maquette and base on one hand and the skull on the other is apparent even on casual inspection. My copies are sitting on a bookcase adjacent to my office door. Sometimes people walking down the hall pop their heads in, and so far the most common comments are that the maquette is “awesome” and that the base is “cool”. People have been genuinely impressed that the base is a realistically detailed chunk of the environment and not just a flat slab. The only people who have commented on the skull have said that it seems “lame” compared to the maquette.
The base is included in the basic package with the maquette, in a limited edition of 500, which as of this writing goes for $289.99 (here). The package with the skull accessory is in an edition of 100, and goes for $299.99 (here). So the skull is only $10 more, and although it is not quite as nice as the maquette, I think it’s a steal at the price. Mine is certainly not going anywhere.
So much for the gross anatomy. You probably noticed that I haven’t said anything about how the maquette is posed or textured or colored. Those will all be topics for next time.
- Baumel, J.J., King, A.S., Breazile, J.E., Evans, H.E., and Vanden Berge, J.C. (eds.) 1993. Handbook of Avian Anatomy: Nomina Anatomica Avium, 2nd ed. Publications of the Nuttall Ornithological Club, No. 23. Cambridge, Massachusetts, 779 pp.
- Czerkas, S.A. 1993. Discovery of dermal spines reveals a new look for sauropod dinosaurs. Geology 20:1068–1070.
- Frey, E. 1988. Anatomie des Körperstammes von Alligator mississippiensis Daudin.
- 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.
- Janensch, W. 1929. Die Wirbelsäule der Gattung Dicraeosaurus. Palaeontographica Suppl. 7(1), 3(2), 37-133.
- Jensen, J.A. 1988. A fourth new sauropod dinosaur from the Upper Jurassic of the Colorado Plateau and sauropod bipedalism. Great Basin Naturalist 48(2):121-145.
- Paul, G.S. 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press, 320 pp.
- Salgado, L., R.A. Coria, and J.O. Calvo. 1997. Evolution of titanosaurid sauropods. I: Phylogenetic analysis based on the postcranial evidence. Ameghiniana 34:3-32.
October 31, 2011
Back when Darren and I did the Xenoposeidon description, we were young and foolish, and only illustrated the holotype vertebra NHM R2095 in four aspects: left and right lateral, anterior and posterior. No dorsal or ventral views.
Also, because the figure was intended for Palaeontology, which prints only in greyscale, I stupidly prepared the figure in greyscale, rather than preparing it in colour and then flattening it down at the last moment. (Happily I’d learned that lesson by the time we did our neck-posture paper: although it was destined for Acta Palaeontologia Polonica, which also prints in greyscale, and though the PDF uses greyscale figures, the online full-resolution figures are in colour.)
As if that wasn’t dumb enough, I also composited the four featured views such that the two lateral views were adjacent, and above the anterior and posterior views — so it wasn’t easy to match up features on the sides and front/back between the views. Since then, I have landed on a better way of presenting multi-view figures, as in my much-admire’d turkey cervical and pig skull images.
So, putting it all together, here is how we should have illustrated illustrated Xenoposeidon back in 2007 (click through for high resolution):
(Top row: dorsal view, with anterior facing left; middle row, from left to right: anterior, left lateral, posterior, right lateral; bottom row, ventral view, with anterior facing left. As always with images of NHM-owned material, this is copyright the NHM.)
Of course, if we’d published in PLoS ONE, then this high-resolution (4775 x 4095), full colour image could have been the published one rather than an afterthought on a blog somewhere. But we didn’t: back then, we weren’t so aware of the opportunities available to us now that we live in the Shiny Digital Future.
In other news, the boys and I all registered Xbox Live accounts a few days ago. I chose the name “Xenoposeidon”, only to find to my amazement that someone else had already registered it. But “Brontomerus” was free, so I used that instead.
April 20, 2011
A few months ago, prosauropod supremo Adam Yates blogged about the Aardonyx cake that the BPI honours class baked in his honour. In the comments, I mentioned that my wife Fiona once made me a BMNH R5937:D9 cake (i.e. a cake in the form of the more posterior of the pair of nicely preserved dorsal vertebrae of The Archbishop, in right lateral view). At the time, I couldn’t find the photo that I knew had been taken, and Adam asked me to post it when it turned up.
And here, once more, is the real thing for comparison:
(Note that the topology of the lateral lamination is spot on, with a single infradiapophyseal lamina which forks into anterior and posterior branches only some way ventral to the diapophysis. That’s what you look for in a cake.)
Update (21 April)
Silly me, of course what I should have shown is the cake and the vertebra side by side. Here they are — together at last!
February 10, 2011
As we all know, the International Code of Zoological Nomenclature is a large and intimidating document. As a result, zoologists naming new animals often do not read it in its entirety (I know I haven’t). It’s probably because of this that many of the more avoidable nomenclatural mistakes occur.
Whatever might or might not eventually be possible in terms of simplifying the Code, everyone recognises that that would be a huge job, and something that would take years to do. So let’s ignore that possibility for now.
In the short term, what would be much more useful would be if someone could work up a very short document — no more than a single page of A4 and hopefully much shorter — that states in simple bullet-points what MUST be done to ensure that a new name is valid. Then there would be no excuse for zoologists venturing into nomenclature for the first time not to read such a document — let’s call it the ICZN Cheat Sheet.
Because it’s easier to steer a moving ship, I wrote to the ICZN email list this morning proposing an initial set of bullet points. I did not for a moment expect that they were complete, consistent or even necessarily correct; but I hoped that they could at least serve as a starting point for a very quick process of putting such a list together.
I am pleased to say that response on the list was fairly positive, and at the suggestion of one of the list members I have now posted the in-progress checklist as a page on this site, having revised it in accordance with several suggestions.
If you’re interested in contributing to this effort — helping us to derive a clear, concise and correct one-page guide to naming new zoological genera and species — please head over to the page and comment there. (Comments on this post are closed, to avoid splitting discussion across two places.)
December 22, 2010
I recently stumbled across this rather good photograph of the holotype vertebra of our old buddy “Ultrasauros“, thanks to Wikipedia contributor Ninjatacoshell, and thought you’d like to see it:
This is a rather legendary vertebra, but until recently there were no good photographs of it on the web (I know because I tried to find one for my talk at the Dinosaurs: A Historical Perspective conference in 2008).
In other news, everyone in palaeontology should read Heinrich Mallison’s recent article No 4WD For Plateosaurus over on the Palaeontologia Electronica blog. He highlights a lot of important issues that have general applicability.