Well, not Xenoposeidon, anyway

November 27, 2007

After eight consecutive posts on Xenoposeidon, I have to admit that even I am getting just a tiny bit bored of it, so I can only imagine how the rest of you feel. So now for something completely different:

BMNH 96 “Chondrosteosaurus”

You see before you a badly battered cervical vertebra, BMNH R96, which if I remember correctly is catalogued as belonging to “Chondrosteosaurus“. That genus, like so many from the Wealden, was erected on non-diagnostic material, and there is really no reason to think that R96 belongs to the same taxon as the Chondrosteosaurus type specimen BMNH R46869. It’s best regarded as Neosauropoda indet. (and, no, before you ask, we will not be naming it and promoting it as “The world’s second most amazing sauropod”).

The interesting thing about this specimen is that its condyle is completely eroded away. We’re looking at it in anterior view, right into the front of the centrum, and we can see a classic camellate pattern. The network of thin lines is bone; everything in between, now filled with matrix, used to be filled with air when the animal was alive. A while back, Matt ran the number on this photo and concluded that this vertebra was 78% air — a very high proportion even by sauropod standards, exceeded only by Sauroposeidon (the world’s third most amazing sauropod).

Of course it’s a shame that this bone is so poorly preserved; on the other hand, if it were complete, we wouldn’t be able to see the internal structure. Matt’s firmly of the opinion that bone not broken is a bone wasted, and I sometimes think that if he had his way, he’d go through the world’s sauropod collections with a sledgehammer, smashing all the vertebrae open in search of pneumaticity. (Note to collections staff: Just kidding! Har har!) It’s certainly true that more is known about the “Angloposeidon” vertebra than would be known if it weren’t snapped in two; and of course, we’d not have known about the internal structure of the Xenoposeidon vertebra were the condyle not blasted off.

Up till now, internal structure has been badly neglected in terms of informing sauropod phylogeny, despite Matt’s work on its evolution and distribution (Wedel 2003a, 2003b). The analyses of Wilson (2002) and Upchurch et al. (2004) each included just a single character for presacral bone texture in their matrices; and the Grand Unified Analysis of Harris (2006), which merged the Wilson and Upchurch matrices, discarded even this one character, as discussed in the supplementary data. That may be fair enough: we might not yet know enough about vertebral bone texture to code it well. But hopefully that will soon change, because there is a lot of information out there that’s not getting used.

References

By now BMNH R2095 must be the best described, most pored-over 2/3 of a vertebra on the planet. What more can we possibly have to show you?

How about this dandy poster for your living room wall, or the entrance to your corporate headquarters?

xenoposeidon-poster-500.jpg

And of course the obligatory rotating “3D” reconstruction…
bmnh-r2095.gif

And a heretofore unpublicized life restoration, courtesy of Mike Taylor. Some details are hypothetical…

xena.jpeg

And finally, the happy authors basking in the glory of Good Science.

geeks-500jpeg.jpg

That concludes our coverage of Xenoposeidon week here at SV-POW! Don’t forget to check back next week–and every week–for even more mind-bending morphology, bleeding-edge science, and soul-crushing-uplifting majesty.

To pneumaticity and beyond!

OK, so it’s actually day 7: I missed my deadline yesterday due to that unfortunate necessity, the day-job, which had me in meetings for half of the day and travelling for the other half. Yes, I could have written this post on the trains and planes, but I had my reasons.

So here we are, at last. Today I’d like to talk a little bit about this idea that Xenoposeidon represents a new “family” of sauropods, which is just a little controversial. However, since this is supposed to be Picture of the Day, let’s start with a pretty picture which is not really related. For some dumb reason, the Xeno paper illustrates the specimen in left and right lateral and anterior and posterior views, but not dorsal view: so here it is!

xeno-dorsal-500px.jpg

If I had more time, I’d prepare an interpretive drawing of this, but since I don’t, let me draw your attention to a few points. All of this will probably make more sense if you look at this picture together with the left-lateral view, and its corresponding drawing, from Day 1.

Anterior is towards the top of the picture, so the flatness you see at the bottom is the cotyle in dorsal view. In reality, of course, the cotyle is gently convex, but all we can see from this angle is the dorsal margin. You’ll see that a pair of symmetrical buttresses run up towards breakages, also symmetrical. The buttresses are the pedicels of the neural arch, and the breakage is part way up the centropostzygapophyseal laminae. We can see that those laminae extend anteriorly until they meet the accessory postzygapophyseal laminae (as we interpreted them), which in dorsal view extend almost directly laterally. Obviously that lamina is only well preserved on the left side; anterior to that is “accessory infraparapophyseal lamina”, which we think is homologous with the widespread posterior centroparapophyseal lamina (PCPL) but which we didn’t feel we could call by that name as it doesn’t get anywhere near the centrum. As we look at it from above, this lamina appears to run anterolaterally, but of course it’s also ascending as it progresses anteriorly, as you can see in lateral view: so its true orientation is anterodorsolateral.

Isn’t this fun?

Well, anyway. The most anterolateral point of that lamina, which in this dorsal view looks like a blunt triangle sticking out to the left, is the site we interpreted as the parapophysis: that is, the more ventral of the two sites where the rib head articulated with the vertebra. The other of these sites, the diapophysis, seems to have been pretty much directly above the parapophysis … and is of course lost, like far too much of the vertebra: see the speculative reconstruction from Day 2. The position of the diapophysis is actually easier to make out in this dorsal view than in lateral view, in which the paradiapophyseal lamina (PPDL) appears to be oriented posterodorsally. One of our reviewers, seeing this apparent trajectory of the PPDL, questioned our interpretation of the lamina, suggesting instead that the diapophysis might be located some way posteriorly (as well as dorsally) of the parapophysis, and that the accessory poztzygapophyseal lamina might instead be an anterior centrodiapophyseal lamina. (He was quite right to raise that point, as the versions of the figures that we originally submitted didn’t point out all the relevant features that support our interpretation.) Anyway, in this dorsal view we can see that the PPDL is a sheet of bone projecting anterolaterally from the body of the neural arch and running directly dorsoventrally (i.e. into the eye of the camera), hence the directly-dorsal position of the diapophysis.

Sorry if all that was a bit dull — just wanted to clear it up before launching into the ‘What is a “family” anyway?’ discussion.

Here’s what we said in the paper on that subject, in the conclusion to the Comparisons and Interpretation section:

While X. proneneukos is clearly a neosauropod, it cannot be referred to any existing neosauropod genus, nor even to any `family’-level or `superfamily’-level group, a conclusion first reached by means of group-by-group comparisons and then verified by the phylogenetic analysis. Its unique characters indicate that it is either a highly derived member of one of the known groups, or, more likely, the first representative of a previously unknown group. While we consider this specimen to represent a new `family’-level clade, raising a new monogeneric family name would be premature; and the indeterminate position of the new genus within Neosauropoda means that no useful phylogenetic definition could be formulated.

Why did we put the scare-quotes around the word “family”? Because the notion of of a “family” in taxonomy is at best a rather slippery one. We felt it was necessary to draw attention to just how weird Xeno is compared with other sauropods, and how very uncomfortably it sits in any of the available groups, and it seemed to us that to talk in terms of a “family-level” distinction was the best way to do that: or, as I said in one of the many TV interviews, Xeno is about as different from other sauropods as bears are from dogs or cats. Of course, a statement like that is necessarily pretty fluffy, and better suited to the News At Ten than to a technical paper, but it does get the message across.

The problem is that as soon as you ask exactly what a “family” is, you start to realise that the answer is “a group that has been designated a family”. There is, and can be, no objective standard for how broad a grouping should be designated a “family”, or even of how such broadness should be assessed — by number of species, morphological disparity, whatever. We felt that the best way to look at this in the Xeno paper was to look at the existing sauropod families (i.e. group names that end with the convenional ending “-idae”) and we concluded that Xeno appears as different from, say, brachiosaurids and diplodocids as they are from each other.

Some people think that we should have avoided using the term “family” at all, notably Randy Irmis who I am as I write this in the middle of an email argument with. Actually, I have plenty of sympathy with that approach: the problem is that the suggestions of what to say instead are much worse than the disease. A common suggestion is that we say Xeno represents a new clade: but that is trivially true of every single organism. Randy Irmis, in fact, represents many new clades, just one of which is the clade of all animals more closely related to Randy Irmis than to Buzz Aldrin. A statement like that is true but contains no information. While the word “family” indicates only a fuzzy idea of morphological disparity, it does at least convey some idea, which is more than you can say for “clade” or “group”. The trick is to avoid being fooled into thinking that “new family” means something more precise than it does.

Finally, let’s remember that, assuming we’re correct in saying that Xeno is a neosauropod (and I’m sure we are), then it must belong to either Diplodocoidae or Macronaria, by the very definition of those names. And if it’s macronarian, then it must be either a basal member of that group of a camarasauromorph; and so on, as clades slide up the phylogeny. So in saying “new family”, we certainly don’t mean that it couldn’t be, for example, a bizarre deviant titanosaur or brachiosaurid: just that, even if it is one of those things, it’s weird enough to merit recognition.

I’m sure plenty of people will disagree with the approach we took; that’s fine, if we’d taken a different approach, plenty of people would have disagreed with that, instead. The use of ranks, even informally, just is controversial, there’s no getting away from it. Maybe in another decade we’ll be closer to a consensus — but I wouldn’t want to guess at this remove what that consensus will be.

Well, that’s plenty for today. Sorry if it’s been a bit hardcore in places: Matt will bring you a helping of your usual wackiness tomorrow, on the seventh and final day of Xenoposeidon Week. Thanks for sticking with it!

MPT on South Today

So… you’re publishing a new, dead exciting and all round outstanding paper on a new dinosaur – like, let’s say, the new Hastings Beds Group neosauropod Xenoposeidon proneneukos Taylor & Naish, 2007 – what now? Well, you might just sit back, carry on with your other work, and just plain hope that your colleagues (and maybe the rest of the world too) will stumble across your latest endeavour and then heap upon you the accolade you deserve. Or you could be rather more proactive, and in the exclusive SV-POW! article you’re about to read, we’re going to look at one particularly successful, highly proactive media campaign that resulted in national and international recognition for the wonder that is Xenoposeidon, world’s most remarkable sauropod.

Now I’ve been involved in dinosaur-related publicity before. Things have happened in two ways. One is that some clever science-journalist type person has seen the research (usually via an online contents list) and has contacted me to cover the story. The other is that I or one of my colleagues has contacted the public relations office at the university (recall that Mike and I are both based at University of Portsmouth, UK); I’ve then spoken to the PR people about the research, and they’ve then written a press release. Understandably, Mike and I are very proud of Xenoposeidon, and (clearly) we both regarded it as newsworthy enough to announce to the world. So we got in touch with UOP’s PR people, and got telling them all about it*. A press release was written, and went through several drafts before everyone was happy with it. Among the ‘everyone’, incidentally, were our colleagues at the Natural History Museum (London). Given that we were talking about a specimen kept in their collections, it is only fair and appropriate that they be kept abreast of what was going on.

* When I say ‘we’, I in fact mean Mike: Xenoposeidon is Mike’s baby more than mine, and I’ve already done quite a lot of this sort of thing anyway, so I sat back and let him get all the glory.

Secrets of success

Let me say here how important timing is. One of the first things we did was to get the official publication date for our paper from the journal where the paper was appearing (the Palaeontological Association’s august publication Palaeontology): that date was November 15th. The press release would go out on the 14th, and the story would be embargoed until the 15th. By putting out a press release on an arranged date, you’re both controlling the publicity, and saving yourself a whole world of hurt. Back when another newsworthy British sauropod – the Isle of Wight specimen that we lovingly know either as MIWG.7306 or ‘Angloposeidon’ – was published, I collaborated with the PR people and, again, organized a press release and official release date. Unfortunately (for us), an online pre-print version of the paper (Naish et al. 2004) was spotted by an enterprising BBC science reporter. After discussing the story with me (I asked if he could wait for the press release, he replied that he couldn’t), he covered the story, and from there all hell broke loose, making our PR efforts entirely redundant (for the full story of that debacle go here). It’s important for journalists to have access to a press release; it provides all the basic info (as well as a quantity of supplementary stuff that they may or may not make use of), includes some key quotes (well, ‘quotes’), and (importantly) shows them how to spell the words properly.

Working with the PR department’s Kate Daniell, Mike had outstanding support and a fantastic amount of help in getting interviews and photo opportunities set up with multiple TV and newspaper companies. When Mike started listing the TV and radio shows that had expressed an interest in featuring the story, I was staggered – the whole world was interested. Besides the timing I just alluded to, several things helped this process run smoothly. One is that Mike put time and effort into producing a media-friendly web page where journalists (and, in fact, anyone) could download a variety of Xenoposeidon pictures. I’ve never done this in any of my PR exercises (partly because I’m all round less computer-savvy than Mike is, but also because I’m less clever in general), but I will definitely be doing it in future and would strongly recommend it to anyone else. I suppose it would save you dealing with constant requests for images – when I handled the ‘Angloposeidon’ publicity, I had to email images many, many separate times.

Luis Astrodon rules

Another incredibly wise tactic involved Mike’s whereabouts: he actually traveled all the way to London on the 15th (he lives in rural Gloucestershire, about 150 km away… let me add that traveling 150 km is a big deal in Britain), and was both able, and prepared, to move from one interview to the next. That proved really, really important. Again, contrast this with what happened with ‘Angloposeidon’: the fossil, and thus any potential photo opportunity, was on the Isle of Wight, and I was unable to get there on that day. Consequently, journalists went to the Isle of Wight and ended up filming interviews with Isle of Wight curator Steve Hutt, a person not involved in the research. Also wise and useful was the last minute appeal for charismatic artwork: Luis Rey very kindly allowed use of his awesome Astrodon vs Utahraptor piece (shown in the adjacent image), and – despite Xenoposeidon’s beauty and striking appearance and, arguably, Mike’s suave charm and chiseled features – some journalists chose to supplement their stories with this memorable, striking picture.

So, in the end, it was all an awesome success and Xenoposeidon received so much coverage on the 15th that it’s difficult to know where to start. National newspaper coverage included that of The Guardian, The Sun and The Times (shown below). Most of those articles are pretty good; in cases surprisingly so. As Mike alluded to in the previous SV-POW! article here, he did quite a few radio and TV interviews. The good news is that you too can now watch at least some of the TV pieces by going here. The Meridian TV pieces – Mike is interviewed by Caroline Hole next to the Camarasaurus skeleton at the NHM – are particularly good, but, having said that, none of them are particularly bad. Channel 4 News broadcast a live feature on Mike and Xenoposeidon during lunchtime: I missed this, and last I heard Mike hasn’t seen it either. Another live TV interview – this time for BBC News 24 – was broadcast about an hour later, and again both Mike and I have failed to see it.

Times online

Because I was working from home on the day the story was released (‘Xeno day’ will forever be November 15th) I decided to keep Sky News on in the background. They advertised the story at 12:50pm and even showed a few NHM dinosaur skeletons. However, perhaps because the 15th wasn’t a particularly light news day (there were high-profile stories about O. J. Simpson, a Russian lady who gave birth to five babies, the deportation from the UK of a muslim charged with inciting racial hatred, and on Barry George, the alleged murderer of TV personality Jill Dando), they never got round to showing it, and by 4pm I gave up and switched the TV off. I did get to see a very abridged version of the piece produced by local BBC news programme South Today at 10:30pm, and very abridged it was too.

As I write (Monday morning), BBC TV’s The One Show have expressed their interest in covering the story. Mike is not available right now for work reasons, so I’m doing this one: if all goes ahead as planned, it’ll be going out live tomorrow (Tuesday 19th) some time between 7 and 7:15pm. If you’re in the UK – make sure you watch it! [UPDATE: it's just been cancelled!]

Almost certainly because of the large amount of information we provided both in the press release and on Mike’s website, there was a general lack of spurious nonsense or silliness in the reports. Admittedly, a few clangers made it through, but nothing major. The most bizarre and amusing statement I heard came from Freddie Rostand’s report for South Today. His (generally quite good) piece on Xenoposeidon opened with a photo of Mike cupping R2095 in both hands, accompanied with the line ‘This is Mike Taylor, holding his future in his hands’. Say what? The sequence also referred to Mike as ‘A quiet phd student’. Anyone that knows Mike will tell you that he’s not particularly noisy – he’s not like Animal from the muppets, or Dilbert’s colleague Loud Howard – but he’s not particularly quiet either, so I have no idea where this comes from.

Of uber-nerdy interest is the fact that this news piece not only showed Luis’s Astrodon vs Utahraptor painting, it also featured the head of a metallic brachiosaur model currently on display at Sandown’s Dinosaur Isle Museum on the Isle of Wight. South Today filmed this model when they were doing their story on ‘Angloposeidon’ in 2004, and I strongly suspect that they recycled the exact same bit of footage for the Xenoposeidon feature. Both news articles also featured the same scene from BBC’s Walking With Dinosaurs (the clip where Brachiosaurus emerges from the woodlands, towering above the diplodocids and engaging in some trademark neck-wobbling).

Local newspaper Portsmouth Today quoted me as saying that the discovery of Xenoposeidon will ‘make other palaeontologists sit up’. I find it hard to believe that I really said that, and I don’t remember doing so. Actually, that particular article did something rather more controversial: they titled their article ‘Meet Pompeysaurus, the new dinosaur’ (Pompey is a vernacular term for the city of Portsmouth) [you can see the article in question here]. I don’t personally have a problem with this and didn’t think anything of it, but it apparently bothered some people in our fine institution, as it intimated that ‘Pompeysaurus’ was the new taxon’s name. Apparently a representative of the newspaper phoned our department to apologise for any offence this may have caused!

Newspapers and TV news programmes have a horrible habit of knocking up their own god-awful in-house graphics, and just as bad is their other habit of recycling artwork from the 1950s or earlier. But, again, this time round things weren’t too bad: I didn’t balk at any of the mediocre sauropod pictures I saw masquerading on TV or in the papers, and nor did Mike I think.

All in all, Mike and Xenoposeidon were all over the global news media on the 15th, and everyone is happy that the entire event was an outstanding success. Sure, Mike got lots of publicity, but so did science in general, the study and awesomeness of sauropod vertebrae, the University of Portsmouth, and The Natural History Museum. We really couldn’t wish for anything more. As most readers will know, the 15th saw the release of some other exciting sauropod news: that on Paul Sereno and colleagues’ work on the African rebbachisaurid Nigersaurus. When I first heard that this long-awaited news was due to break on the 15th I thought that it would overshadow Xenoposeidon. It didn’t… in fact there didn’t seem much on Nigersaurus at all, and Xenoposeidon very much got its time in the limelight.

The blogosphere reacts

Cryptomundo does Xeno

Finally, many of our fellow bloggers agreed with us about the awesomeness of Xenoposeidon and wrote about it on their sites. I kicked things off over on Tet Zoo: incidentally, I had huge problems posting that article, and gave up on it entirely several times. Bora Zizkovic of A Blog Around the Clock put up a piece here: this is awfully nice of him, given that he’s editor of PLoS ONE (where the Nigersaurus paper appeared). Matt Celeskey of Hairy Museum of Natural History covered us in A great day for goofy sauropods; Brian Switek of Laelaps wrote about us here; Julia of The Ethical Palaeontologist said nice things here; Matt Bille’s Sci/Tech blog covered us here; Loren Coleman covered the story on Cryptomundo [see adjacent image]; and Matt Wedel, aka Dr Vector, told us how awesome we are here. That’s not all of it – there’s even more coverage if you can be bothered to search for it! There is now a Xenoposeidon wikipedia entry; it’s a start, but leaves much to be desired I’m sorry to say (it’s nothing to do with any of us).

So, all in all, the Xeno PR drive was huge, and a total success that went very, very well. I suppose I haven’t really congratulated Mike on his many excellent media appearances, nor have I thanked him for bigging up research that is not only relevant to me, but does everyone in palaeontology, and indeed science in general, a great servive. Well done Mike, and thanks indeed for putting so much time and effort into this.

PS – I thought this site was called ‘Sauropod Vertebra Picture of the Day’?

Refs – -

Naish, D., Martill, D. M., Cooper, D. & Stevens, K. A. 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 25, 787-795.

Taylor, M. P. & Naish, D. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50 (6): 1547-1564. doi: 10.1111/j.1475-4983.2007.00728.x

[Sorry about the late posting today: I had to leave the house at 7:15 to fly to Copenhagen for Christmas lunch -- long story -- and I am completing today's post from my hotel room.]

There’s no getting away from it: everyone wants to know how big dinosaurs are. Xenoposeidon is based on a single partial vertebra, so there is no way to be at all sure about the size and shape of the whole animal; but we knew that everyone would want to know, so in the paper (Taylor and Naish 2007, natch) we made the best guesses we could. Details on how we did this follow below.

Then, a few months after the revised manuscript was accepted by Palaeontology, purely as a joke, I put together what I called “the first scientifically rigorous skeletal reconstruction of Xenoposeidon“. The joke is based on a very well-established style for skeletal reconstructions of complete or nearly complete skeletons, first popularised by Greg Paul, in which the animal is shown in left lateral view, with bones drawn in white and the soft tissue outlined as a black silhouette — as in these rather beautiful Morrison Formation diplodocids from Paul (1998: fig. 1b).  F is Diplodocus carnegii CM 84 with skull CM 3542 scaled to fit, G is Barosaurus lentus AMNH 6341 (with a fair bit of guesswork to fill in the gaps) and E is Apatosaurus louisae CM 3018 with skull CM 11162 scaled to fit:

paul1998-fig1b-diplodocids-500px.jpeg

I thought it would be funny to do this for an animal known only from a single bone, showing the bone floating in the middle of a big black silhouette. Har har. (You may not find that funny. The key point here is that Matt and Darren both did, which is all I was aiming for. And it turns out that John Hutchinson agrees, which proves it.)

xenoposeidon-skeleton-500px.jpeg

In fact the only things that are remotely scientific about this “reconstruction” are that the bone is in roughly the right place (i.e. a posterior dorsal) and the human is about the right size. The actual shape of the “reconstruction” is a total guess: given that Xenoposeidon could belong in any part of the huge clade Neosauropoda, the only reason I went with a brachiosaurid body-shape rather than, say, a diplodocid was that I like brachiosaurus more. They’re just cooler. (This is how science is done, kids! Don’t tell your parents!)

It wasn’t until much later, when the publicity was in full swing, that it occurred to me that if the media were going to use the “skeletal reconstruction” it would be better to give them one with all the bones, greyed out. I made this almost as soon as it had occurred to me, and made it available to newspapers and TV stations, but it was a bit too late in the day — hardly any of them used it. Here it is, anyway:

xenoposeidon-skeleton2-500px.jpeg

Now that all the bones are back in place, it’s easy to recognise this as a knock-off of Matt Wedel’s Brachiosaurus reconstruction, as discussed in a much-overlooked Prehistoric Times article and which has since cropped up in various places. If I’d had my wits about me, I’d have credited Matt for the original “reconstruction” that went out to newspapers, but since it was only done as a joke it didn’t occur to me. Sorry, Matt!

So how did we figure out the probable size of Xenoposeidon? Since we had only one vertebra to go on, and since even that was missing the neural spine and other processes, all we had to work with were the centrum measurements. We reconstructed the centrum to be 20 cm long, with a cotyle diameter of 16.5 cm (the average of 16 cm width and 17 cm height). Then we compared that with the dimensions of vertebrae from the same position in the dorsal column of other sauropods. For this, we chose Brachiosaurus brancai and Diplodocus carnegii, because they are both known from nearly complete skeletons, and pretty much bracket the range of neosauropod body shapes.

Guessing length is easy: we just assume that the total length of Xenoposeidon would be in the same proportion to the length of one of its posterior dorsals as in the comparison taxa. The Xenoposeidon dorsal is 60% as long as the 33 cm D7 (seventh dorsal) of the Brachiosaurus brancai type specimen HMN SII (Janensch 1950: 44). If Xeno were built like a brachiosaurid, then it would be 60 per cent as long as HMN SII, yielding a length of 15 m based on Paul’s (1988) estimate of 25 m for that specimen. Similarly, the Xenoposeidon dorsal is 74% as long as the 27 cm vertebrae in the Diplodocus carnegii type specimen CM 84 (the average of the lengths of D7 and D8 as stated in Hatcher 1901:38). Therefore, a Diplodocus-like Xenoposeidon would be about 20 m long, based on the widely quoted figure of 27 m for CM 84.

But these figures are subject to a fair degree of uncertainty, and shouldn’t be taken too seriously. Suppose for example that we compared instead with D9 of Diplodocus, which is 29 cm long: the corresponding length estimate for Xenoposeidon would have been reduced to 20/29 of 27 m, which is 18.5 m.

And now to the much more handwavy problem of estimating mass. We can roughly extrapolate the mass of an animal as being proportional to the centrum volume, which in turn is proportional to centrum length times the square of its average cotyle diameter, and this is what we did in the paper. For Brachiosaurus brancai, this means that we estimate Xenoposeidon mass as (20 x 16.5 x 16.5) / (33 x 27 x 27) = 22% the mass of Brachiosaurus brancai; or as (20 x 16.5 x 16.5) / (27 x 29.5 x 29.5) = 23% the mass of Diplodocus carnegii, depending on which it most resembled.

But weight just a moment! (Har har.) What actually is the mass of Brachiosaurus brancai? An astonishingly wide range of figures have been calculated, all based on the same specimen (HMN SII). In chronological order (and do let me know if I’ve missed any):

  • 78 tonnes (Colbert 1962), based on the volume of sand displaced by a scaled plastic model
  • 15 tonnes (Russell et al. 1980) based on the dimensions of limb-bones, plotted on a best straight line through limb-bone-thickness vs. mass for extant animals
  • 47 tonnes (Alexander 1985), based on the volume of water displayed by a different model from the one that Colbert used
  • 29 tonnes (Anderson et al. 1985), using a similar though slightly more rigorous method than that of Russell et al. (1980)
  • 32 tonnes (Paul 1988), using, I think, graphic double integration or something similar (the paper is not very explicit)
  • 74 tonnes (Gunga et al. 1995), based on a computer model built using data scanned with lasers — very high-tech!
  • 37 tonnes (Christiansen 1997) by suspension of scale models
  • 26 tonnes (Henderson 2004) by measurement of computer model built by hand

We ignored the Russell et al. (1980) and Anderson et al. (1985) estimates because they are not actual measurements of anything, and depend instead on additional assumptions about scaling. We ignored the Colbert (1962) estimate, too, as it was based on a grotesquely overweight model. Worse still is the Gunga et al. (1995) estimate, which starts with ultra-precise measurements of the skeleton and then throws it away by fleshing that skeleton out in a computer model composed entirely of circular conic sections. Needless to say this makes the neck, torso and tail all hugely too wide, and the resulting volume estimate is near worthless. When they redo this work using elliptical conic sections, I will be interested to see how much their result comes down by. That leaves the more reliable estimates of Alexander, Paul, Christiansen and Henderson, and the average of their estimates 35322 kg — which seems correct using the well-it’s-way-bigger-than-an-elephant-anyway method. Using that figure (as we did in the paper), we got a probable mass of 7600 kg for Xenoposeidon — and this is course is the source of the statement, much quoted in the media, that it was “about as big as an elephant”. A big elephant.

But remember how vague this is: the lightest of the published estimates of Brachiosaurus brancai mass is 42% of the value we used, and the heaviest is 2.2 times as great. If we’d used these values in extrapolating the mass of Xenoposeidon we could have arrived at 3200 kg or 16720 kg!

For Diplodocus carnegii, we just used the estimate of Wedel 2005, 12 tonnes, and got a mass of 2800 kg for Xenoposeidon. There is rather less divergence in the various published mass estimates for this animal; but whether that’s because people’s work on it is more consistent, or just because not so many people can be bothered estimating the mass of so relatively uncharismatic a sauropod, I wouldn’t like to say.

All this means that Xenoposeidon was small — for a sauropod. In our poxy extant ecosystems, elephants are considered tolerably large, but in the Mesozoic they would hardly have raised an eyebrow, and neither would Xenoposeidon. Why the small size? Is it a juvenile? Apparently not: in archosaurs (that is, crocodiles, birds and all descendents of their most recent common ancestor, including dinosaurs), the neural arches fuse to their centra only some way into growth (Brochu 1996), so a vertebra such as that of Xenoposeidon in which the arch is fully fused and the sutures completely obliterated indicates that the animals was mostly or fully grown. Just small. Like Paul Simon. That’s nothing to be ashamed of.

Coming up next on SV-POW!’s Xenoposeidon week: on day 5, Darren will talk about the joys and hazards of dealing with the media. Stay tuned. (And, folks, please do make the occasional comment. Just so we know someone’s listening.)

References

  • Alexander, R. McNeill. 1985. Mechanics of posture and gait of some large dinosaurs: Zoological Journal of the Linnean Society 83: 1-25
  • Anderson, J. F., A. Hall-Martin and Dale A. Russell. 1985. Long-bone circumference and weight in mammals, birds and dinosaurs. Journal of Zoology 207: 53-61
  • Brochu, Christopher A. 1996. Closure of neurocentral sutures during crocodilian ontogeny: implications for maturity assessment in fossil archosaurs. Journal of Vertebrate Paleontology 16: 49-62.
  • Christiansen, Per. 1997. Locomotion in sauropod dinosaurs. Gaia 14: 45-75
  • Colbert, Edwin H. 1962. The weights of dinosaurs. American Museum Novitates, 2076: 1-16
  • Gunga, Hans-Christian, K. A. Kirsch, F. Baartz, L. Röcker, Wolf-Dieter Heinrich, W. Lisowski, A. Wiedemann and J. Albertz. 1995. New Data on the Dimensions of Brachiosaurus brancai and Their Physiological Implications. Naturwissenschaften 82: 190-192
  • Hatcher, Jonathan B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum, 1: 1-63 and plates I-XIII
  • Henderson, Donald M. 2004. Tipsy punters: sauropod dinosaur pneumaticity, bouyancy and aquatic habits. Proceedings of the Royal Society of London, B (Supplement) 271: S180-S183. doi 10.10998/rsbl.2003.01.36
  • Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3: 27-93
  • Paul, Gregory S. 1988. The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs. Hunteria 2 (3): 1-14
  • Paul, Gregory S. 1998. Terramegathermy and Cope’s Rule in the land of titans. Modern Geology 23: 179-217
  • Russell, Dale, Pierre Béland and John S. McIntosh. 1980. Paleoecology of the dinosaurs of Tendaguru (Tanzania). Memoires de la Societe Geologique de France 139: 169-175
  • Taylor, Michael P., and Darren Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50 (6): 1547-1564. doi: 10.1111/j.1475-4983.2007.00728.x
  • Wedel, Mathew J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates. pp. 201-228 in: Jeffrey A. Wilson and Kristina Curry-Rogers (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley

Welcome to our continuing coverage of the wackiness that is Xenoposeidon. I drew the ‘pneumaticity’ straw, not surprisingly, so I get to introduce the anterior and posterior views of the vertebra, which reveal some of the internal structure. But they also reveal another bit of weirdness, which is the neural canal, so let’s start there.

Neural Canal

As you’ll recall from an earlier post, the neural canal is the hole in a vertebra through which the spinal cord passes. As you can see above, in posterior view the opening of the neural canal is a nicely-behaved, nearly circular hole. It would be completely unremarkable if it wasn’t so different from the opening on the front side, a scant 6 inches away. The anterior opening is slightly wider, about three times as tall, and vaulted like a cathedral.

Now, admittedly the anterior opening is filled with matrix, so it’s quite likely that we’re just seeing some kind of antrum and that lurking within that bony cathedral there is another nicely-behaved, nearly circular hole. But I’ve never seen a sauropod vertebra with such divergent neural canal openings, and neither have Mike or Darren, and they’ve both looked at a lot more dorsals than I have.

Still, I can offer a pretty good guess about why the anterior canal opening is vaulted that way. In birds, pneumatic diverticula not only run alongside the vertebrae, they also pass through the neural canal above the spinal cord. So birds occasionally have pneumatic fossae and foramina at the openings of the neural canal or even in the walls of the tube. We are fairly certain that sauropods also had these supramedullary airways, partly because they often have pneumatic features around the openings of the neural canals, and also because a handful of vertebrae actually show connections from the neural canal to the surrounding pneumatic cavities. More on that another time. For now, our inference is that the anterior opening of the neural canal of Xenoposeidon is so big because it held pneumatic diverticula in addition to the spinal cord. The posterior opening probably held the spinal cord alone. Why that should be is beyond us for now, and it will probably stay that way until someone does a big comparative study and maps the precise location of the diverticula in a bunch of sauropods.

Symmetry, Schmymmetry

William Blake asked, “What immortal hand or eye / could frame thy fearful symmetry?” None, in this case, because symmetry is in short supply. In the first Xenoposeidon post you probably noticed that the pneumatic features are also different on the left and right sides of the centrum. On both sides you have a pneumatic foramen (air hole) sitting inside a larger pneumatic fossa (depression or excavation), but the similarity ends there. The foramen on the left is twice as big as the one on the right, and the fossa on the right is partly divided by a small lamina and has a smaller accessory fossa above it, to boot.

Now, this asymmetry is also weird, but it’s expected weirdness. Pneumaticity seems to just be inherently variable, whether we’re talking about human sinuses or the facial air sacs of whales or the vertebrae of chickens. It appears that the form of pneumatic features is entirely determined by local tissue interactions, with little or no genetic control of the specific form. Think of it this way: genes prescribe certain developmental events, and those events bring tissues into contact–such as pneumatic epithelium and bone. The morphology of the bone arises out of that interaction, and each interaction of bone and pneumatic epithelium has the potential to produce something new. In this case, the diverticula on the left side of the vertebral column come from the lungs or air sacs on the left, and those on the right side come from the lungs or airs sacs on the right, so it’s really two sets of diverticula contacting the bone independently. The wonder, then, is not that pneumatic bones are so variable, but that we see any regularities at all.

Mike and Darren didn’t count the left-right asymmetry when they listed the diagnostic features of Xenoposeidon. If these features can vary so much from one side of a single bone to the other, they probably also vary among bones and among individuals and populations in increasing proportion, which makes them fairly useless for taxonomy. They did count the differences in the shape of the neural canal openings, but those are midline structures with contributions from diverticula on both sides (at least in birds, and we have no reason to suspect otherwise in sauropods), so the presence of a big pneumatic antrum on the front and the absence of one on the back is much more likely to represent a real, heritable, taxonomically useful difference.

How do we know? Partly because we’ve looked at a lot of vertebrae and have seen a lot more left/right asymmetry than anything else, and also because we have a plausible, testable explanation for why that should be so. But, like everything we tell you, this is a hypothesis, and it’s open to falsification. We’re not just cool with that–we prefer it that way.

Internal Affairs

The anterior part of the centrum is sheared off at an angle to reveal some of the ‘guts’ of the vertebra. The centrum was hollow in life, with a vertical midline septum separating the left and right halves, and a couple of projections sticking down and in at roughly 11:00 and 1:00. What is all this mess?

In most sauropods, the pneumatic diverticula on either side of the vertebra invaded the centra and hollowed out a pair of big chambers, called camerae. ‘Camera’ is Latin for ‘chamber'; a variant spelling forms part of the name of Camarasaurus, the “chambered reptile”, a dorsal vertebra of which is shown below.

camarasaurus-internal-structure.jpg

You can see from the horizontal section (slice 2, above) that big chambers are all you get in this vertebra. But you’ve seen pictures of more complicated stuff here before–vertebrae with lots of little chambers inside. This is something else I’ve beat to death in my papers, so here’s the short, short version: primitive sauropods have simple pairs of chambers; in most derived sauropods the vertebrae have a mix of big and small chambers, and in the most derived (and longest necked) sauropods the vertebrae are completely filled with small chambers.

To see what the internal structure of Xenoposeidon might have looked like when the vertebra was complete, let’s look at a couple of relatives that are probably comparable in terms of internal structure (recall that we have very little idea where Xenoposeidon actually fits into the evolutionary tree of sauropods; that’s part of what makes it so cool).

apatosaurus-omnh-500.jpg

brachiosaurus-byu-500.jpg

These vertebrae of Apatosaurus and Brachiosaurus have large, paired camerae in the middle of the centrum, but the ends of the centra are divided into smaller chambers by radial walls of bone that form septa between the cavities. The Apatosaurus vert is shown in anterior and lateral view. The Brachiosaurus vert might be a bit tougher to interpret. The roof of the centrum and the neural spine are detached (preserved, just as a separate piece) and we’re looking at the vertebra in left antero-dorso-lateral view. What’s left of the condyle is visible in the lower left foreground, and you can see the prominent median septum connecting it to the cotyle, which is facing away toward the stack of books on the upper right. Anyway, the Xenoposeidon vertebra probably had a whole ring of those septa, but when the front of the centrum was sheared off they were all lost, except for the two closest to the top.

xeno-septa-500.jpg

This type of internal structure, with a combination of big camerae and smaller chambers, is only found in mamenchisaurids and neosauropods, and it’s one of the pieces of evidence that Xenoposeidon is a neosauropod, albeit a strange one. If you want the full phylogenetic story, don’t forget that you can read the paper for free, but also stay tuned for the other 4/7 of Xenoposeidon Week here at your number one sauropod vertebra news source.

So, by now, most people in the known universe have heard about Xenoposeidon, know what a big deal it is, and understand its immense value and significance. A longish article on the history and anatomy of Xenoposeidon, and about how interesting it is in terms of Wealden dinosaur diversity, is now up at Tetrapod Zoology (here). And as you’ll know if you’ve seen Mike’s article from yesterday, the story was all over the national and global media yesterday. To their credit, not one reporter or interviewer said ‘but it’s just a single bone’. After Sky News advertised a piece on Xenoposeidon at 12-50pm yesterday, I kept the TV on. But by 4pm they hadn’t shown it, and I was so maddened by hearing the same several news stories about 400 times each that I could not stomach any more TV that day. So I missed Mike’s many actual appearances… bar a very brief one on the 10-30pm edition of local news programme South Today. Anyway…

figure5-reconstruction1.jpeg There’s so much to say about Xenoposeidon; so much more ground to cover [if you need help with some of the following anatomical terms do remember you've got our excellent tutorial on vertebral anatomy to help you]. The picture shown here (it’s Fig. 5 from Taylor & Naish 2007) shows Xenoposeidon as, we think, it would have looked when complete. As interesting and anatomically revealing as the single known specimen is, it lacks the anterior condyle, the neural spine, and the zygapophyses, so we had to do some reasonable extrapolation when imagining what these missing bits looked like. Because the posterior articular surface of the centrum is concave in Xenoposeidon, it makes sense to assume that the (mostly missing) anterior condyle was somewhat convex, as it is in macronarians (the group of sauropods that includes camarasaurs, brachiosaurs and titanosaurs). The condition where the centrum is concave posteriorly and convex anteriorly is known as opisthocoely. Note, however, that the opisthocoely of Xenoposeidon is not as well developed as that of macronarians.

The neural arch of Xenoposeidon is strikingly tall: about as tall as the centrum. That’s odd. The forward-sloping of the neural arch is even more odd, and in fact is a unique feature of the taxon – we have yet to see this character in any other sauropod (making it a Xenoposeidon autapomorphy). We can see several structures on the side of the neural arch: the parapophysis (the more ventral of the two attachment points for the two rib heads) is located really high up, and it’s this high location which has led to our conclusion that this vertebra comes from the posterior part of the dorsal sequence (the articular processes for the rib heads don’t stay in the same place along the vertebral sequence. In anterior dorsals, the parapophyses [plural of parapophysis] are positioned way down on the centrum, but in mid- and posterior dorsals, they rise up onto the neural arch). Because Xenoposeidon doesn’t preserve any trace of its prezygapophyses, we have to conclude that these were located even further dorsally than were the parapophyses. This indicates that the specimen is not among the most posterior of the dorsals in the sequence for, in those vertebrae, the parapophyses are located further dorsally than are the prezygapophyses.

Darren in Wealden

The least knowable thing here is how tall the neural spine was; what we depict is a generic not-too-gracile, not-too-robust conservative sort of neural spine. It will be interesting to see how this reconstruction matches reality when a complete Xenoposeidon dorsal vertebra – hopefully associated with the rest of the skeleton – is discovered, which of course it will, one day, now that everyone in the English Weald is looking (in the adjacent image I’m looking for dinosaurs in Weald Clay Group rocks of East Sussex; if Mike can include a photo that shows him posing with a dalek, I can justify one involving field work).

The Xenoposeidon image above shows the left side of the specimen. Curiously, the right side is rather different: it exhibits a shallow accessory fossa located dorsal to the large lateral pneumatic opening, and also has an extra bony boss positioned about half-way up and near the anterior margin of the neural arch. We don’t really know what’s going on here. Asymmetry in vertebrae – particularly in complicated ones like the heavily pneumatised vertebrae of some birds – is fairly common, and a small amount of asymmetry in the limbs, skulls and pelvic girdles of vertebrates is also pretty widespread and not that remarkable. Asymmetry in pneumatic openings is (so I understand) common, and – partly because of this – some workers have suggested that pneumatic diverticulae can be imagined as opportunistic structures that will ‘invade’ spaces on or in a bone when the opportunity arises. Matt might want to correct me or elaborate on this point, as he’ll know what he’s talking about. More on the wonder that is Xenoposeidon tomorrow!

Ref – -

Taylor, Michael P. and Darren Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50 (6): 1547-1564. doi: 10.1111/j.1475-4983.2007.00728.x

Postscript, added by Mike at 16:57

I know it’s a bit cheeky to add a postscript to someone else’s post, but I don’t want to make a “day 2-and-a-half” post, and I do just want to mention a bit more media coverage. I’ve heard from Vin Morgan in America that they’ve been running Xenoposeidon on CNN, and I know that the Canadian Discovery Channel is going to do something, probably tonight. And I know from my brother-in-law, who emigrated to Spain, that it’s in Spanish newspapers today. I’ve also seen it mentioned on Greek, Russian and Chinese web sites — although not being able to read any of those languages I can’t tell whether the articles just say “Xenoposeidon stinks”. Spanish TV slot still to come. Not bad for a paper that was rejected WITHOUT REVIEW from Name Of Journal Withheld on the grounds that “the paper is rather of a local significance”. (Sorry, was that last part a bit petty?)

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