Happy Xenoposeidon day!  Today, November 15, 2008, is the one-year anniversary of the publication of Xenoposeidon Taylor and Naish 2007.

By happy coincidence, I’ve just been sent a courtesy copy of Kids Only, a new guide-book for the Natural History Museum … and there is Xenoposeidon on page 5, exemplifying dinosaur diversity.  Rock!


It’s good to see our baby out there educating people!

For much more of Xeno, see Xenoposeidon week.

Today, we bring you the long-overdue third installment in everyone’s  favourite Mystery Sauropod Dorsals serial, our trawl through the NHM’s collection of mostly isolated elements from the Wealden Supergroup.

Many of these elements are too bashed up to be diagnostic (with the Xenoposeidon holotype R2095 being an honourable exception).  But there are one or two that are much better preserved, and arguably the best of these are the pair of elements BMNH R88/R89, which in some sense belong to “Eucamerotus” (read on).  These are difficult to photograph well, because they are in a glass case in the public gallery, but fortunately Hulke (1880: plate IV) illustrated the more anterior and better preserved of the two:

plate IV)

Like far too many British sauropod specimens, this one is mired in a taxonomic hell-hole. It was described by Hulke as belonging to Ornithopsis, a genus based on a horribly non-diagnostic type specimen, and it is this name that appears on the exhibit label (along with the incorrect specimen numbers R89/90 … oh well, One Out Of Two Ain’t Bad.)

Here is my least bad photo of R88 and R89, in left lateral view, with R88 on the left:


Blows (1995) referred this pair of dorsals, and a bunch of other specimens, to another ancient British name, Eucamerotus — in fact, he nominated them as paratypes — but didn’t give any reason for doing so.  (He also referred to the R88/R89 pair jointly as R90, thus further muddling the specimen numbering.)  Blows’s reassignment to Eucamerotus is puzzling, because while the Eucamerotus type specimen is also pretty undiagnostic, consisting only of a partial neural arch, it does have one obvious apomophy, which is huge robust parapophyses supported on what I like the call The Prezygaparapophyseal Laminae Of Doom.  (Remind me to show you this specimen some time.)  That feature, of course, R88 and R89 completely lack.

So what are they?  I don’t think they can be referred with any confidence whatsoever to either Ornithopsis or Eucamerotus, two questionable genera of which at least the first is invalid.  So perhaps the right thing to do would be to torpedo those names and raise R88/89 as the type specimen of a new taxon?  There’s more work to do before taking such a step, not least an exhaustive trawl through the historical literature, but I think that might eventually prove the way to go.

Based on general proportions and overall “gestalt”, these vertebrae appear to be brachiosaurid — but I put them in a cladistic analysis a while back (so far unpublished) and they didn’t clade unambiguously with Brachiosaurus, so we’ll have to see how that develops when I finally get around to adding my thirty-odd new characters of the dorsals.  Don’t hold your breath.  At least, these elements are much more convincingly brachiosaurid than anything else I’ve seen from the Wealden.  So do they consitute Britain’s best brachiosaur?

Well, maybe.  Not if you count The Archbishop, Migeod’s Tendaguru brachiosaur, which I’ve been working on for waaay too long now, but really, really will describe Real Soon Now.  (Amazingly, this specimen has yet to appear on SV-POW!, unless you count my T-shirt in one of the photos of our Oxford Museum visit.)  But since this specimen is from the Tendaguru Formation of Tanzania, it should probably be discounted from the BBB competition.

In fact, Britain’s Best Brachiosaur is probably the “Barnes High Sauropod” from the Isle of Wight. But that’s in private hands and the ownership/availability situation is complex.  For that reason, no-one has yet published on it, and in fact I have never seen any of the material except what’s embedded in a wall-mount at Dinosaur Isle.  I’m not sure what’s happening with this specimen (I don’t think anyone is) but if I ever get a chance to find out, I will!


  • Blows, William T.  1995.  The Early Cretaceous brachiosaurid
    dinosaurs Ornithopsis and Eucamerotus from the Isle of
    Wight, England.  Palaeontology 38 (1): 187-197.
  • Hulke, J. W.  1880.  Supplementary Note on the Vertebræ of Ornithopsis, Seeley, = Eucamerotous, Hulke.  Quarterly Journal of the Geological Society 36: 31-35.  doi:10.1144/GSL.JGS.1880.036.01-04.06

In this article I’d like look at something that I’ve just spoken about at a conference: the ‘Dinosaurs – A Historical Perspective’ meeting held in London on May 6th and 7th (my thoughts on the conference can be found here and here). Mike attended too (and, like me, gave a talk), but Matt couldn’t make it. Anyway…



Today, the idea that sauropods (and non-avian theropods) were pneumatic animals is well established and universally accepted (a minority view – promoted by those who insist that birds cannot be dinosaurs – maintains that non-avian dinosaurs were not pneumatic, but I see no indication that the workers concerned know what they’re talking about). Indeed, sauropod pneumaticity has been discussed a lot here at SV-POW! But have people always regarded sauropods as pneumatic? As someone particularly interested both in pneumaticity and in the dinosaurs of the Lower Cretaceous Wealden Supergroup of southern England, the whole ‘Pneumaticity: the Early Years’ story is of special interest to me. I hope you get something out of it too…


Actually, the very first dinosaur (not just sauropod, but dinosaur) identified as exhibiting skeletal pneumaticity is from the Wealden, and it’s a theropod: it’s the large tetanuran Becklespinax altispinax, discovered prior to 1855 in the Hastings Beds Group of East Sussex (the Hastings Beds Group is the oldest unit in the Wealden Supergroup: for more see the Tet Zoo article here). Consisting only of three articulated posterior dorsal vertebrae, Becklespinax exhibits deep fossae on the sides of the neural arches (by now you’ll all be familiar with the names for the different vertebral laminae present in saurischians, but the fossae have names too: in Becklespinax, we’re talking about the infraprezygapophyseal fossa, the infradiapophyseal fossa, and the infrapostzygapophyseal fossa). The key thing is that, in describing these vertebrae, Richard Own (1804-1892) realised that these fossae were probably pneumatic as they are in birds, and in his 1856 article on Megalosaurus (he assumed that the Becklespinax vertebrae belonged to Megalosaurus), he wrote that ‘Three deep depressions, probably receiving parts of the lungs in the living animal, divide these lamelliform butresses from each other’ (Owen 1856, p. 5). His ‘lamelliform butresses’ are what we call laminae. This is the very first reference to pneumaticity in any Mesozoic dinosaur (Britt 1993), so Becklespinax is the first non-avian dinosaur for which pneumaticity was ever suggested.


The next milestone in pneumaticity came from Harry Seeley (1839-1909) in his description of the Wealden sauropod Ornithopsis hulkei (Seeley 1870). O. hulkei was named for two dorsal vertebrae: BMNH R2239 from East Sussex and BMNH R28632 from the Isle of Wight, but the former was later removed from O. hulkei (then becoming the type for Bothriospondylus elongatus), leaving BMNH R28632 alone associated with this name and as the lectotype* [the specimen is shown below, from Seeley 1870]. The strong opisthocoely, large lateral foramina and camellate internal anatomy show that BMNH R28632 is from a titanosauriform (it can’t really be identified more precisely than that and whether it’s diagnostic is arguable: see Naish & Martill 2007. For previous SV-POW! comments on the specimen go here). It’s often noted that Seeley suggested that these vertebrae belonged to an animal ‘of the Pterodactyle kind’. However, he did not think that these vertebrae belonged to a giant pterosaur (as, oops, Naish & Martill (2001) said): rather, he thought that O. hulkei represented something entirely new, the first member of a ‘new order of animals which will bridge over something of the interval between birds and Pterodactyles, and probably manifest some affinity with the Dinosaurs’ (Seeley 1870, p. 280).


* When a species is erected for more than one specimen, the specimens are all called syntypes. When one syntype from a series is later elected to serve as the type specimen for the species, it is called the lectotype.




Seeley – who has been described as ‘the most defiant’ of Victorian palaeontologists, of exhibiting ‘anarchic tendencies’, and of being considered ‘strikingly individualistic’, even in his own day (Desmond 1982) – gets a lot of flack these days, in particular for his rampant taxonomic splitting and naming of new dinosaur and pterosaur species, and also for his unusual views on how vertebrate groups were related to one another. But I often think that his conclusions on lifestyles and comments on palaeobiology are really not unreasonable in view of what we think today, and in fact often seem quite far-sighted.


Here’s where we come back to pneumaticity: Seeley (1870) was very impressed with the enormous lateral foramina present in O. hulkei (these were the main feature which led him to regard O. hulkei as allied to pterosaurs and birds), and he wrote: ‘Seeing that in living animals these foramina exist for the prolongation of the peculiarly avian respiratory system into the bones, and that no other function is known for them, we are compelled to infer for this animal bird-like heart and lungs and brain’ (Seeley 1870, p. 280). In describing the worn condyle of BMNH R28632, Seeley noted the presence within the bone of ‘enormous honeycomb-like cells of irregular polygonal form … divided by exceedingly thin and compact films of bone’ (Seeley 1890, p. 281). Elsewhere in the paper, he referred to the internal cavities as ‘air-cells’, and he also wrote of the Ornithopsis vertebrae (both BMNH R2239 and BMNH R28632) as ‘being constructed after the lightest and airiest plan’. He never explicitly stated it, but I infer from these statements that Seeley imagined the internal cavities of the centrum to be pneumatic: he was describing what today we call the camellae (that is, the numerous small pneumatic cavities that occupy the centrum in mamenchisaurs and titanosauriforms). So, all in all, I say well done Seeley for correcting inferring vertebral pneumaticity in O. hulkei.


Like most Victorian palaeontologists, Seeley did not get on particularly well with the most prolific, most respected and most politically powerful Victorian palaeontologist, Richard Owen [although it’s not really accurate to regard Owen just as a palaeontologist: sure, he did palaeontology, but his contribution to mainstream zoology and anatomy was massive and equally significant, if not more so]. In 1876, Owen described another Wealden sauropod and, like the O. hulkei lectotype (BMNH R28632), it was from the Isle of Wight’s Wessex Formation: it’s based on two cervical vertebrae (BMNH R46869 and BMNH R46870: one is shown below). Today, it is obvious that these vertebrae are from sauropods, and their enormous lateral foramina and camellate internal anatomy show that they’re from titanosauriforms (and not from camarasaurs as has been suggested in the past: see Naish & Martill 2001, 2007). However, Owen couldn’t be this confident that identified the material as ‘Dinosauria (?)’.




The big deal for our story is that these vertebrae have massive lateral fossae housing large lateral foramina, and again Owen correctly interpreted them as pneumatic, writing: ‘The whole of the side of the centrum is occupied by a deep oblong depression which, probably, lodged a saccular process of the lung’ (Owen 1876, p. 6). So far so good. But Owen had one of these two Wessex Formation specimens (BMNH R46870) sectioned, revealing its incredible (and beautiful) interior [it’s the image shown at the very top]. The internal anatomy of this specimen illustrates camellate texture so well that it’s almost becoming a poster-child in talks and articles on sauropod vertebrae. But while, as we just saw, Seeley had implied that camellae were pneumatic, Owen interpreted them quite differently. He wrote ‘I deem it much more probable that the large cancelli obvious at every fractured surface of this vertebra were occupied in the living reptile by unossified cartilage, or chondrine, than by air from the lungs, and consequently have no grounds for inferring that the whale-like Saurian, of which the present vertebrae equals in length the largest one of any Cetacean recent or fossil, had the power of flight, or belonged to either Pterosauria or Aves’ (Owen 1876, p. 6). To reflect the presence of ‘chondrine-filled’ spaces in the vertebrae of this animal, Owen coined for it the new name Chondrosteosaurus gigas, meaning ‘giant cartilage and bone lizard’.


Quite why Owen was happy with pneumatic lateral fossae, but not with pneumaticity within the body of the centrum itself, seems odd, especially when Owen was very familiar with avian anatomy (he specifically referred to the internal anatomy of avian vertebrae in, for example, his 1859 article on pterosaur vertebrae [Owen 1859]). As you can see in Tutorial 3, the internal anatomy of bird and sauropod centra are so similar that it is difficult not to conclude that what applies for one applies for the other. However, it is clear from Owen’s quote given above that, when interpreting C. gigas, he was not just doing an objective description, but also had an axe to grind: he was specifically refuting Seeley’s statements on O. hulkei, hence the rejection of the idea that C. gigas might have been capable of flight, or that it might be allied to pterosaurs or birds. For whatever reason, Owen was also making note of the fact that he disagreed with Seeley’s idea of a pneumatic vertebral interior: the name Chondrosteosaurus itself almost seems like a snub to Seeley.


Despite this one-upmanship, ultimately, both Seeley and Owen come out of this early phase in research pretty well, as both workers still win citations for having made key early statements on saurischian pneumaticity (e.g., Wedel 2003, O’Connor 2006). Edward Cope (1840-1897), who liked Seeley and said nice things about him, was to note during the 1870s that sauropod vertebrae were probably pneumatic, and Othniel Marsh (1831-1899) did likewise. What happened in the field of dinosaur pneumaticity after this? Well, that’s a story for another time: for the time being I will direct you to Wedel (2003).




  • Britt, B. 1993. Pneumatic Postcranial Bones in Dinosaurs and Other Archosaurs. Unpublished PhD thesis, University of Calgary (Alberta).
  • Desmond, A. J. 1984. Archetypes and Ancestors: Palaeontology in Victorian London 1850-1875. The University of Chicago Press, Chicago. 
  • Naish, D. & Martill, D. M. 2001. Saurischian dinosaurs 1: Sauropods. In Martill, D. M. & Naish, D. (eds) Dinosaurs of the Isle of Wight. The Palaeontological Association (London), pp. 185-241.
  • Naish, D. & Martill, D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164, 493-510.
  • O’Connor, P. M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs. Journal of Morphology 267, 1199-1226.
  • Owen, R. 1856. Monograph on the fossil Reptilia of the Wealden and Purbeck Formations. Part III. Dinosauria (Megalosaurus). Palaeontographical Society Monographs 9, 1-26.
  • Owen, R. 1859. On the vertebral characters of the Order Pterosauria, as exexmplified in the genera Pterodactylus (Cuvier) and Dimorphodon (Owen). Philosophical Transactions of the Royal Society of London 149, 161-169.
  • Owen, R. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck Formations. Supplement 7. Crocodilia (Poikilopleuron). Dinosauria (Chondrosteosaurus). Palaeontographical Society Monographs 30, 1-7.
  • Seeley, H. G. 1870. On Ornithopsis, a gigantic animal of the pterodactyle kind from the Wealden. Annals and Magazine of Natural History, Series 4, 5 279-283.

Invading the postzyg

March 30, 2008


Again, another exclusive peek at an interesting specimen: the MIWG.7306 vertebra, aka ‘Angloposeidon’ (Naish et al. 2004). Apologies if, by now, you’re bored of my show-casing of this specimen, but – not only is it the only sauropod vertebra of which I personally have multiple unpublished images – it is also a really nice demonstration of the fact that, even in just a single vertebra, there are multiple interesting, bizarre, and sometimes under-studied or even un-studied details.

What we’re looking at here is the medial (‘inside’) surface of the left postzygapophysis, with the centrum down below the bottom of the image, and the cotyle off to the left (the opposite side of what’s shown here). The image below should help with orientation. The focus of interest is the unusual matrix-filled space in the middle of the image: just what is it? Because it has sharp, clean edges, I am pretty convinced that it’s natural, and I assume it’s a pneumatic foramen. Similar structures are present on the medial side of the right postzygapophysis, and are different in position and shape (Naish et al. 2003, p. 790). We think, based on several lines of evidence, that the space between the postzygapophyses (limited anteriorly by the neural spine) was occupied by an air-sac (Schwarz & Fritsch (2006) called this the interspinal diverticulum), so is this evidence that diverticula from the interspinal air-sac invaded the bodies of the postzygapophyses on their medial sides? If so, was this just a one-off in MIWG.7306, or was it widespread in brachiosaurs, in macronarians, in neosauropods, or even in sauropods as a whole? I admit that I haven’t yet taken the time to check properly, but the big problem is that this part of the vertebra – the medial surface of the postzygapophysis – is rarely figured. Based on what has been published, I have yet to see a similar structure, even in Brachiosaurus (which is very well figured, as sauropods go).


I’m sure that someone is now going to make me look very, very silly. But, whatever. I can’t pretend to know everything. Note that, again, this is a world first. Yes, all of this stuff should be published… and in time in will, in time.


  • 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.
  • Schwarz, D. & Fritsch, G. 2006. Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus. Eclogae geol. Helv. 99, 65-78.

The heart of the matter

March 12, 2008

It’s a lonely night here at the Fortress of Sauropoditude. Darren is off at one of his numerous conferences, and Mike is in hiding, trying to avoid the reality that 4% of a millennium has passed since he was loosed upon the world. I gave the serfs the night off, which means it’s just me here in this lonely tower, surrounded by arcane devices, mouldering tomes and piles of ancient bones. The candles are lit, the wine is open on the sideboard, and I am in quest of something appropriately baroque for our evening’s contemplation. How about…a vertebra with no outsides?


Here is a sauropod specimen with no external morphology whatsoever. This is a cut and polished section of a fragmentary vertebra from the Isle of Wight. The black lines are bony septa that make up the internal structure of the vertebra. The brownish gray stuff between the septa is matrix (rock) filling the air spaces.

How much can we infer about the animal whose mortal remains these are, in the utter absence of soft tissue or external form?

The first thing that we note is that the vertebra has a complex internal structure, one that is highly subdivided into lots of irregular cavities. Complex internal structures are present in the vertebrae of mamenchisaurs, diplodocids, and most titanosauriforms, so we know that this chunk is not from a cetiosaur or dicraeosaur or camarasaur. It is from Early Cretaceous rocks from England, so we can provisionally rule out mamenchisaurs as possible donors. Diplodocids are represented in the Early Cretaceous of England by perhaps one bone or perhaps none at all. However, titanosauriforms were all over the place in the Early Cretaceous in the Northern Hemisphere generally, and in England particularly, and on the Isle of Wight especially. So we might guess that this is a chunk of a titanosauriform.

We should also pay attention to the size of the specimen: the vertebra of which it was a part was somewhat more than 15 cm in diameter, and may have been much larger. Now, 15 cm is not huge, but it means that is not from a very small sauropod like Europasaurus. And it is another line of evidence against a dicraeosaurid or rebbachisaurid identification.

Finally, we might be curious about the ratio of bone to air space. As frequent commenter Mike From Ottawa noted of another pneumatic vertebra, “There’s almost nothing but nothing there.” In fact, the plane exposed here is about 85% space and only 15% bone, which puts it up into “Angloposeidon”-Sauroposeidon territory. Most pneumatic sauropod vertebrae were about 60% air by volume, which is remarkable enough when you stop and think about it.

So based on qualitative (complex) and quantitative (85% air) assessments of its form, and given its size and stratigraphic and geographic context, my best guess is that this is a chunk of “Angloposeidon” or a closely related brachiosaurid. I can’t rule out the possibility that it belongs to a titanosaur or a weird giant rebbachisaurid or something even more unlikely, but that’s not where the balance of the evidence points.

Which, I think, is not too bad for a skinless piece of crap shard of excellence* that most people wouldn’t look at twice.

Well, thanks for your company. Mind the stairs on your way down, and if the side door in the hall is open, walk by quickly and don’t look inside. With any luck, one of my compatriots will be back here to greet you next week.

*That’s what small chunks of sauropods are called. Honest!

Credit where it’s due

January 11, 2008

A hat-tip to Paul Barrett, who’s reminded us that technically we’re not supposed to be using photographs of Natural History Museum specimens — at least, not without acknowledgement. Our apologies go the museum for having overlooked this: we’d like to remind you all that all photographs of specimens owned by the museum are also copyright the museum, and we’ll try to remember to make that point explicitly in all future posts that show NHM specimens.

For the same reason, unfortunately, we can’t sell you Xenposeidon shirts — to do that would require a marketing agreement with the museum, which is not really a direction we want to go in … as you can imagine. So with apologies to those of you who didn’t snap one up while they were available, we’ve removed all the links from this site. (Congratulations to Mike From Ottawa, who, so far as I can tell, is in fact the only person outside the three of us who had the good taste to buy a shirt. Note to NHM commercial staff: our markup on that sale was £0.00 (or $0.00 in US funds) which we will be happy to hand over if you wish :-)

Finally, since we do promise “all sauropod vertebrae, all the time”, I sign off with a photograph: and a historically significant one at that:

Cetiosaurus brevis type caudals and chevrons

Image copyright the Natural History Musuem, since it’s the museum’s material.

What we have here are, in a sense, the first sauropod specimens ever: the caudal vertebrae, and associated chevrons, that are the type material of the first named sauropod species, Cetiosaurus brevis Owen 1842. From the Wealden, natch. The vertebrae, from the anterior part of the tail, are BMNH R2544­-2547, and are shown in anterior view; the chevrons are BMNH R2548-­2550. These elements may belong to the same species, and maybe even the same individual, as the holotype of Pelorosaurus conybeari Mantell 1950. If you care to wade through the taxonomic quagmire associated with this series, you can find a discussion on pp. 1559-1560 of Taylor and Naish (2007) (the Xenoposeidon paper) — a discussion which I am more than happy to state, for the record, Darren wrote.

Update — 1 April 2009 (but not an April Fool)

Cetiosaurus brevis is not after all the first validly named Cetiosaurus species, because we (Darren and I) followed Upchurch and Martin (2003) in conflating nomenclatural and taxonomic validity. According to a strict interpretation of ICZN rules, C. medius is the type species, but we now have an ICZN petition out that should change that and fix C. oxoniensis as the type species, which is what everyone means in practice anyway.


Things are pretty quiet at SV-POW! Towers: Matt’s on the road and can’t post, I’ve been working way too hard on day-job work and haven’t had much time for anything else, and Darren seems to have gone to ground (probably holed up somewhere with a stack of lissamphibian cladograms). Until the new year, then we give you the following lame picture:

Ornithopsis lectotype BMNH R28632

What we have here is one of the lamer sauropod type specimens: it’s BMNH R28632, the lectotype of the venerable Wealden “brachiosaurid” Ornithopsis hulkei Seeley 1870. I won’t blame anyone who can’t immediately see what it is: it’s a badly eroded dorsal centrum in left lateral view. Perhaps surprisingly, this genus was judged valid in Upchurch et al.’s (2004) survey of sauropods.
There’s a lot that could be said about this specimen, and maybe we’ll revisit it in the New Year, but right now I need to go and watch Sonic Underground Volume 2 with my boys, so for now you’ll have to content yourselves with the picture.

Happy new year!

7306 anterior half in section

Inspired by Mike’s recent post on the interior of Chondrosteosaurus from the Isle of Wight’s Wessex Formation, what could I do but weigh in yet again with one of my most-loved specimens: the beauty that is MIWG.7306 (aka ‘Angloposeidon’), a big brachiosaurid also from the Wessex Formation (Naish et al. 2004). As mentioned previously, it’s perhaps intuitively surprising that one of the most useful things about MIWG.7306 is that it’s broken in two, allowing us to see the broken faces of both halves of the vertebra. This allows us to see the internal structure of the specimen and, potentially, to work out, not just what the internal architecture was like, but also how pneumatic this beast was. To date Matt and I have done some preliminary work on this, but we have yet to publish anything, so what you’re getting here is a world first, never-before-seen by anyone outside.. well, me and Matt. In fact I can’t recall whether even Mike has seen this stuff: IT’S THAT SECRET.

Anyway, what we’re looking at here is the posterior broken face of the anterior half of MIWG.7306. The specimen was photographed lying on its side but I’ve reoriented the photo such that the dorsal surface is at the top, of course. The broken surface looks at first sight like a big mess, mostly obscured by sediment which has gotten preserved within the pneumatic spaces. However, it you look carefully you’ll see very dark (blackish) spars of bone scattered about the interior. These are the thin bony walls that surround the internal cavities, called camellae, that made up the vertebra’s interior. Much of the ventral part of the cross-section is taken up by the vertical median septum: much of the space lateral to the septum (on both its left and right sides) would have been occupied by large air sacs. I was hoping to use a fully labelled version of this photo but cleverly seem to have lost it (and don’t have time to knock up a new version). For the full details you’ll have to wait for the paper!

7306 section, ventral part

Ventral to the median septum, the vertebra is again wide when seen in cross-section, and in the photo here we’re looking at that ventral part, though this time we’re looking at the anterior face of the posterior half of the vertebra. What’s nice is that there are clearly at least four distinct camellae aligned along the centrum’s ventral edge, and they don’t appear to be equal in size (nor arranged symmetrically around the midline). The actual ventral floor of the centrum can also be clearly seen in cross-section, and it’s pretty thin. All of this is particularly interesting because we have comparative data from North American brachiosaurids (in particular from a specimen that Matt has scanned, BYU 12866) and from Sauroposeidon (Wedel et al. 2000a, b). ‘Angloposeidon’ is similar enough to both of these in its details to convince us that the same sort of thing is going on, but it’s also different in various subtle ways: the ventral floor of the centrum is not the same thickness in all of these animals for example.

In the article on Chondrosteosaurus, Mike noted that we can work out how much of a vertebra’s interior was occupied by air if we can calculate the bone : air space ratio. We did just this with MIWG.7306, using the photos shown here and several others. The result: MIWG.7306 approached Sauroposeidon in terms of its pneumaticity, being 80-90% air. This gives us some remarkable and significant data on the palaeobiology of this animal, as pneumaticity has all sorts of implications for the animal’s respiration, physiology and mass (Wedel 2003, 2005). And on that note, I shall say goodbye.


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.


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!


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!