Cetiosaurus, Pelorosaurus, Streptospondylus or maybe Iguanodon(?!) in bizarre Fused Chevrons scandal!

March 9, 2009

We have sometimes neglected tails on SV-POW!, in favour of the more obviously charismatic charms of presacral vertebrae, but every now and then you come across a caudal vertebra so bizarre that it just cries out to be blogged.

One such is this specimen, which may or may not be BMNH R 2144:

Sauropod caudal with co-ossified chevrons, lateral view

Sauropod caudal with co-ossified chevrons, right lateral view

Sauropod caudal with co-ossified chevrons, right posterolateral view

Sauropod caudal with co-ossified chevrons, right posterolateral view

The reason I’m not sure whether this is BMNH R2144 is that I noticed this at the very last minute while visiting the NHM collections to see a different specimen, and just had time to take a couple of quick photos before kicking-out time.  The label on the side of the vertebra has the unexplained number 2144 written on it, so I am guessing this is the specimen number, but I wouldn’t stake my life on it.

(By the way, both these photographs are copyright the NHM.)

The interesting thing about this vertebra is of course that that the chevrons are co-ossified with the centrum — an extremely rare condition in sauropods, in fact unique as far as I know.  As we’ve shown here and here, among other places, the chevrons are usually separate bones from the vertebrae.

This vertebra caught my eye not only because it’s, well, weird, but also because I’d seen it a couple of times in published figures.  It’s in Mantell’s (1850) description of Pelorosaurus, where it appears as figure 11 in plate XXIII, and is considered to belong to Pelorosaurus; and also in Owen (1859: plate V: figs. 3-4).  Owen seems pretty confused about the identity of this element, and in this paper alone assigns it to Streptospondylus (p. 22), Iguanodon(!) (p. 25) and implicitly Cetiosaurus (p. 34).  So what is it?  Well, its provenance is vague in the extreme, so given that it’s not associated with any more diagnostic material, about the best we can say with any honesty is that it’s Sauropoda incertae sedis.

Let’s take a look at those old figures:

Mantell (1850: plate XXIII, fig. 11)

Mantell (1850: plate XXIII, fig. 11)

Owen (1850: plate V, figs 3-4)

Owen (1850: plate V, figs 3-4)

If you’re like me, your first thought was that Owen’s figures are simply mirror images of Mantell’s.  I checked this out by Photoshopping the two sets of figures, flipping them horizontally, scaling and rotating as necessary, and found to my mild surprise that Owen’s figures are in fact redrawn, despite the startling resemblance they bear to Mantell’s.  As it happens, the same is true with the Owen 1859 plate that is the humerus of Pelorosaurus figured by Mantell 1850, and in that case Owen’s figure is rather better than Mantell’s, so let’s give a bit of credit to Owen here.  Most embarrassing for Mantell (not that he cares, having been dead for 157 years) is that Owen’s flipped images seem to be correct (at least, as best I can judge from the photographs I took) — looks like Mantell or his illustrator badgered this up.

So what is going on with these co-ossified chevrons?  As is so often the case, we just don’t know.  Some possibilities: this might be a pathology of an individual, caused either by injury or infection; it might be a natural ontogenetic character in very old individuals; or it might by a taxonomically significant character of a taxon we’ve not yet found — or one that we have found, but don’t yet recognise as being the same thing.  It’s perfectly possible that this is a chevron of Xenoposeidon, for example, but until someone finds a nice complete specimen we’ll never know.

Not much is known about skeleton fusion in sauropods, and most of what’s in the literature is anecdote.  That is set to change, I am pleased to say, as Matt is putting together a paper with his colleague Elizabeth Rega that will survey and interpret the various fusions known in sauropod vertebrae.  I’m looking forward to seeing what they have to say about this vertebra.


  • Brusatte, Stephen L., Roger B. J. Benson, and Stephen Hutt.  2008.  The osteology of Neovenator salerii (Dinosauria: Theropoda) from the Wealden Group (Barremian) of the Isle of Wight.  Monograph of the Palaeontographical Society 162 (631): 1-166.
  • Calvo, Jorge O., Juan D. Porfiri, Claudio Veralli, Fernando Novas and Federico Poblete.  2004.  Phylogenetic status of Megaraptor namunhuaiquii Novas based on a new specimen from Neuquen, Patagonia, Argentina.  Ameghiniana 41 (4): 565-575.
  • Mantell, Gideon Algernon.  1850.  On the Pelorosaurus: an undescribed gigantic terrestrial reptile, whose remains are associated with those of the Iguanodon and other saurians in the strata of Tilgate Forest, in Sussex.  Philosophical Transactions of the Royal Society of London 140: 379-390.
  • Owen, R.  1859a.  Monograph on the fossil Reptilia of the Wealden and Purbeck formations.  Supplement no. II (pages 20-44 and plates V-XII): Crocodilia (Streptospondylus, &c.) [Wealden].  Palaeontographical Society, London.


Thanks to Mickey Mortimer for pointing out that this kind of centrum-chevron fusion is known in the theropod Megaraptor.  Here is the relevant figure from Calvo et al.’s (2004) revision of that genus:

Calvo et al. (2004: fig. 5). Caudal vertebrae of Megaraptor with co-ossified chevron

Calvo et al. (2004: fig. 5). Caudal vertebrae of Megaraptor with co-ossified chevron

The strange thing is this comment in the text (p. 569): “Two articulated caudal vertebrae are preserved (figure 5), slightly laterally compressed.  Their centra and the neural arches are firmly co-ossified, as well as their respective haemal arches [i.e. chevrons].  This fusion, not infrequent among dinosaurs, may be pathological.”  Not infrequent?  Is this going on all over the place and I’ve just never noticed it?  Anyone have any more examples?

Update 2

Here is that pair of fused Neovenator caudals with a co-ossified chevron, which Darren mentions in the comments below.

Brusatte et al. (2008: fig. 16d), fused Neovenator caudals with co-ossified chevron

Brusatte et al. (2008: fig. 16d), fused Neovenator caudals with co-ossified chevron


14 Responses to “Cetiosaurus, Pelorosaurus, Streptospondylus or maybe Iguanodon(?!) in bizarre Fused Chevrons scandal!”

  1. Nima Says:

    It’s a thing of beauty…. but with no fossae it’s probably not a Brachiosaur or Xenoposeidon.

    It looks like a basal sauropod, probably a Cetiosaur caudal. Seems like England just has tons of these bones dug up centuries ago that were never properly identified. And though Owen may have redrawn this one, he was known for stealing a lot of Mantell’s research and renaming his discoveries.

  2. Nathan Myers Says:

    But really, who wouldn’t have?

  3. Nima Says:

    You make a good point! … but from what I’ve read, Owen was a total jerk to just about everyone else in the field at that time. Mantell, Wallace, Darwin, Huxley, Seeley, Hulke, and many others.

  4. This happens in theropods sometimes, Megaraptor being the only example I can think of off the top of my head.

  5. Darren Naish Says:

    I hadn’t mentioned this earlier because it didn’t occur to me that it was the same sort of thing, but maybe it is. Fusion of two caudals – with the ‘bridging’ chevron being fused to the vertebrae too – is known in Neovenator (figured by Naish et al. and more recently bu Brusatte et al.), Allosaurus (Madsen and Peterson et al.), Tyrannosaurus (figured by Larson in various articles), and Poekilopleuron (see original description by Eudes-Deslongchamps). I thought it was present in Aucasaurus too but I might be thinking of another abelisaur.

  6. Mike Taylor Says:

    Thanks for the pointers, Darren. I couldn’t figure out which Naish et al. paper you meant, but I found the Neovenator fusion in the appalling PDF of Brusatte et al.’s (2008) monograph, and I think your first reaction was right — it doesn’t look like the same thing (in their fig. 16d), but like a rather obvious and unhealthy pathology rather than the nice smooth fusion in the sauropod caudal. I don’t have time to look up the others, though.

  7. Zach Miller Says:

    I didn’t know Megaraptor was redescribed. How was it classified? “Megalosaur?” Spinosauroid? Something else entirely?

  8. DDeden Says:

    I hope you don’t mind me drifting waay off topic, but all this fusion confusion has me curious about a more closely related species, us.

    Humans, back in the days before chairs/TVs/computers/horses/boats/cars didn’t sit vertically so much off the ground, with the backbone perpendicular more or less. Humans suffer from a lot of back problems especially with age, but is there indications of increased vertebral co-ossification, aside from the tailbone? Apes hang as much as they sit, so I wouldn’t expect as much of an effect as with a biped that sits alot. Just curious. I guess dinosaurs didn’t sit vertically like many mammals can.

  9. Jaime A. Headden Says:

    Correct me if I am wrong, but at least one Mongolian titanosaur, Opisthocoelicaudia, and one Thai titanosaur (Thaitanosaur?), Phuwiangosaurus, have haemals fused to their preceding caudal vertebrae.

  10. Sorry to butt in about a mere non-pneumatic squamate, but I also have a ‘rare fused chevron’ scandal story. I’ve been studying extinct madtsoiid snakes for a couple of decades, and despite doing quite a bit of my own prep and sorting work, in that time I’ve seen precisely one snake chevron. I could tell, because it was fused (with visible and asymmetric suture/fusion-scar) to a centrum of Wonambi naracoortensis (Scanlon and Lee 2000, full ref on linked web page). I often notice loose chevrons from mammals, crocs, and lizards while sorting disarticulated bits from Riversleigh (also meiolaniid turtles, but their chevrons are normally fused), but loose snake chevrons persist in not showing up. Of course in extant snakes the ‘chevron’ is utterly different, fused to the centrum but with the two branches unfused and usually separated distally.

    BTW, I like Jaime’s ‘Thaitanosaur’. I expect to see a restaurant of this name next time I stroll down King Street, Newtown (that’s in Sydney); there’s an extremely high turnover of (mostly very good) Thai joints there, often with punny names. Always makes me think of Douglas Adams, and I’ve been predicting the ‘Thai restaurant event horizon’ for a while.

  11. […] (It’s interesting that caudals 30 and 42 have those cute fused chevrons.) […]

  12. Sander Says:

    Dear misters Taylor, Wedel and Naish,
    I have a vertebra centrum which is said to be from a theropod but it looks more like the vertebra you decribe here, only without the fused chevron and neural spine. I have read much papers searching for what it could be and the only vertebra that is somewhat similar to my example is this one. Would one of you perhaps want to take a look at it?
    Thanks in advance,

  13. Mike Taylor Says:

    Hi, Sander. We’re always happy to look at vertebrae. Send me your photos at sauropoda@gmail.com, and I will pass them on to the others.

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