Lurdusaurus: stupidest looking iguanodontian, and... a pneumatic ornithischian at last?

One of the strangest Mesozoic dinosaurs ever described has to be the African iguanodontian Lurdusaurus arenatus, named in 1999 for remains from the Lower Cretaceous Elrhaz Formation of Gadoufaoua, Niger (Taquet & Russell 1999). The Elrhaz Formation has also yielded the sail-backed iguanodontian Ouranosaurus, the rebbachisaurid sauropod Nigersaurus, the theropods Kryptops, Suchomimus and Eocarcharia, and the crocodilians Anatosuchus and Sarcosuchus. [Adjacent Lurdusaurus image by Luis Rey, used with permission.]

As is well known among dinosaur researchers, Lurdusaurus was first described in a 1988 doctoral thesis by S. Chabli and named therein Gravisaurus tenerensis. I wish that this name had been used for the animal in Philippe Taquet and Dale Russell's final published paper instead of Lurdusaurus, but it's too late for that now. And, unfortunately, the one paper that's been published on Lurdusaurus just doesn't do it justice: everyone who's commented on it has expressed a sense of frustration that its anatomy has yet to be adequately reported. This is actually a pretty common problem in palaeontology. While people can find the time to publish a (sometimes hastily written) preliminary descriptive article, they frequently fail to follow through with the detailed monograph that the material deserves (and, yes, I am among the guilty... am working on it though).

What we do actually know from Taquet and Russell's paper? We know that Lurdusaurus has proportionally short, massive limb bones compared to those of other iguanodontians, and that - combined with the flaring anterior processes of the ilia in its pelvis - these short limbs would have made the live animal short at the hips, broad-bodied, and with a belly close to the ground. Taquet and Russell noted the presence in the animal of a relatively long neck, a proportionally short tail, and they reconstructed a low, shallow, superficially hadrosaur-like skull. Like other 'Iguanodon-grade' iguanodontians, its thumb was a conical bony spike [photo of forelimb skeleton below by Eduard Solà Vázquez, from wikipedia].

But, but - - what did it look like?

Taquet & Russell (1999) suggested that the animal's squat posture must have made it superficially ankylosaur-like, but they also noted a general resemble to ground sloths. The message I take away from this is that didn't really have much idea what it really looked like at all. Their paper is not too bad at reporting measurements and proportions, but they didn't illustrate many of the skeletal elements they described, and they didn't include any sort of reconstruction.

That's a real shame for such an apparently remarkable animal: I'm not ashamed to say that, on reading a technical palaeontological paper, I often wonder what the animal concerned would have looked like when alive - and I know I'm not alone. So an awful lot of people have been consistently frustrated by the absence of a reconstruction of Lurdusaurus. I tried one myself (but wouldn't want to share it) and Luis Rey produced a very nice life restoration for Tom Holtz's outstanding Dinosaurs (still easily the best popular-level general book on dinosaurs: my brief 2007 review is here; find it here on Amazon). Luis's picture [shown above; used with permission] is great, but - because it shows the animal as seen obliquely from the front - it doesn't give an obvious indication as to what's going on with the animal's overall proportions and form. Incidentally, Tom Holtz speculates in his book that Lurdusaurus might perhaps have been hippo-like and amphibious: an interesting idea that certainly looks plausible based on its proportions and spreading hand (the idea is testable: there's scope here for a project).

If you're wondering, Greg Paul didn't reconstruct the animal for his fairly comprehensive Dinosaurs: A Field Guide (a book that I'm due to review here some time soon). And, while there are a few Lurdusaurus reconstructions online, none of them are any good, nor do they accurately portray the animal's proportions.

Enter my long-standing friend Pete Buchholz, long-time ornithischian nut. By drawing to proportion the known elements of Lurdusaurus (some of them not included in the Taquet & Russell (1999) paper), and filling in the gaps based on the estimated lengths Taquet & Russell (1999) provided for the various segments of the body, Pete succeeded in producing a brand-new reconstruction, and that's what you're looking at here. The reconstruction above shows a skeletal reconstruction with those elements figured by Taquet & Russell (1999) shown in white. The bones crossed by diagonal lines are preserved but weren't illustrated by Taquet & Russell (1999), and the bones crossed by vertical lines (most of the skull essentially) are unknown, but are reconstructed based on those of related iguanodontians. An 'extrapolated' complete-ish skeleton is shown below, and a life restoration based on it (with a Buchholz for scale) is shown below that.

As per statements made by Taquet & Russell (1999), Lurdusaurus appears peculiarly long-necked for an iguanodontian, with stocky forelimbs and a belly that's close to the ground. Little appreciated is that the form of the hindlimb bones (especially the short metatarsals) might indicate sauropod-like graviportality. The metatarsals were said by Taquet & Russell (1999) to not only be short and robust, but also to lack strong contact with one another, suggesting a short, slightly spreading metatarsus backed by an enlarged foot pad. In keeping with the massive, spreading hand, this could conceivably be an adaptation for movement on soft substrates and hence perhaps an amphibious mode of life. A long-necked iguanodontian with stocky forelimbs and massive, spreading feet - I suppose you could suggest that this was a sauropod-mimicking ornithopod... and how weird that it lived in the same area as a small, short-necked diplodocoid sauropod. Hey, if I can hold off on the speculative possibilities here, so can you :)

Thanks, Pete, for permission to use the images.

More new iguanodontians

This brief discussion of a fairly newish iguanodontian gives me the opportunity to discuss something else that's also interesting, and has also recently been published in the world of iguanodontian research. As you'll know if you follow the literature (or if you read the series of articles I published here and on the Scientific American blog earlier this year: see links below), the Northern Hemisphere iguanodontians long lumped together in Iguanodon have recently been extensively revised, and a whole slew of new taxa (or alleged taxa) have been named. Already the validity of various of these new taxa has been challenged (Norman 2010, McDonald et al. 2010, McDonald 2011a). A few other new iguanodontian taxa have been named since I wrote those articles, including the Cedar Mountain Formation taxa Iguanacolossus fortis McDonald et al., 2010 and Hippodraco scutodens McDonald et al., 2010, the Yixian Formation's Bolong yixianensis Wu et al., 2010 and Xuwulong yueluni You et al., 2011 from the Xinminpu Group. McDonald (2011b) has also revised Camptosaurus: the new names Uteodon and Osmakasaurus are now used for species previously included in Camptosaurus. The distinction of Cumnoria (see previous discussion here) has also been supported.

Anyway, within recent weeks yet another new animal previously lumped into Iguanodon has been published: it's the Barremian Spanish form Delapparentia turolensis Ruiz-Omeñaca, 2011, originally described in 1960 by Albert de Lapparent and identified by him as a specimen of I. bernissartensis. [Montage of Delapparentia images below from here.]

As argued by Ruiz-Omeñaca (2011), a number of characters appear unique to Delapparentia and demonstrate that it can be distinguished from other iguanodontians. They include the detailed shape of the rib heads, the form of the ilium, and the presence of ossified sternal ribs. I'm sceptical that the last of those features should be used in a diagnosis, since cartilaginous ribs were surely widespread in ornithischians, and their ossification probably occurred randomly across phylogeny. A similar thing seems to have happened with the (usually cartilaginous) intercostal plates present in various taxa (Butler & Galton 2008).

Anyway... one thing in particular makes Delapparentia extremely interesting. It has pneumatic foramina on its ribs. Or, rather, one dorsal rib referred to it possesses a pneumatic foramen located close to the tuberculum (Ruiz-Omeñaca 2011, p. 7). The suggestion is made that the presence of this foramen is a diagnostic character of Delapparentia since one hasn't been documented elsewhere in iguanodontians. [Figure showing Delapparentia ribs shown here from Ruiz-Omeñaca (2011).]

However, there's a 'big picture' story here that isn't elaborated upon in the paper: if we really do have a pneumatic foramen here in Delapparentia, then we have - for the first time ever - a pneumatic ornithischian. As you may know, it's well established that post-cranial skeletal pneumaticity was widespread across saurischians (theropods and sauropodomorphs), and was also present outside of Dinosauria in pterosaurs. Its presence outside of Ornithodira (the pterosaur + dinosaur clade) has also been suggested based on the presence of deep neural arch fossae, bound by bony laminae, in near-dinosaurs like silesaurids (Butler et al. 2009) and possible evidence for post-cranial skeletal pneumaticity has also been suggested for some stem-archosaurs and crocodile-line archosaurs (Gower 2001). The figure below - from Wedel (2006) - shows which ornithodirans do, and do not, exhibit post-cranial skeletal pneumaticity (though, since this figure was produced, post-cranial skeletal pneumaticity has proved widespread in 'prosauropods').

The origins of skeletal pneumaticity within Archosauria remain controversial: that is, there's argument and uncertainty as to which, if any, non-ornithodiran archosaurs exhibited the trait. Nevertheless, it appears most likely from our understanding of archosaur phylogeny that post-cranial skeletal pneumaticity was present in the common ancestor of all dinosaurs, and in the common ancestor of all ornithodirans. The great paradox surrounding this pattern has been the apparent total absence of post-cranial skeletal pneumaticity in ornithischians. So - is Delapparentia that animal we've long been looking for: an ornithischian with post-cranial skeletal pneumaticity?

I wish it were so, since the existence of such an animal would refute predictions (Wedel 2006, 2007, Naish 2010, Yates et al. in press) that post-cranial skeletal pneumaticity was altogether lost in the ornithischian lineage and remove what otherwise appears to be an anomaly (namely, the total absence of pneumatic ornithischians). As usual, however, things are not simple.

Delapparentia is far from undoubtedly pneumatic. Firstly, that pneumatic foramen said by Ruiz-Omeñaca (2011) to be present on one of Delapparentia's ribs is not at all obvious in the one figure provided in the paper and requires verification. Secondly, foramina are associated with all kinds of structures: even if one is definitely present on the rib in question, close examination is required to show that it's a pneumatic structure, and not anything associated with vasculature, the nervous system, or pathology. Thirdly, the rib concerned was originally identified as that of a sauropod (specifically, Aragosaurus ischiaticus). Ruiz-Omeñaca says that the rib can confidently be referred to Delapparentia, but this issue means that it's reasonable to be sceptical about the rib's identification.

So - do we have a pneumatic ornithischian or not? Need more data, need more work.

For previous Tet Zoo articles on iguanodontians and Elrhaz Formation dinosaurs, see...

• Early abelisaurs and fan-crested and stretch-jawed hadrosaurs
• Where the scelidosaurs and iguanodontians roam
• Pads and notches in the necks of tube-crested hadrosaurs... SAY WHAT?
• There are dwarf, island-dwelling, cursorial, tridactyl hadrosaurs now: didn't you get the memo?
• The explosion of Iguanodon at Scientific American
• Goodbye super-inclusive Iguanodon, hello Mantellisaurus, Owenodon, Dakotadon, Dollodon, Barilium, Kukufeldia, Hypselospinus, Sellacoxa, Proplanicoxa etc. etc.

And for the Scientific American series on the 'explosion of Iguanodon', see...

• The Iguanodon explosion: How scientists are rescuing the name of a "classic" ornithopod dinosaur, part 1
• The explosion of Iguanodon, part 2: Iguanodontians of the Hastings Group
• The explosion of Iguanodon, part 3: Hypselospinus, Wadhurstia, Dakotadon, Proplanicoxa ...when will it all end?

You can download the Delapparentia paper for free, and see some supplementary images, here.

Refs - -

Butler, R. J., Barrett, P. M. & Gower, D. J. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters 5, 557-560.

- ., & Galton, P. M. 2008. The 'dermal armour' of the ornithopod dinosaur Hypsilophodon from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal. Cretaceous Research 29, 636-642.

Gower, D. J. 2001. Possible postcranial pneumaticity in the last common ancestor of birds and crocodilians: evidence from Erythrosuchus and other Mesozoic archosaurs. Naturwissenschaften 88, 119-122.

McDonald, A. T. 2011a. The status of Dollodon and other basal iguanodonts (Dinosauria: Ornithischia) from the upper Wealden beds (Lower Cretaceous) of Europe. Cretaceous Research doi:10.1016/j.cretres.2011.03.002

- . 2011b. The taxonomy of species assigned to Camptosaurus (Dinosauria: Ornithopoda). Zootaxa 2783, 52-68.

- ., Kirkland, J. I., DeBlieux, D. D., Madsen, S. K., Cavin, J., Milner, A. R. C. & Panzarin, K. 2010. New basal iguanodonts from the Cedar Mountain Formation of Utah and the evolution of thumb-spiked dinosaurs. PLoS ONE 5(11): e14075. doi:10.1371/journal.pone.0014075

Naish, D. 2010. Pneumaticity, the early years: Wealden Supergroup dinosaurs and the hypothesis of saurischian pneumaticity. In Moody, R. T. J., Buffetaut, E., Naish, D. & Martill, D. M. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications 343, pp. 229-236.

Norman, D. 2010. Wealden Group iguanodontians: their history and taxonomy. In Symposium of Vertebrate Palaeontology and Comparative Anatomy and Symposium of Palaeontological Preparation and Conservation 2010, University of Cambridge. University of Cambridge, Cambridge, pp. 20-21.

Ruiz-Omeñaca, J. I. 2011. Delapparentia turolensis nov. gen et sp., un nuevo dinosaurio iguanodontoideo (Ornithischia: Ornithopoda) en el Cretácico Inferior de Galve. Estudios Geológicos 67 doi: 10.3989/egeol.40276.124

TAQUET, P., & RUSSELL, D. (1999). A massively-constructed iguanodont from Gadoufaoua, lower Cretaceous of Niger Annales de Paléontologie, 85 (1), 85-96 DOI: 10.1016/S0753-3969(99)80009-3

Wedel, M. J. 2006. Origin of postcranial skeletal pneumaticity in dinosaurs. Integrative Zoology 2, 80-85.

- . 2007. What pneumaticity tells us about 'prosauropods', and vice versa. Special Papers in Palaeontology 77, 207-222.

Yates, A. M., Wedel, M. J. & Bonnan, M. F. In press. The early evolution of postcranial skeletal pneumaticity in sauropodomorph dinosaurs. Acta Palaeontologica Polonica doi: 10.4202/app.2010.0075