Where the scelidosaurs and iguanodontians roam

Before I begin, let me say: yay Raeticodactylus. Would say more but haven't had time (plus I've had no internet access for the last few days). Last year Dave Martill and I published part 1 of our review of the British dinosaur fauna (Naish & Martill 2007). While several published lists provide overviews of Britain's dinosaur assemblage (Swinton 1934, Olshevsky 2000, Weishampel et al. 2004), it seemed like a good idea to produce a more extensive review, especially given the substantial taxonomic confusion that surrounds British dinosaurs, and the large amount of recent work that has resulted in reappraisals and reassignments. Originally submitted as a special paper for the bicentennial volume of the Geological Society of London, our review got split into two for length reasons, and - last week - I am happy to report that part 2, the ornithischian half, finally saw publication...

Of course most of what we say is well known - if not tediously familiar - to dinosaur workers: Britain has a really good, diverse dinosaur assemblage, with excellent specimens and 'first appearances' of several clades, blah blah blah (Naish & Martill 2007, 2008) [image below shows the excellent holotype of the Kimmeridge Clay stegosaur Dacentrurus armatus, from Owen's 1875 monograph]. Our long history of scientific interpretation and our excellent Middle Jurassic and Lower Cretaceous records combine with this genuinely diverse fossil record to make the country one of the best in the world for dinosaur finds. But you've heard all this before. What do we say in the review that's new? Well, not much really, because it's... a review. But it's worth bringing to better attention a few areas that aren't tremendously well known.

Heterodontosaurids, best known from the Lower Jurassic of South Africa, are represented in Britain by the late survivor Echinodon becklesii from the Berriasian Lulworth Formation of Dorset (Norman & Barrett 2002). You might remember from the work on the Spanish dinosaurs of the Camarillas Formation at Galve (go here) that Lower Cretaceous heterodontosaurids seem to be present there as well (Sánchez-Hernández et al. 2007), and a few possible heterodontosaurid records are known from the British Middle and Upper Jurassic too. These discoveries suggest that heterodontosaurids might have been a constant presence in the Jurassic and Early Cretaceous of Europe.

We looked briefly at Scelidosaurus previously, in part because Naish & Martill (2007) figured an awesome, complete new specimen with curving skull horns and rows of spikes on its limbs. While Scelidosaurus is (nowadays*) universally regarded as a thyreophoran, it's been suggested on several occasions that it might be the sister-taxon to Ankylosauria (most recently by Carpenter (2001), who coined the new name Ankylosauromorpha for Scelidosaurus + Ankylosauria). In the most inclusive analysis of Ornithischia published to date, Butler et al. (2008) supported the more conventional, basal thyreophoran position.

* It was regarded as an ornithopod by a few workers during the 1970s, back when 'ornithopod' had a far more inclusive meaning than it does now.

Scelidosaurus is particularly interesting from a historical perspective. First published in 1861, it is the first dinosaur for which a good, articulated skeleton was discovered. David Norman has noted how surprising it is that Richard Owen failed to make more out of Scelidosaurus: in contradiction to Gideon Mantell, who had imagined dinosaurs to be elongate and lizard-like, and to Joseph Leidy (who was proposing at this time that dinosaurs were kangaroo-like bipeds), Owen had described dinosaurs as heavy-limbed quadrupeds. Here, in Scelidosaurus, Owen had a fossil that he could have used to demonstrate his correctness [adjacent image shows Owen posing with a moa leg].

So why Owen didn't make better use of Scelidosaurus is a good question. Norman (2001) proposed that Owen had simply become involved in too many disparate projects by the late 1850s to keep abreast of everything: he was appointed Superintendent of the Natural History Collections at the British Museum in 1856, published work on brain structure and was involved in the 'hippocampus debate' with Huxley between 1858 and 1860, gave lecture courses at the Royal School of Mines between 1857 and 1861, was elected President of the British Association for the Advancement of Science in 1858, submitted formal plans for a dedicated 'Museum of Natural History' in 1859, and in 1859 alone published work on the pterosaur Dimorphodon (and on other pterosaurs), on new moa fossils coming out of New Zealand, on Megatherium, on the new Australian fossils Megalania, Thylacoleo and Zygomaturus, on great apes and their classification, on assorted non-mammalian synapsids from South Africa, and on much else besides. And of course Darwin's Origin was published in 1859, giving Owen plenty to think about (his hostile anonymous review of this book appeared in 1860). Maybe he would have made more of Scelidosaurus had he less to worry about.

In terms of the other thyreophorans (the eurypodans), Britain is pretty good for both ankylosaurs and stegosaurs. Among ankylosaurs, our best known taxa are Polacanthus and Hylaeosaurus, both from the Wealden Supergroup and both of which are close relatives within Polacanthidae according to some workers. Of the many ankylosaur species named from the Upper Cretaceous Lower Chalk, Folkestone Beds, Gault Clay and Cambridge Greensand, only Anoplosaurus major has proved valid (Pereda Suberbiola & Barrett 1999). Several really obscure British ankylosaurs are known from very fragmentary remains. Sarcolestes leedsi from the Oxford Clay Formation, known only from an incomplete lower jaw (though some other fragments have been referred to it), is the world's oldest nodosaurid [hypothetical skull reconstruction of Sarcolestes leedsi shown in adjacent image]. Even more obscure is Cryptosaurus eumerus (long known as Cryptodraco), described from a femur from the Ampthill Clay of Cambridgeshire. Little known is Galton's (1983) suggestion that Cryptosaurus might have been a facultative biped, though I don't think anyone ever took this too seriously.

Britain's stegosaurs include the earliest member of the group to be named, Regnosaurus northamptoni Mantell, 1848 from the Hastings Beds Group. This is also one of the youngest known stegosaurs (it's probably Valanginian in age). Our Jurassic stegosaurs are much better known and include Dacentrurus armatus from the Kimmeridge Clay and Lexovisaurus durobrivensis from the Oxford Clay [there are ver 1 articles on the Kimmeridge Clay here and on the Oxford Clay here]. As I always like to point out, Dacentrurus armatus was a very large animal, with some individuals having femora over 1.2 m long [image below shows Dacentrurus armatus above and Lexovisaurus durobrivensis below; reconstructions by Tracy Ford].

On the subject of British stegosaurs, one of the most remarkable proposals about this group is that two incomplete bone segments from the Rhaetian Westbury Formation of Avon belong to this group, and represent big animals on par with Stegosaurus (Galton 2005). The idea that gigantic stegosaurs were living in the Late Triassic is surprising to say the least, and if correct it would drag most of the major divergences within Ornithischia down into the Triassic: we should have Triassic ankylosaurs, for example, and the ghost lineages for Scelidosaurus, Lesothosaurus and Neornithischia (the branch-based ornithopod-marginocephalian clade) would all extend into the Triassic too. However, the fossils concerned are poorly preserved sub-cylindrical fragments, preserving very little information, and Galton's suggestion has been roundly condemned: Butler et al. (2006) and Norman et al. (2007) suggested that the fragments concerned could only be identified as Reptilia indet. while Irmis et al. (2006) argued that they could only be identified to Tetrapoda indet. We join the chorus of disquiet (Naish & Martill 2008). One question though: if the fragments aren't from giant stegosaurs, what do they belong to? The point is, of course, that it's not possible to say, but I wonder if they might be propodial segments from big sauropterygians.

Finally we come to the ornithopods and marginocephalians: the node-based clade containing these dinosaurs is Cerapoda Sereno, 1986 while the branch-based clade is Neornithischia Cooper, 1985. Butler et al. (2008) found several Jurassic taxa to be stem-neornithischians outside of Cerapoda, including Agilisaurus, Hexinlusaurus and Othnielosaurus. Britain doesn't have any such taxa and, among ornithopods, we're low on basal taxa, the exception being Hypsilophodon foxii, known from the many excellent specimens that come from the Barremian Wessex Formation. H. foxii was contemporaneous with the dryosaurid Valdosaurus canaliculatus, and British dryosaurid material is also known from the Hastings Beds Group.

Callovosaurus leedsi from the Oxford Clay has also recently been identified as a dryosaurid (Ruiz-Omeñaca et al. 2007). If this is correct, the Callovian age of this specimen (it's currently the world's oldest iguanodontian) would pull the ghost lineages of several ornithopod lineages, including thescelosaurs, parksosaurs, rhabdodontids, and tenontosaurs, down into the Middle Jurassic. Some of these groups already have ridiculously long ghost lineages: that of Thescelosaurus is more than 90 million years long, though one controversial British fossil has been suggested to help fill it (Naish & Martill 2008) [adjacent image, from wikipedia, is of Cumnoria, on which read on...].

Dryosaurids are basal members of the ornithopod clade Iguanodontia, a group that also includes the camptosaurids, Iguanodon and its relatives, and the hadrosaurs. Among British camptosaurids, Naish & Martill (2008) did a daring thing and - shock horror - used the name Cumnoria prestwichii for the Kimmeridge Clay camptosaurid. This name has fallen out of favour in recent decades, with most authors following Galton & Powell (1980) in regarding the species as part of Camptosaurus, best known from the Upper Jurassic Morrison Formation. However, the characters that have been used to support this referral are unconvincing as they're widely distributed in iguanodontians. Furthermore, the skull material that Galton & Powell (1980) used as their examplar for Camptosaurus is now known not to belong to that genus, but to instead represent a distinct taxon, the Lower Cretaceous Theiophytalia. So, pending further study, I think that we should refer to the Kimmeridge Clay camptosaurid as Cumnoria.

If any dinosaur is associated with the British fossil record, it is the Lower Cretaceous iguanodontian Iguanodon [adjacent map from Naish & Martill (2008) shows SE English and some of the most interesting and/or significant iguanodontian finds]. But, perhaps more so than any other ornithischian, Iguanodon has become a real mess, housing multiple highly disparate taxa that span three continents and over 20 million years. Complicating the whole story is the fact that Mantell's original species, Iguanodon anglicus Holl, 1829 (from the Valanginian Grinstead Clay Formation), is no longer the type species for the genus: following an ICZN proposal by Charig & Chapman (1998), Iguanodon bernissartensis is now the type species. On the one hand this is good, because I. bernissartensis is the species which has most often been associated with the name Iguanodon in the literature, but on the other hand it is not because I. bernissartensis is very far removed, both morphologically and temporally (and probably phylogenetically), from I. anglicus. Furthermore, if I. anglicus is no longer Iguanodon proper, then Mantell never really discovered Iguanodon.

The two best known species usually associated with the genus, Iguanodon bernissartensis and I. atherfieldensis, are substantially different animals that group apart from each other in at least some phylogenies, and I agree with Greg Paul's recent proposal to give I. atherfieldensis its own genus, Mantellisaurus (Paul 2007), though Mantellodon would have been a better name. Of the several other 'Iguanodon' species, none really resemble I. bernissartensis enough to belong in the same genus: Paul's latest paper (Paul 2008: published just a couple of weeks before our review appeared) is a start in sorting this out. The long-skulled taxon that Paul has recognised for the gracile Bernissart iguanodontian, Dollodon, is definitely present in the British Wessex Formation. We'll be coming back to all of this later [adjacent image, from Paul (2008), shows (top to bottom) Iguanodon bernissartensis, Dollodon bampingi and Mantellisaurus atherfieldensis].

And, ah yes, Yaverlandia. In this paper we make the point again that Yaverlandia - originally proposed to be a pachycephalosaur - is almost certainly not one, nor even a marginocephalian nor an ornithischian, but is instead a maniraptoran theropod. I realise how frustrating it is for me to keep mentioning this idea while failing to elaborate on it: a full paper is in preparation and will appear eventually. Britain might not have any marginocephalians, but we should perhaps expect them actually given that Berriasian Germany has Stenopelix. Note also that, since we submitted the paper, Europe has yielded a ceratopsian: the Campanian leptoceratopsid from Sweden described by Lindgren et al. (2007). It's been suggested on a couple of occasions that basal ceratopsians like psittacosaurs might one day be found in Lower Cretaceous Europe, but this is speculative.

So there we have it. Some of the newspaper write-ups I've seen sort of imply that Naish and Martill want Britain to be exceptional, with a dinosaur record that soars over and above that of other countries. We never said that, but the point remains that the British record is good, and indeed among the best. And even in the country with the longest history of palaeontological discovery and interpretation, there is still tons of work to do.

As usual, email me if you want the pdf. Another personally significant publication appears next month... have to survive Dinosaurs - A Historical Perspective first though.

Refs - -

Butler. R. J., Porro, L. B. & Heckert, A. B. 2006. A supposed heterodontosaurid tooth from the Rhaetian of Switzerland and a reassessment of the European Late Triassic record of Ornithischia (Dinosauria). Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 2006, 613-633.

- ., Upchurch, P. & Norman, D. B. 2008. The phylogeny of the ornithischian dinosaurs, Journal of Systematic Palaeontology 6, 1-40.

Carpenter, K. 2001. Phylogenetic analysis of the Ankylosauria. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 455-483.

Charig, A. J. & Chapman, S. D. 1998. Iguanodon Mantell, 1825 (Reptilia, Ornithischia): proposed designation of Iguanodon bernissartensis Boulenger in Beneden, 1881 as the type species, and proposed designation of a lectotype. Bulletin of Zoological Nomenclature 55, 99-104.

Galton, P. M. 1983. Armored dinosaurs (Ornithischia: Ankylosauria) from the Middle and Upper Jurassic of Europe. Palaeontographica Abteilung A 182, 1-25.

- . 2005. Bones of large dinosaurs (Prosauropoda and Stegosauria) from the Rhaetic Bone Bed (Upper Triassic) of Aust Cliff, southwest England. Revue de Paléobiologie, Genève 24, 51-74.

- . & Powell, H. P. 1980. The ornithischian dinosaur Camptosaurus prestwichii from the Upper Jurassic of England. Palaeontology 23, 412-443.

Irmis, R. B., Parker, W. G., Nesbitt, S. J. & Liu, J. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19, 3-22.

Lindgren, J., Currie, P. J., Siverson, M., Rees, J., Cederström, P. & Lindgren, F. 2007. The first neoceratopsian dinosaur remains from Europe. Palaeontology 50, 929-937.

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.

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Norman, D. B. 2000. Professor Richard Owen and the important but neglected dinosaur Scelidosaurus harrisonii. Historical Biology 14, 235-253.

- . 2001. Scelidosaurus, the earliest complete dinosaur. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 3-24.

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Olshevsky, G. 2000. An Annotated Checklist of Dinosaur Species by Continent. Publications Requiring Research, San Diego.

Paul. G. S. 2007. Turning the old into the new: a separate genus for the gracile iguanodont from the Wealden of England. In Carpenter, K. (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press (Bloomington & Indianapolis), pp. 69-77.

- . 2008. A revised taxonomy of the iguanodont dinosaur genera and species. Cretaceous Research 29, 192-216.

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Ruiz-Omeñaca, J. I., Pereda-Suberbiola, X. & Galton, P. M. 2007. Callovosaurus leedsi, the earliest dryosaurid dinosaur (Ornithischia: Euornithopoda) from the Middle Jurassic of England. In Carpenter, K. (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press (Bloomington & Indianapolis), pp. 3-16.

Sánchez-Hernández, B., Benton, M. J. & Naish, D. 2007. Dinosaurs and other fossil vertebrates from the Late Jurassic and Early Cretaceous of the Galve area, NE Spain. Palaeogeography, Palaeoclimatology, Palaeoecology 249, 180-215.

Swinton, W. E. 1934. The Dinosaurs, A Short History of a Great Group of Reptiles. Thomas Murby, London.

Weishampel, D. B., Barrett, P. M., Coria, R. A., Le Loeuff, J., Xu, X., Zhao, X., Sahni, A., Gomani, E. M. P. & Noto, C. R. 2004. Dinosaur distribution. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria, Second Edition . University of California Press (Berkeley), pp. 517-606.