Wednesday, July 20, 2011

Ornithopods of the British Isles, Part I


Fig 1.- Callovosaurus leedsi might have look like Dryosaurus although it is hard to tell from a single bone.

If you were asked to cite one dinosaur that lived in the British Isles, chances are that you will mention Iguanodon. Since Mary Ann Mantell discovered the first teeth of this animal while going for a walk in Sussex in the year 1822, countless bones have been unearthed and attributed to Iguanodon extending the geographical presence of this genus from Europe to North America, Africa and Asia and its temporal range from the Middle Jurassic to the Late Cretaceous. In effect, Iguanodon became a so-called wastebasket taxon. Most of the Ornithopods (the group of bird-hipped dinosaurs to which Iguanodon belongs) remains from the British Isles were originally described as “Iguanodon”.  In recent years, scientists have started going through this mess resulting in the naming of a number of new genera and restricting the use of the generic name to a single species, I. bernissartensis from the Barremian-Aptian of England and Belgium. One notable consequence of this exercise is that Ornithopod dinosaurs of the British Isles now look way more diversified than previously thought (instead of 3 genera, we now have a dozen or more). This is the first of a two-part post on the Ornithopod dinosaurs of the United Kingdom.

The herbivorous Ornithopods can be classified into a few types or families: the lightly built bipedal Hypsilophodonts and Dryosaurs, the medium sized Rhabdodonts, the more heavily built and mostly quadrupedal Camptosaurs and Iguanodonts, and the variously crested and non crested “Duck-billed” dinosaurs (the Hadrosaurs). Except for the Rhabdodonts, all are represented in the British Isles, although the remains of Hadrosaurs are to date very scrappy and questionable.


Fig 2.- Cumnoria prestwichii.

The most geologically ancient Ornithopod of the UK is known from a single isolated femur:  Callovosaurus leedsi (originally “Camptosaurus leedsi”) is from the Oxford Clay Formation, near Peterborough, Cambridgeshire, dating from the Middle Jurassic (Callovian, ~163 MYA). It is hard to say much from a single bone but the animal is either a Camptosaur (Galton, 1980) or a Dryosaur as recently proposed (Ruiz-Omeñaca et al., 2007). Either way, it is the earliest recorded of its kind worldwide. It probably measured something like 2.5 m in length.

Fig 3.- Barilium dawsoni.


The next known Ornithopod in geological order is Cumnoria prestwichii (Originally “Iguanodon prestwichii”) from the Kimmeridge Clay Formation in Oxfordshire and dating from the Late Jurassic (Kimmeridgian, ~153 MYA). This one is known from a partial skull and some postcranial elements. Cumnoria was probably bipedal, measuring about 3 to 3.5 meters in length and looked a lot like the North American Camptosaurus.
 
Fig 4.- Hypselospinus fittoni.

From the Early Cretaceous (Berriasian ~142 MYA) Purbeck Limestone formation in Dorset, there is a right dentary, which was named Owenodon hoggii (Originally “Iguanodon hoggii”), probably another Camptosaur.

The Wadhurst Clay Formation in East Sussex of Early Cretaceous (Middle Valanginian, ~138 MYA) age is home to at least two species of Iguanodonts, the large size (8 m) and heavily built Barilium dawsoni (Originally “Iguanodon dawsoni”) and the medium size (6 m) and more lightly built Hypselospinus fittoni (Originally “Iguanodon fittoni”), both known from partial postcranial remains. A large skull recovered at Henfield, West Sussex, might belong to Barilium. The two new generic names were coined by David Norman in 2010. However, Ken Carpenter and Yusuke Ishida unknowingly gave the name Torilion dawsoni and Wadhurstia fittoni the very same year to the very same fossils, but since their publication came out a few weeks later, Norman’s names for the two animals have priority and thus prevailed.  As for differences in the two studies, Carpenter and Ishida made one specimen that Norman included in Barilium, as a separate species and named it Sellacoxa pauli and considered  “Iguanodon holligtonensis” distinct from Hypselospinus.

From the Tunbridge Wells Sand Formation in West Sussex of Early Cretaceous (Middle-Upper Valanginian age, ~136 MYA), a right dentary was named Kukufeldia tilgatensis (this fossil was previously taken as a specimen of “Iguanodon anglicus”). This is probably another Iguanodont of some sort.

This is all for now, folks! Stay tuned for the second part with Hypsilophodon and Iguanodon.

References:

Carpenter, K. and Ishida, Y. 2010. Early and "Middle" Cretaceous Iguanodonts in Time and Space. Journal of Iberian Geology 36 (2): 145–164.

Galton, P. M. 1980. European Jurassic ornithopod dinosaurs of the families Hypsilophodontidae and Camptosauridae. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 160 (1): 73–95.

McDonald, A.T., Barrett, P.M. and Chapman, S.D. 2010. A new basal iguanodont (Dinosauria: Ornithischia) from the Wealden (Lower Cretaceous) of England. Zootaxa, 2569: 1–43.

Naish, D., and Martill, D. M. 2008. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, London 165: 613–623.

Norman, D. B. 2010. A taxonomy of iguanodontians (Dinosauria: Ornithopoda) from the lower Wealden Group (Cretaceous: Valanginian) of southern England. Zootaxa 2489: 47–66.

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



1 comment:

  1. Grand post! Cannot wait for the second installment!

    ReplyDelete