Denizens of the Oxford Clay

In many ways, Britain is the birth-place of palaeontology, and the heady years of the 19th century saw the discovery of creatures that have inspired the imagination of small boys ever since – myself included. I’m talking, of course, about the dinosaurs.

A vast plethora of names abound for the various scraps of bone that were discovered in those days and, unfortunately, many finds today still suffer from this taxonomical mess. Fortunately, however, the British dinosaur scene is undergoing something of a revival with new research and, more importantly, new finds coming to light. This is the story of one of those finds and the bigger picture it fits into.

deposits-lateral-viewOrnithopoda incertae sedis – PFL03 in lateral view. Note the prominent projection at A (prezygapophysis) that would have articulated with the next vertebra behind and provided the rigidity in the spinal column. The attachment site for a bony chevron can be seen to the bottom right at B. The neural spine is broken along its width, but would have extended an estimated 1 to 2cm at C.

‘PFL 03’ is probably not the most exciting name in the world. I came up with it, and even I agree it is fairly dull. However, this is my collection number for a small bone that thudded to the floor inside a parcel during August 2008. The parcel’s various contents were the result of a trade with Fiona Jennings (a fellow fossil-hunter), and the small bone was thrown in due to the lack of Ichthyosaur material  – Ichthyosaurs being my special interest. Secure inside a foam-padded plastic box, the attached label read:

“Plesiosaur vertebra, Old Flyover Ashpit, Nr A15, Fletton, Peterborough. Lower Oxford Clay. 14/09/03.”

Not having much experience of the Oxford clay, I dug out a few books and began to skim through them. I chanced across a plate of Stenosaurus, a rather ferocious looking marine crocodile, and found a vague similarity between the two bones. That was enough for me, so I wrapped it up and decided to take it with me into town.

My home town of Cambridge is a wonderful place, from both historical and architectural points of view. But, perhaps, the best things about it are the various free university museums and, of these, there is one I’m quite often found in – The Sedgwick Museum of Geology. Depending on meetings and coffee breaks, there is usually someone around to identify finds that are brought in, a service I make regular use of. However, on this day, the fossil first drew little but puzzled silence …

… and, an hour later, I held a receipt to pick up the fossil once it had been identified. Written into the ‘Description of find’ box was “Reptile vertebra – Croc or Dino?”.

Oxford Clay and dinosaurs

The Oxford Clay lies across a vast swathe of the UK, stretching from Dorset in the south to Yorkshire in the north. It was laid down during two periods of geological time – the Callovian and Oxfordian – and contains an abundance of Middle Jurassic marine fossils. It is also known for its occasional, albeit rare, dinosaur remains. The impressive theropod, Eustreptospondylus oxoniensis, was discovered in 1964 north of Oxford and is one of the most complete European dinosaurs known. Metriacanthosaurus, another British theropod of similar age, is known from a partial post-cranial skeleton and was named in the same year. Other species are known from dispersed and scattered fragments – a disarticulated, possibly dermal, spine attributed to the stegosaur Dacentrurus comes from the Oxford Clay of Weymouth, while scattered skeletal material forms the basis of a similar creature, Lexovisaurus.

Presumably, the vast majority of dinosaur remains found in these strata originate from corpses washed out to sea, hence, the scarcity of finds. The Oxford Clay of Peterborough certainly has a marine origin, with oysters of the species Gryphea dilatata being abundant, and yet it also has its own share of dinosaur remains. By the turn of the twentieth century, two sauropods, a stegosaur, an ankyliosaur and an ornithopod had been attributed to the various clay pits in the area (Leeds 1956; Martill 1988), with the theropod, Megalosaurus, represented by a fibula (CAMSM J46881*) found at Fletton and described by Dr von Huene in 1901. Fletton is also the site where CAMSM J46886 was found – a phalangeal bone attributed to Camptosaurus. The Sedgwick museum holds one further bone from the site – a large limb bone referred to as “dinosauria indeterminate” (CAMSM J46888). Clearly, Peterborough – and the Oxford Clay in general – is no stranger to these denizens of the past.

mid-cuadal-vertebrae-iguanodon-camsm-castA lateral view of the mid-caudal vertebrae of Iguanodon bernissartensis, demonstrating the role of prezygapophyses in maintaining rigidity. This specimen is a cast and stands in the entrance hall of the Sedgewick Museum.

The identity of PFL 03

After leaving the find in the care of the museum, it was time for holidays. Over the next four weeks, I found crinoids in Devon, an ichthyosaur paddle at Charmouth and went hunting for fossil brachiopods, corals and sea urchins in France. I also received my GCSE results into the bargain. But a month passes slowly when you are itching for a result of a different kind …

The verdict of the Sedgwick museum staff was that it was a distal caudal vertebra belonging to an adult ornithschian (‘bird hipped’) dinosaur. To say I was excited is something of an understatement! I think it’s a good job I took notes as otherwise this article would be fairly short! Apparently, the small tail bone compared well with the mid-distal caudals of Iguanodon, specifically the 15th caudal (as starting from the sacral or tail end) despite the obvious difference in size. A single ornithopod has previously been noted from near this locality – in 1901, Huene referred an isolated tibia to the small ornithopod Dryosaurus sp., but it has since been decided that the specimen is indeterminate (D.M.Martill/D. Naish 2001).

For now, PFL03 will have to remain nameless. As far as I am aware, no small ornithschian dinosaur species have been named in Britain from the Oxford Clay, making referral to any species impossible. It is possible it represents a new species – but the material is insufficient to raise a new name. Further research and (hopefully) fresh finds will be required to do this. Suffice to say that, 154mya, a small bipedal dinosaur was running around somewhere near proto-Peterborough. Due to its small size, it could have been omnivorous, feeding off available plant and insect material on the various small islands and landmasses that existed there at that time. Perhaps, it was capable of swimming between these islands while in search of food, much as red deer do in the outer islands of Scotland today. Or, it may simply have been washed out to sea as a carcass that slowly decomposed, hence the isolated nature of the find.

The fossil has been donated to the Sedgwick Museum and is now in its collection. It is being prepared and I will have a cast returned to me, while the original goes on display. At the time of writing, it does not yet have a CAMSM catalogue number.

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For the help provided to me in preparing and writing this article, I would like to give special thanks to Fiona Jennings for her valuable correspondence and to the staff of the Sedgwick museum for their work on this and other finds.

*  In this article the abbreviation CAMSM has been used to refer to the Cambridge Sedgwick Museum