One Day in the Field.Pdf

Home , Asteracanthus, Cryptoclidus, Liopleurodon, Metriorhynchus, Oxford Clay, Simolestes

ONE DAY IN THE FIELD This is a detailed account of our branch day-in-the-field, as seen through the eyes of our Branch Organiser, Mike Friday...... Enjoy July 08, 2006 Introduction On July 8 2006, a good number of us met at the Bedford Museum for a talk and presentation by the Keeper of Natural History, Chris Andrew. This consisted of a potted history of the Oxford Clay Quest Brick-Pit at Stewartby, to the south west of Bedford, which was the location for our afternoon trip. Stories derived from a number of its workers, an insight into the kind of machinery used and the kinds of fossils that can be found at the site provided an entertaining morning. The essential details of the pit are explained by Chris, below, who very kindly supplied me with the text. The Jurassic Oxford Clay marine sediments extensively cover South East England from Dorset to Yorkshire. Although still appearing in the Late Jurassic as the Late Oxford Clay stage of the Oxfordian series, the majority occurs in the Middle Jurassic Callovian stage as the Early and Middle Oxford Clay, see Figure 1.

Figure 1 The stratigraphy and age of the Oxford Clay

Tom Miller, in Quest Pit

Quest Pit (from Chris Andrew)

Quest Pit is currently the only working Oxford Clay brick-pit in Bedfordshire. The pit exposes Lower Oxford Clay and the base of the Middle Oxford Clay; drainage trenches expose the very top of the more silty Kellaways Beds. The Oxford Clay is most famous for its vertebrate fauna. The most common vertebrate remains are definitely those of plesiosaurs, see Figure 2, especially Cryptoclidus.

Quest Pit has yielded at least fragments of the plesiosaurs Muraenosaurus and Cryptoclidus, the ichthyosaur Opthalmosaurus and teeth of several species of pliosaur (Simolestes, Liopleurodon, Peloneustes).

Figure 2 Plesiosaur vertebrae

A partial pliosaur skeleton found at Quest Pit is currently being researched at Cambridge University. It was originally identified as Peloneustes philarchus but may well turn out to be a new species. Two distinct types of crocodile can be found, the marine crocodile Metriorhynchus is by far the most common. This crocodile had its feet adapted into paddles. The other crocodile is Steneosaurus which looked a bit like a modern Gharial.

Last year amateur collectors found part of the dinosaur Sarcolestes leedsi. Dinosaurs are a very rare find in the Oxford Clay; this is the first one from Bedfordshire, and the species is to be renamed and described based on the new material. Fish and shark remains can also be found, mostly only as isolated teeth. Because of their small size and fragility, fish remains are harder to find than those of the large reptiles, see Figure 3.

Figure 3 Leptolepsis

Teeth are particularly common as fossils because reptiles and sharks continually shed and replace teeth throughout their lives. Shark remains are almost always teeth or fin spines (2 on each shark) as sharks have a cartilaginous skeleton which does not easily preserve. On the trip to Quest someone found a nice small tooth of the shark Asteracanthus, see Figure 4. This shark had teeth designed for crushing and probably fed on the abundant small bivalves.

Figure 4 Teeth of the shark Asteracanthus

Shell beds in the clay are easily spotted by their abundant pyrite content. They weather orange in the old faces and are easily seen. They represent times of slow deposition.The clay at Quest is at present extracted with a dragline and moved to the plant by conveyor belt (about 2 miles long). Owing to the mechanisation of extraction, fewer fossils are now found than when the work was more labour intensive. Large reptile remains are also frequently smashed, at least partly, by the machinery.

At present it looks like Quest Pit may well close in about 2 year’s time. Depending on negotiations it may become the site for the National Institute for Research into Aquatic Habitats (NIRA) project.

The photos are fairly self explanatory. I have sent images of the ‘Tooth Quest’, Figure 5, found on the visit, to the Natural History Museum and the results should be back in the next week or two.

Figure 5 ‘Tooth Quest’ The plesiosaur vertebrae images show adult and juvenile vertebrae (juvenile has unfused neurals), middle vertebra shows crushing.

Summary

In fact the Natural History Museum have not been able to identify the ‘Quest Tooth’ from the photos Chris sent and when he is able, he will take it to the museum in person and hopefully obtain an identification for us; though initially thoughts are that it may be from Asteracanthus.

The Oxford Clay holds an abundance of marine fossils, though the more fragile are not preserved in their original three dimensional configuration. Only the Callovian Mid and Early beds are present at the Quest Pit, with the preceding Kellaways Beds being exposed in places at the base.

The bony fish Leptolepsis in Figure 3 was possibly a predecessor of the herring living in shoals. It was probably eaten by Cryptoclidus and Metriorhynchus. From a personal viewpoint, finding the shark tooth, Figure 6, from the Genus Hybodus, Family Hybodontidae, was significant, though common enough for the reasons given by Chris.

Figure 6 Tooth from the shark genus Hybodus

For those familiar with the BBC series ‘Walking with Dinosaurs’ Hybodus featured, unnamed, in the ‘Cruel Sea’ episode as a danger to the Opthalmosaurus pups, though itself prey to the Liopleurodon. This sometimes reached 150 tonnes, 25 metres in length, and with teeth twice the length of Tyrannosaurus in its 3 m long mouth. The BBC video vividly brings to life the concepts and some of the creatures reviewed by Chris, and if you don’t have this, it is well worth ordering from your local library. Hybodus grew to about 2.5 m with strange brow ridges, possible an ancestor of today’s bullhead sharks. The tooth shown was one of two types employed by Hybodus, and was for catching fish, small reptiles or squid, whilst a second crushing variety enabled shelly animals to be tackled.

I now read that research on the Liopleurodon skull shows that it had a stereo sense of smell by passing water through its mouth and up into the nostrils as it swam. Strange what you find out when trying to write an article.

The NIRA project, Chris mentions, aims to 'build the world’s largest freshwater aquarium (although the aquarium will also contain some brackish and marine habitats), four times bigger than the Eden project and include a rainforest dome'. Many thanks and a small gift were given to Chris for the considerable effort he put into organising the day, not least in liaising with the pit owners. I would also like to thank the members who turned out, for making the day so memorable and worthwhile.

Mike Friday