The fish Leedsichthys problematicus is the largest fish known to have ever inhabited Earth's oceans. It lived during the Middle Jurassic, at a time that gigantic dinosaurs inhabited the land - so perhaps it is not surprising that there were also giants in the sea. In contrast to the marine reptiles and sharks more popularly known from the seas at this time, this fish appears to have been a planktivorous filter-feeding animal, growing to great sizes. Some estimates, based on isolated skeletal components, have suggested that this fish might have grown well over 20 metres in length, but conservative figures of over 15 seem much safer.
One of the reasons for the uncertainty surrounding the size - and, indeed, the appearance - of this fish, is that its bones are exceptionally thin, and are crushed by the weight of clay over millions of years. This means that some specimens are in over a thousand pieces before attempts are made to try to glue them together into whole bones. This means that the bones are hard to identify. Another problem is that many of the fish from this family (Pachycormidae) had only limited calcification of their skeleton - so many parts (for example, the backbone) simply do not preserve in the Jurassic Oxford Clay. A fish without a backbone is a series of small clusters of bones - from which it is very hard to tell how large it might have been in life. Only limited partial skeletons have ever been collected of this animal.
In July 2001, I received a bone in the mail which I identified as being part of a dorsal fin of Leedsichthys. Visiting the site 3 months later, it was apparent that there were over a dozen bones belonging to this fish emerging from the same clay level of a cliff in a Peterborough brick pit. The bones protruded over a length of more than 8.5 metres. This was extremely likely to be one individual animal, possibly still articulated, spread over a bed of clay - an opportunity for excavation that simply could not be missed, as the last substantial partial skeleton of this fish was found in 1913. A 20 metre cliff was removed during the last week of June the following year (2002), and diggers began to work with dental tools, paring away the cliff from the fragile bone fragments that saturated the now revealed bed of clay. The expected dig-time of 2 weeks proved to be ludicrously optimistic - the dig ran for a solid 10 weeks, and some more work was done (primarily for the benefit of the cameras, it has to be said) over a weekend in November. By the end of that time, over 2,100 bones had been recovered (in the course of 3,119 staff hours), and their positions thoroughly recorded on plastic mapping sheets - with one or two exceptions: one extremely experienced digger, all too eager to perform for the cameras, excavated and lifted a huge skull bone, neglecting to map it first - then could not remember where it had come from!
But aside from this exception, the diggers performed the all-too difficult task of extracting the delicate bone fragments from the clay and numbering them against recorded locations with aplomb, acquitting themselves well in a dig that was uniquely difficult through the exceptional fragility and large size of the fossil remains.
The fish gained the nickname 'Ariston' (because the quantity of bone simply went on...and on...), and the resulting television programme (which does not feature the rash removal of the skull bone!) was broadcast on Monday 8th September, 2003 at 8.30pm on Channel 4 as part of the RDF series 'The Big Monster Dig'. Since that programme was made a team has returned to clear the bed over two weeks in August this year (2003), and it is planned to excavate more of the bed next summer. So far, the dig has yielded many paired bones (left and right equivalents), something never before recorded for the fish, many bones recorded in isolated specimens, and some completely new bone morphologies.
Palaeontological digs rely heavily on the enthusiasm and effort of volunteers, but this excavation was extremely fortunate in being financially supported by a number of bodies - without whom, the dig simply could not have happened. NERC's emergency funding route, and the Aggregates Levy Sustainability Fund are particular contributors, but the major funder, helping both field seasons in particular to cover the costs of hiring excavating machinery from R & R Plant Hire, was the Palaeontological Association . The Royal Society generously gave a COPUS grant to support the display of some of the new material at the Hunterian Museum, and Peterborough Museum. Logistical support in the 2003 field season was given by the National Museums of Scotland. Other contributors were English Nature , the Stamford Geological Society, the East Midlands Geological Society, and the Friends of Peterborough Museum. Help in kind was in particular provided by the Hunterian Museum (University of Glasgow) and also by the University of Portsmouth - but the most significant contributor in this respect was all the diggers, who gave their time for no remuneration whatsoever - making a total of over 3,000 working hours in the pit over both field seasons.
Jeff Liston - Dig Leader
Email : [email protected]