Fossil beetles of Bognor Regis, West Sussex

David Bone (UK)

Bognor Regis in West Sussex was wheret I spent my teenage years (a long time ago) and it is still a locality that I regularly visit and to where I also lead fossil hunting expeditions. Having said that, like many foreshore localities with no eroding cliffs, there are times when beach sand hides the underlying geology and a casual visitor can be very disappointed.

Alistair describes the London Clay around the sandstone ‘Bognor Rocks’ and their many fossil molluscs, but he also briefly mentions that fossil beetles have been found at this locality. Bognor is one of very few places in Britain where Eocene fossil insects can be found and I have the privilege of being one of only a handful of people that have found them here. I believe that none have been found for at least 30 years due to lack of suitable foreshore exposures or, possibly, sufficiently dedicated collectors.

My collections were mainly created in the 1970s and ‘80s, when ideal conditions periodically exposed large tracts of London Clay in the right area of foreshore known as the ‘Beetle Bed’, which is a narrow strip of clay just to the west of the Bognor Rocks (Fig. 1). Here, the London Clay (Division B) is a grey-brown, sticky clay, with occasional claystone nodules known as septaria.

The London Clay is a fully marine deposit around 55Ma old, with molluscs, crabs and sharks’ teeth being common at this level, as well as rarer examples of nautilus (Fig. 2), turtle and crocodile.

However, this part of the sequence is also full of plant debris, including abundant twigs, seeds (over 120 species) and small Nipa palm fruits. This suggests periods of significant input of terrestrial material into the marine environment, probably by large rivers. Most of the fossil flora and fauna are pyritised and wash out of the eroding London Clay to collect as surface concentrations in hollows in the clay or against rocks on the foreshore (Fig. 3). This is very similar to the better known London Clay site on the Isle of Sheppey in Kent. In fact, rare insects have also been found at Sheppey as well as Herne Bay.

The ‘Beetle Bed’ was first recognised by EM (Martin) Venables in 1936, when specimens were discovered in pyrite residues that he was collecting and searching in for small sharks’ teeth. He was a local fossil collector, so had the advantage of living close to the beach and being one of very few people locally interested in the London Clay. Over 400 pyritised beetles were found, all by using the same technique:

• Locate a suitable drift of fine-grained pyrite, freshly eroded from the London Clay and not too weathered or abraded.
• Place the pyrite by hand or using a trowel into a sieve (a domestic kitchen flour sieve works well) and wash in the sea or a convenient pool.
• Discard pieces of clay, large lumps of pyrite, seaweed and the ubiquitous small live crabs.
• Take the pyrite home and wash again in clean water, further discarding unwanted material.
• Spread the pyrite out on a tray to dry. A warm location will aid the drying process.
• Search the pyrite by eye, if you have good eye-sight, or with the aid of a magnifying glass.

Theoretically, it should be possible to process samples of London Clay for beetles, but Venables calculated that huge volumes of clay would be required, so letting the tide erode and concentrate the pyrite debris is a far more efficient and practical way of collecting. I used to process several tens of kilos of pyrite at any one time. With luck, the pyrite residues not only included small molluscs, sharks’ teeth and seeds, but also the occasional fossil insect.

The beetles are small, ranging between 0.5 and 6.2mm in length. Only about 10% of specimens are more or less complete, with head and thorax preserved, but the legs are often missing, although these may be pyrite-cemented to the underside of the body. Details of the elytra (wing cases) can be wonderfully preserved. Unfortunately, they are very difficult to photograph without the proper equipment, so I have used a drawing by Venables to illustrate a typical fossil beetle (Figs. 4 and 5). The fauna is almost exclusively of Coleoptera (beetles) of several families, genera and many species, with curculionids (weevils) greatly predominating. Three examples of Hemiptera (true bugs) have also been found. The fauna is mainly of species with a wood-feeding habit and this suggests a climate that was Mediterranean or subtropical, which is generally consistent with the paratropical rainforest environment envisaged for the London Clay flora.

It does require a lot of effort to collect these delicate little creatures and, so far, only five people are known to have been successful at Bognor and nobody since the mid 1990s due to the lack of foreshore exposures in the right areas. However, the Beetle Bed still lies beneath the cover of beach sand and, one day perhaps, new exposures will reveal fossil treasures for a new generation of collectors.

References

Britton, E. B. 1960. Beetles from the London Clay (Eocene) of Bognor Regis, Sussex. Bulletin of the British Museum (Natural History) Geology, 4: 27-50.

Jarzembowski, E. A. 1992. Fossil insects from the London Clay (Early Eocene) of southern England. Tertiary Research, 13: 87-94.

Venables, E. M. 1962. The London Clay of Bognor Regis. Proceedings of the Geologists’ Association, 73: 245-71.

Venables, E. M. & Taylor, H. E. 1962. An insect fauna of the London Clay. Proceedings of the Geologists’ Association, 73: 273-9.