Megafaunal Support Versus Adulteration

Nigel Larkin - Natural History Department, Norfolk Museums and Archaeology Service

• Discovery
• Excavation
• The Elephant
• Condition
• Preparation
• Storage
• Special Problems
• Storage Conditions
• Summary
• Suppliers of materials
• Reading on this subject

The Discovery

During the storms of 1990, some large bones of a "steppe mammoth", Mammuthus trogontherii, were found falling out of the cliffs at West Runton on the North Norfolk Coast. These bones were followed by more during the winter storms of 1992. By this point about ten percent of the skeleton had been carefully collected by volunteers and staff of Norfolk Museums and Archaeology Service (http://www.norfolk.gov.uk/tourism/museums/) and more bones could be seen pointing into the cliff. However, it was too dangerous to tunnel in to get them, overlain as they were by a few thousand tonnes of soft glacial sands and gravels.

The specimens were found poking out of the world-famous West Runton Feshwater Bed, a SSSI which is the type site for the Cromerian Interglacial, representing a river about 650-700,000 years old. Anything found there is important, and the opportunity to have an excavation to rescue the rest of the elephant skeleton from erosion by the sea represented a unique opportunity to look at the deposit holistically for the first time and re-evaluate its contents.

It took a while to find the money, but in 1995 the Heritage Lottery Fund agreed to finance most of the excavation costs. The ensuing palaeontological dig was undertaken to unprecedentedly high levels of detail and thoroughness - perhaps because it was a palaeontological excavation that was actually funded for a change.

Excavation

A Total Station Theodolite planned the hundreds of finds as National Grid Co-ordinates, and we had specialists from all over the country scrambling over themselves to be involved - studying the large mammals, the microfauna, macroflora, palynology, stratigraphy, sedimentology, clay mineralogy, sulphur geochemistry, veterinary pathology, taphonomy etc.

That's not to say it was easy - thousands of tonnes of overlying sediment had to be removed from the cliff-face above the site first, to make the deposit accessible.

Dozens of species were recovered - not just elephantine in nature. About four hundred bones were recovered, including those of various extinct deer, bovids, rhino, giant beaver, bear, big cats, and birds - plus 10 tonnes of sediment still to be sieved for all the microfaua. The most problematical aspect of the excavation, once the few thousand tonnes of overburden had been removed, was removing the large bones and skull. These had to be wrapped carefully in tissue and foil, then be wrapped with many layers of plaster of paris with scrim roll, and heavy-duty wire mesh, with splints of metal and wood added for good measure. Once these rigid supportive jackets had set, several people were needed, and occasionally cranes, to move them off site.

The Elephant

The elephant can have so many superlatives justifiably thrown at it. The skeleton finally ended up being, amazingly, 85% complete. That not only makes it the oldest relatively complete skeleton in the UK, but it is the most complete specimen of its species anywhere in the world, by far - the other two most complete skeletons of this species are about ten and fifteen percent complete, residing in Russia and Germany. Therefore this specimen is of great scientific importance.

However, importantly, it is also impressively big - possibly the largest elephant skeleton in the world. Mammuthus trogontherii is probably the biggest species of elephant to have lived, and this seems to have been quite a large adult male. It would have stood about four and a half metres high at the shoulder, much bigger than todays elephants, and would have weighed about ten tonnes - a modern African bull elephant would weigh only about five tonnes. It would have been much bigger than most dinosaurs.

The sheer size and weight of the limb bones, and their very nature, gave us our biggest problems. Also, the material had suffered all sorts of damage including scavenging by hyaenas, weathering by the elements and trampling by other elephants. And, as it lay in the ground for over half a million years, several major glacial periods sent glaciers a kilometre thick to bear down upon them.

Condition

The damaged nature of the specimens has been compounded by their age.

Over 700,000 years they have lost all their collagen and other organic material, reducing their strength and flexibility to the bare minimum - all we are left with is the brittle mineral matter of the bones.

We investigated the chemical nature of the bones (see the reading list below) and found that although pyrite minerals were present in small quantities, they were stable and there had been no secondary mineralisation of the bones over this time - they are truly sub-fossil. Had we left them another 50 million years to fossilise properly, our task would have been much easier!

So, we had quite a problem. We had some truly huge bone to prepare, store, and make available to researchers. But these bones were extremely heavy, and although they had perfect surface detail, they were riddled with cracks that penetrated through to their worryingly sizeable marrow cavities so they had very little internal strength.

The limb bones were like fragile hollow tubes, shattered throughout their length, just waiting to fall apart if you tried to lift them unsupported.

Although the limb bones presented us with a particular suite of challenges, all the specimens were quite fragile, and, given the scientific importance of the material needed to be handled very carefully. Throughout the project we chose the least invasive techniques, trying to preserve the integrity of the material as much as possible. All the specimens were cleaned with the method that would be gentlest in each case, moving on to more serious preparation tools as the matrix on the specimen required.

Preparation

For all the specimens we would start cleaning off the sediment with soft brushes (after removing the topside of the plaster jacket in the case of the limb bones, skull and tusk) and progressed to wooden tools for stubborn sediment, to compressed air, then the airbrasive machine using only sodium bicarbonate. The very last resort, for specimens with a lot of mineral matter adhering to the bones, would be an engraving tool, which was used to vibrate individual grains until they flicked off, rather than to gouge out chunks of matrix.

As we were preparing one of the largest and most complete elephantid skeletons in the world using a microscope for all mechanical preparation, we were fortunate to have got the project completed inside of 4 person-years.

The only chemicals used on the whole collection of over 400 specimens were the methacrylate co-polymer Paraloid B72 used with acetone. It was used as an adhesive, as a consolidant, and as a gap-filler. I decided to use just the one product, as it is the most tried and tested, stable, reliable and reversible adhesive there is. It is particularly useful for subfossil material, penetrating it well, and it bonds very well to itself. It is best to utilise just the one product, as otherwise you can create a cocktail of chemicals, and you cannot be sure of the long-term stability of the situation you are creating. For the gap-filler I mixed Paraloid B72, at 25 percent in acetone, with the inert airbrasive powder No.9 glass beads, as detailed in the article published in The Geological Curator in 2000 (see below).

However, we made sure that the consolidant and adhesive was always used extremely sparingly on the material. There have been leaps and bounds in the last few years in dating methods, DNA extraction, dietary analyses and other isotope studies of subfossil material. Heaven knows what they'll be able to tell us about our specimens in another 50 years time - if we don't adulterate them with an overdose of adhesives as soon as we get our hands on them, that is. New biomolecular and dating analyses are not only popping up all the time, but the age of the material that can be used is constantly being pushed back. DNA is currently thought to deteriorate over about 30-40,000 years. The WRE material is 650-700,000 years old, but it looked in such good condition that we took samples of it anyway for amplified DNA analyses at the Natural History Museum, just to push back the boundaries of failure - which we did with resounding success.

It would have been easy to have looked at the fragile nature of this material and decided that the only way forward was to consolidate everything that looked fragile - about ninety percent of what was before us. Instead, we decided that we would only use adhesives, consolidants and gap-fillers where strictly necessary, would support everything from underneath using archival quality products, and would store the material in a fashion that would reduce handling of the specimens to an absolute minimum.

Storage

After preparation and remedial conservation the smaller bones were stored in specially made boxes. Each bone lay on archival "Plastazote" (a chemically inert, low density, closed cell, cross-linked polyethylene foam) in a depression carved to its particular shape. Written on the foam were further details about the specimen and indications of where the bone was to be picked up. This foam and the bone would lay in a box made by hand to the appropriate size and shape, out of archival fluted polypropylene display board (also known as "Corex" - the sort of board estate agents now use for their signs. This method provided a soft bed for the bone to lie on, inside a firm box with a lid, all of archival materials. The bones were fully supported from underneath, and the specimens could be move and transported - and often studied - without being handled at all. Specimens of a similar nature are stored together in each box. For instance all the coprolites are laid out neatly in one box, and all the cervid and bovid material in another box, so everything can be found and studied easily. Larger boxes were attached to a simple wooden base to keep them rigid. Boxes for a single, large and fragile specimen had sides that were not connected at the vertical corners, and were hinged at the base so that when the lid was lifted off the sides dropped away to rest flat on the table and the specimen could be studied without removing it from its Plastazote nest. The hinges were made by attaching the sides of the box to the base with polypropylene cable ties.

All the specimens were labelled with "Permadry" archival ink on "Resistall" archival paper, glued on with PB72, in an orientation that was consistent - when replacing the specimens, you know that the label should be on the upper surface, the right way round, and this facilitates specimens being returned to the right place. Having the specimens embedded in specially carved nests in plastazote foam not only means that they are supported, and can be moved around quite safely without being actually handled, but there is often a large area of foam right next to the specimen that can be used for adding additional information with a permanent marker. It is useful to carve out fingerholes to show where it is safe for the specimen to be lifted by.

All these storage containers have been made with archival materials, except for the wooden bases of the larger containers. These bases are on the outside of the containers, reducing the chances of any contamination from acids in the wood. The archival products were chosen for their stability, longevity, and the fact that they are completely inert. However, we did undertake studies on a range of Tupperware type containers for the smaller material, and found some interesting results -cue the two most boring papers in the world, published in The Conservator in 1998 and 2000. Basically, I would recommend that any materials bought for storing your collections should be unwrapped and allowed to breathe for some time before use, especially if it is a container with a lid. We looked at tupperwares that had remained in packaging with their lids on for two years and found that they still had extremely high levels of chemicals inside them from their manufacturing processes - levels similar to brand new boxes straight from the factory. Old boxes that had been hanging around for a while with their lids off emitted hardly any chemicals.

Therefore if you are putting a specimen into a sealed container for simple storage purposes, or to stabilise the relative humidity of its environment, then make sure you use a container that has been breathing with the lid off for some months at least, or you risk adulterating the biochemical integrity of your specimen.

Large Elements

The large limb bones presented some of the biggest problems, considering how big, heavy, and fragile they were and because we didn't want to use a lot of glue and consolidant. The simplest response to storing these bones, once prepared and conserved, was to make a wooden base with batons on the underside so fingers can be slid underneath. Plastazote foam was secured to the board with screws and large washers, on which the bone rested on specially-shaped blocks of wood (treated with three layers of Dacrylate) on a plastazote foam layer.

Storage and handling

The larger, heavier, limb bones needed more heavy-duty treatment, with some different materials. They each needed purpose-made permanent rigid jackets to support them throughout their length. After the plaster field jacket was removed from the topside of the bone, plastazote sheets were cut into shape and fitted around the top half of the bone. This was held to itself temporarily with masking tape. Barrier foil (Moistop) was then sewn very carefully to the Plastazote with a polypropylene thread and a curved darning needle, taking great care not to touch the bone with the needle (the foil was sewn to the foam so that when the resin was applied to the foil, it would set on the thread, gripping it so that the foam was secured to the jacket and would not "ping" across the room when the jacket was removed). Jesmonite acrylic resin was then applied, with multi-axial glass woven glass fibre fabric, to create a strong, rigid jacket along the to[p of the length of the specimen. When the jacket was completed, it was strapped to the bone and the remains of the field jacket and the bone and the jackets were carefully tuned over through 180 degrees by two people. The remains of the field jacket were then removed, and the rest of the bone prepared and conserved and a jacket made in the same way for the other side, the jackets meeting for much of the length of the bone. Holes were drilled, and bolts with wing nuts used to fasten the jackets together.

They are stored without the top half of the jacket on, but when it comes to moving them or studying the other side, the jackets are bolted together first. When the underside needs to be studied, the jackets are bolted together, and two or three people can turn the bone gently over and remove the jacket that was underneath. In each case most of the bone, about 60-80%, is visible at any one time, and therefore the bone often does not have to be touched at all to be studied.

Therefore all the large limb bones now rest on cushioning Plastazote foam, underlain by barrier foil, on a rigid support made from acrylic-based Jesmonite resin. The bones are labelled, but the jackets themselves can have additional labelling on them, describing the bone, showing which way up it was in the field, and where it should be stored etc.

The acrylic resin used is much more stable and reliable that polyester and epoxy resins, and has far fewer health and safety problems associated with it. It is stronger, driers quicker, doesn't shrink and doesn't stink. It is a little heavier, though.

Special Problems

The huge skull, the tusk and the fragile scapula all needed variations on the same theme.

Scapula

The scapula was wrapped in a plaster jacket with a great deal of sediment, and was extremely fragile indeed. It is very rare to find an elephant scapula as complete as this because so much of their shape is so thin and delicate.

The plaster and sediment had to be removed carefully and repairs made to the horribly shattered bone. The scapula was delicate, thin and shattered, and yet so large and heavy that it could not be turned over to remove the jacket from below, or make a new one easily. So, as I removed small areas of the plaster jacket (mostly working upside-down), replacing it with individual small supporting structures of plastazote foam and barrier foil making a cushioning jacket, held in place with "polyrods". This is a very strong rod manufactured from polyester resin and was held in place with acrylic resin and woven glass fibre.

Many of these individual supports were then joined together, but in the end I managed to leave quite a proportion of the underside available for study, whilst leaving the whole specimen secure. This bone can never be lifted out of this support, as it would just crumple and fall apart. But it can easily be moved within the storage area on its purpose-built trolley with four polypropylene wheels.

This wasn't the only specimen to need a trolley - all the very heaviest bones rest on trolleys just above floor height. They would otherwise need more than two people to move them. Bones that can comfortably be moved by people are at waist height, so they can be lifted across to the study desk, bones more easily move are stored on the next shelf up, and bones that are the smallest, and less likely to be studied - all the hundreds of skull fragments for example - these are on the very top shelf.

Tusk

The tusk, which had been lifted from the excavation in a very sturdy plaster jacket, was treated in much the same way as the scapula. Because it had been trodden on and crushed by another elephant, it was in poor condition - but of course was preserving a great deal of taphonomic information. Before preparation started, the tusk was lifted and placed upon a thick wooden double-skinned base, with plastic ant-vibration doughnut feet. Such a double-thickness sandwich base is more resistant to flexing when being moved or transported, and a fork-lift can get in underneath. Some consolidation and gluing was necessary, and the cushioning jacket of foam and barrier foil with polyrod and acrylic resin supports were put in place piece by piece as the jacket was removed. Unlike the scapula, individual pieces of this jacket can be dropped away to give access to the underside.

Skull

The skull and right tusk, with its bomb-proof and rigid plaster, wire mesh, wood and polyeurethane foam field jacket now removed, now sits supported from beneath in a similar fashion. The whole skull rests upon a rigid ten-inch thick double skinned wooden base, on plastic anti-shock doughnut-shaped feet, ready for eventual transport to a display facility in the future. The base of the original supportive cage made in the field is bolted through this base with long coach bolts, and the whole skull rests upon steel supports, on top of which the subfossil material rests on Plastazote foam, on contoured supports of Jesmonite resin. Ultimately the whole skull can be displayed as if sitting on a pedestal of sediment, with none of the supporting structure visible.

Storage Conditions

Sub-fossil material, and in particular elephant teeth and tusks need permanently stable and comfortable environments. We are lucky in Norfolk in that over the last five years we have had two new "superstores" built, to store some of our collections in very stable conditions. These buildings are designed to be low-tech, passively controlled - and they are fantastic -they are the only stores that produce anything like a straight line on a thermohygrograph.

Thankfully, this is where we have managed to get the West Runton material stored.

All the cupboards and shelves are numbered, with locations marked on the shelves every six inches. Each spot has a unique and easy to understand code, so that every single specimen can be located exactly using an index where you can search by common name, species name, or by accession number - and to keep it simple the accession number includes the unique number it was given in the field. This is all to reduce the handling of the material - no rummaging is necessary. We also store copies of all the fieldwork notes and plans in the store itself, to assist with studies.

Summary

So, in summary, we had a lot of very important, often quite large, very heavy, very fragile bones to prepare, conserve and curate. We decided not to drown them in a cocktail of glues and consolidants to make them more robust and handleable. We decided to keep the material as unadulterated as possible, to support them from underneath at all times, and to reduce their vulnerability by reducing the amount they needed to be directly handled.

All the specimens are all kept in archival storage media in a fashion that means the media is picked up, not the specimen itself, and many of the specimens can be studied without being handled at all. The storage area is designed to be relatively ergonomic, to facilitate the locating of specimens and to reduce handling of containers and specimens themselves.

Suppliers of materials:

Acetone: BDH Ltd, Broom Road, Poole, BH12 4NN, United Kingdom. Tel 01202 669700. Suppliers of industrial chemicals.
Airbrasive powders including glass beads: Production Equipment Sales Ltd, Unit 2/7 Horstead Square, Belbrook Industrial Estate, Uckfield, East Sussex. TN22 1QL. Tel 01825 766644.
Correx: Tony Britain Packaging, Tel: 01482 227400
Jesmonite Acrylic Resin: Canonbury Artshop, 266, Upper Street, Islington, London, NR1 2UG. Tel 0207 72264652.
Paraloid B72 (tubes of ready made adhesive, or raw granules): Conservation Resources (UK) Ltd, Unit 1 Pony Road, Horspath Industrial Estate, Cowley, Oxfordshire. OX4 2RD. Tel 01865 747755. Suppliers of conservation materials.
Plastazote: Polyformes Ltd, Cherry Court Way, Stanbridge Road, Leighton Buzzard, Bedfordshire, LU7 6UH.

Reading on this subject

Ashwin T and Stuart A., 1996; The West Runton Elephant. Current Archaeology 149, 164-168.
Larkin, N., Makridou, E. and Comerford, G., 1998; Plastic containers: a comparison. The Conservator, 22.
Larkin, N. and Makridou, E., 1999; Comparing gap-fillers used in conserving sub-fossil material. The Geological Curator 7 (2), 81-90.
Larkin, N., Alexander, J., and Lewis, M., 2000; Using experimental studies of recent faecal material to examine hyaena coprolites from the West Runton Freshwater Bed, Norfolk, England. Journal of Archaeological Science 27, 19-31.
Larkin, N., Makridou, E. and Blades, N., 2000; Analysis of volatile organic compounds in plastic containers used for museum storage. The Conservator, 24.
Stuart, A.J., 1991; An elephant skeleton from the West Runton Freshwater Bed (Early Middle Pleistocene:Cromerian Temperate Stage) Bulletin of the Geological Society of Norfolk 41, 75-90.
Turner -Walker, Gordon., 1998; The West Runton Fossil Elephant: a pre-conservation evaluation of its condition, chemistry and burial environment. The Conservator, 22.
"The West Runton Elephant Discovery and Excavation", Norfolk Museums Service booklet, 1997.