Quaternary Sciences Institute: extraction of fossil insect remains from peat

Thursday, November 23, 1989

A.V. Morgan

Introduction

Fossil insect remains have been noticed in a number of different types of deposits for 150 years. At first these specimens were attributed to animals which had been trapped in the biblical flood. By the mid 1800’s Charles Lyell, person who had a great influence on the life of Charles Darwin, commented on fossil beetle remains in peats in eastern England and related them to species alive today. In the late 1800’s fossil beetle elytra were found in peat deposits in the Scarborough Bluffs, and also in the Don Valley brick year. These specimens were collected by a Canadian geologist, names Coleman, and sent to Samuel Scudder in the United States. Scudder obviously had a great deal of difficulty in matching the specimens with present day living forms. Because of the zoological ideas of the day, which dictated that the ice ages caused wide-spread extinctions and speciation, he described nearly all the specimens as being extinct forms. The names he gave were quite amusing, specimens, such as Lathrobium frustum, Phloeosinus squalidens, Bembidian damnosum and Coelambus infernalis seem to indicate his degree of frustration at preservation and the problems of identification.

Over a quarter of a century passed before a group of Scandinavian entomologists next attempted to classify the fossil remains. In the early 1930’s fossil specimens found in Iceland, Denmark and Sweden were identified to the species level. Little else was done and this work also disappeared into obscurity. The third attempt was by a group at the University of Birmingham in England in the mid 1950’s. Had G.R. Coope and F.W. Shotton been entomologists they may have quailed at the thought of the taxonomic problems which faced them, but being geologists they moved ahead, and, with the assistance of P.J. Osborne began identifying a large number of fossil specimens from the English Midlands. This resulted in the establishment of a school of students of paleoentomology which has been successful in unravelling many of the rapid climatic changes which have taken place in the British Isles over the last 130,000 years. In the early 1970’s a number of investigations were started in North America, one of these research groups is located at the University of Waterloo.

Introduction to the Technique

Paleoentomology studies are based on several premises. The first is that although beetle fragments become disarticulated after the death of the insect, they remain relatively intact and can be identified. The fragments which are used are composed of chitin, a relatively resistant material which suffers little from chemical attack. The chitinous exoskeleton of the beetle is very similar to the outer layers of a pollen grain. The fragments which are most easily identifiable are the elytra (the non-flying wings) the thorax, and the head. Frequently all three are needed for species identification. Quite often one finds detailed microsculpture, readily seen under a high powered binocular microscope, which enable some to match the elytra with a thorax. University groups frequently have the good fortune of being able to use the scanning electron microscope which reveals even more detail. For example the scales on fossil weevils, 10 thousand years or more old, are quite comparable with the scales of the living form of the same species.

The second factor which initially had to be assumed, but has now been shown to be true, is that fossil Coleoptra appear to have undergone little speciation. That is, there appears to be very little evolution of this insect group in at least the last one or two million years. A third assumption is that the ecological requirements of the species have not changed; that the ecology of the species is the same now as it was in the past.

What are the advantages and disadvantages of using fossil beetles? We believe that fossil beetles provide a far more accurate tool for assessing climatic change. In detailed studies in Britain it has been shown that beetles appear to respond much more rapidly to climatic change than, for example, do plants. In a way this appears to be logical. It seems fairly obvious that if a climatic amelioration occurs then the beetles (which are very mobile) can respond much more rapidly than the plants. Beetles also appear to respond to a greater degree than the plant communities and an interpretation made from fossil insect assemblages can differ from that made based entirely upon the pollen at a certain site. It is for these reasons that there is a great deal of interest by Pleistocene geologists in trying to analyse coleopterous faunas.

There are, however, tremendous difficulties. In North America one is faced with a lack of good collections. In Europe there has been a long history of Victorian collectors who amassed large and well curated collections. There was no similar movement in Canada. The large modern collections at the National Museum in Ottawa, or at the Smithsonian Institute in the United States are geographically remote from the research centres where the fossil beetles are being studied. When one examines these modern collections one will find that there are tremendous gaps in the collecting localities for any of the species which are examined. For example, it is very important to be able to describe accurately the full geographical range of a modern species. However, in practice, it is exceptionally difficult to do so, since collecting records may only be from, for example Churchill, Manitoba; Hebron, Labrador; and Inuvik, Northwest Territories. Obviously these sites have something in common but it is difficult to say just what. Yet another factor is the tremendous diversity present in the North American fauna. There are over 4,000 described species of Coleoptera from Western Europe, and there are probably 10 times that number in North America. Finally, ecological information which is so important in reconstructing the type of environment which existed in the past, is often missing. For these reasons the research group at Waterloo has collected on an annual basis in the Canadian Arctic and sub-arctic for the last eighteen years. With the addition of donated specimens we now have an excellent comparative collection with good ecological records to use in paleoclimate reconstruction.

Methods

Almost any type of non-glacial deposit which contains plant fragments will contain beetles. Beetles can therefore be found in deposits ranging from clay through silt to peat. They are not generally found in sandy deposits. This is due to the fact that the chitin tends to become oxidized and cracks up under sandy conditions. Probably the best material for the preservation of Coleoptera fragments is an organic silt. However, for ease of collection, and for relatively lucrative results one could examine peat deposits.

A sample is collected in the field either from a hand-dug pit, or from large diameter augers if the site is too wet. Be very careful about safety in both these operations! Conditions of lithology and depth of burial are noted. The stratigraphy of the site is documented by photographs and by sketches and the sample is returned to the laboratory. The sample is then washed from the bowl through a 300 micron (No. 50) mesh sieve. The clay and silt fragments wash through the sieve and go down the drain. (Some caution should be observed since if substantial quantities of material are washed the drains can clog). The organic debris is trapped upon the surface of the sieve. This washing process is carried on for several times until one is left with a sieve full or organic debris, and a bowl which may contain any coarse residue which is present. One should ensure that the organic debris is thoroughly washed in water so that any clay or silt adhering to the plant or animal fragments has been effectively dislodged. One method of doing this is to place the sieve full of organic debris in an empty polythene bowl and gradually flood the bowl while moving the sieve up and down in the water. This should remove any loose clay or silt particles from the organic fraction. The coarse residue should be decanted and kept; it may contain mollusc shells, teeth or bones, which can aid in the interpretation of the ecology of the site. The organic debris which is now in the sieve is decanted once again into an empty polythene bowl. The sample is thoroughly soaked in kerosene, and the kerosene is worked into the organic debris by a kneading process with your hands. Once you are satisfied that the kerosene thoroughly impregnates the sample, the excess kerosene should be decanted. Be careful that organic residue in the kerosene does not go back into your kerosene container. Cold water is added to the mass of organic material. You will find that by jetting water into the sample the organic material will be thoroughly mixed and will swirl through the bowl. After you have allowed this to settle you will find that there is a kerosene film which will coat the water surface. It is most important to use cold water at this stage. By looking closely at the surface film you may be able to discern small shiny black, or coloured, fragments. Some of these fragments will be seed cases but many of them will be fragments of Coleoptera, or other types of insect. Allow the bowl to sit quietly for about 10-15 minutes. This enables material in suspension in the water to gradually fall out. The chitinous exoskeletal fragments of the insects adhere to the surface film. One should then carefully decant the surface film only back through the clean 300 micron sieve. The bulk of the residue should be kept in the bowl. You should make sure that there is at least 3-4 inches of water between the surface film and the main mass of organic debris below. This will enable you to effectively separate the surface film without having lots of organic debris spilling over from the lower level of the bowl. You now have in your sieve the contents of the surface film consisting largely of insect, seed and plant fragments. Carefully wash the residue to one side of the sieve; a flexible hose on water tap will assist you in this, and then add detergent. Thoroughly wash the specimens in detergent and water. This will effectively remove the kerosene. Next, dehydrate the sample in pure alcohol which will remove the detergent and water. You should now carefully wash the insect and plant residue from the sieve into a clean beaker using alcohol and sort, in alcohol, under a binocular microscope. You will be able to separate out seed fragment, insect remains and plant debris and possible other invertebrate groups which may be present. It is very difficult to describe what one should be looking for and I would suggest that you contact somebody who is familiar with insect fragments in order to determine which is plant and which is animal. I would be interested in discussing this technique further with anyone who has specimens that need identification. (Dr. A.V. Morgan, Earth Sciences Department, University of Waterloo, Waterloo, Ontario N2L 3G1). The specimens can be mounted, using gum tragacanth on a clean white card or on a microscope slide. Once they are mounted they can be shipped or stored as required.

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