| Themes > Science > Paleontology / Paleozoology > Paleozoology > Fossil Invertebrates > Extraction Techniques |
In the field, fossil insects may be observed on bedding planes in peat or within fine silts which have thin detrital organic horizons. If insects are observed they are sometimes worth isolating because associated fragments may be together on the stratum. Generally, splitting of organic debris is not conducted because it is time consuming, and because the insects observed often are the largest and most brightly coloured, thus introducing a sampling bias. Rather, bulk samples (approximately 5-10 kg per 5 cm interval) are collected for laboratory treatment. The standard technique for extracting fossil insect fragments has been described many times; - first by Coope (1968b), and by many others in the intervening years, including. The technique illustrated in the flow chart is from Morgan (1988a). The basic procedure involves placing the field sample in a polyethylene bowl and washing the organic debris through a 300 micron (No. 50 or 52) mesh sieve. The fine silt and clay fraction passes through, while organic material is retained. Organic debris trapped on the sieve is placed in a clean polyethylene bowl. Kerosene is added and kneaded into the sample, the excess decanted, and cold water added. The insect fragments tend to rise to the surface on the water/kerosene interface. Variants on this theme can be used; for example, using other flotants to supplement the kerosene process such as a calcium chloride solution, or heptane. After the kerosene (or alternate) separation the flotant is carefully decanted into a clean sieve, washed thoroughly with detergent, and rinsed in clean water until free of detergent. The sample is dehydrated in alcohol and sorted in alcohol under the binocular microscope at 8-10 X magnification. Insect fragments (and other associated fossils) can be picked out with fine forceps and stored in alcohol until they are mounted. A second sorting is needed to isolate fragments which belong to the 100 plus families of Coleoptera. Following this second sorting, heads, thoraces and elytra are mounted on standard (white background) micro-paleontological slides with water-soluble gum tragacanth. Semi-transparent specimens (thin elytra or thoraces, caddis and dipteran remains, together with other arthropod fragments) can be mounted in polyvinyl lactophenol mounting medium on glass microscope slides with a cover slip. |
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