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Desiccation occurs when an animal dies in a very dry environment. Water is drawn out of the tissues slowing the process of decay. The drying process may also reduce the probability of scavenging. This process is similar to human mummification. In fact, some authors use the term mummification to describe this process. Ground sloths preserved through desiccation have been found in South America (Garcia & Miller, 1998, p. 15). Moa remains preserved through desiccation have been found in New Zealand (Walker & Ward, 2002, p. 13). Many of these specimens have been found in dry caves. Naturally mummified insects have been found in association with Pleistocene mammals frozen in tundra permafrost. Insects preserved through desiccation have also been found in Egyptian mummies and the stomachs of Eocene aged bats (Martinez-Delclos & Jarzembowski, 2000). When is a preserved remain considered a fossil? Walker and Ward (2002) do not consider organisms preserved through desiccation to be fossils because they are only temporarily spared from decay (p. 13). Grimaldi and Engel (2005) point out that many include the idea that the remains must be of a species that has become naturally extinct. They argue that having this knowledge is problematic. Grimaldi and Engel suggest the following practical definition, "...a fossil is the remains or workings of any species, living or extinct, that have been naturally preserved for several thousand years or more (p. 62). Many definitions have time limits, which are set somewhat arbitrarily. This definition is similar to the one we have adopted for our website. Under this definition desiccation may be considered a fossilization process. Interestingly, there is evidence that insects in amber are preserved through dessication. Insects preserved in amber appear to be hollow. Presumably, bacteria present when the organism died decayed the internal organs. However, studies have revealed that some specimens possess mummified internal organs. Studies using scanning electron microscopes as well as transmission electron microscopes have revealed internal organ preservation in Baltic amber spiders and gnats. It seems that many orangisms are preserved through mummification. In the process of mummification, dehydration results in up to a 30% decrease in volume of tissues. The decrease in tissue volume gives the organisms the appearance of an empty husk (Selden & Nudds, 2004, p. 134).
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Bibliography |
Garcia, F.A. & Miller, D.S. (1998). Discovering Fossils: How to Find and Identify Remains of the Prehistoric Past. Pennsylvania: Stackpole Books. Grimaldi, D. & Engel, M.S., (2005). Evolution of the Insects. New York: Cambridge University Press. Martinez-Delclos, X., & Jarzembowski, E. (2000). Fossil insects in rocks. Meganeura Website. http://www.ub.edu/dpep/meganeura/52inrocks.htm Selden
P. & Nudds, J. (2004). Evolution of Fossil Ecosystems.
Chicago: The University of Chicago Press. |