Ostracodes (also spelled ostracods) are tiny, swimming, crustaceans (same family as the lobster, crab and shrimp) but with clam-like shells
formed by two-valves of calcite (CaCO3). They are planktic, swimming, or benthic, crawling on or in the mud on the bottom. Many are less than
1 mm long, but there are freshwater types up to 5 mm (about 1/4 inch) long and marine types up to 30 mm long. Ostracodes are found throughout
the world and include more than 50,000 species. Many ostracodes eat decaying organic matter. Some fish eat Ostracodes.As with all arthropods, ostracodes grow by molting. Most individuals will molt eight times before becoming an adult, leaving 8 sets of juvenile shells to collect in the sediment. The shells allow ostracodes to occur as fossils, since the shells tend to be preserved after the softer body tissues are lost. Ostracode fossils are easily identified to species, using shell characteristics. The shells are abundant in most marine and terrestrial environments. Their fossil record extends back to the Cambrian (about 600 million years ago). Ostracodes are transported by water, wind and by hitchhiking on insects and birds. Eggs and adults of some species are able to tolerate months of desiccation and freezing.
Ostracode fossils are used to interpret the age, depth, salinity and other parameters of sedimentary deposits. The shell shape helps identify the species of the fossil while the shell chemistry tells us about the environment that existed while the ostracode was alive. Different ostracode species prefer different habitats (such as underground springs, fast-running streams, lakes and wetlands). Each species has its own tolerances for chemicals in the environment (both naturally occurring chemicals and those introduced by humans), temperature and habitat stability. By finding out which species of ostracodes lived at a particular place in the past, we can tell what the past environment was like.
The chemistry of the ostracode shell also provides important environmental information about the past because the growing shell absorbs different weights (isotopes) of a chemical depending on temperature and salinity of the surrounding water.
The shells can also be analyzed by radiocarbon and amino acid racemization techniques to determine how much time has passed since the death of the ostracode. In this way, the ostracode provides an age for the mud around the shell. Check out the Ostracode Results.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://esp.cr.usgs.gov/info/lacs/ostracode.htm
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Page Last Modified: Wed 2-May-2001 10:08:19 MDT