Further Information about

Trilobite Specimen "Flexicalymene with Bryozoan"

As this trilobite grew, it is theorized that eventually it reached a point after which it did not grow or molt anymore. This stage of growth is called the "terminal-molt stage." This condition is known from modern arthropods such as Limulus (horse shoe crab). It is suggested for fossil arthropods such as trilobites. The evidence for terminal-molt stage in trilobites is supported by the presence of epifauna on large individuals.

Very rarely a large individual of a trilobite population is found with bryozoans encrusting the shell. This is attributed to the trilobite having reached the terminal-molt stage, so that it no longer molted, which allowed the bryozoan colony which had begun to grow on the shell to continue to enlarge without being cast off when the trilobite molted. It is also be possible that the trilobite may have ultimately died because the encrustation prevented molting or other necessary life functions of the individual. This situation could have arisen if the interval between molts became so long in an old trilobite that an encrustation of bryozoans over the sutures prevented successful molting.

Encrusted trilobites are always large individuals in a given population, and for this reason are thought to be geriatric. Danita Brandt's May 1996 paper in the Journal of Paleontology considers many of the aspects of this fascinating subject. She examined over 2000 Flexicalymene and found only six individuals with bryozoan encrustation. Most of the specimens have small patches of bryozoa, and none displays the striking "antlered" appearance of this individual.

In addition to the encrusted Flexicalymene, there are a great many of the tiny Cincinnatian brachiopod Zygospira modesta on this one-of-a-kind piece.

Go to Flexicalymene Retorsa Specimen Photos

Go to Main Trilobite Page


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