Shell size

From Foraminifera

Foraminifera range in size from a few tens of micrometers to 20-30 centimeters. They are mostly microscopic, usually ranging from 0.1 to 1.0 mm. The small size of most foraminifera make them much more useful for biostratigraphic or paleo/environmental applications, petroleum exploration etc. than larger fossils because there can be thousands of specimens in a small sediment sample.

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Smithsonian photographs presenting dramatic shell (test) size differences before and after the end-Cretaceous event.