Figure 9.17 Morphology of some tintinnids in cross-section from limestones (x100-200).
group of extinct, cup-shaped, calcareous microfossils that were abundant in Late Jurassic and Early Cretaceous pelagic sediments, especially in the Tethyan realm. As an extinct group with no complex characters, no definitive evidence of their affinities has been found; however, they are strikingly similar in shape and size to an important group of ciliates, the tintinnids.
Tintinnids are part of the zooplankton, grazing on phytoplankton and providing a food source for larger members of the plankton. The cell is enclosed within a cup-shaped test or lorica, often 10 times larger than the cell itself. Modern tintinnids have an organic lorica with, in some cases agglutinated mineral grains or coccoliths, but without biomineral-ization, whereas the fossil calpionellids had a primary calcareous test (Fig. 9.17).
Two families of fossil tintinnid have been recorded, together ranging in age from the Tithonian (Upper Jurassic) to the Albian (Middle Cretaceous).
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