Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland.In contrast to excretion, the substance may have a certain function, rather than being a waste product.ecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland.
The oldest shark fossils. The oldest fossilized evidence of prehistoric sharks comes from shark-like scales that date to 455 million years ago during the Ordovician Period, in Colorado. Some paleontologists do not agree that these scales are sufficiently shark-like to pronounce them sharks.
The skin of a shark is made of tiny denticles, which are made of the same enamel that teeth have, meaning they too can fossilize. Some more primitive sharks have spines in their fins that will fossilize. Finally, shark feces, or coprolites, are sometimes found preserved.