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.
Fossil Shark Teeth - What are shark teeth made of anyhow? Shark teeth are the most common type of fossil for a number of reasons. First, shark teeth, like most teeth, are made of dentin, a hard calcified tissue that does not easily decompose. Dentin is harder and denser than bone. In a tooth, the Dentin is surrounded by a very hard enamel shell.