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. Shark teeth are made of a solid substance called dentin. This material is slow to decompose, which is part of the reason why fossil shark teeth are so plentiful. When a shark loses a tooth, it ends up on the bottom of the ocean, where it's covered with protective layers of sediment.hark teeth are made of a solid substance called dentin. This material is slow to decompose, which is part of the reason why fossil shark teeth are so plentiful. When a shark loses a tooth, it ends up on the bottom of the ocean, where it's covered with protective layers of sediment.