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.
Glikmanius has a large central crown surrounded by a series of cusps on either side. The cusps are broken off on one side of this specimen. This fossil shark tooth is 1.2 cm across, and would be about 1.5 cm if complete. The Permian - The Near Extinction of Sharks This is a Permian Orthacanthus shark fossil from Germany on display at the Natural History Museum in Vienna.