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ORDOVICIAN PERIOD

488-444 million years ago

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THE ENDOCRINE SYSTEM

Early gnathostomes evolved modifications of their endocrine system which are shared with their terrestrial descendants.


In gnathostomes, a number of changes affected the endocrine system. The GnRH gene was duplicated (Lovejoy, 1992) and POMC gene was translated to produce multiple signaling molecules (Alrubaian, 2003). A portal system developed between the hypothalamus and pituitary and the pars nervosa became defined (Hoar, Vol. 2, p. 186-7). Growth hormone's function was amplified to include both growth and diabetogenic effects (Hoar, Vol. 2). Gnathostomes evolved an ultimobranchial body (Hoar, Vol. 2;Shinohara-Ohtani, 1998), endocrine pancreatic islets located in compact exocrine tissue (Hoar, Vol. 2; Youson, 1999), adrenal glands composed of adrenocortico tissue (Hoar, Vol. 2), and androgen receptors (Thornton, 2001).