The observation that calcitonin (CT) at supraphysiological doses is hypocalcemic, led to the mistaken conclusion that it was important for calcium homeostasis and this idea has persisted to this day.  Despite these findings there is no readily apparent pathology due to CT excess or deficiency and there is no evidence that circulating CT  is of substantial benefit to any mammal. ���.. .   
Mammalian CT at physiological doses is not essential and very likely the CT gene has survived because of the gene�s alternate mRNA pathway to produce calcitonin-gene-related peptide found in neural tissues.