Answer:
A prehistoric reptile that lives today and the inspiration for the name of a popular sports drink.
Retired people want these to be large and birds want them to hatch.
Passed from father to son and shared between brothers, its importance is unquestioned though it is used more by others.
When it's dirty this should never be aired in public.
One am I, among six others: Largest, smallest, cold, dark and two brothers
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.