The origins of Capricorn mythology are practically unknown. The ancient Greeks had sea-goats, but there was little told about them.
The Capricorn zodiac sign is often interpreted as being either a goat or a sea-goat, which is basically a creature with the front half of a goat and the tail of a fish. In actuality, both goat and sea-goat are appropriate symbols to represent Capricorn mythology.
The story behind the Capricorn zodiac sign begins with the sea-goat Pricus. Pricus is the father of the race of sea-goats, who are known to be intelligent and honorable creatures who live in the sea near the shore. They can speak and think and are favored by the gods.
Pricus is tied to Chronos (Greek mythology), the god of time. Chronos is the creator of the immortal Pricus, who shares Chronos's ability to manipulate time.
The legend that ties Pricus to Capricorn mythology begins when the younger sea-goats, Pricus's children, find their way onto the shore. The sea-goats seem to be naturally drawn to the shore. They can use their front goat legs to pull themselves onto the beach and lay in the sun. The longer they stay on shore, though, the more they "evolve" from sea-goats into regular goats. Their fish tails become hind legs and they lose their ability to think and speak, essentially becoming the goats that we know today.
This upsets Pricus a great deal. As the father of the sea-goat race, he is determined to make sure that his children never get to the shore. If they do, he fears they will become mindless animals who can never return to sea.
After losing several of his children to the land, Pricus decides to use his ability to reverse time to force his children to return to the sea. During this time reversal, everything on earth, except Pricus, reverses itself to where it was previously, thus the goats revert back to the time to before they returned to land.
Pricus, being unaffected by the time shift, is the only one who knows what is to become of the sea-goats. He tries to warn them, even forbid them from setting foot onto the shore, but no matter what he does, or how many times he reverses time, the sea-goats eventually still find their way onto land and become regular goats.
The pivotal moment in Capricorn mythology occurs when Pricus finally realizes that he cannot control the destiny of his children, and that trying to keep them in the sea will never work, no matter how many times to tries to "start over". He resigns himself to his loneliness, and chooses to no longer reverse time, instead letting his children live their lives out to their own destiny.
In his misery, Pricus begs Chronos to let him die, as he cannot bear to be the only sea-goat left. Chronos instead allows him to live out his immortality in the sky, as the constellation Capricorn. Now he can see his children even on the highest mountain tops from the stars.