In ancient times, what god beast represented longevity?

turtle

Xuanwu is a spiritual thing composed of turtles and snakes. Xuanwu originally meant Xuanming, and the ancient sounds of Wu and Ming are interlinked. Xuan means black; Ghost means yin. At first, Xuan Ming described the tortoise divination as follows: the tortoise's back is black, and the tortoise divination is to let the tortoise go to the underworld to ask his ancestors, bring back the answers and show them to the world in the form of divination. Therefore, the earliest Xuanwu is the tortoise. Later, the meaning of Xuanming expanded:

Turtles live in rivers, lakes and seas (including turtles), so Xuan Ming became a water god;

The tortoise lives long, and Xuan Ming has become a symbol of immortality;

The first underworld was in the north, and Oracle Bone Inscriptions's divination in the Shang Dynasty meant "divination must go north", so Xuan Ming became a northern god again.