30 million years ago, manatees swam in the Mainz Basin. They were relatives of today's dugong. In addition to the dugong, there are three species of manatees (manatis) still in existence today. Today's manatees inhabit the coastal regions of tropical seas or live in rivers.

From land back into the water
Manatees are aquatic mammals that evolved from land animals. The ancestors of all manatees were large herbivores that trudged through primeval swamps on four legs. They gave rise to manatees and their closest relatives, elephants. Manatees are perfectly adapted to life in the water: their front legs have been transformed into pectoral fins, their hind legs have been reduced, and a horizontally aligned tail fin has formed at the end of their spine, which they use to propel themselves up and down. Fish, on the other hand, have a vertically aligned tail fin and move by wriggling. The bones of manatees, especially the ribs, are extremely massive. The high bone weight compensates for the buoyancy created by the lungs filled with air and thus functions like a lead belt. This makes it easier for the animals to graze at the bottom of the water.

A rich variety of marine life flourished in the tropical sea of the Upper Rhine Graben and the extensive bay of the Mainz Basin with its offshore islands. Finds of corals, sea urchins, and other marine animals prove that a marine habitat existed at that time. A total of around 500 species are known today, which mainly inhabited the oxygen-rich and sun-drenched coastal areas. In the deposits near the rocky coastline covered with oysters, barnacles, and corals, there are numerous species of snails and mussels that populated the coastal floor. Thick-shelled sea almonds are particularly common.
There are also large quantities of shark teeth, chewing plates and spines from various rays, and even gill rakers from plankton-eating basking sharks. Numerous complete fish skeletons have been found at other sites, including mackerel, bream, tuna, and stingrays. A total of over 100 fish species have been identified so far.