(6) The plesiosaurs were considered to be apex predators. This means that there were the top position predators in the ocean in their time. They didn’t have to fear from other predators.
(7) Though they were not good swimmers they had four flippers which allowed them to glide in the water. No modern animal has four flippers.
(8) Though there are disputed opinions the Plesiosaurs are supposed to come to the shore to lay their eggs. They covered the eggs with sand to protect them from the predators. This ensured that their species lived on.
(9) The stones in the stomach are also considered to act as ballast. The Plesiosaurs had to float to the surface for breathing air as they can’t absorb oxygen from the water like fish. The stones must have helped them to go down or come back when they wanted.
(10) They were found in oceans around the world. This means that they were adapted to live in any temperature. This must have made them one of the marine reptiles that had the maximum population. This is what the availability of so many fossils also tell us.