linguistic:translation, quality:corruption
Diving

Few data are available that show exactly how deep plesiosaurs dived. That they dived to some considerable depth is proven by traces of decompression sickness. The heads of the humeri and femora with many fossils show necrosis of the bone tissue, caused by a too rapid ascent after deep diving. However, this does not allow to deduce some exact depth as the damage could have been caused by a few very deep dives, or alternatively by a great number of relatively shallow descents. The vertebrae show no such damage: they were probably protected by a superior blood supply, made possible by the arteries entering the bone through the two foramina subcentralia, large openings in their undersides.

Descending would have been helped by a negative Archimedes Force, i.e. being denser than water. Of course, this would have had the disadvantage of hampering coming up again. Young plesiosaurs show pachyostosis, an extreme density of the bone tissue, which might have increased relative weight. Adult individuals have more spongy bone. Gastroliths have been suggested as a method to increase weight or even as means to attain neutral buoyancy, swallowing or spitting them out again as needed. They might also have been used to increase stability.

The relatively large eyes of the Cryptocleididae have been seen as an adaptation to deep diving.