Pachyostosis

It often occurs together with bone densification (osteosclerosis), reducing inner cavities.

However, especially in the older literature, "pachyostosis" is often used loosely, referring to all osseous specializations characterized by an increase in bone compactness and/or volume.

[2] In aquatic animals, such as seacows (manatees and dugongs), Thalassocnus,[3] and plesiosaurs, pachyostosis in the thoracic region provides (or provided) ballast against the air-filled lungs.

Most giant deer showed pronounced pachyostosis of the mandible and skull.

[6] Many Pachycephalosauria and most members of the Dinocephalia clade of therapsids had thickened skull bones, probably used in head-butting contests.