Condition in which bones have an abnormally elevated density
Pachyostosis[1] is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (
osteosclerosis), reducing inner cavities. This joint occurrence is called
pachyosteosclerosis. 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] It occurs in both terrestrial and, especially, aquatic or semi-aquatic vertebrates.[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. This maintains neutral buoyancy in aquatic habitats.
Most
giant deer showed pronounced pachyostosis of the mandible and skull.[4][5] It has been suggested that this served to store minerals for antler growth.[6] Many
Pachycephalosauria and most members of the
Dinocephalia clade of
therapsids had thickened skull bones, probably used in head-butting contests.[7]
^Domning, D. P.; Debuffrenil, V. (1991). "Hydrostasis in the Sirenia - Quantitative Data and Functional Interpretations". Marine Mammal Science. 7 (4): 331–368.
doi:
10.1111/j.1748-7692.1991.tb00111.x.
^Vislobokova, I. A. (2013). "Morphology, taxonomy, and phylogeny of megacerines (Megacerini, Cervidae, Artiodactyla)". Paleontological Journal. 47 (8): 833–950.
doi:
10.1134/s0031030113080017.
S2CID86697746.
^Lister, A. M. (1994). "The evolution of the giant deer, Megaloceros giganteus (Blumenbach)". Zoological Journal of the Linnean Society. 112 (1–2): 65–100.
doi:
10.1111/j.1096-3642.1994.tb00312.x.
^Snively, E.; Cox, A. (2008). "Structural Mechanics of Pachycephalosaur Crania Permitted Head-Butting Behavior". Palaeontologia Electronica. 11: 17.