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Strictly speaking,[1] pachyostosis 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) and plesiosaurs it provides, or provided, ballast as an adaptation for an aquatic existence.

Most giant deer showed pronounced pachyostosis of the mandible and skull.[3][4] It has been suggested[5] that this served to store minerals for antler growth. Many Pachycephalosauria and most members of the Dinocephalia clade of therapsids had thickened skull bones, probably used in head-butting contests.[6]

See also[edit]


  1. ^ Domning, D. P. and V. Debuffrenil (1991). Hydrostasis in the Sirenia - Quantitative Data and Functional Interpretations. Marine Mammal Science 7(4): 331-368.
  2. ^ a b Houssaye, A. (2009). "Pachyostosis" in aquatic amniotes: a review. Integrative Zoology 4(4): 325-340.
  3. ^ van der Made, J. and H. W. Tong (2008). Phylogeny of the giant deer with palmate brow tines Megaloceros from west and Sinomegaceros from east Eurasia. Quaternary International 179: 135-162
  4. ^ Vislobokova, I. A. (2013). Morphology, taxonomy, and phylogeny of megacerines (Megacerini, Cervidae, Artiodactyla). Paleontological Journal 47(8): 833-950
  5. ^ Lister, A. M. (1994). The evolution of the giant deer, Megaloceros giganteus (Blumenbach). Zoological Journal of the Linnean Society 112(1-2): 65-100
  6. ^ Snively, E. and A. Cox (2008). Structural Mechanics of Pachycephalosaur Crania Permitted Head-Butting Behavior. Palaeontologia Electronica 11(1,3A): 17