Pachyostosis
The pachyostosis is a thickening of the bone by the ossification of connective tissue material of the bone skin ( periosteum ).
Pachyostosis is both the name for the pathological thickening of bones in animals and humans, where it occurs as a special form of hyperostosis , as well as for an adaptation of the terrestrial vertebrates (tetrapods) to a life in water, acquired in the course of evolution , in order to compensate for the static buoyancy of the body . Of the ( recent ) animals living today , only manatees have pachyostosis, particularly noticeable on the rib bones.
Adaptation to an aquatic way of life
The groups of terrestrial vertebrates that returned to the water throughout their tribal history solved the problem of buoyancy in different ways. Some forms, e.g. B. the crocodiles , avoided anatomical adaptation and instead swallowed stones, the so-called gastroliths (stomach stones), as ballast to compensate for buoyancy. However, this theory is still controversial. The additional weight means that their representatives can float in the water without using energy.
The physical adaptation in the form of pachyostosis occurred several times independently in different tetrapod groups. One of the first adaptations to a life in water, in addition to the spread of the extremities to the oar organs, is the thickening of the bones, which can be caused by various histological changes. It already occurs with the Mesosauria , the first terrestrial vertebrates with a secondary aquatic way of life, for example with Mesosaurus . In addition, it is still in some original sauropterygians such as the pachypleuosaurs and plesiosaurs , z. B. Kronosaurus , the champosaurs and Claudiosaurus known.
Individual evidence
- ↑ Glossary of Palaeos.com
- ^ Pachyostosis - Homepage of the paleontologist Adam Stuart Smith ( Memento from July 18, 2011 in the Internet Archive )
- ^ The Riddle of the Gastroliths - Weighing up the evidence
- ↑ Martin Sander: Reptiles . Haeckel-Bücherei Volume 3. Enke Verlag, Stuttgart, 1994