ScienceDaily (Aug. 14, 2012) — Although clearly discernible in the embryo, shortly afterwards it fuses with other bones beyond recognition. Consequently, researchers have often missed it. Now, however, paleontologists from the University of Zurich have rediscovered it: the "os interparietale," a skull bone also referred to as the interparietal. Using imaging methods, they were able to detect its presence in all mammals -- including humans, which is new as it was previously believed to have been lost in the course of evolution.
The mammalian skull, including that of people, is composed of about 20 bones. Fish, reptile and bird skulls, however, have considerably more. After all, when mammals evolved from reptile-like vertebrates 320 million years ago, the skull's structure became simplified during its development and the number of skull bones decreased.
Some bones were lost in the lineage leading to mammals in the course of evolution, especially a number of skull roof bones. The skull's interparietal, which is one of the skull roof bones, particularly puzzled researchers: on the one hand, it seems to have survived, such as in humans, carnivores and ungulates (especially horses); on the other hand, it is not found in all mammals.
Continued: http://www.sciencedaily.com/releases/2012/08/120814085443.htm
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