Evolution of mammalian auditory ossicles
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The evolution of mammalian auditory ossicles was an
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
ary event that resulted in the formation of the bones of the mammalian
middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is t ...

middle ear
. These bones, or ossicles, are a defining characteristic of all
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
. The event is well-documented and important as a demonstration of
transitional forms A transitional fossil is any fossil A fossil (from Classical Latin: , literally "obtained by digging") is any preserved remains, impression, or trace of any once- living thing from a past geological age. Examples include bones, shells, ...
and
exaptation Exaptation and the related term co-option Co-option (also co-optation, sometimes spelt coöption or coöptation) has two common meanings. It may refer to the process of adding members to an elite group A group is a number A number is a mat ...
, the re-purposing of existing structures during evolution. The ossicles evolved from skull bones present in most tetrapods, including the
reptilian
reptilian
lineage. The reptilian
quadrate Quadrate may refer to: * Quadrate bone * Quadrate (heraldry) * Quadrate lobe of liver * Quadrate tubercle of femur See also *Quadrat (disambiguation) {{disambig