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The mammalian dentition is uniquely characterized by a combination of
precise occlusion, permanent adult teeth, and a unique tooth attachment
system. Unlike the ankylosed teeth in most reptiles, mammal teeth are
supported by a ligamentous tissue that suspends each tooth in its socket,
providing flexible and compliant tooth attachment that prolongs the life
of each tooth and maintains occlusal relationships. Here we investigate
dental ontogeny through histological examination of a wide range of
extinct synapsid lineages to assess whether the ligamentous tooth
attachment system is unique to mammals and to determine how it evolved.
This study shows for the first time that the ligamentous tooth attachment
system is not unique to crown mammals within Synapsida, having arisen in
several non-mammalian therapsid clades as a result of neoteny and
progenesis in dental ontogeny. Mammalian tooth attachment is here
re-interpreted as a paedomorphic condition relative to the ancestral
synapsid form of tooth attachment.
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