Data from: Dental ontogeny in extinct synapsids reveals a complex evolutionary history of the mammalian tooth attachment system

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.

哺乳动物牙列的独有特征，在于兼具精确咬合、恒齿，以及独特的韧带型牙齿附着系统（ligamentous tooth attachment system）。与多数爬行动物的固着齿不同，哺乳动物的牙齿由韧带样结缔组织支撑，该组织将每颗牙齿悬挂于牙槽内，可提供柔韧且顺应性优良的附着方式，既能延长单颗牙齿的使用寿命，又能维持咬合关系。本研究通过对多种已灭绝的合弓纲（Synapsida）类群开展组织学检测（histological examination），以此探究牙齿发生（dental ontogeny），旨在评估韧带型牙齿附着系统是否为哺乳动物所独有，并阐明其演化历程。本研究首次证实：在合弓纲类群中，韧带型牙齿附着系统并非仅冠群哺乳动物（crown mammals）所独有，该系统已在若干非哺乳类兽孔目（Therapsida）演化支中出现，其形成源于牙齿发生过程中的幼态持续（neoteny）与发育早熟（progenesis）。此外，本研究重新诠释了哺乳动物的牙齿附着模式：相较于合弓纲祖先的牙齿附着形式，哺乳动物的牙齿附着属于幼态延续性状。