Mestriner Gabriel, Funston Gregory F, Marsola Júlio C A, Nesbitt Sterling J, Langer Max C, Evans David C, LeBlanc Aaron R H
Biologia, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil.
Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Biol Lett. 2025 Sep;21(9):20250316. doi: 10.1098/rsbl.2025.0316. Epub 2025 Sep 24.
'Thecodont' refers to teeth implanted in sockets within the jaw, a condition traditionally associated with living mammals and crocodylians, which also coincidentally have teeth attached by ligaments to the socket walls (gomphosis). For over a century, the bony periodontium of many other amniotes has been described as a single tissue, 'bone of attachment', causing confusion over dental tissue homology. The conventional definitions of 'thecodonty' exclude species with fused teeth ('ankylothecodonts'), implying a fundamental difference between mammals, crocodylians and most other vertebrates. However, the stereotypically 'thecodont' attachment tissues have been discovered in representatives of all major amniote clades, showing that gomphosis and ankylosis likely stem from heterochronic changes in the timing and extent of cementum and alveolar bone mineralization. This challenges (i) previous hypotheses regarding the evolution of the amniote periodontium, (ii) the 'bone of attachment' paradigm, and (iii) the significance of 'thecodonty'. We suggest a new nomenclatural approach that incorporates recent histological and evolutionary research and divides thecodonty into anatomical categories to clarify their origin and evolution. We propose the terms anisothecodont and isothecodont to denote, respectively, asymmetric and symmetric implantation of teeth in their sockets. Regardless of the geometry of the connection, we propose using ankylosis and gomphosis to denote the mode of tooth attachment.
“槽生齿”指的是植入颌骨牙槽窝内的牙齿，这种情况传统上与现存的哺乳动物和鳄目动物相关，巧合的是，它们的牙齿也通过韧带附着在牙槽窝壁上（齿槽连接）。一个多世纪以来，许多其他羊膜动物的骨牙周组织一直被描述为单一组织，即“附着骨”，这导致了牙齿组织同源性方面的混淆。“槽生齿”的传统定义排除了牙齿融合的物种（“固着槽生齿”），这意味着哺乳动物、鳄目动物与大多数其他脊椎动物之间存在根本差异。然而，在所有主要羊膜动物类群的代表中都发现了典型的“槽生齿”附着组织，这表明齿槽连接和齿骨结合可能源于牙骨质和牙槽骨矿化时间和程度的异时变化。这对以下几点提出了挑战：（i）先前关于羊膜动物牙周组织进化的假说；（ii）“附着骨”范式；（iii）“槽生齿”的重要性。我们建议采用一种新的命名方法，该方法结合了近期的组织学和进化研究，并将槽生齿分为解剖学类别，以阐明它们的起源和进化。我们提出anisothecodont和isothecodont这两个术语，分别表示牙齿在牙槽窝内的不对称和对称植入。无论连接的几何形状如何，我们建议使用齿骨结合和齿槽连接来表示牙齿附着的方式。
