Table_1_Tooth Structure and Replacement of the Triassic Keichousaurus (Sauropterygia, Reptilia) From South China.pdf

The small-sized sauropterygian Keichousaurus hui was one of the most abundant marine reptiles from the Triassic Yangtze Sea in South China. Although Keichousaurus has been studied in many aspects, including the osteology, ontogeny, sexual dimorphism, and reproduction, the dentition of this marine reptile was only briefly described in external morphology. In this study, we provide new information on Keichousaurus tooth implantation, histology, and replacement based on a detailed examination of well-preserved specimens collected in the past decades. The tooth histology has been investigated for the first time by analyzing cross-sections of premaxillary teeth and the tooth attachment and implantation have been further revealed by X-ray computed microtomography. We refer the tooth replacement of Keichousaurus to the iguanid replacement type on the basis of the observed invasion of small replacement tooth into the pulp cavity of the functional tooth. Given the resemblance to other extinct and modern piscivorous predators in the morphology and structure of teeth, Keichousaurus might mainly feed on small or juvenile fishes and some relatively soft-bodied invertebrates (e.g., mysidacean shrimps) from the same ecosystem.

小型蜥脚类海生爬行动物——汇齿龙（Keichousaurus hui）是来自中国南部的三叠纪扬子海中最为丰富的海洋爬行动物之一。尽管汇齿龙在骨学、发育学、性别二形性和繁殖等多个方面已有所研究，但其牙齿结构在海生爬行动物的外部形态学描述上却仅被简要提及。在本研究中，我们基于过去几十年收集的保存完好的标本，对汇齿龙的牙齿植入、组织学和替换提供了新的信息。首次通过分析上颌牙齿的横截面，对牙齿的组织学进行了研究，并通过X射线计算机断层扫描进一步揭示了牙齿的附着和植入过程。基于观察到的替换牙齿侵入功能牙齿的牙髓腔，我们将汇齿龙的牙齿替换类型归为鬣蜥科替换类型。鉴于其牙齿形态和结构与已灭绝和现代的肉食性捕食者相似，汇齿龙可能主要捕食小型或幼年的鱼类以及一些较为柔软的无脊椎动物（例如桡脚类虾）等同一生态系统中的生物。