Appearances can be deceptive: bizarre shell microanatomy and histology in a new Triassic turtle (Testudinata) from Argentina at the dawn of turtles

The origin and homology of the turtle shell are one of the most captivating topics in amniote evolution. In this contribution, we present a new species of turtle from the Late Triassic of Argentina whose peripheral plates question the homology of these bones in turtles. The external morphology of the peripheral plates of Waluchelys cavitesta gen. et sp. nov. (Testudinata: Australochelyidae) is as in any other turtle, however, appearances can be deceiving. Internally, these plates exhibit an unexpected internal cavity. The absence of structural similarities and of ontogenetic or phylogenetic transitional forms between the peripheral plates of W. cavitesta and other testudinatans might suggest that the periphery of turtles represents a case of deep homology. Furthermore, the present and recent findings suggest that the structure and ossification patterns of the periphery of the turtle shell were more plastic and subject to variation than other elements of the shell, at least in the earlie...龟甲的起源与同源性是羊膜动物（amniote）演化中最引人入胜的议题之一。本研究报道了一件产自阿根廷晚三叠世的龟类新物种，其外周板（peripheral plates）对龟类该类骨骼的同源性提出了质疑。腔纹瓦鲁龟（Waluchelys cavitesta gen. et sp. nov.，龟类总目（Testudinata）：澳龟科（Australochelyidae））的外周板外部形态与其他龟类并无二致，但外观往往具有迷惑性。而在内部结构上，这类骨骼却呈现出出人意料的内腔。腔纹瓦鲁龟（W. cavitesta）的外周板与其他龟类总目成员之间既缺乏结构相似性，也不存在个体发育（ontogenetic）或系统发育（phylogenetic）的过渡类群，这或许表明龟类的外周骨骼属于深层同源性（deep homology）的典型案例。此外，本研究及近期的相关研究成果均表明，龟甲外周骨骼的结构与骨化模式（ossification patterns）相较于龟甲其他组成部分具有更强的可塑性与变异潜力，至少在早期演化阶段……