Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, 14040-901, Ribeirão Preto, Brazil.
Fachbereich Geowissenschaften der Eberhard Karls Universität Tübingen, Hölderlinstraße 12, 72074, Tübingen, Germany.
Sci Rep. 2020 Mar 26;10(1):5505. doi: 10.1038/s41598-020-62179-5.
The origin of turtles is one of the most long-lasting debates in evolutionary research. During their evolution, a series of modifications changed their relatively kinetic and anapsid skull into an elongated akinetic structure with a unique pulley system redirecting jaw adductor musculature. These modifications were thought to be strongly correlated to functional adaptations, especially to bite performance. We conducted a series of Finite Element Analyses (FEAs) of several species, including that of the oldest fully shelled, Triassic stem-turtle Proganochelys, to evaluate the role of force distribution and to test existing hypotheses on the evolution of turtle skull architecture. We found no support for a relation between the akinetic nature of the skull or the trochlear mechanisms with increased bite forces. Yet, the FEAs show that those modifications changed the skull architecture into an optimized structure, more resistant to higher loads while allowing material reduction on specific regions. We propose that the skull of modern turtles is the result of a complex process of progressive correlation between their heads and highly flexible necks, initiated by the origin of the shell.
海龟的起源是进化研究中最持久的争论之一。在进化过程中，一系列的改变将它们相对活跃的无孔颅骨变成了拉长的无动力结构，并具有独特的滑轮系统，重新引导下颚的收缩肌。这些改变被认为与功能适应密切相关，尤其是与咬合性能有关。我们对包括最古老的完全有壳的三叠纪原始海龟 Proganochelys 在内的几个物种进行了一系列有限元分析（FEA），以评估力分布的作用，并检验关于海龟颅骨结构进化的现有假说。我们没有发现无动力颅骨或滑车机制与更大的咬合力之间存在关系的证据。然而，FEA 表明，这些改变将颅骨结构变成了一个优化的结构，使其在承受更高负载的同时，能够减少特定区域的材料使用。我们提出，现代海龟的颅骨是由其头部和高度灵活的颈部之间的复杂的逐步相关过程所导致的，这一过程始于壳的起源。
