Constraints and adaptations in crocodyliform skull evolution

Crocodyliforms display a diverse range of skull morphologies throughout their evolutionary history. Extant crocodilians possess platyrostral (broad and flat) snouts, thought to be sub-optimal for resisting feeding loads due to the conflicting demands of feeding and hydrodynamic constraints. In contrast, numerous Mesozoic crocodyliformes possessed oreinirostral (dome-shaped) skulls, were terrestrial, and hence free from hydrodynamic constraint. This study aims to examine the role of function in determining skull shape in crocodyliformes and assesses the difference in stress resistance between oreinirostral and platyrostral taxa. We hypothesize that in the absence of hydrodynamic constraints, oreinirostral taxa have skulls that are better suited for resisting feeding-induced loads. Using finite element analysis (FEA), we evaluated biomechanical performance in oreinirostral notosuchian taxa Baurusuchus salgadoensis, Montealtosuchus arrudacamposi, and Caipirasuchus paulistanus; compared to the extant platyrostral Alligator mississippiensis, Crocodylus niloticus, and Paleosuchus palpebrosus. Results show that oreinirostral morphologies are comparatively better suited for resisting forces generated during feeding, with increased muscular efficiency, supporting the hypothesis that hydrodynamic constraints influence crocodyliform skull evolution.

鳄形类（Crocodyliformes）在其演化历程中展现出丰富多样的头骨形态类型。现生鳄类拥有扁吻型（platyrostral，宽扁吻部）的吻部，这类结构因取食需求与流体动力学约束的冲突，被认为在抵抗取食载荷方面并非最优。与之相反，众多中生代鳄形类拥有圆顶吻型（oreinirostral，穹顶状）的头骨，且为陆生类群，因此不受流体动力学约束的限制。本研究旨在探讨功能在决定鳄形类头骨形态中的作用，并评估圆顶吻型与扁吻型类群在抗应力能力上的差异。我们提出假说：在不受流体动力学约束的情况下，圆顶吻型类群的头骨更适于抵抗取食过程中产生的载荷。本研究采用有限元分析（FEA），对圆顶吻型诺托鳄类类群——萨尔加多包鲁鳄（Baurusuchus salgadoensis）、阿鲁达坎波斯蒙特阿尔托鳄（Montealtosuchus arrudacamposi）以及保利斯塔凯皮拉鳄（Caipirasuchus paulistanus）——的生物力学性能进行评估，并与现生扁吻型类群：密西西比短吻鳄（Alligator mississippiensis）、尼罗鳄（Crocodylus niloticus）以及盾吻古鳄（Paleosuchus palpebrosus）进行对比。研究结果显示，圆顶吻型形态在抵抗取食过程中产生的作用力方面表现更优，且肌肉效率更高，这支持了“流体动力学约束影响鳄形类头骨演化”的假说。