Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637.
Department of Vertebrate Zoology, Academy of Natural Sciences of Drexel University, Philadelphia, PA 19103.
Proc Natl Acad Sci U S A. 2021 Feb 16;118(7). doi: 10.1073/pnas.2016421118.
Changes to feeding structures are a fundamental component of the vertebrate transition from water to land. Classically, this event has been characterized as a shift from an aquatic, suction-based mode of prey capture involving cranial kinesis to a biting-based feeding system utilizing a rigid skull capable of capturing prey on land. Here we show that a key intermediate, , was capable of cranial kinesis despite significant restructuring of the skull to facilitate biting and snapping. Lateral sliding joints between the cheek and dermal skull roof, as well as independent mobility between the hyomandibula and palatoquadrate, enable the suspensorium of to expand laterally in a manner similar to modern alligator gars and polypterids. This movement can expand the spiracular and opercular cavities during feeding and respiration, which would direct fluid through the feeding apparatus. Detailed analysis of the sutural morphology of suggests that the ability to laterally expand the cheek and palate was maintained during the fish-to-tetrapod transition, implying that limited cranial kinesis was plesiomorphic to the earliest limbed vertebrates. Furthermore, recent kinematic studies of feeding in gars demonstrate that prey capture with lateral snapping can synergistically combine both biting and suction, rather than trading off one for the other. A "gar-like" stage in early tetrapod evolution might have been an important intermediate step in the evolution of terrestrial feeding systems by maintaining suction-generation capabilities while simultaneously elaborating a mechanism for biting-based prey capture.
摄食结构的改变是脊椎动物从水生到陆生的基本转变。传统上，这一事件的特征是从涉及颅骨运动的水生、吸力型的捕食方式转变为利用刚性颅骨进行捕食的基于咬噬的进食系统，这种刚性颅骨能够在陆地上捕获猎物。在这里，我们展示了一个关键的中间过渡物种，尽管颅骨发生了重大重构以促进咬噬和猛咬，但它仍能够进行颅骨运动。颊部和真皮颅顶之间的侧向滑动关节，以及舌颌骨和方骨之间的独立活动性，使 的悬器能够以类似于现代鲟鱼和多鳍鱼的方式侧向扩张。这种运动可以在进食和呼吸时扩大鳃腔和鳃盖腔，从而将流体引导通过进食器官。对 的缝合形态的详细分析表明，在鱼类到四足动物的过渡过程中，颊部和 palate 侧向扩张的能力得以保留，这意味着有限的颅骨运动是最早有附肢的脊椎动物的原始特征。此外，最近对鲟鱼进食的运动学研究表明，侧向猛咬捕食可以协同结合咬噬和吸力，而不是相互替代。在陆地进食系统的进化中，早期四足动物进化中的“鲟鱼样”阶段可能是一个重要的中间步骤，因为它在同时保留吸力产生能力的同时，还发展了一种基于咬噬的捕食机制。
