Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria, Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England
Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria, Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England
复制标题
英国约克郡托阿尔阶（下侏罗统）大型水生捕食者 Rhomaleosaurus zetlandicus（蛇颈龙目，爬行动物）头部的功能解剖学
DOI：
--
复制
发表时间：
1992
期刊：
影响因子：
--
通讯作者：
M. Taylor
中科院分区：
文献类型：
--
作者：
M. Taylor
来自英格兰托阿尔西亚的大型上龙类蛇颈龙Rhomaleosaurus zetlandicus的模式标本的头骨和下颌骨是细长的，并适应于在水中进行强大的捕食活动。下颌骨包含了原始爬行动物下颌骨的所有元素。宽的犬齿表明，菱形龙以各种活跃的猎物为食，并通过摇晃和扭曲它们来强行肢解较大的猎物。这是蛇颈龙第一次重建头部肌肉组织。它适应于在水中进食。内收肌包括一个大的翼前肌附在眶下窗，一个大的翼后肌，和一组大的背肌，包括下颌外收肌。前翼肌在下颌张开时产生最大扭矩，使其迅速闭合;背侧肌在下颌闭合时产生最大扭矩，以制服和肢解猎物;后翼肌的作用不确定或介于两者之间。肌肉系统结合了Olson（1961）认为的水生四足动物的“动力惯性”系统和他认为的陆生四足动物的“静压”系统。奥尔森认为，大翼肌肌肉系统典型的“动能惯性”系统的功能，赋予动能的下颌骨。然而，它的功能可能是补偿下颌骨的惯性和阻力。降颌肌包括降颌肌和咽纵肌，能迅速撑开下颌以抵抗阻力。颈部肌肉组织无法详细重建。有一个强大的颈部韧带。头部内的力量进行了分析，使用箱梁和梁作为类比。大体形态、组成骨骼的形状和缝合处的形态都证实了这种适应性，它们能够抵抗咬猎物时肌肉作用产生的巨大弯曲力矩。当颌骨闭合时，翼突支持下颌骨对抗内收肌肌力的向内分量。菱形龙是视觉掠食者。眼睛很大。镫骨存在。可能是水下嗅觉。没有证据表明有鼓膜，但不知道这是否是类形爬行动物的状态，还是从鼓膜祖先派生而来。耳朵在听觉上并没有与脑壳隔离，所以水下的定向听力很差，也不可能使用声纳。Rhomaleosaurus的头部结构是一种功能性的折衷，既要最大限度地提高结构强度，又要最大限度地提高游泳和进食效率。特别重要的是能够维持大的肌肉和反作用力，以提供足够的咬合力在年底的长吻，和广泛的张口允许吞咽大的猎物。即使是更大的物品也会通过摇动和扭转进料被肢解成更小的碎片。主要的未解决的问题是比例因子的影响，以及不对称咬合或将大型猎物扭成碎片时引起的扭转载荷。
The skull and mandible of the type specimen of the large pliosauroid plesiosaur Rhomaleosaurus zetlandicus from the Toarcian of England are elongate, and adapted for powerful predatory activity in water. The mandible contains all elements found in primitive reptilian mandibles. The broadly caniniform dentition suggests that Rhomaleosaurus fed on a wide range of active prey, and forcibly dismembered larger prey by shaking and twisting them. The cranial musculature is reconstructed for the first time in plesiosaurs. It was adapted for feeding in water. The adductor musculature included a large anterior pterygoideus attached to the suborbital fenestra, a large posterior pterygoideus, and a group of large dorsal muscles including the adductor mandibulae externus. The anterior pterygoideus exerted maximum torque when the jaws were wide open, snapping them shut quickly, and the dorsal muscle mass exerted maximum torque when the jaws were closed on prey to subdue and dismember it. The role of the posterior pterygoideus is uncertain or intermediate. The musculature combines elements of the \`kinetic inertial' system ascribed to aquatic tetrapods by Olson (1961), with his \`static pressure' system ascribed to terrestrial tetrapods. Olson suggested that the large pterygoideus musculature typical of the `kinetic intertial' system functioned to confer kinetic energy on the mandible. However, its function may instead have been to compensate for the inertia and drag of the mandible. The depressor musculature comprised the depressor mandibulae and the longitudinal pharyngeal muscles, and opened the jaw quickly against drag. The cervical musculature cannot be reconstructed in detail. There was a strong nuchal ligament. The forces within the head are analysed by using box and girder beams as analogues. Gross form, shape of constituent bones, and sutural morphology confirm adaptations to resist great bending moments arising from the action of the muscles when biting on prey. When the jaws were closed, the pterygoid flange supported the mandible against the inward component of the adductor muscle force. Rhomaleosaurus was a visual predator. The eyes were large. The stapes is present. Underwater olfaction was likely. There is no evidence for an eardrum, but it is not known whether this is the plesiomorphic reptilian state or secondarily derived from a tympanate ancestor. The ears were not acoustically isolated from the braincase, so underwater directional hearing was poor, and sonar was not possible. The structure of the head of Rhomaleosaurus is a functional compromise between the needs to maximize structural strength and to maximize swimming and feeding efficiency. Especially important were the ability to sustain large muscle and reaction forces to provide an adequate bite force at the end of a long snout, and the wide gape allowing the swallowing of large picces of prey. Even larger items were dismembered into smaller pieces by shake and twist feeding. The major unresolved problems are the effects of scaling factors, and the torsional loadings induced when biting asymmetrically, or twisting large prey to pieces.