ABSTRACT

Caviomorphs, the ctenohystrican rodents endemic to the Neotropics, have a long evolutionary history during the Cenozoic, and is one of the more abundant mammalian groups with striking morphological disparity. Several living taxa have auditory regions adapted to hearing low-frequency sounds, yet almost nothing is known about the basicranium in fossil taxa. The octodontoid Prospaniomys priscus from the lower Miocene of Patagonia, Argentina, exhibits a skull with a curious combination of generalized dental characters and supposed derived tympanic cavity. Owing to the basal phylogenetic position of P. priscus, the study of its basicranium based on high resolution X-ray computed tomography represents an excellent opportunity to study an ancestral morphological pattern. Comparisons with living octodontoids permit the evaluation of the auditory region in an evolutionary context. Our results identified that at least since the early Miocene octodontoids, and certainly caviomorphs, have specializations to enhance low-frequency hearing: highly coiled cochlea, small secondary bony laminae, well-developed tympanic cavity, and reduced or absent stapedius muscle, characters that seem not to be directly related to the environment. Possible generalized or specialized states for the latter features are discussed. The significance of this work lies in the fact that it is the first detailed anatomical description of the auditory regions of a fossil caviomorph, providing a new framework with regards to this region of the skull.

摘要

新生代特有的豚鼠啮齿类动物，在新生代具有悠久的进化历史，是形态学差异显着的较丰富的哺乳动物群体之一。几个活的类群的听觉区域适合听低频声音，但化石类群中的碱性铀几乎一无所知。来自阿根廷巴塔哥尼亚下中新世的八齿类Prospaniomys priscus颅骨显示出一个颅骨，具有一般牙齿特征和假定的鼓室的奇异组合。由于P. priscus的基础系统发育位置，基于高分辨率X射线计算机断层扫描对其碱性铀的研究为研究祖先的形态学模式提供了极好的机会。与活八肽类的比较允许在进化的背景下评估听觉区域。我们的研究结果表明，至少从中新世早期的八倍体类固醇（当然还有腔静脉类动物）开始，就可以增强低频听觉的专长：高度盘绕的耳蜗，小的继发性骨片，鼓膜腔发达，骨肌减少或缺失、,骨特征似乎与环境没有直接关系。讨论了后一种功能的可能的广义或专门状态。这项工作的意义在于，它是化石豚形的听觉区域的第一个详细的解剖学描述，