Clack J A
University Museum of Zoology, Cambridge, UK.
Brain Behav Evol. 1997;50(4):198-212. doi: 10.1159/000113334.
In the earliest tetrapods, the fenestra vestibuli was a large hole in the braincase wall bounded by bones of different embryological origins: the otic capsule and occipital arch components, and also, in all except the Devonian Acanthostega, the dermal parasphenoid. This means that the hole lay along the line of the embryonic metotic fissure. Early tetrapod braincases were poorly ossified internally, and no specialized opening for a perilymphatic duct is evident. It is arguable that the earliest tetrapods had neither a perilympllatic duct crossing the otic capsule nor a specialized auditory receptor in a separate lagenar pouch. The primitive tetrapod condition is found in the earliest amniotes, and the separate development of (1) a fenestra vestibuli confined to the limits of the otic capsule, (2) a specialized pressure relief window also derived from components on the line of the metolic fissure, (3) a nonstructural, vibratory stapes and (4) increased internal ossification of the internal walls of the otic capsule, can be traced separately in synapsids, lepidosauromorph diapsids, archosauromorph diapsids, probably turtles, and amphibians. This suggests separate development of true tympanic ears in each of these groups. Developments indicating the existence of a true tympanic ear in amniotes are first found in animals from the Triassic period, and a correlation with the evolution of insect sound production is suggested.
在最早的四足动物中，前庭窗是脑颅壁上的一个大洞，由不同胚胎起源的骨骼界定：耳囊和枕弓成分，而且，除了泥盆纪的棘螈外，所有四足动物的真皮副蝶骨也参与界定。这意味着这个洞沿着胚胎颞骨裂的线分布。早期四足动物的脑颅内部骨化程度很低，没有明显的外淋巴导管专用开口。可以说，最早的四足动物既没有穿过耳囊的外淋巴导管，也没有在单独的瓶状囊中专门的听觉感受器。原始四足动物的状态见于最早的羊膜动物中，并且（1）局限于耳囊范围内的前庭窗、（2）同样源自颞骨裂线上成分的专门减压窗、（3）无结构的振动镫骨以及（4）耳囊内壁内部骨化增加的单独发育情况，在合弓类、鳞龙形双孔类、主龙形双孔类、可能还有龟类以及两栖动物中都能分别追溯到。这表明这些类群中的每一个都独立演化出了真正的鼓膜耳。表明羊膜动物存在真正鼓膜耳的发育特征最早见于三叠纪时期的动物，并且有人提出这与昆虫发声的演化存在关联。
