Mason Matthew J, Bennett Nigel C, Pickford Martin
University of Cambridge, Department of Physiology, Development & Neuroscience, Downing Street, Cambridge, CB2 3EG, United Kingdom.
Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002, South Africa.
J Morphol. 2018 Mar;279(3):375-395. doi: 10.1002/jmor.20779. Epub 2017 Dec 4.
Many living species of golden moles (Chrysochloridae) have greatly enlarged middle ear ossicles, believed to be used in the detection of ground vibrations through inertial bone conduction. Other unusual features of chrysochlorids include internally coupled middle ear cavities and the loss of the tensor tympani muscle. Our understanding of the evolutionary history of these characteristics has been limited by the paucity of fossil evidence. In this article, we describe for the first time the exquisitely preserved middle and inner ears of Namachloris arenatans from the Palaeogene of Namibia, visualised using computed tomography, as well as ossicles attributed to this species. We compare the auditory region of this fossil golden mole, which evidently did not possess a hypertrophied malleus, to those of three extant species with similarly sized ear ossicles, Amblysomus hottentotus, Calcochloris obtusirostris, and Huetia leucorhinus. The auditory region of Namachloris shares many common features with the living species, including a pneumatized, trabeculated basicranium and lateral skull wall, arteries and nerves of the middle ear contained in bony tubes, a highly coiled cochlea, a secondary crus commune, and no identifiable canaliculus cochleae for the perilymphatic duct. However, Namachloris differs from extant golden moles in the apparent absence of a basicranial intercommunication between the right and left ears, the possession of a tensor tympani muscle and aspects of ossicular morphology. One Namachloris skull showed what may be pneumatization of some of the dorsal cranial bones, extending right around the brain. Although the ossicles are small in absolute terms, one of the Huetia leucorhinus specimens had a more prominent malleus head than the other. This potentially represents a previously unrecognised subspecific difference.
许多现存的金毛鼹物种（金毛鼹科）的中耳听小骨都大大增大，据信这是用于通过惯性骨传导来探测地面振动的。金毛鼹的其他不寻常特征包括中耳腔内部相连以及鼓膜张肌的缺失。由于化石证据稀少，我们对这些特征进化历史的了解一直有限。在本文中，我们首次描述了来自纳米比亚古近纪的沙地纳米鼹保存精美的中耳和内耳，通过计算机断层扫描进行可视化展示，以及归属于该物种的听小骨。我们将这种化石金毛鼹的听觉区域（显然不具有肥大的锤骨）与三种现存耳听小骨大小相似的物种——南非金毛鼹、钝吻金鼹和白鼻金鼹的听觉区域进行了比较。沙地纳米鼹的听觉区域与现存物种有许多共同特征，包括气化的、有小梁的颅底和外侧颅壁、中耳的动脉和神经包含在骨管中、高度盘绕的耳蜗、次生总脚，以及没有可识别的用于外淋巴导管的蜗小管。然而，沙地纳米鼹与现存的金毛鼹不同之处在于，左右耳之间明显没有颅底连通、拥有鼓膜张肌以及听小骨形态的某些方面。一个沙地纳米鼹的头骨显示出一些背侧颅骨可能存在气化，一直延伸到大脑周围。尽管听小骨的绝对尺寸较小，但白鼻金鼹的一个标本的锤骨头比另一个更突出。这可能代表了一个以前未被认识到的亚种差异。
