Based on high-resolution computed tomography scanning, we provide new insights into the inner ear and stapedial morphology of Morganucodon from the Early Jurassic of St Brides. At the base of mammaliaforms, Morganucodon plays a pivotal role in understanding the sequence of character acquisition from basal cynodonts to mammals, including the detachment of the middle ear and the evolution of high-frequency hearing. Advancements in imaging technology enabled us to revise or newly describe crucial anatomy that was not accessible for the original description of Morganucodon. Based on 37 petrosals, we can confirm that the apex of the cochlear canal is expanded in Morganucodon, suggestive of a lagena macula. A gently raised crest along the abneural margin is reminiscent of (although much shallower than) the secondary lamina base of other Mesozoic mammaliaforms. The venous circum-promontorial plexus, which surrounded the inner ear in several basal mammaliaforms, was connected to the cochlear labyrinth in Morganucodon through numerous openings along the secondary lamina base. Two petrosals contain fragmentary stapes, which differ substantially from previously described isolated stapes attributed to Morganucodon in having peripherally placed crura and an oval and bullate footplate. Based on the revised stapedial morphology, we question the traditional view of an asymmetrical bicrural stapes as the plesiomorphic condition for Mammaliaformes.

中文翻译：

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重温基底哺乳动物摩根古顿的内耳和镫骨：迷路形态和前额血管化的新信息


基于高分辨率计算机断层扫描，我们对圣布里德斯早侏罗世摩根古龙的内耳和镫骨形态提供了新的见解。在哺乳动物的基础上，摩根齿兽在理解从基础犬齿兽到哺乳动物的特征习得序列方面发挥着关键作用，包括中耳的分离和高频听力的进化。成像技术的进步使我们能够修改或重新描述摩根古龙原始描述无法获得的关键解剖结构。根据 37 个岩骨，我们可以确认摩根古龙的耳蜗管顶端扩张，暗示有黄斑。沿着神经边缘轻轻凸起的嵴让人想起（尽管比）其他中生代哺乳动物的次生椎板基部。在几种基底哺乳动物中，环岬环静脉丛围绕着内耳，在摩根古龙中，它通过沿次级椎板基底的许多开口与耳蜗迷路相连。两个岩骨含有碎片镫骨，其与先前描述的归因于摩根古顿的分离镫骨有很大不同，因为其具有位于外围的脚和椭圆形和泡​​状的足板。基于修订后的镫骨形态，我们对不对称双足镫骨作为哺乳动物形目拟态条件的传统观点提出了质疑。