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首页> 外文期刊>Zoological Journal of the Linnean Society >The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals
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The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals

机译：侏罗纪克拉克拉德晚期哺乳动物的Dryolestes leiriensis的岩耳和内耳及其对Therian哺乳动物的耳朵进化的影响

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摘要

Dryolestes leiriensis is a Late Jurassic fossil mammal of the dryolestoid superfamily in the cladotherian clade that includes the extant marsupials and placentals. We used high resolution micro-computed tomography (mCT) scanning and digital reconstruction of the virtual endocast of the inner ear to show that its cochlear canal is coiled through 270°, and has a cribriform plate with the spiral cochlear nerve foramina between the internal acoustic meatus and the cochlear bony labyrinth. The cochlear canal has the primary bony lamina for the basilar membrane with a partially formed (or partially preserved) canal for the cochlear spiral ganglion. These structures, in their fully developed condition, form the modiolus (the bony spiral structure) of the fully coiled cochlea in extant marsupial and placental mammals. The CT data show that the secondary bony lamina is present, although less developed than in another dryolestoid Henkelotherium and in the prototribosphenidan Vincelestes. The presence of the primary bony lamina with spiral ganglion canal suggests a dense and nely distributed cochlear nerve innervation of the hair cells for improved resolution of sound frequencies. The primary, and very probably also the secondary, bony laminae are correlated with a more rigid support for the basilar membrane and a narrower width of this membrane, both of which are key soft-tissue characteristics for more sensitive hearing for higher frequency sound. All these cochlear features originated prior to the full coiling of the therian mammal cochlea beyond one full turn, suggesting that the adaptation to hearing a wider range of sound frequencies, especially higher frequencies with rened resolution, has an ancient evolutionary origin no later than the Late Jurassic in therian evolution. The petrosal of Dryolestes has added several features that are not preserved in the petrosal of Henkelotherium. The petrosal characters of dryolestoid mammals are essentially the same as those of Vincelestes, helping to corroborate the synapomorphies of the cladotherian clade in neural, vascular, and other petrosal characteristics. The petrosal characteristics of Dryolestes and Henkelotherium together represent the ancestral morphotype of the cladotherian clade (Dryolestoidea + Vincelestes + extant Theria) from which the extant therian mammals evolved their ear region characteristics.
机译：Dryolestes leiriensis是侏罗纪晚期化石哺乳动物，属于克拉屈特氏进化枝中的干燥雌激素超家族，包括现存的有袋动物和胎盘。我们使用高分辨率微计算机断层扫描（mCT）扫描和内耳虚拟内窥镜的数字重建，显示其耳蜗管盘绕了270°，并且具有一个筛状板，其耳蜗内部有螺旋状耳蜗神经孔。耳道和耳蜗骨迷宫。耳蜗管具有基底膜的主要骨板，而耳蜗螺旋神经节具有部分形成（或部分保留）的管。这些结构在充分发育的状态下，在现存的有袋和胎盘哺乳动物中形成完全盘绕的耳蜗的盘绕结构（骨螺旋结构）。 CT数据显示，尽管比另一类骨干类动物Henkelotherium和原tribosphenidan Vincelestes中发育得少，但存在继发性骨板层。原发性骨椎板和螺旋神经节管的存在提示毛细胞的密布和分布均匀的耳蜗神经支配神经，以改善声音的分辨率。主要的（也可能是次要的）骨性椎板与基底膜的更坚硬的支撑和该膜的较窄宽度相关，这两者都是关键的软组织特征，对于更高频的声音，听觉更敏感。所有这些耳蜗特征都起源于Therian哺乳动物的耳蜗完全盘绕超过一整圈之前，这表明适应听力范围更广的声音频率，尤其是具有高分辨率的较高频率的声音，具有晚于晚期的古老进化起源。侏罗纪在人类演化中。 Dryolestes的岩石增加了Henkelotherium的岩石中未保留的几个功能。干燥雌激素类哺乳动物的岩质特征与长鞭毛类动物的岩质特征基本相同，有助于在神经，血管和其他岩质特征上证实克拉屈德进化枝的同形亚型。 Dryolestes和Henkelotherium的岩性特征一起代表了cladotherian进化枝（Dryolestoidea + Vincelestes + extant Theria）的祖先形态型，现存的therian哺乳动物从中进化出了它们的耳朵区域特征。

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