Data_Sheet_1_Allometric and Phylogenetic Aspects of Stapes Morphology in Ruminantia (Mammalia, Artiodactyla).zip

The stapes is the smallest bone of the mammalian skeleton. Being the innermost middle ear ossicle, it is in contact with the inner ear and is directly responsible for sound transmission into it. Today, Ruminantia are one of the most diversified groups of large mammals with more than 200 species. However, their stapes has been very little studied. Here we investigate the shape of 66 stapes from 44 species of extant and extinct Ruminantia, including intra-individual and intra-specific observations, based on 3D tomographic data. Shape differences and similarities are quantitatively discussed thanks to 3D geometric morphometrics. The overall size of the stapes scales with a negative allometry in comparison to body mass. Moreover, the overall shape of the stapes informs about phylogeny. A trend is observed from a concave posterior crus with an enlarged stapes capitulum in Antilocapridae to a relatively straight posterior crus with a little reduced stapes capitulum in Cervidae, Bovidae being intermediate. In addition, the stapes of Antilocapridae is relatively trapezoid in lateral view; that of Cervidae is more triangular in lateral view; and that of Bovidae is relatively rectangular in lateral view. The stapedial footplate shape also gives phylogenetic information. The Tragulidae stapedial footplate is antero-posteriorly asymmetrical. The stapedial footplate is ovoid in stem Pecora. It is asymmetrical in Bovidae, while it is more symmetrical in Cervidae. This is in agreement with previous studies on the ruminant bony labyrinth showing that the oval window, the counterpart of the stapedial footplate on the inner ear, bears a strong phylogenetic signal already distinguishable in early Miocene ruminants.

镫骨（stapes）是哺乳动物骨骼中最小的骨块。作为最内侧的中耳听小骨，它与内耳直接相连，并负责将声音传递至内耳。如今，反刍亚目（Ruminantia）是大型哺乳动物中物种多样性最高的类群之一，现存物种超过200种，但目前针对反刍类镫骨的研究却相对匮乏。本研究基于三维断层扫描数据，对44种现存及已灭绝反刍亚目物种的66件镫骨标本形态展开研究，涵盖个体内及种内观测数据，并借助三维几何形态测量学（3D geometric morphometrics）对镫骨形态的异同进行定量分析与讨论。研究结果显示，镫骨的整体大小与体重呈负异速生长关系；此外，镫骨的整体形态能够反映类群的系统发育关系：从叉角羚科（Antilocapridae）的凹形镫骨后脚（posterior crus）与膨大的镫骨头（stapes capitulum），到鹿科（Cervidae）相对笔直的镫骨后脚与略有缩小的镫骨头，牛科（Bovidae）则处于二者的过渡状态。除此之外，叉角羚科的镫骨侧视呈类梯形，鹿科镫骨侧视更偏向三角形，牛科镫骨侧视则相对呈矩形。镫骨底板（stapedial footplate）的形态同样蕴含系统发育信息：鼷鹿科（Tragulidae）的镫骨底板呈前后不对称形态；基干反刍上类（stem Pecora）的镫骨底板为卵圆形；牛科的镫骨底板不对称，而鹿科的镫骨底板则更为对称。这一结论与此前针对反刍类骨迷路的研究结果一致：作为镫骨底板在内耳中的对应结构，前庭窗（oval window）具有显著的系统发育信号，该信号甚至可在中新世早期的反刍类化石中被辨识。