Department of Anatomy, Midwestern University, Glendale, AZ 85308, USA.
Anat Rec (Hoboken). 2012 Apr;295(4):615-31. doi: 10.1002/ar.22422. Epub 2012 Jan 27.
Mammals are unique in being the only group of amniotes that can hear sounds in the upper frequency range (>12 kHz), yet details about the evolutionary development of hearing patterns remain poorly understood. In this study, we used high resolution X-ray computed tomography to investigate several functionally relevant auditory structures of the inner ear in a sample of 21 fossil primate species (60 Ma to recent times) and 25 species of living euarchontans (primates, tree shrews, and flying lemurs). The structures examined include the length of the cochlea, development of bony spiral lamina and area of the oval window (or stapedial footplate when present). Using these measurements we predicted aspects of low-frequency and high-frequency sensitivity and show that hearing patterns in primates likely evolved in several stages through the first half of the Cenozoic. These results provide temporal boundaries for the development of hearing patterns in extant lineages and strongly suggest that the ancestral euarchontan hearing pattern was characterized by good high-frequency hearing but relatively poor low-frequency sensitivity. They also show that haplorhines are unique among primates (extant or extinct) in having relatively longer cochleae and increased low-frequency sensitivity. We combined these results with additional, older paleontological evidence to put these findings in a broader evolutionary context.
哺乳动物是唯一能够听到高频声音（>12 kHz）的羊膜动物群体，但有关听觉模式进化发展的细节仍知之甚少。在这项研究中，我们使用高分辨率 X 射线计算机断层扫描技术，对 21 种化石灵长类物种（6000 万年前至现代）和 25 种现存的真兽类（灵长类、树鼩和飞狐猴）的内耳的几个功能相关的听觉结构进行了研究。所检查的结构包括耳蜗的长度、骨螺旋板的发育和卵圆窗的面积（或存在时的镫骨足板）。利用这些测量值，我们预测了低频和高频敏感性的各个方面，并表明灵长类动物的听觉模式可能在新生代的前半段经历了几个阶段的进化。这些结果为现存谱系听觉模式的发展提供了时间界限，并强烈表明祖先真兽类的听觉模式具有良好的高频听觉，但低频敏感性相对较差。它们还表明，在灵长类动物（现存或已灭绝）中，原猴类具有相对较长的耳蜗和增加的低频敏感性，这是独一无二的。我们将这些结果与其他更早期的古生物学证据相结合，将这些发现置于更广泛的进化背景中。
