Heesy Christopher P, Hall Margaret I
Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ 85308, USA.
Brain Behav Evol. 2010;75(3):195-203. doi: 10.1159/000314278. Epub 2010 Aug 20.
Evidence from the early paleontological record of mammalian evolution has often been interpreted as supporting the idea that mammals were nocturnal for most of their early history. Multiple features of extant mammal sensory systems, such as evolutionary modifications to the light-regulated circadian system, photoreceptor complement, and retinal morphology, support this nocturnal hypothesis for mammalian evolution. Here, we synthesize data on eye shape and orbit orientation in mammals as these data compare to other amniotes. Most mammals differ from other amniotes in retaining an eye design optimized for high visual sensitivity, with the requisite reduction in acuity, which is typically restricted to scotopically (i.e. low light) adapted amniotes. Mammals also possess the more convergent (similarly facing) orbits and, on average, the largest binocular visual fields among amniotes. Based on our analyses, we propose that extant mammals retain a scotopic eye design as well as expanded binocular zones as a result of their nocturnal origin. Only anthropoid primates notably differ from general mammalian patterns, and possibly have evolved an eye shape more typical of the ancestral amniote condition.
早期哺乳动物进化的古生物学记录中的证据常常被解释为支持这样一种观点，即哺乳动物在其早期历史的大部分时间里都是夜行性的。现存哺乳动物感觉系统的多个特征，如对光调节的昼夜节律系统、光感受器组成和视网膜形态的进化改变，都支持了这种关于哺乳动物进化的夜行性假说。在这里，我们综合了有关哺乳动物眼睛形状和眼眶方向的数据，并将这些数据与其他羊膜动物的数据进行比较。大多数哺乳动物与其他羊膜动物的不同之处在于，它们保留了一种为高视觉敏感度而优化的眼睛设计，同时相应地降低了敏锐度，而这种设计通常只限于适应暗视（即低光）的羊膜动物。哺乳动物还拥有更趋同（同样朝前）的眼眶，并且平均而言，在羊膜动物中具有最大的双眼视野。基于我们的分析，我们提出，现存哺乳动物由于其夜行性起源而保留了暗视眼睛设计以及扩大的双眼区域。只有类人灵长类动物明显不同于一般的哺乳动物模式，并且可能已经进化出了一种更典型的祖先羊膜动物状态的眼睛形状。
