Mackay-Sim A, Duvall D, Graves B M
Brain Behav Evol. 1985;27(2-4):186-94. doi: 10.1159/000118729.
Completely aquatic marine mammals of the order Cetacea such as whales and dolphins have a reduced or absent olfactory system and neither a vomeronasal organ nor an accessory olfactory bulb. In comparison, seals, which are only partially aquatic, have olfactory and accessory olfactory systems including the vomeronasal organ. Thus, there seems to be a strong relation between the degree of adaptation to an aquatic environment and the degree of reduction in olfactory structures. Sirenians, such as manatees and dugongs, are another family of marine mammals which have secondarily adapted to a fully aquatic existence, yet there is dispute about the status of their olfactory structures. In the present study there was no evidence for a vomeronasal organ in the adult West Indian Manatee, Trichechus manatus. Additionally, the main olfactory system appeared quite rudimentary. These observations support the hypothesis that, in mammals, secondary adaptation to an aquatic environment leads to the reduction or loss of the olfactory senses.
鲸目完全水生的海洋哺乳动物，如鲸鱼和海豚，嗅觉系统退化或缺失，既没有犁鼻器也没有副嗅球。相比之下，只是部分水生的海豹具有包括犁鼻器在内的嗅觉和副嗅觉系统。因此，对水生环境的适应程度与嗅觉结构的退化程度之间似乎存在着紧密的联系。海牛目动物，如海牛和儒艮，是另一类海洋哺乳动物，它们在次生阶段适应了完全水生的生活，但它们嗅觉结构的状况存在争议。在本研究中，没有证据表明成年西印度海牛（Trichechus manatus）存在犁鼻器。此外，主嗅觉系统显得相当原始。这些观察结果支持了这样一种假说，即在哺乳动物中，对水生环境的次生适应会导致嗅觉的退化或丧失。
