Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water
Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water
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DOI：
10.1073/pnas.2002146117
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发表时间：
2020-05-12
影响因子：
11.1
通讯作者：
Brusatte, Stephen L.
中科院分区：
文献类型：
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作者：
Schwab, Julia A.;Young, Mark T.;Brusatte, Stephen L.
动物发展新的身体计划并适应新的栖息地和生活方式的重大进化转变，已经打断了生命的历史。鲸目动物从陆地哺乳动物的起源是这些事件中最著名的。更早的时候，在中生代，许多爬行动物也从陆地迁移到水中，但这些转变却知之甚少。我们使用计算机断层扫描来研究内耳前庭系统的变化，涉及感知平衡和平衡，作为这些群体之一，灭绝的鳄鱼亲戚称为thalattosuchians，从陆地祖先转变为远洋（公海）游泳者。我们发现，前庭系统的形态与栖息地相对应，远洋thalattosuchians表现出更紧凑的迷宫，更广泛的半规管直径和扩大前庭，让人想起修改和小型化的其他海洋爬行动物和鲸类动物。具有改良内耳的远洋海鳄类是具有长半水生阶段的进化趋势的顶点，并且它们的远洋前庭系统在颅后骨骼的第一次变化后出现，这增强了它们的游泳能力。这与鲸目动物有着显著的不同，鲸目动物在进入水中后很快就缩小了它们的触角，没有延长的半水生阶段。因此，海鳄类和鲸类以不同的方式和不同的速度成为次生水生动物，这表明同一类型的转变有不同的途径。
Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but these transitions are more poorly understood. We use computed tomography to study changes in the inner ear vestibular system, involved in sensing balance and equilibrium, as one of these groups, extinct crocodile relatives called thalattosuchians, transitioned from terrestrial ancestors into pelagic (open ocean) swimmers. We find that the morphology of the vestibular system corresponds to habitat, with pelagic thalattosuchians exhibiting a more compact labyrinth with wider semicircular canal diameters and an enlarged vestibule, reminiscent of modified and miniaturized labyrinths of other marine reptiles and cetaceans. Pelagic thalattosuchians with modified inner ears were the culmination of an evolutionary trend with a long semiaquatic phase, and their pelagic vestibular systems appeared after the first changes to the postcranial skeleton that enhanced their ability to swim. This is strikingly different from cetaceans, which miniaturized their labyrinths soon after entering the water, without a prolonged semiaquatic stage. Thus, thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition.