Inner ear biomechanics reveals a Late Triassic origin for mammalian endothermy
Inner ear biomechanics reveals a Late Triassic origin for mammalian endothermy
复制标题
内耳生物力学揭示了哺乳动物吸热的晚三叠纪起源
DOI：
10.1038/s41586-022-04963-z
复制
发表时间：
2022-07-20
期刊：
影响因子：
64.8
通讯作者：
Angielczyk, Kenneth
中科院分区：
文献类型：
--
作者：
Araujo, Ricardo;David, Romain;Angielczyk, Kenneth
在不同的环境设置中，恒温动物是哺乳动物和鸟类的生态优势的基础。然而，目前还不清楚这一关键特征是在哺乳动物进化史上何时出现的，因为大多数化石证据都是模糊的。在这里，我们表明，这一关键的进化过渡可以使用内淋巴填充的内耳半圆管的形态学进行研究，它监测头部旋转，对运动协调，导航和空间意识至关重要。在哺乳动物祖先的外温-吸热转换期间，体温升高会降低内淋巴粘度，对半规管生物力学产生负面影响，同时增加行为活动可能需要改善性能。膜管和封闭骨管的形态学变化是必要的，以保持最佳的功能，在这个过渡。为了跟踪这些形态功能的变化，在56个灭绝的突触物种，我们开发了热运动指数，代理骨管形态的基础上。结果表明，在晚三叠世期间，哺乳动物门突然进化出吸热现象，这与体温的急剧增加（5-9摄氏度）以及有氧和无氧能力的扩张有关。与以前的建议相反，所有茎类都很可能是外温动物。恒温，作为一个重要的生理特征，加入了其他独特的哺乳动物的特点，出现在这一时期的气候不稳定。
Endothermy underpins the ecological dominance of mammals and birds in diverse environmental settings. However, it is unclear when this crucial feature emerged during mammalian evolutionary history, as most of the fossil evidence is ambiguous. Here we show that this key evolutionary transition can be investigated using the morphology of the endolymph-filled semicircular ducts of the inner ear, which monitor head rotations and are essential for motor coordination, navigation and spatial awareness. Increased body temperatures during the ectotherm-endotherm transition of mammal ancestors would decrease endolymph viscosity, negatively affecting semicircular duct biomechanics, while simultaneously increasing behavioural activity probably required improved performance. Morphological changes to the membranous ducts and enclosing bony canals would have been necessary to maintain optimal functionality during this transition. To track these morphofunctional changes in 56 extinct synapsid species, we developed the thermo-motility index, a proxy based on bony canal morphology. The results suggest that endothermy evolved abruptly during the Late Triassic period in Mammaliamorpha, correlated with a sharp increase in body temperature (5-9 degrees C) and an expansion of aerobic and anaerobic capacities. Contrary to previous suggestions, all stem mammaliamorphs were most probably ectotherms. Endothermy, as a crucial physiological characteristic, joins other distinctive mammalian features that arose during this period of climatic instability.