Devonian climate change, breathing, and the origin of the tetrapod stem group
Devonian climate change, breathing, and the origin of the tetrapod stem group
复制标题
DOI：
10.1093/icb/icm055
复制
发表时间：
2007-10-01
影响因子：
2.6
通讯作者：
Clack, Jennifer A.
中科院分区：
文献类型：
--
作者：
Clack, Jennifer A.
四足动物茎群的多样化发生在中世纪晚期到泥盆纪晚期，即大约385-3.65亿年前的吉维阶到法门阶。代表这种辐射的已知分类群之间的关系目前已达成合理的共识，因此可以解释四足动物特征的出现顺序。最早的有肢四足动物的近亲鱼类显示出气孔室逐渐增大及其向外开口的现象。在这里，这被推断与呼吸空气能力的增加有关。人们认为大多数早期硬骨鱼都存在肺，并且最有可能通过吞气进行换气。这可能带来了兼性呼吸空气的能力，四足动物茎群最大限度地利用了这种能力。这些适应不仅体现在淡水形式中，而且也体现在河口和边缘海洋形式中。对这一时期氧气水平的估计表明，吉维蒂安和弗拉斯尼时期的氧气水平史无前例地低。与此同时，植物多样化速度最快，改变了景观特征，并通过土壤、可溶性养分和腐烂的植物物质，导致所有水系统缺氧。这些全球事件的同时发生可能解释了至少两个叶鳍类群的呼吸空气适应的进化，直接促进了四足类茎群的兴起。与最近的研究相反，低大气氧不被认为是缺乏记录早石炭世演化的化石的原因
The diversification of the tetrapod stem group occurred during the late Middle through the Late Devonian, that is from the Givetian to Famennian stages about 385-365 million years ago. The relationships between the known taxa representing this radiation have currently reached a reasonable consensus so that interpretations of the order of appearance of tetrapod characters is possible. The immediate fish relatives of the earliest limbed tetrapods show what is interpreted as a progressive increase in the spiracular chamber and its opening to the outside. Here, this is inferred to be associated with an increased capacity for air-breathing. Lungs are thought to have been present in most early bony fishes, and were most likely ventilated by air-gulping. This could have brought about a facultative capacity for air-breathing, which the tetrapod stem group exploited to the greatest degree. These adaptations are shown not only in freshwater forms but also in estuarine and marginal marine forms. Estimates of oxygen levels during this period suggest that they were unprecedentedly low during the Givetian and Frasnian periods. At the same time, plant diversification was at its most rapid, changing the character of the landscape and contributing, via soils, soluble nutrients, and decaying plant matter, to anoxia in all water systems. The co-occurrence of these global events may explain the evolution of air-breathing adaptations in at least two lobe-finned groups, contributing directly to the rise of the tetrapod stem group. In contrast to recent studies, low atmospheric oxygen is not considered to be a causal factor in the lack of fossils documenting the evolution of Early Carboniferous