短吻鳄的呼吸。
资料来源: C.G. Farmer

据1月15日的《科学》杂志报道说，短吻鳄的肺与鸟的肺类似，即空气是沿着一个单向通路进行流通，而非进出一个盲端通路。 这种肺的结构一般被认为是鸟类所独有的专门结构，因为鸟类在飞翔的时候需要大量的氧气。但新的研究结果提示，这种单向的气流模式最有可能是起源于鸟类和短吻鳄所共有的祖先，例如早期的爬行动物，或三叠纪中的“祖龙”。

Collen Farmer 和Kent Sanders研究了美洲短吻鳄肺内的空气和水流模式，他们的研究包括了活体动物的肺以及切割下来的人工通气的肺。 他们发现，在短吻鳄中的气流是单向的而且与鸟类极为相似，尽管现在仍不清楚短吻鳄究竟是如何进行这种类型的呼吸的，因为它们并没有鸟肺所具有的气囊。 文章的作者提出，这种气流模式可追溯到三叠纪早期的祖龙，并可能一直存在于不同的祖龙后裔之中，即除了鳄鱼和鸟类之后还包括恐龙。 这些作者进一步猜测，这种肺结构可能赋予早期祖龙种群某种优势，使它们能够进行剧烈的运动。

原始出处：

Science 15 January 2010: DOI: 10.1126/science.1180219

Unidirectional Airflow in the Lungs of Alligators

C. G. Farmer1,* and Kent Sanders2

The lungs of birds move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi), whereas in the lungs of mammals and presumably other vertebrates, air moves tidally into and out of terminal gas-exchange structures, which are cul-de-sacs. Unidirectional flow purportedly depends on bellowslike ventilation by air sacs and may have evolved to meet the high aerobic demands of sustained flight. Here, we show that air flows unidirectionally through parabronchi in the lungs of the American alligator, an amphibious ectotherm without air sacs, which suggests that this pattern dates back to the basal archosaurs of the Triassic and may have been present in their nondinosaur descendants (phytosaurs, aetosaurs, rauisuchians, crocodylomorphs, and pterosaurs) as well as in dinosaurs.

1 Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA.
2 Department of Radiology, Musculoskeletal Division, 50 North Medical Drive, Room 1A71, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.