Previous scenarios for the evolution of unidirectional airflow are that it arose in dinosaurs of coelurosaurian grade (12), convergently in theropods and pterosaurs (13, 15), or not at all in dinosaurs because of a hepatic piston mechanism of breathing (14).
目前的观点认为双重呼吸产生于虚骨类恐龙，在兽脚类和翼龙中存在趋同演化，并不是所有恐龙都具有，因为更多恐龙是肝瓣活塞呼吸。
Our findings contrast with these previous views in several ways.
我们的研究与现行观点在几个方面形成了鲜明的比较。
They demonstrate that the hepatic piston mechanism of breathing, which crocodilians have but birds lack, does not preclude the evolution of unidirectional flow and that pneumaticity, which crocodilians lack, cannot be used to diagnose unidirectional airflow in fossil taxa, as previously suggested (13, 15).
肝瓣活塞呼吸，鳄鱼具有而鸟类没有；气囊，鳄鱼没有而鸟类具有。这些过去常常用来作为双重呼吸的鉴定，在化石研究中也是。
目前的观点认为双重呼吸产生于虚骨类恐龙，在兽脚类和翼龙中存在趋同演化，并不是所有恐龙都具有，因为更多恐龙是肝瓣活塞呼吸。
Our findings contrast with these previous views in several ways.
我们的研究与现行观点在几个方面形成了鲜明的比较。
They demonstrate that the hepatic piston mechanism of breathing, which crocodilians have but birds lack, does not preclude the evolution of unidirectional flow and that pneumaticity, which crocodilians lack, cannot be used to diagnose unidirectional airflow in fossil taxa, as previously suggested (13, 15).
肝瓣活塞呼吸，鳄鱼具有而鸟类没有；气囊，鳄鱼没有而鸟类具有。这些过去常常用来作为双重呼吸的鉴定，在化石研究中也是。
