Data from: The dipnoan buccal pump reconstructed in 3D and implications for air breathing in Devonian lungfishes

Lungfishes are known for, and indeed take their name from, their bimodal respiratory abilities. All three extant genera can use their lungs to extract oxygen from the atmosphere, although their reliance upon this capability differs among taxa. Lungs are considered primitive for the Osteichthyes, however the distinctive buccal pump mode of air gulping exhibited by extant lungfishes appears to be a specialization. It is associated with a number of derived skeletal characters (cranial ribs, long parasphenoid stalk, midline gap between palatal tooth plates) that first appeared during the Devonian. These have been described individually, but in no Devonian lungfish has their three-dimensional (3D) spatial relationship been reconstructed and analyzed. Here we present the 3D morphology of Rhinodipterus, a Mid-Late Devonian lungfish from Australia and Europe, based on synchrotron tomography and conventional microtomography scans. Unlike less crownward contemporaneous lungfishes such as Griphognathus and Chirodipterus, Rhinodipterus has a full set of skeletal buccal pump components that can be directly compared to those of extant lungfishes, suggesting that it made more extensive use of air breathing than other Gogo or Bergisch Gladbach genera. This is interesting in relation to the environmental context as Gogo and Bergisch Gladbach are both marine, contrasting with the frequently hypoxic tropical to subtropical fresh water environments inhabited by modern lungfishes. The evolution of buccal pump-supported lung ventilation was evidently not necessarily associated with a transition to non-marine habitats.肺鱼（Lungfishes）以其双模式呼吸能力闻名，并正因该特性得名。目前现存的三个属均能借助肺从大气中摄取氧气，不过不同类群对该呼吸策略的依赖程度存在差异。肺被视为硬骨鱼纲（Osteichthyes）的原始性状，但现生肺鱼所特有的颊泵式吞气模式实则属于特化特征。该特征与一系列衍化骨骼性状相关，包括颅肋、细长的副蝶骨柄、腭骨齿板间的中线间隙，这些性状最早出现于泥盆纪（Devonian）时期。此前这些性状虽已被单独描述，但尚无泥盆纪肺鱼类群的三维（3D）空间关联关系得到重建与分析。本研究基于同步辐射断层扫描与常规显微断层扫描数据，呈现了产自澳大利亚与欧洲的中晚泥盆世肺鱼——鼻鳍鱼属（Rhinodipterus）的三维形态学特征。与同期更接近冠群的肺鱼（如栅齿鱼属Griphognathus与歧鳍鱼属Chirodipterus）不同，鼻鳍鱼属拥有一套完整的颊泵骨骼组件，可直接与现生肺鱼的对应结构进行比对，这表明其空气呼吸的应用范围比同期戈戈（Gogo）与贝尔吉施格拉德巴赫（Bergisch Gladbach）的肺鱼属类群更为广泛。这一发现与环境背景存在有趣的关联：戈戈与贝尔吉施格拉德巴赫的沉积环境均为海洋，而现代肺鱼多栖息于经常处于低氧状态的热带至亚热带淡水环境中。由此可见，依赖颊泵的肺通气演化过程，未必与向非海洋生境的转变存在必然关联。