Dataset from: Lung evolution in vertebrates and the water-to-land transition

A crucial evolutionary change in vertebrate history was the Palaeozoic
(Devonian ~400 million years ago) water-to-land transition, allowed by key
morphological and physiological modifications including the acquisition of
lungs. Nonetheless, the origin and early evolution of vertebrate lungs
remain highly controversial, particularly whether the ancestral state was
paired or unpaired. Due to the rarity of fossil soft tissue preservation,
lung evolution can only be traced based on the extant phylogenetic
bracket. Here we investigate, for the first time, lung morphology in
extensive developmental series of key living lunged osteichthyans using
synchrotron X-ray microtomography and histology. Our results shed light on
the primitive state of vertebrate lungs as unpaired, evolving to be truly
paired in the lineage towards the tetrapods. The water-to-land transition
confronted profound physiological challenges and paired lungs were
decisive for increasing the surface area and the pulmonary compliance and
volume, especially during the air-breathing on land.