Pulmonary development in Squamata: Insights from embryonic studies using micro-CT

Abstract

Background: Pulmonary development in tetrapods is a complex process, especially within squamates, where single-chambered, transitional, and multi-chambered lungs can be found in adult animals. While the embryological development of the respiratory system of lizards and snakes was studied in a number of species between the 1830s and 1940s, the subject has only received sporadic attention since then. With the advancement of imaging technology, non-invasive methods can be used to explore the degree of respiratory system development in embryos of different ages. Results: Micro-computed tomography (micro-CT) was used to reconstruct three-dimensional extrapulmonary airways and pulmonary structures and to analyze lung development in five species of lizards (two species of Teiidae, one Anguidae, one Iguanidae, and one Tropiduridae) and one species of snake (Lamprophiidae). Results indicate that pulmonary parenchyma development was undetectable in the earliest embryonic stages, likely due to technical or developmental limitations. In later stages, structures such as faveolar parenchyma and intrapulmonary subdivisions were clearly observable, resembling the morphology seen in adult animals. Conclusions: These findings provide valuable insights into the viability of micro-CT scans to investigate embryonic respiratory systems, as well as into the evolution and development of the respiratory system in Squamata.