The Lungs of Frogs

The typical lungs of your average frog are similar in general shape to the lungs of other terrestrial vertebrates in that they appear as lobes of soft tissue at the end of a trachea. They are also similar in function as they allow for blood and air to interact allowing for gas exchanges within the organ itself in specialized structures called alveoli; frogs have a much lower concentration of these structures in their lungs than other vertebrates. The lungs of Palaeobatrachus were not too different from those of their descendants in function, but their morphology was considerably different. Whereas extant frogs possess centrally located lungs housed in the thorax, the lungs of Palaeobatrachus were located within the dorsal sides of their thorax. Extant frogs, of course, do not only use their lungs to breathe. Gas exchange occurs within the mouth (minimally) and cutaneously while submerged; frogs make use of dissolved oxygen in the water to exchange gases through their skin. It could be hypothesized that the dorsal lungs of Palaeobatrachus laid the groundwork for these centralized lungs and also that they aided in enhancing the development of the system of cutaneous respiration we see in extant frogs. Cutaneous respiration may have, at the time, been the main method of filling the lungs of Palaeobatrachus as well, meaning that the lungs were an added adaptive characteristic of this frog; there exist today many small terrestrial amphibians completely lacking lungs. Perhaps these lungs enabled the frog to take in a large amount of air before diving and stay submerged longer in potentially oxygen poor aqueous environments. The evolutionary history of amphibian lungs is far more complex than we have time for today, unfortunately, but there are many resources available to delve into this history.