Even though they lack a diaphragm muscle, most reptiles do possess a diaphragm-like respiratory system, and they can breathe through the use of lungs. This is true of all reptiles, however, some have also evolved less common and highly specialized breathing methods that they use to prolong the amount of time they can spend underwater and maximize their ability to use the oxygen found in the specific habitat they are based in. From the use of unique lung structures to alveoli and the ability to use their own skin to absorb the added oxygen they need, many reptiles have evolved more similarly to deep ocean fish, being capable of spending significant amounts of time submerged at considerable depths.
Squamates such as lizards and snakes use axial musculature ventilation to maximize their lungs’ ability to retain oxygen. Other lizards manage to increase their aerobic capabilities through buccal pumping, managing to bring a greater amount of air to their longs at any given time. Also, marine snakes are capable to extend their trachea while ingesting large quantities of food, so their respiratory system isn’t affected by the fact that, like other reptiles, they lack a secondary palate. These are only a few of the many examples of diverse respiratory methods and challenges that are associated with reptilian species.
Despite all the various adaptations that reptile use in order to enhance their breathing practices, their lungs are still their primary organs in charge of breathing. Reptiles use the same musculature to breathe that they use for locomotion, and some species, like the Tegu lizards, are also able to increase pulmonary activity through the use of proto-diaphragm, which separates the viscera from the lungs. Marine reptiles like crocodiles have the most similar breathing techniques to humans, using a muscular diaphragm that is similar to the type of diaphragm most mammals use, and also bringing the liver down to make additional space for the oxygen they require.
Breathing methods are not entirely understood in the case of all species of turtles and tortoises. Scientists have determined that some of them breathe continuously, while others only breathe in tune with their locomotion rhythm. Their carapaces present a challenge to breathing, since they do not allow them to expand and contract their trachea enough to provide their lungs with their necessary air supply. As a result, turtles and tortoises have their lungs closely attached to their carapace and are able to move their viscera in order to breathe, using a series of muscles similar to a diaphragm. Many species of tortoises have also developed sheets of muscle that envelop the lungs and force air in and out of the lungs. These species have probably the most unique breathing method of all reptiles.