Crocodiles breathe air using a sophisticated respiratory system centered around their lungs. Their lungs are spongy and multi-chambered, designed for efficient gas exchange. Air enters through the nostrils, travels down the trachea, and reaches the lungs.
Crocodile respiration features a “hepatic piston” mechanism. This involves a diaphragm-like muscle attached to the liver. When this muscle contracts, it pulls the liver backward, expanding the thoracic cavity and creating negative pressure to draw air into the lungs. Exhalation occurs as muscles relax, pushing the liver forward and expelling air.
At the water’s surface, a crocodile’s nostrils take in air, while a palatal valve (a flap of tissue at the back of its throat) seals off the airway from the mouth. This allows breathing even when its mouth is submerged or holding prey. The glottis, the opening to the trachea, also regulates airflow.
Adapting to Life in Water
Despite relying on lungs, crocodiles exhibit physiological and behavioral adaptations allowing them to spend extended periods underwater. They can hold their breath for several minutes to over an hour, depending on activity and water temperature. This breath-holding capacity is supported by a reduced metabolic rate during submersion.
Bradycardia, the ability to slow their heart rate while diving, is a key adaptation. This conserves oxygen by reducing the demand from various tissues. Valves in their nostrils and a glottal seal close off respiratory passages, preventing water from entering the lungs during dives.
Crocodiles can selectively redirect blood flow, a process known as blood shunting. During a dive, blood shunts away from less oxygen-sensitive organs to prioritize the brain and heart, ensuring these organs receive a continuous oxygen supply. Their bodies can also tolerate higher levels of carbon dioxide and lactic acid accumulation, which are byproducts of anaerobic respiration during prolonged submersion.
Why Crocodiles Don’t Have Gills
Crocodiles are reptiles, not fish, and their respiratory system reflects their evolutionary lineage. Gills extract dissolved oxygen directly from water, a characteristic of aquatic vertebrates like fish and some amphibians. Reptiles, including crocodiles, evolved from terrestrial ancestors that breathed air.
Their lung-based respiratory system, coupled with physiological and behavioral adaptations, suits their semi-aquatic lifestyle. These adaptations allow them to hunt, hide, and rest underwater for extended periods without the need for gills. The presence of lungs in crocodiles is consistent with their classification as air-breathing vertebrates adapted to both terrestrial and aquatic environments.