Crocodilian Biology Database

Palatal Valve

General Biology / Adaptations to diving: Unlike most reptiles, crocodiles have many adaptations to a semi-aquatic lifestyle.

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GENERAL BIOLOGY

Palatal Valve

Location of palatal valve within mouth

LOCATION:	Fleshy extension at the rear of lower palate/tongue covering the opening to the back of the throat. Present in all species.
TYPE:	Morphological adaptation
FUNCTION:	Seals the opening to the throat, preventing water from entering when the crocodile is submerged. Can be opened when feeding in air.

A crocodile's mouth is not watertight when closed, and water easily enters when the crocodile submerges. The palatal valve is present in all species and plays an essential role in preventing water in the mouth from entering the throat, oesophagus and trachea when the crocodile is underwater. This enables the crocodile to open its mouth at any time underwater (see right), and is particularly useful during prey capture. When taking an aquatic prey item, the crocodile can open its mouth without flooding its throat. Terrestrial prey can also be dragged into the water and drowned.

If you've ever wanted to look down a crocodile's throat, take a look at the diagram on the left! Here, the palatal valve at the back of the throat has been pushed down to reveal the opening to the trachea (the 'glottis'), which leads to the crocodile's lungs. Above that is the beginning of the oesophagus, which leads to the stomach. When the palatal valve is sealed, neither water nor air can enter the throat from the mouth - no matter how much the crocodile's head is thrashed around in the water. But how does the crocodile breathe when it's in the water?

A crocodile spends a considerable period of time with its head partially submerged, and hence the mouth flooded. Only the crocodile's eyes and nostrils are visible above the water surface (a 'minimum exposure profile'). In this position the crocodile can still breathe because of an evolutionary adaptation that has caused the internal nares (where the nostrils open internally) to move right to the back of the upper palate. Therefore, as long as the nostrils are open and above the water surface, the crocodile can effectively by-pass the palatal valve and breathe. When the crocodile's head is totally submerged, however, the nostrils are sealed to prevent influx of water. The crocodile can survive underwater without taking a fresh breath for a considerable period of time (see FAQ), although a voluntary dive normally lasts no longer than 20 minutes. This is far longer than terrestrial mammalian prey can achieve, and is a common strategy used to subdue struggling prey.

In order to eat captured prey, the crocodile must do so out of water. Any attempt to swallow the food underwater would result in a considerable amount of water also being imbibed. So, the crocodile either leaves the water, or holds its head at an angle out of the water. In this position, the prey can be manipulated by the jaws and crushed with assistance from the teeth. If the prey is too large to swallow, pieces are either ripped off by rolling the body, or whipping the head violently to one side. Once in the stomach, strong acids quickly break down most organic materials.

In order to swallow on land, the crocodile tips its head back and throws the food towards the back of its mouth with a flick of the head. Muscles pull the palatal valve down towards the tongue, allowing the food to enter the throat and oesphagus. From here it passes towards the stomach. As you can see from the above photograph, the opening to the throat is relatively large once the palatal valve has been pulled down.