The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (birds and other dinosaurs, crocodiles, alligators, pterosaurs), earthworms, some gastropods, some fish, and some crustaceans. This specialized stomach constructed of thick muscular walls is used for grinding up food, often aided by particles of stone or grit. In certain insects and molluscs, the gizzard features chitinous plates or teeth.
Etymology The word gizzard comes from the Middle English giser, which derives from a similar word in Old French gésier, which itself evolved from the Latin gigeria, meaning giblets.
Structure
In birds Birds swallow food and store it in their crop if necessary. Then the food passes into their glandular stomach, also called the proventriculus, which is also sometimes referred to as the true stomach. This is the secretory part of the stomach. Then the food passes into the gizzard (also known as the muscular stomach or ventriculus). The gizzard can grind the food with previously swallowed grit and pass it back to the true stomach, and vice versa. In layman's terms, the gizzard 'chews' the food for the bird because it does not have teeth to chew food the way humans and other mammals do. By comparison, although in birds the stomach occurs in the digestive tract prior to the gizzard, in grasshoppers the gizzard occurs prior to the stomach, while in earthworms there is only a gizzard, and no stomach.
Koilin lining In order to protect the muscles of the gizzard, the organ has a multi-layered membrane - or gastric cuticle - made of koilin, a carbohydrate-protein complex (and not keratin as once believed) to protect the muscles. The thickness of this membrane varies with the types of food the animal eats, with diets heavier in grains, seeds, and insects creating thicker membranes than those consisting of fruits, worms, meat, and other softer edibles. In some animals the membrane is slowly worn and replaced over time, while others will discard the worn lining in its entirety periodically. The lining is critical to the proper functioning of the gizzard, but in some animals it can play an additional role as well. The male hornbill, for example, will fill its gizzard with fruit and then slough off the entire membrane to present it like a 'bag of fruit' to its mate during the nesting season.
Gizzard stones Some animals that lack teeth will swallow stones or grit to aid in fragmenting hard foods. All birds have gizzards, but not all will swallow stones or grit. Those that do employ the following method of chewing:
A bird swallows small bits of gravel that act as 'teeth' in the gizzard, breaking down hard food such as seeds and thus helping digestion. These stones are called gizzard stones or gastroliths and usually become round and smooth from the polishing action in the animal's stomach. When too smooth to do their required work, they may be excreted or regurgitated.
Animals with gizzards
Mammals Pangolins lack teeth and grind their food in a gizzard-like structure alongside pebbles.
Birds and other archosaurs All birds have gizzards. The gizzards of emus, turkeys, chickens, and ducks are most notable in cuisine (see below). Crocodilians such as alligators and crocodiles also have gizzards. Dinosaurs that are believed to have had gizzards based on the discovery of gizzard stones recovered near fossils include:
Psittacosaurus Massospondylus Sellosaurus Omeisaurus Apatosaurus Barosaurus Dicraeosaurus Seismosaurus The belief that Claosaurus had a gizzard has been discredited on the grounds that the fossil remains this claim was based on were another species and the stones merely from a stream. At least some pterosaurs seemingly had gizzards. The most notable cases are Pterodaustro (inferred via gastroliths) and Rhamphorhynchus (directly preserved). Carnivorous birds such as birds of prey as well as kiwis have membranuous gizzards as opposed to the sub-compressed gizzards of most birds. Conversely, it is thought that some extinct birds like Enantiornithes did not have gizzards.
Fish The mullet (Mugilidae) found in estuarine waters worldwide, and the gizzard or mud shad, found in freshwater lakes and streams from New York to Mexico, have gizzards. The gillaroo (Salmo stomachius), a richly colored species of trout found in Lough Melvin, a lake in the north of Ireland, has a gizzard which is used to aid the digestion of water snails, the main component of its diet.
Crustaceans
Some crustaceans have a gizzard although this is usually referred to as a gastric mill.
Earthworms Earthworms also have gizzards.
In cuisine
Poultry gizzards are a popular food throughout the world. Grilled chicken gizzards are sold as street food in Haiti and throughout Southeast Asia. They are considered offal. Giblets consist of the heart, liver and gizzard of a bird, and are often eaten themselves or used as the basis for a soup or stock. Gizzard and mashed potato is a popular dish in many European countries.
Europe Stewed gizzards are eaten as a snack in Portugal, with a tomato based sauce. In Spain, they are cooked on the plancha, and eaten while they are crispy on the outside. In Hungary, it is made with paprika as zúza pörkölt. In France, especially the Dordogne region, duck gizzards are eaten in the traditional Périgordian salad, along with walnuts, croutons and lettuce. In Italy, gizzards are often used mixed with other offal. In eastern Slavic countries, gizzards are the basis of many soups, such as rassolnik. In Yiddish, gizzards are referred to as pupik'lech (also pipiklach, in its less normative form), literally meaning navels. The gizzards of kosher species of birds have a green or yellowish membrane lining the inside, which must be peeled off before cooking, as it lends a very bitter taste to the food. In traditional Eastern European Jewish cuisine, the gizzards, necks and feet of chickens were often cooked together, although not the liver, which per kosher law must be broiled. Kosher butchers often sell roasting chickens with the gizzard, neck and feet butchered and left in the cavity to be used for making chicken soup.
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