So What's a Gastrolith?
Gastroliths are rocks or stones that animals, not just crocodiles, swallow and store in their gizzards. For this reason the rocks are also referred to as gizzard stones. The term gastrolith is a combination of the two Greek words gastro and lith, with the former meaning "stomach" and the latter meaning "stone" (Cochise College). The size of the gastrolith depends on how big the animal is, ranging from sand to cobbles that are several inches in diameter. Any kind of rock can become a gastrolith if it is swallowed by an animal.
Gastroliths are rocks or stones that animals, not just crocodiles, swallow and store in their gizzards. For this reason the rocks are also referred to as gizzard stones. The term gastrolith is a combination of the two Greek words gastro and lith, with the former meaning "stomach" and the latter meaning "stone" (Cochise College). The size of the gastrolith depends on how big the animal is, ranging from sand to cobbles that are several inches in diameter. Any kind of rock can become a gastrolith if it is swallowed by an animal.
Animals store gastroliths in their gizzards, earning them the alternate title of "gizzard stones."
Gastroliths vary greatly in size, ranging in diameters from just a few millimeters to several inches.
Functionality
Gastroliths function as a digestion aid in, particularly in herbivorous animals that lack suitable grinding teeth. When the gizzard contracts the gastroliths grind against each other and break down ingested food. Eventually the jagged rocks become smooth and less effective from the repeated grinding, so the animal vomits them out and find new, sharp rocks to swallow.
Among terrestrial carnivorous animals such as the crocodile, the function of gastroliths is widely debated, but many believe that they help regulate the buoyancy of animals. Many also assert that the gastroliths function as ballasts, stabilizing the animal and aiding in balance. Click on the "Gastroliths in Crocodiles" tab to learn more about the scientific research that has been conducted on the stone-swallowing behavior of crocodiles.
Pictured below are an assortment of gastroliths. Notice the smooth appearance which is caused by the repeated grinding of the stones against other stones in the animals' gizzards.
Gastroliths function as a digestion aid in, particularly in herbivorous animals that lack suitable grinding teeth. When the gizzard contracts the gastroliths grind against each other and break down ingested food. Eventually the jagged rocks become smooth and less effective from the repeated grinding, so the animal vomits them out and find new, sharp rocks to swallow.
Among terrestrial carnivorous animals such as the crocodile, the function of gastroliths is widely debated, but many believe that they help regulate the buoyancy of animals. Many also assert that the gastroliths function as ballasts, stabilizing the animal and aiding in balance. Click on the "Gastroliths in Crocodiles" tab to learn more about the scientific research that has been conducted on the stone-swallowing behavior of crocodiles.
Pictured below are an assortment of gastroliths. Notice the smooth appearance which is caused by the repeated grinding of the stones against other stones in the animals' gizzards.
Identification
The primary distinctive features of gastroliths are similar to ordinary sedimentary rocks. Like these rocks, gastroliths are polished and rounded due to the abrasion caused by the contents of the gizzard. When the gizzard is contracted by the animal, the grinding of the gastroliths against each other has a polishing effect on the rocks. In differentiating gastroliths from normal sedimentary rocks, the presence of hairline fractures on the surface of the rock confirm its identity as a gastrolith (Cochise College). These fractures are presumably caused by contact with a sharp corner of a freshly swallowed stone. Furthermore, gastroliths are even more highly polished than sedimentary rocks.
The primary distinctive features of gastroliths are similar to ordinary sedimentary rocks. Like these rocks, gastroliths are polished and rounded due to the abrasion caused by the contents of the gizzard. When the gizzard is contracted by the animal, the grinding of the gastroliths against each other has a polishing effect on the rocks. In differentiating gastroliths from normal sedimentary rocks, the presence of hairline fractures on the surface of the rock confirm its identity as a gastrolith (Cochise College). These fractures are presumably caused by contact with a sharp corner of a freshly swallowed stone. Furthermore, gastroliths are even more highly polished than sedimentary rocks.
References
Cochise College. (No Date). Gizzard Stones (Gastroliths). [Online]. Available: http://skywalker.cochise.edu/wellerr/students/gastrolith/project.htm
Cochise College. (No Date). Gizzard Stones (Gastroliths). [Online]. Available: http://skywalker.cochise.edu/wellerr/students/gastrolith/project.htm