DINOSAUR GASTROLITH
Gastroliths are the dinosaur equivalent of gizzard
stones in birds. Some birds (e.g., chickens) & some modern reptiles
(e.g., crocodilians) swallow pebbles and retain them in their gizzards.
The stones help to grind down food as it passes through the upper digestive
tract. The rocks themselves get polished in the process. Some
dinosaur skeletons have been found with concentrations of highly polished,
somewhat size-sorted rocks associated with the rib cage area. These have
been reasonably identified as dinosaur gizzard stones (gastroliths; a.k.a.
gastric stones). Gastroliths have only been reported to be associated
with the remains of sauropods, some early ceratopsians, and some ankylosaurs.
Dinosaur gastrolith (6.1 cm across) attributed to the Morrison Formation
(Upper Jurassic) of western USA.