The study of fossil bones is extremely important to our understanding of dinosaurs because, in most instances, this is the only way to obtain knowledge about these animals. Other than footprints and rare fossil remains of skin, eggs, and certain (rarely found) petrified internal organs, dinosaur fossilized bones (and teeth) are the most common parts that survive over long spans of time. Depending on the way the bones lie within the rock strata, they provide important clues as to how these animals looked, ate, walked, socialized, lived, and, in some cases, died.