Diane also found the first fossil of the day... a whale's tympanic bulla in a concretion... A tympanic bulla is a bone found in the skull of cetaceans (whales, dolphins, & porpoises) that is involved in hearing through echolocation. Because of the extreeme density of the bone (among the densest bones known in the animal kingdom) it preserves as a fossil well. It has a distinctive "wrinkle" and a thin "lip" of bone. It is characteristically egg-shaped and one can determine whether it came from the right or left side by cupping the lip between the thumb and index finger with the bulbous part down. The one below is from the right side of the skull as the lip is on the right.