VERY SMALL, VERY RARE, VERY SPINY

The dark shell of this small ammonite is filled with black rock. But why do the light-colored tips of the spines appear translucent in the light? Although the spines of the ammonites were also hollow, they were separated from the inside of the shell by a membrane. If a spine broke off during the animal’s lifetime, no water could enter the shell. Conversely, the marine mud that was washed into the chambers after the animal’s death could not get into the spines that remained intact.