A nice palm sized Sand Dollar from Baha, Mexico.
The term sand dollar (also known as a sea cookie or snapper biscuit in New Zealand, or pansy shell in South Africa) refers to species of extremely flattened, burrowing sea urchins belonging to the order Clypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits. Related animals include other sea urchins, sea cucumbers, and starfish. Sand dollars, like all members of the order Clypeasteroida, possess a rigid skeleton known as a test. The test consists of calcium carbonate plates arranged in a fivefold radial pattern. The ancestors of sand dollars diverged from the other irregular echinoids, namely the cassiduloids, during the early Jurassic, with the first true sand dollar genus, Togocyamus, arising during the Paleocene. Soon after Togocyamus, more modern-looking groups emerged during the Eocene.
Miocene (3.6-23 Million years ago)