By Kirsti Scott
The many species of modern sand dollars are prized finds of beachcombers around the world today. But, there were many ancient species, as well. On a few beaches along Monterey Bay in Central California, it’s possible to find fossils of some of these extinct creatures, which share the same biological family, phylum Echinodermata, as sea urchins, sea lilies, basket stars, brittle stars, sea stars, and sea cucumbers.
Sedimentary rocks in the cliff walls in the area are filled with millions of ancient clams, rays, shrimp, snails, starfish, and fossilized bones. The relentless waves and weather gradually erode the cliffs until the fossils drop the beach, where waves continue to wear away the relatively soft stone surrounding the fossils.
To date, two species of fossil sand dollars have been identified along Monterey Bay, according to paleontologist Wayne Thompson. “There may be more species once we finish with our research, but there are two common ones found in the area,” Wayne explains.
Above left is the Dendraster sullivani Durham and Morgan (1978), an extinct species with a central petal. “This is a particularly important specimen,” says Wayne, “because it shows the anus, at the lower middle of the photo (I know, sand dollar anus, right?), which typically breaks off (ouch!).”
Above right is the second species, Dendraster ashleyi Kew (1920), an extinct species with a marginal petal and splayed out fronds.
No matter which species you come across, they are always a fun find. With a grinder bit on a drill, you can clean off more of the sandstone coating the fossil and reveal its hidden beauty.
Pro tip: Look for a rock that looks like an Oreo cookie, with grey outside and a white line (above).
Learn more about beach fossils:
Learn more about fossils found on modern and ancient shores around the world. Fossil Articles ›
This article appeared in the Beachcombing Magazine May/June 2022 issue.