Echinoderms are some of the most recognizable and most overlooked fossils a collector can find. From star-shaped impressions to stacks of tiny stone discs, their remains are scattered through marine rocks around the world. With more known fossil species than living ones, echinoderms offer a remarkable window into ancient seas and the conditions that once shaped them.
Echinoderms: Key Takeaways
- Echinoderms include crinoids, starfish, sea urchins, and related marine animals with a long fossil history.
- More echinoderm species are known from fossils than are living today.
- Their calcareous plates and five-part symmetry make them especially likely to fossilize.
- Echinoderm fossils help reveal ancient ocean conditions, including water depth and clarity.
- Crinoid columnals are among the most common and accessible fossils for collectors.
About Echinoderms
This group of marine animals includes sea lilies (Crinoidea), blastoids, cystoids, starfish (Asteroidea), brittle stars (Ophiuroidea), sea urchins and sand dollars (Echinoidea) and sea cucumbers (Holothuroidea). Both the 6,500-plus living species and the 14,000-plus fossil species are marine.
Echinoderms are found as fossils as far back as 540 million years, the most common being crinoids and blastoids. Echinoderms are conducive to forming fossils because their bodies consist of a series of interlocking calcareous (CaCo3) plates, usually with five-point symmetry. This is readily seen in the interlocking discs that make up the stem of crinoids. These discs frequently get separated after the animal dies and they fossilize as individual circles.
Clues to Ancient Oceans
Fossil echinoderms offer valuable clues about the environments in which they lived. Because most echinoderms thrived in shallow, clear, oxygen-rich waters, their fossils often indicate similar conditions in the rock layers where they are found. Crinoids, for example, were typically anchored to the seafloor and flourished in calm marine settings, while certain echinoids adapted to burrowing in softer sediments. The presence, abundance, and types of echinoderm fossils within a formation can help paleontologists interpret water depth, energy levels, and even changes in sea level over time. For collectors, this means that a simple crinoid stem or sea urchin test is more than just a fossil—it’s a snapshot of an ancient ocean ecosystem.
What Collectors Should Look For
Echinoderm fossils are among the most accessible finds for beginners and seasoned collectors alike. They are most commonly found in marine sedimentary rocks such as limestone and shale, where ancient seabeds have been preserved. Crinoid columnals are those small, round, disc-like segments of the stem. They are especially abundant and often appear as tiny stacked “beads” or scattered rings within the rock.
Star-shaped patterns from crinoids or the five-part symmetry of sea urchins and sand dollars can also stand out on weathered surfaces. In some regions, entire crinoid stems, calyxes, or even starfish impressions can be found, though these are less common. Careful splitting of rock layers and close inspection of surfaces can reveal details that are easy to miss at first glance, making echinoderms both a rewarding and approachable group for fossil hunters.
Echinoderms as State Fossils
The abundance and visibility of echinoderms in the fossil record have earned them recognition at the state level. While dinosaurs often dominate fossil designations, some states have turned to these marine invertebrates to represent their geologic heritage.
Missouri, for example, named the crinoid Delocrinus missouriensis as its official state fossil, highlighting the importance of sea lilies in the region’s limestone formations. In Iowa, crinoids have long been considered for similar recognition due to their prevalence in the state’s bedrock. A 2018 resolution noted significant crinoid deposits in Burlington, Le Grand, and Gilmore City, with Burlington often referred to by paleontologists as the “crinoid capital of the world.”
Farther south, there have been proposals to designate the sea biscuit—a type of flattened sea urchin—as the state fossil of Florida, underscoring the widespread presence of echinoderms in coastal and marine deposits across the United States.
FAQs About Echinoderms
What are echinoderms?
Echinoderms are a group of marine invertebrates that include sea stars, crinoids, sea urchins, and sea cucumbers. They are characterized by radial symmetry and bodies made of calcareous plates.
Why are echinoderms common in the fossil record?
Their skeletons are composed of calcium carbonate plates (CaCO₃), which fossilize readily. After death, these plates often separate and are preserved as individual pieces.
What is the most common echinoderm fossil?
Crinoid columnals—small, disc-shaped stem segments—are among the most commonly found echinoderm fossils.
Where can I find echinoderm fossils?
They are typically found in marine sedimentary rocks such as limestone and shale, which formed in ancient seabeds.
What do echinoderm fossils tell us?
They provide clues about ancient marine environments, including water depth, sediment conditions, and ocean chemistry.
From scattered crinoid discs to rare, fully preserved starfish, echinoderms connect collectors to oceans that vanished hundreds of millions of years ago. Their abundance in the fossil record and their sensitivity to environmental conditions make them more than just interesting finds—they are enduring records of Earth’s marine history. Whether discovered in a slab of limestone or carefully extracted from shale, each specimen offers a small but meaningful glimpse into the ancient seas that once covered much of our world.
This story about echinoderms previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Richard Gross and Pam Freeman.
