Fossil Echinoderms in National Parks: Crinoids, Blastoids and Their Kin

Fossils of echinoderms turn up in national parks all over the country, and most of them are crinoids. Crinoid fossils are most common in Paleozoic marine sedimentary rocks, though echinoderms can appear in rock from any part of the Phanerozoic. Most are found in place in the rock. The round disks that make up crinoid stems resist erosion, though, so they also often weather out of bedrock and lie loose on the ground. Crinoids can even make up much of a building stone — including the stone of the Capitol Reflecting Pool in Washington, DC.

Crinoid fossils in the building stone of the Capitol Reflecting Pool. Image from the National Park Service's page.

What an echinoderm is

The name means "spiny skin," from the ancient Greek words for "hedgehog" and "skin." These marine invertebrates are known for their five-sided radial symmetry, and they have an internal hydraulic system — the water vascular system — that handles nutrient distribution, breathing and movement.

Today echinoderms live from the shallowest ocean waters down to abyssal depths. The major living groups are:

• sea urchins
• starfish
• brittle stars
• sea cucumbers
• crinoids (feather stars and sea lilies)

Echinoderms first appeared in the Cambrian. Three groups are especially common as fossils: crinoids, blastoids and sea urchins. The skeleton is built from many small pieces, often of calcium carbonate. When the animal dies, the body falls apart into those pieces — which are common fossils — so complete or even partial echinoderm fossils are quite rare.

Blastoids

A blastoid in the Middle Mississippian Ste. Genevieve Formation. NPS photo by Rick Olson.

Blastoids are known from at least 7 park areas, mostly in Mississippian rock — the time when they were especially abundant. Examples include Mammoth Cave National Park in Kentucky, Russell Cave National Monument in Alabama and Buffalo National River in Arkansas.

Crinoids

Assorted crinoid columnals from Grand Canyon-Parashant National Monument. NPS, 2020 field inventory.

Star- and pentagon-shaped columnals, Grand Canyon-Parashant National Monument. NPS, 2020 field inventory.

Crinoid fossils occur in at least 55 parks, mostly in Paleozoic rock. Nearly all are single columnals — small round or gear-shaped disks — or short stretches of stalk made of a few of them. They're only a small part of the animal: the disks formed the stalk that anchored it to the seafloor, while the crown broke up after death and survives, at most, as an occasional stray plate. Columnals can be so abundant, though, that they are the main component of a rock.

• Some columnals are star-shaped, reflecting the five-sided symmetry — for example at Grand Canyon-Parashant National Monument in Arizona and Zion National Park in Utah.
• At Mammoth Cave, crinoids are common in the cave's Mississippian limestones; when that rock was being laid down, the area may have been a kind of "crinoid thicket."
• Several crinoid species have been named from Ordovician fossils in what is now Mississippi National River and Recreation Area in Minnesota.
• At Grand Canyon National Park, crinoids appear in many rock units, including the Mississippian Redwall Limestone and the Permian Kaibab Formation.
• Besides the Reflecting Pool, crinoid-rich building stone is common at Fort Scott National Historic Site in Kansas.

Crowded crinoid columnals in the Mississippian St. Joe Limestone, Buffalo National River. NPS photo by Aliera Konett.

Large crinoid stem fragments in building stone at Fort Scott National Historic Site. Image from the National Park Service's page.

Sea urchins, starfish and stranger relatives

A fossil sea urchin from Guadalupe Mountains National Park, Texas; the red arrow marks the spines and the yellow arrow the body. Image from the National Park Service's page.

Sea urchins and other echinoids have been found in at least 50 units of the National Park System, in marine rock from the Paleozoic through the Cenozoic. Notable records:

• Paleozoic urchins at Grand Canyon National Park and Grand Canyon-Parashant National Monument (Arizona), Guadalupe Mountains National Park (Texas) and Mammoth Cave National Park (Kentucky)
• Cenozoic echinoids at Glacier Bay National Park and Preserve (Alaska) and Channel Islands National Park (California)

Echinoid fossils from Grand Canyon-Parashant National Monument: a spine socket (A), a spine with its attachment (B) and a spine in cross section (C). Scale bars are 3 cm in A and C, 1 cm in B. Image from the National Park Service's page.

Starfish (asteroids) have been reported from six parks, including Mesa Verde National Park in Colorado and Delaware Water Gap National Recreation Area. Their look-alikes, the brittle stars (ophiuroids), are known from only four.

A handful of parks also hold fossils of unusual groups, most of which died out during the Paleozoic. Great Basin National Park in Nevada and Mississippi National River and Recreation Area in Minnesota have especially varied collections, including:

• cystoids — some stalked, others odd creatures that look like armored fish from another planet, their stalk turned into a kind of whip
• edrioasteroids — something like a starfish sitting on a bean-bag chair
• eocrinoids — stalked echinoderms once thought to be the ancestors of crinoids, now known to be closer to blastoids

Sources

Based on "Fossil Echinoderms – Crinoids, Blastoids, and Others," part of the series Invertebrate Fossils in National Parks, National Park Service; a work of the United States government in the public domain.