Fossil Echinoderms – Crinoids, Blastoids, and Others

Crinoid fossils in the building stone of the Capitol Reflecting Pool.

Introduction

Echinoderm fossils—mostly of crinoids—are found in national parks throughout the country. Crinoid fossils are most common in Paleozoic marine sedimentary rocks, but echinoderms may be found in rocks deposited throughout the Phanerozoic. Most echinoderm fossils in parks are found in situ, but because the round disks that make up crinoid columns are resistant to erosion, they are also often found loose as float after weathering out of bedrock. Crinoid fossils also may be a major constituent of building stone, including that of the Capitol Reflecting Pool in Washington, DC.

Phylum Echinodermata

Echinoderms—“spiny skinned” invertebrates (from the ancient Greek words for “hedgehog” and “skin”)—are known for their five-sided radial symmetry. These marine animals have an internal hydraulic system called a water vascular system that is used for nutrient distribution, respiration, and movement.

Today echinoderms inhabit the oceans from its shallowest waters to abyssal depths. Major groups of living echinoderms include:

• Sea urchins

• Starfish

• Brittle stars

• Sea cucumbers

• Crinoids (feather stars and sea lilies)

Echinoderms first appeared in the Cambrian, with three groups being particularly common as fossils: crinoids, blastoids, and sea urchins. The echinoderm skeleton is composed of numerous small pieces, commonly made of calcium carbonate. When the animals die, the body breaks into its component pieces, which are common as fossils, but complete or even partial echinoderm fossils are quite rare.

Blastoids are extinct, but crinoids, sea urchins (echinoids), starfish, and other groups still live today. Blastoids and most crinoids lived attached to the seafloor by a stalk.

Blastoids, also known as “sea buds,” had bud-like bodies with five food-gathering grooves. Slender tentacle-like structures called brachioles grew from them and trapped food particles, but these are rarely fossilized. Unlike many other echinoderms, blastoid body structures (except for the brachioles) are often found intact.

Crinoids are commonly called “sea lilies,” even though they were animals like other echinoderms. This is because many stalked crinoids look something like a flower on a long stem. The “flower” part, known as the crown, actually contains the vital organs and arms, which filter for food. “Feather stars” are crinoids that do not have stalks, instead living in the water column. Stalkless “feather stars” have become more common over geologic time compared to stalked “sea lilies.”

The fossil record of sea urchins and other echinoids begins in the Ordovician. Most fossils consist of either the calcareous plates or spines.

Echinoderm Fossils in National Parks

Blastoids

Blastoid fossil in the Middle Mississippian Ste. Genevieve Formation.

NPS photo by Rick Olson.

Blastoid fossils are known from at least 7 national park areas, mostly in Mississippian-aged rocks like those in Mammoth Cave National Park in Kentucky when these stalked echinoids were particularly abundant. Other places where blastoids have been reported include Russell Cave National Monument in Alabama and Buffalo National River in Arkansas, also in Mississippian rocks.

Crinoids

^{Various crinoid columnals from Grand Canyon-Parashant National Monument.
NPS/2020 Field Inventory.}

^{Star- and pentagon-shaped crinoid columnals. Grand Canyon-Parashant National Monument.
NPS/2020 Field Inventory.}

^{Abundant crinoid columnals from 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.

Crinoid fossils are present in at least 55 parks, mostly in Paleozoic rocks. Almost all crinoid fossils in national parks consist of single columnals or stalk fragments made up of a few columnals. These fossils, which are usually small circular or gear-shaped discs, represent only a small part of the crinoid animals. The discs made up the stalks that were attached to the sea floor, and the animals’ crowns disintegrated after they died. These columnals can be extremely abundant, though, sometimes being the main component of a rock. Fossils of the crown were are rarely present, except as the occasional isolated plate.

Crinoids, like other echinoderms, have five-sided symmetry, and some columnals, including from Grand Canyon Parashant National Monument in Arizona and Zion National Park in Utah, have a star shape.

Crinoid fossils are common in Mammoth Cave National Park in Kentucky in the cave’s Mississippian limestones. When the rocks were being deposited, the area may have been a sort of “crinoid thicket.” Several species of crinoids have been named from fossils discovered in Ordovician rocks now within Mississippi National River and Recreation Area in Minnesota. At Grand Canyon National Park in Arizona, crinoids are present in many stratigraphic units, including the Mississippian Redwall Limestone and the Permian Kaibab Formation.

Crinoids are also common components of limestone blocks used as building stone. In addition to the reflecting pool in the National Mall, crinoid fossils are common in building stone at Fort Scott National Historic Site in Kansas.

Learn More

• Grand Canyon—Crinoid Fossil

Other Echinoderms – Sea Urchins (Echinoids) and Starfish

^{Sea urchin. The red arrow points to the spines and the yellow arrow points to the body. Guadalupe Mountains National Park, Texas.}

^{Echinoid fossils: Spine socket (A), spine with basalt attachment (B), and spine in cross section (C). Grand Canyon-Parashant National Monument. Scale bars are 3 cm in A and C, 1 cm in B.}

A fossil starfish from the Cretaceous Cliff House Sandstone of Mesa Verde National Park, Colorado.

Photo by Bianca Santucci.

Sea urchins and other echinoids have been found in at least 50 units of the National Park System, in marine rocks in national parks ranging in age from the Paleozoic through the Cenozoic. Some notable park records include Paleozoic sea urchins at Grand Canyon National Park and Grand Canyon-Parashant National Monument in Arizona, Guadalupe Mountains National Park in Texas, and Mammoth Cave National Park in Kentucky; and Cenozoic echinoids at Glacier Bay National Park and Preserve in Alaska and Channel Islands National Park in California.

Starfish (asteroid) fossils have been reported in six national parks, including Mesa Verde National Park in Colorado and Delaware Gap National Recreation Area in Pennsylvania. The somewhat similar brittle stars (ophiuroids) are known from only four national parks.

In addition to these groups, there are several other groups represented by fossils at a small number of parks. Most of these are unusual groups that went extinct during the Paleozoic. Great Basin National Park in Nevada and Mississippi National River and Recreation Area in Minnesota have especially diverse assemblages of these unfamiliar animals, such as cystoids (both stalked forms and strange-looking animals resembling alien armored fish with the stalk turned into a sort of flagellum), edrioasteroids (resembling a starfish attached to a bean-bag chair), and eocrinoids (stalked echinoderms once thought to be ancestral crinoids, but now known to be more like blastoids).

Coloring Book Pages

Related Parks

• Buffalo National River (BUFF), Missouri—[BUFF Geodiversity Atlas] [BUFF Park Home] [BUFF npshistory.com]

• Channel Islands National Park (CHIS), California—[CHIS Geodiversity Atlas] [CHIS Park Home] [CHIS npshistory.com]

• Colonial National Historical Park (COLO), Virginia—[COLO Geodiversity Atlas] [COLO Park Home] [COLO npshistory.com]

• Delaware Water Gap National Recreation Area (DEWA), New Jersey and Pennsylvania—[DEWA Geodiversity Atlas] [DEWA Park Home] [DEWA npshistory.com]

• Fort Scott National Historic Site (FOSC), Kansas—[FOSC Geodiversity Atlas] [FOSC Park Home] [FOSC npshistory.com]

• Glacier Bay Park and Preserve (GLBA), Alaska—[GLBA Geodiversity Atlas] [GLBA Park Home] [GLBA npshistory.com]

• Grand Canyon National Park (GRCA), Arizona—[GRCA Geodiversity Atlas] [GRCA Park Home] [GRCA npshistory.com]

• Grand Canyon-Parashant National Monument (PARA), Arizona—[PARA Geodiversity Atlas] [PARA Park Home] [PARA npshistory.com]

• Great Basin National Park (GRBA), Nevada—[GRBA Geodiversity Atlas] [GRBA Park Home] [GRBA npshistory.com]

• Guadalupe Mountains National Park (GUMO), Texas—[GUMO Geodiversity Atlas] [GUMO Park Home] [GUMO npshistory.com]

• Mammoth Cave National Park (MACA), Kentucky—[MACA Geodiversity Atlas] [MACA Park Home] [MACA npshistory.com]

• Mesa Verde National Park (MEVE), Colorado—[MEVE Geodiversity Atlas] [MEVE Park Home] [MEVE npshistory.com]

• Mississippi National River and Recreation Area (MISS), Minnesota—[MISS Geodiversity Atlas] [MISS Park Home] [MISS npshistory.com]

• National Mall and Memorial Parks (NAMA), Washington DC—[NAMA Geodiversity Atlas] [NAMA Park Home] [NAMA npshistory.com]

• Russell Cave National Monument (RUCA), Alabama—[RUCA Geodiversity Atlas] [RUCA Park Home] [RUCA npshistory.com]

• Zion National Park (ZION), Utah—[ZION Geodiversity Atlas] [ZION Park Home] [ZION npshistory.com]

Body Fossils