Description: Because many crinoids resemble flowers, with their cluster of waving arms atop a long stem, they are sometimes called sea lilies. But crinoids are not plants. Like their relatives--starfishes, sea urchins, sea cucumbers, and brittle stars--crinoids are echinoderms, animals with rough, spiny surfaces and a special kind of radial symmetry based on five or multiples of five.
Crinoids have lived in the world's oceans since at least the beginning of the Ordovician Period, roughly 490 million years ago. They may be even older. Some paleontologists think that a fossil called Echmatocrinus, from the famous Burgess Shale fossil site in British Columbia, may be the earliest crinoid. The Burgess Shale fossils date to the Middle Cambrian, well over 500 million years ago. Either way, crinoids have had a long and successful history on earth.
Stem fragments from assorted Pennsylvanian crinoids show some of the variation in the fossils found in Kansas rocks.
Crinoids flourished during the Paleozoic Era, carpeting the seafloor like a dense thicket of strange flowers, swaying this way and that with the ocean currents. They peaked during the Mississippian Period, when the shallow, marine environments they preferred were widespread on several continents. Massive limestones in North America and Europe, made up almost entirely of crinoid fragments, attest to the abundance of these creatures during the Mississippian. Mississippian rocks crop out only in the extreme southeast corner of Kansas, but crinoid fossils are common in Pennsylvanian and Permian rocks in the eastern part of the state.
Crinoids came close to extinction towards the end of the Permian Period, about 250 million years ago. The end of the Permian was marked by the largest extinction event in the history of life (see mass extinctions). The fossil record shows that nearly all the crinoid species died out at this time. The one or two surviving lineages eventually gave rise to the crinoids populating the oceans today.
In general, crinoids have three main body parts. The first, the stem, attaches the animal to the ocean floor and consists of disk-shaped pieces stacked on top of each other. These stem pieces come in a variety of shapes--round, pentagonal, star-shaped, or elliptical--and each stem piece is perforated in its center.
Individual stem pieces are common fossils in Kansas rocks. These samples of different Pennsylvanian crinoid species are from the Spring Branch Limestone Member, Lecompton Limestone, Greenwood County, Kansas.
At the top of the stem is the cuplike calyx, which contains the mouth, the digestive system, and the anus. The lower part of the calyx is made up of rigid, five-sided plates, arranged radially in rows of five.
This calyx of the Pennsylvanian crinoid Ulocrinusshows the radial arrangement of the five-sided plates. This specimen is from the Iola Limestone, Allen County, Kansas.
These plates form the base of the third part, the food-gathering arms. The arms, which are also segmented, have grooves with cilia, or tiny hairs, that capture suspended food particles and direct them back towards the mouth. The number of arms varies from five, common in primitive species, to as many as 200 in some living species. The number of arms is always a multiple of five.
This plaster cast of the Pennsylvanian crinoid Delocrinus preserves the segmented arms sitting on top of the calyx. The flower-like shape of this fossil suggests how these animals came to be known as sea lilies. The original specimen was found west of Emporia, Kansas.
Based on the fossil record of crinoids, especially the details of the plates that made up the arms and calyx, experts have identified hundreds of different crinoid species. Though most crinoids had stems, not all did. Today, stemless crinoids live in a wide range of ocean environments, from shallow to deep, whereas their relatives with stems normally live only at depths of 300 feet or more. These modern crinoids are an important source of information about how the many different extinct crinoids lived.
Rarely are crinoids preserved in their entirety: once the soft parts of the animal decayed, sea currents generally scattered the skeletal segments. By far the most common crinoid fossils are the stem pieces. These are abundant in eastern Kansas limestones and shales. Only occasionally is the cuplike calyx found. Kansas, however, is home to a spectacular and rare fossil crinoid called Uintacrinus, which was preserved in its entirety. These fossils, which were discovered in the Niobrara Chalk of western Kansas, lived during the later part of the Cretaceous Period, roughly 75 million years ago. Uintacrinus is a stemless crinoid, and specimens of these beautifully preserved crinoids from Kansas are on display in many of the major museums of the United States and Europe.
Uintacrinus socialis is a stemless crinoid that lived in the shallow Cretaceous seas that covered much of North America roughly 70 million years ago. Among the numerous arms preserved in the top photo, a segmented calyx is also visible. These specimens were collected from the Niobrara Chalk, Gove County, Kansas. In this close-up of another specimen (lower photo), the individual arm segments are easy to see.
Stratigraphic Range: Ordovician (or possibly Middle Cambrian) to Holocene.
Taxonomic Classification: Crinoids belong to the Kingdom Animalia, Phylum Echinodermata, Subphylum Crinozoa, Class Crinoidea.
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Text by Liz Brosius, Kansas Geological Survey. Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey.