Name
Date
Class
Enrichment
LESSON 1
Crinoids, anyone?
If you were visiting the beach at the
southern end of Lake Michigan, you would
probably see some of the beachgoers walking
Their delicate skeletons usually fall to
pieces within hours of the animal’s death.
Crinoid fossils are important because
along the shore, heads bent, looking closely
they are Paleozoic index fossils. An index
at the shallow piles of small stones that
fossil is one that is characteristic of a
have been washed up by waves. A lucky
particular geologic time or place. Index
searcher might find a crinoid fossil that
fossils are use to determine the divisions in
could be up to 490 million years old. The
the geologic time scale. Crinoids have a
fossils, which resemble small cylinders, are
distinctive internal skeleton, which allows
fragments of the crinoids’ stem. Crinoid
them to be easily identified.
fossils are usually up to three-fourths of an
inch in length and are brownish-grayishgreenish in color.
Where and When?
Crinoids have lived in the world’s oceans
since at least the beginning of the Ordovician
When Crinoids Swayed in Ancient Seas
Crinoids live only in seawater. Though
period. During the Carboniferous period, all
of what is now the United States, except for
commonly known as sea lilies, they are not
a small part of the upper midwest, and all
plants. Crinoids are invertebrate animals
of the states along the east coast, except for
that have a stem that is attached to the
Florida, was covered by a warm, shallow
seafloor. The stem consists of disk-shaped
inland sea. During this time, Lake Michigan
pieces stacked on top of each other, and it
was located south of the equator. The equator
is topped with a crown-shaped body, the
has not moved during the history of Earth,
calyx, which has feathery arms. The arms
but the tectonic plates that make up Earth’s
wave back and forth as they gather small
crust have slowly moved around, changing
food particles from the water and transfer
the positions of the continents. At the time
them to the mouth.
of the Carboniferous period, this
Many crinoids resemble flowers because
paleoequator ran diagonally across North
of the cluster of waving arms atop a long
America from what is now central
stem. About 700 species of crinoids still live
California to the area of Canada that is
today, including feather stars and sea lilies.
north of Lake Superior.
Applying Critical-Thinking Skills
Directions: Respond to each statement.
1. Define index fossil.
2. Hypothesize whether crinoids could grow in the midwestern part of the United States
today if the area were again covered with an inland sea. Explain your hypothesis.
3. Explain why crinoid fossils can be found on the shore of Lake Michigan, which is a
freshwater lake.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________________