We went fossil hunting at Russell Wildlife while visiting Iowa. We found lots of different fossils. Snow covered most of the ground, but we found exposed soil near the edge of the pond.
Here are some of the brachiopods we found.
Brachiopods are benthic (bottom
dwelling), marine (ocean),bivalves (having two
shells). They are considered living fossils, with 3 orders
present in today’s oceans. They are rare today but during
the Paleozoic Era they dominated the sea floors.
Though they appear to be similar to clams or oysters they are
not related. They are not even mollusks. They belong to the
phylum Lophophorata and are related to bryozoans.
One characteristic unique to brachiopods is the pedicle. It is
a long thin fleshy appendage. The pedicle is used to burrow into the
sea floor as an anchor.
Some Brachiopods have a muscular pedicle. They can raise
themselves up off the bottom, looking like they are standing on their
heads. For others it is more like a tether.
Not all orders have a pedicle. Some lay on the sand on one side.
With these the bottom shell is usually larger than the top shell.
There are even some types that cement themselves to the ocean floor.
All members of this phylum are filter feeders. They feast upon
microscopic organisms and bits of organic matter, which they gather
from the water with a specialized organ called a lophophore.
This is a tube like structure with cilia(hair like
projections). The cilia move food particles down the lophophore to
the mouth.
The lophophore takes up about 2/3 of the space inside the shell,
with the body of the animal occupying the remaining third.
The Valves
The two shells are each symmetrical about the midline but they are
most often not equal to each other.
In contrast clams are asymmetrical about the midline with each
valve or shell equal mirror images of each other.
Each valve or shell has its own name. The valve that the pedicle
is attached to is called, surprisingly enough the pedicle
valve. It is usually the larger of the two and has the pedicle
opening.
The other valve holds the lophophore or brachia and of course is
called the brachial valve. The lophophore is supported
by a calcerous structure called the brachidium. This
structure varies greatly in complexity from a simple loop to a double
spiraled coil. The shape of the brachidium is important in
determining brachiopod classification.
There is usually a central raised area on the pedicle valve called
a fold with a corresponding depression on the brachial valve called
the sulcus.
Geologic History
Brachiopods have a long geologic history. They have been around
since the Cambrian Period. From the Ordovician
Period through the Permian Period they were abundant
in numbers, but the Permian extinctions reduced their
numbers severely.
Several orders survived the extinction but brachiopods have never
regained the abundance they enjoyed during the Paleozoic Era.
However, they may be the most plentiful fossil on earth. They are
used as index fossils.
Most of this information comes from
Fossils-Facts-and-Finds.com
