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The fossils are even better on the other side of the trail from here—the left side as you ascend. Look in all the ledges and outcrops. You will surely find dozens of fossils of many types. With a little care you can find all the species in this booklet--all photos were taken here. 
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 structures
of an organism, but usually the soft tissue is lost.
Many sea animals have hard shells that readily fossilize. Such fossils are often encased in solid stone that was once the mud of an ancient sea bed. In most instances, as the stone erodes away, so does the fossil. When a fossil is preserved by the durable rock chert, however, the enclosing limestone can wear away, leaving the fossil protruding from the rock. In the Kaibab Formation, fossils are often preserved in chert and exposed by this differential erosion. Differential erosion is especially prominent at this site in the form of chert nodules, brown protruding spheres and tubes. The tube-shaped nodules may be fossil worm burrows that were later replaced by chert. |
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 The sponge is so simple! Just a loose colony of cooperating single cells—some for catching food with their tiny hair-like cilia, some wandering amoeba-like through the colony to distribute food, some engineering skeletal supports: little needles or stars of silica called spicules. Altered masses of spicules make the white color. Because the skeleton is silica, altering later to durable chert, the sponge is responsible for making the Kaibab Formation hard and durable. For this reason, erosion has lowered the land only as far as the Kaibab and no farther. Thus, in a sense, the lowly sponge is the reason we have a Grand Canyon instead of a broad valley.
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 The coelenterata have taken a step beyond the simple sponge, developing bodily tissues for different functions. The living coral, a tentacle-ringed polyp, has built this cone shaped skeleton for its support. Corals are symbiotic with green algae that live inside (living together to the advantage of each). Without the algae, the coral can’t grow. Without sunlight, the algae can’t grow. So corals live only in relatively shallow, clear water where sunlight penetrates. Corals also require relatively warm water of normal salt content. Thus, the presence of corals has told us something about this ancient Kaibab sea! Many corals are colonial, forming large masses and reefs. But the horn coral is solitary, a single polyp and its skeleton. |
Bryozoans are tiny polyp-like animals that
always form small coral-like colonies. Bryozoans are common on modern seashores
but are often over-looked or mistaken for corals or seaweed. The tiny polyps
differ from corals in having complete organ systems, the next step beyond
the coral’s tissue level of development. Organs include a complete digestive
system, muscles for retracting into their chambers, |
 
Fenestrellina is one of the screen-like forms called the fenestrate bryozoans.
The easily visible holes are not the chambers that the animals lived in.
The animals lived in tiny chambers called zooecia in the walls of the screen
(tiny circles in picture). Don’t be fooled by the similar brachiopod molds
with little holes where the spines emerged.
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 Some bryozoans form a thin crust on top of shells or rocks. These can be difficult to recognize. But other colonies grow massive folded forms as in the photo. Fistulipora is one of these. Use a magnifier or look very closely to see the thousands of tiny dots or zooecia on the white outer surfaces of this common Kaibab bryozoan. |
 While this form is often called “branching,” there may be no branches. The colony grows up from the sea floor. Many of the twig-like forms in this area have their outer covering worn away, as in this photo. This permits a view of the internal structure. There are long tubes (the zooecia) that grow out from the center of the twig. As the colony grew, each individual bryozoan lengthened its tube outward, often forming tiny platforms to support its body in the tube.
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The Phylum Brachiopoda was immensely important
in Paleozoic seas. While a few species live today, most of their former
niches have been usurped by the clams.
In some brachiopods, the two valves fit into each other, sort of like a pie plate on top of a bowl. This kind, such as Peniculauris, rested on the sea floor raised up on its many spines. Others, like Composita, were attached by a fleshy tube called a pedicle. |
 Peniculauris bassi belongs to the family Productidae, so we call it a “productid” brachiopod. The name Peniculauris is 
the genus of the animal, and Peniculauris bassi indicates the species.
Since only various parts protrude from the rocks, it is difficult to form
a mental picture of the shell: see the drawing on page 10. Here is
a cross section of this large, robust shell. Another productid genus, Rugatia,
is also common here. Rugatia is usually smaller and more strongly
bi-lobed than Peniculauris.
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 You can recognize Derbyia by its fine radiating lines called costae that extend outward from the beak (top of shell in photo). The beak is where the two shells or valves meet in a long, straight hinge. Much of the hinge is not visible in this photo. See if you can find a Derbyia with visible hinge. Some specimens are very large, up to 4 inches across. Both valves of the shell are quite flat.
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 The surface of Meekella looks like the ruffles of a curtain. Such coarse surface folds are called rugae: they are visible on the inside of the shell as well. Cross sections of this species appear zig-zag because of the plications of the shell. Meekella and Derbyia occur only in rocks of the Pennsylvanian and Permian Periods. Because of this restricted time zone, the fossils are guide fossils. We can use them to date rocks. Many sedimentary rock units are dated in this way.
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  The photo below shows several Composita specimens collected from a different site. Composita held itself to the sea floor by a fleshy stalk called a pedicle, which emerged from a hole in the shell called the foramen.  |
  These two large shells are pelecypods (clams). The photo on the left above may be the mold of the shell, where the shell itself has eroded away. As you hunt clams here, look for the assymmetrical shell. A line drawn down the middle of a single valve does not divide it into equal halves as it would a  brachiopod
shell. Clams were scarcer in the Paleozoic than they are today, but they
were common in some localities. Here they are inconspicuous except for
those above.
Clams and oysters are in the Phylum Mollusca, as are snails, scaphopods, chitons, squids and octopi.
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 Phylum
Mollusca
Class Gastropoda (snails) Bellerophon Snails are rare at this locality. These photos
were taken at the large rocks that border the parking area and rim just
east of the Bright Angel trailhead.
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 The abundance
of crinoids in Paleozoic seas is almost incredible. Many thick beds of
limestone are composed almost entirely of crinoid remains. If you look
closely you will see many tiny crinoid columnals in the Kaibab. The crinoid
animal is called a sea lily. It has a flower-like crown and a long stem
or column consisting of many columnals like the one shown below. The skeleton
tends to fall apart after death.
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  Sea urchins and sand dollars are called echinoids. They look like a pincushion. The type here in the Kaibab had very thick, bumpy spines. Shown on the right is a partially concealed spine. The swollen base of the spine is to the right where there is a hole. The left photo shows a single plate of the urchin’s body with concentric circles called the axial boss—this is where the spine attached. Dozens of such plates make up the urchin’s pincushion-shaped body—like crinoids, they fall apart after death. Sea urchins are related to starfish and crinoids. Most such animals display a five-rayed or pentamerous symmetry in some parts of their bodies, and most are spiny. “Echino-“ means spine. |
and
a unique feeding mechanism called a lophophore that is shared only by the
brachiopods. All this in such a minuscule creature!
Phylum Mollusca