INTRODUCTION TO THE KAIBAB FOSSIL SITE
ON THE SOUTH RIM

There are many fossil sites in the Grand Canyon, but none is more prolific than the 270 million year old Kaibab Formation beds near the start of the West Rim Trail. To find the site, park near Bright Angel Lodge and walk west along the Rim. You will pass the bus stop at bottom of the hill. Walk up the trail about 200 yards (300 steps) to the first really spectacular open views on huge semi-flat rocks jutting out over the Canyon to your right.

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 on these pages--all photos were taken here.

Remember: there is no collecting allowed at Grand Canyon. But for a fabulous family activity, see how many fossils you can find and check off. Take a magnifier!

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WHAT ARE FOSSILS?

Fossils are the remains or traces of ancient life—some scientists say it must be over 10,000 years old. Even ancient tracks, trails, and burrows are fossils. Sometimes original material is preserved: shells, wood, or bones. More often, the original material is petrified by soaking in mineral-laden groundwater. Molecule by molecule, the remains are mineralized. Mineralization can preserve even the minute 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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CLASSIFICATION OF FOSSILS

All organisms are classified according to the Linnean Hierarchy. Linné was a Swedish naturalist that introduced this method in 1758. All organisms are given a genus and species name which are written together, such as Homo sapiens or Composita subtilita: both names in italics or underlined, genus capitalized, species lower case. The species is never written without the genus, but the genus may stand alone. Thus you will see Homo and Homo sapiens, but never sapiens alone. The levels of classification are shown here, using Homo sapiens as an example:

• Kingdom - Animalia
• Phylum - Chordata
• Class - Mammalia
• Order - Primates
• Family - Hominidae
• Genus - Homo
• Species – sapiens
• Complete scientific name: Homo sapiens

Scientific names are shown under each photo when known. Common marine invertebrate fossil groups of the Kaibab include: Phylum Porifera (sponges), Phylum Coelenterata (corals), Phylum Bryozoa (bryozoans), Phylum Brachiopoda (brachiopods), Phylum Mollusca which includes Class Pelecypoda (clams), Class Gastropoda (snails), and Class Scaphopoda, and Phylum Echinodermata which includes Class Crinoidea (crinoids) and Class Echinoidea (sea urchins or echinoids).

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SPONGES: Actinocoelia

Phylum Porifera Actinocoelia maeandrina

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 CORALS

Phylum Coelenterata: Horn Coral

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. Most 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 most 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.

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INTRODUCTION TO THE BRYOZOANS

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, and a unique feeding mechanism called a lophophore that is shared only by the brachiopods. All this in such a minuscule creature!

One can usually recognize bryozoans by the tiny dots that cover the surfaces of the colony. Each dot is a hollow chamber or zooecium (plural zooecia) where a bryozoan lived. To see these zooecia well, use a magnifier. Your binoculars used upside down make a good magnifier. The drawing to the left is a cross-section of a bryozoan in its chamber, showing muscle fibers behind the stomach. width of this drawing is 1/32 inch!

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BRYOZOA 1: SCREEN-LIKE OR FENESTRATE FORMS

Phylum Bryozoa Fenestrellina

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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BRYOZOA 2: SURFACE CRUSTS AND FOLDED FORMS

Phylum Bryozoa Fistulipora

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.

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BRYOZOA 3: TWIG-LIKE FORMS

Phylum Bryozoa Meekopora

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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INTRODUCTION TO THE BRACHIOPODS

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.

Like clams, brachiopods are bivalves. Each half of the shell is called a valve. However, brachiopod shells differ from clam shells. Most clam valves are mirror images of each other, like a pair of hands. Most brachiopod valves are not mirror images. While the two brachiopod valves differ in shape, each individual valve is bilaterally symmetrical. If you draw a line down the center of a brachiopod valve, the two halves are mirror images. This is not true for the clams (see page 16).

Peniculauris (left two), Composita, right

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.

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BRACHIOPODS 1: Peniculauris

Phylum Brachiopoda: Peniculauris bassi

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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BRACHIOPODS 2: Derbyia

Phylum Brachiopoda Derbyia crassa

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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BRACHIOPODS 3: Meekella

Phylum Brachiopoda Meekella

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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BRACHIOPODS 4: Composita

Phylum Brachiopoda Composita

Composita is hard to find among the larger, more conspicuous fossils at this site. The examples above show only the aperture area, where the shell opened.

This photo 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.

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MOLLUSKS 1: CLAMS

Phylum Mollusca, Class Pelecypoda Aviculopecten

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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MOLLUSKS 2: SNAILS & SCAPHOPODS

Phylum Mollusca Class Gastropoda 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.

Phylum Mollusca Class Scaphopoda Plagioglypta

This is a scaphopod, the faint, elongated cone to the left of the penny. Both this and the snail above are molds—open spaces where the actual shell dissolved away. The scaphopod’s foot and feeding tentacles emerged from the wider end of the cone, much like a snail with a straight shell.

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ECHINODERMS 1: CRINOIDS

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ECHINODERMS 2: SEA URCHINS

Echinoid Plate (left) Echinoid Spine (right)

Phylum Echinodermata, Class Echinoidea, Archaeocidaris

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.

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