Lost River - Karst Information Portal

2007 NSS Convention Guidebook
layers which are about 0.5 mm across. Today,
charophyte algae can be found in bodies of
water where calcium is dissolved. During the
Devonian, islands with freshwater ponds must
have been common, allowing billions of algae
eggs to get washed into the sea.
The uppermost layer, or the youngest rock,
is the Paraspirifer Acuminatus Zone, which
contains fossils of brachiopods (including
paraspirifers, a two-shelled animal similar to a
clam); bryozoans (commonly called lace coral);
trilobites; and some solitary, branching, and
colonial corals.
The second layer is called the Fenestrate
Bryozoan-Brachiopod Zone. Named for
the predominant fossils found there, this
layer contains many of the same corals and
brachiopods as the Paraspirifer Acuminatus
Zone. Here one also can find crinoid stems in
abundance. Crinoids are animals that looked
like plants, sporting “roots” and “flowers.” When
the crinoid died, the body segments separated
and fossilized, leaving small, doughnut-shaped
segments. Prehistoric man used these very
popular fossils, which are often called “Indian
beads,” to make necklaces.
A six-inch-thick layer called the Brevispirifer
Gregarius Zone is next lowest, and contains
fossils of brachiopods and gastropods (sea
snails). The smallest horn corals, or cup
corals, begin to appear here. One of the Falls’
most unusual corals, called a stromatoporoid,
first appears in this layer. It is unclear if the
stromotoporoid is a reef-building colonial
coral or a sponge, but the creature played an
important role in the makeup of the fossil bed.
The Amphipora Ramosa Zone, commonly
called the Cave Zone, attracts attention for
reasons other than the matlike stromotoporoids
or the branching corals. Pocket caves have
developed here due to the powerful erosive
powers of the Ohio River rushing across the
rock. This zone occurs along the vertical cliffs
of the river channel, where the cutting force
of the river reaches its peak. When water and
oxygen come into contact with the limestone,
a weak carbonic acid forms and dissolves the
limestone. This phenomenon, combined with
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freeze and thaw erosion and the sweeping
power of the river, causes the bedrock to erode
quickly and erratically, leaving shallow caves
where the rock once lay.
T h e l a r g e s t h o r n c o r a l i s c a l l e d
Siphonophretis elongata. It was the first fossil
from the Falls of the Ohio described in scientific
literature (in 1820). This was the largest horn
coral that ever lived. It is generally thought to
lie prostrate on the sea floor, curving upward
to catch plankton with its stinging tentacles.
To reach lengths of up to 5 feet (1.6 meters),
meant it had a long life span.
Other contributors of mass to the reef
include stromatoporoid sponges, some forming
bumpy mounds, others short and grass-like.
Lacy bryozoans - moss animals which had
sieve-like fans, which allowed water currents
to flow through. These microscopic animals
fed on plankton. Perhaps because they shared
an ecological niche similar to corals, bryozoans
were not abundant while the coral patch reef
was living. Trilobites were mobile scavengers,
crawling around the sea bottom, much like
lobsters today. Trilobites shed their skin by
molting as they grew. Most fossil finds are of
these molts.
Shelly animals include snails big and small,
brachiopods and clams.. Brachiopods are
not clams, their internal anatomy and shell
symmetry is different. These were stationary
creatures, like barnacles are today. The shelly
animals were much more abundant after the
coral patch reef had been buried by sediment.
Clams lived buried in the sediment and were
usually found on the sea floor as empty shells.
Coiled and straight-coned cephalopods swam
in the Devonian sea, preying upon soft-bodied
animals.
Stalked echinoderms were more common
after the corals had perished. Large flower like
crinoids and nut-like blastoids fed on plankton,
elevated above the sea floor into nutrient-rich
currents. Mobile echinoderms like starfish and
echinoids (urchins) existed, but are almost
never found intact as fossils.
The Devonian is sometimes called the “Age
of Fishes” because they became abundant at