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Escarpment Origins – Ancient Seas and Fossils
Nearly half a billion years ago, this whole region was covered by ancient shallow seas. The Niagara Escarpment
contains the fossilized remains of the lifeforms which lived in those seas.
The layers of rock which form the Niagara Escarpment date back to roughly 450 million years ago (give or take
a couple million years!), when this region of what is now North America lay under a shallow warm sea. This
sea lay in a depression of the earth’s crust, the centre of which is now called the State of Michigan. Now
geologically known as the Michigan Basin, the outer rim of this massive saucer-shaped feature defines the
Niagara Escarpment.
The rocks at the base of the Niagara Escarpment of are Late Ordovician age (approximately 450 million years
ago). Those that comprise the major part of the Escarpment proper belong in the Early and Middle Silurian age
(approximately 400 million years ago). When we talk about the age of the Escarpment, the dates vary from
location to location. Some parts of the Escarpment have been more recently (well, 10,000 years or so recently)
eroded or dragged or scraped away by the last glacier. So, different sections of the escarpment can represent
completely different time periods within that 50 million-year time-frame.
So, the Niagara Escarpment is made up of rocks formed over time from the sediment washed into the sea, and
the remains of the creatures who lived there. The specific make-up of these rocks and how this process worked
is explained in our Formation of the Escarpment section.
This ancient sea contained coral reefs in the shallows, teeming with some of the first complex life forms to exist
on the planet. Now, 30 to 50 million years is a long period of time. The sea was on a continent which sat below
the equator and was migrating south. During this period, the continent collided with another, the sea
experienced extinctions and, in fact, the sea even dried up and re-filled!
So it’s no surprise that over this long period of time life was evolving at a rapid rate. This is a time when the
first fishes appeared in the seas, some of the very first vascular plants were forming on land, and when some
forms of life in the ancient seas began to venture up on land.
In this section you will find information on the most common forms of life found in the fossil record of the
Giant’s Rib.
Brachiopods
Brachiopods were an ancient line of seafloor shellfish inhabiting
this area half-a-billion years ago. They had two shells (or valves) joined along a common hinge. Inside the
shells were complex sets of muscles that both opened and closed the shell.
Paleobiologists estimate that 99% of all documented brachiopod species are extinct. They are common fossils in
shale, sandstone and limestone throughout the Niagara Escarpment. Brachiopods survive today, but are now
limited to cool and temperate waters along the North Atlantic coastline of North America and other parts of the
world.
For you fossilheads out there, here is some more technical information about brachiopods:
Phylum Brachiopoda
Modified from Clarkson (1986) courtesy State University of New York
Brachiopods are a smaller phylum of benthic invertebrates. They are sessile, two valved, marine animals
superficially resembling Molluscan bivalves to which they are not closely related. Paleobiologists estimate that
99% of all documented brachiopod species are both fossils and extinct. Bivalves usually have a plane of
symmetry between the valves of the shell, which are mirror images of each other; most brachiopods have a
plane of bilateral symmetry through the valves and perpendicular to the hinge. The two brachiopod valves differ
in shape and size from one another.
Modern Brachiopod
Photo courtesy U of Vermont
Brachiopod with pedicle
Photo courtesy U of London
Brachiopods have a feeding organ called a lophophore. Articulate brachiopods attach to the substrate by a
pedicle (stalk) protruding from one valve. The photograph to the left shows the lophophore inside an opened
modern brachiopod.
Brachiopods on display at the Discovery Centre
(along with trilo-bits and crino-bits)
Cephalopods
Cephalopods are highly active and well-developed marine carnivores.
They had complex eyes and brains, tentacles with sucker pads, and
parrot-like beaks.
They used jet propulsion to move through the water. Many forms
had coiled shells or straight shells (such as the nautiloid depicted
here). Many of their modern day descendants, however, such as the
nautilus, squid and jellyfish, did not develop shells at all.
Fossils of these creatures are often found in the Medina and Queenston
layers of the Escarpment.
Nautiloid Illustration
by Nobu Tamura
Modern nautiloid
Nautiloid on display at the Discovery Centre
Corals
The ancient shallow seas which covered these lands more than 440 million years ago were filled with coral
reefs of many shapes and sizes including pinnacle reefs, barrier reefs and patch reefs. Coral reefs made their
first appearance on the planet during this time (Silurian Period 443 to 416 million years ago). These reefs
assisted in the development of other species, providing food for some of the first fishes which were beginning to
appear in the oceans.
While there were many species of corals, we can generally group them into a few categories.
Bryzoans
Bryzoans are colonial animals that live in both freshwater and seawater. A colony
is composed of hundreds of very tiny individuals, each of which has a special organ
that filters small food particles from the water. Bryozoan colonies are attached to
the seafloor or to other organisms. At least 7 species of bryzoa existed during the
Silurian period and many species still exist today.
Rugosa
Rugosa are an extinct order of coral that were abundant in the ancient seas. They are
also referred to as horn corals because of a unique horn-shaped chamber which
supported a single animal, similar to the modern sea anemone. Some solitary rugosans
reach nearly a metre in length. Some species of rugose corals were not solitary and
could form large colonies. Rugose corals have a skeleton made of calcite that is often
fossilized.
Tabulate Corals
Tabulate Corals were tube-shaped corals like a series of joined organs
or pan pipes looking much like a honeycomb. These corals once
numbered around 300 species but are now also extinct.
Bryzoan corals on display at the Discovery Centre
Rugosa (horn) coral on display at the Discovery Centre
Tabulate coral on display at the Discovery Centre
Crinoids
Crinoids, also known as “Sea Lilies”, are marine animals not
plants. Crinoids usually have a stem to attach themselves to a
surface but many live attached only as juveniles and
become free-swimming as adults. They have a stem which
is attached to the sea floor, topped with a crown-shaped
body (calyx) which holds feathery arms. These arms
capture small food particles and transfer them to the
mouth at the top of the calyx. Crinoids are an
echinoderm, a group which includes sea urchins and
starfish.
There are only a few hundred known hundred known
modern forms, but Crinoids were much more numerous in the
past. Some thick limestone beds dating to the formation of
Niagara Escarpment rock are entirely made up of disarranged
Crinoid fragments.
Dendrocrinus longidactylus
On permanent display
at the Discovery Centre
Eurypterids
Eurypterids , or Giant Sea Scorpions, were a type of
Arthropod, or creature with its skeleton on the outside
(exoskeleton) with a segmented body and jointed
limbs. Eurypterids, or Giant Sea Scorpions, appeared
on the scene about 460 million years ago. They were
one of the Earth’s first large predators. It is believed
that these were one of the first animals to venture up
on land. Smaller arthropods lived in the ancient seas
from around 540 million years ago and included smaller
creatures like trilobites and crustaceans.
Anatomy of a Sea Scorpion
Most eurypterids probably preyed on other
eurypterids or fishes and some may have been
the dominant macropredator of the time. There
were approximately 15 species of Giant Sea
Scorpions. Some eurypterids exceeded a meter
in length, making them the largest arthropods.
Fossil records have been found only in two
parts of the world; Eastern Europe and North
America near the Niagara Escarpment. Their
closest modern-day relative is the horseshoe crab, with similarities as well to arachnids (spiders) and today’s
scorpions.
Eurypterus remipes
Giant Sea Scorpion!
The fossil you see here is on permanent display at the Centre.
Eurypterus remipes, was the most common of the species and is
the State Fossil of New York. This fossil came from a section of
the Bertie Lime formation in New York State, formed 417
million years ago. Back then, that area was a shallow lagoon
thought to be a breeding ground for the species. Giant Sea
Scorpion habitat consisted of shallow waters where food sources
would be plentiful.
Gastropods
Gastropods, or snails, had a single long tubed shell coiled into a spiral. The name means “stomach foot”, since
they possessed a muscular foot which they used to glide along the sea bottom.
Although they look like Ammonites, the latter is a cephalopod (“Head Foot”) which is more evolved and more
like modern squids and octopuses.
Gastropod on display at the Discovery Centre
Gastropod on display at the Discovery Centre
Trilobites
Trilobites were the ruling form of life from 540 to 500
million years ago (“The Age of Trilobites”). These marine
animals went extinct 250 million years later. Trilobites
were the most numerous and successful marine
organisms of the early Paleozoic era. It is estimated
there were more than 20,000 species of trilobites
over their long history.
They had many legs, each with a set of gills and
sophisticated, multifaceted eyes. Like most
arthropods, trilobites could only grow by shedding
their old skins. Trilobites lived in shallow ocean
waters, and on reefs. Their skeletons are found in all
types of sedimentary rock on the Niagara Escarpment, from
limestone to shale.
Trimerus delphinocephalus
On permanent display at the
Discovery Centre
Dalmanites limulurus
On permanent display at the
Discovery Centre
Arctinerus boltoni
On permanent display at the
Discovery Centre
The chart above gives an indication of the relationships of the trilobite orders, and their extent over geological
time. The Cambrian origin and proliferation of trilobites is very apparent, as well as the loss of the orders
Agnostida, Ptychopariida, and Asaphida in the Ordovician, the loss of the majority of remaining orders in the
late Devonian, and the final extinction of the class in the Permian. The Ordovician extinction event is
particularly apparent in the chart of family diversity (second chart on this page). Click on any of the order
names immediately above this paragraph to learn more about each order.
Formation of the Escarpment
Approximately 450 million years ago,
the area was covered in an ancient
shallow sea just south of the Equator.
This shallow sea covered most of North
America. Locally the sea was a pooled in
a depression we call the Michigan Basin.
The seas were full of early life which
lived on the muddy bottom and coral
reefs in the shallows. As these early
creatures died, their bodies settled to the
bottom of the sea.
Dirt and mud and sand we call
“sediment” would be washed into the sea
and cover the remains of these creatures.
This sediment came from the mountains
to the east as time and weather wore
them down.
Most of the sediment settled in deltas and reefs around the rim of the Michigan basin, depositing various
colours of clay and sand.
Over time, these layers of deposited sediments and remains were compressed and turned to rock. We call this
“sedimentary” rock. Mud and silt would form layers of shale; sand into sandstone; and corals, calcium-rich
exoskeletons and lime mud into limestone. The remains of the many species of sea creatures became fossils
within the layers of sediment.
The lower, softer, older layers contain fossils of early, more primitive life. The upper, newer, harder layers
contain fossils of more complex and diverse life. The rocks layers of the Niagara Escarpment are a fossil record
of nearly 30 million years of evolution.
A chemical reaction between calcium carbonate (lime) of the reefs and shells, and liquid magnesium over a long
period of time created a hard, resistant layer of magnesium-calcium carbonate known as dolomite (dolostone).
About 415 million years ago, the sea became increasingly shallow. Once the sea dried up, a plain emerged, and
erosion began to reshape the landscape. By 135 million years ago, the continent was moving northward. The
erosive forces of water and wind thinned the dolomite cap rock and eroded the softer rock layers beneath
forming a small ridge of exposed rock, along the edge of the dry seabed of the Michigan Basin.
This left behind a ridge, a vertical face of exposed rock, creating the Escarpment cliffs. The most recent shaping
of the Niagara Escarpment occurred with the end of the last ice age, around 10,000 years ago.
