Mass Extinction - Trilobites
What are Trilobites?
One of the earliest forms of
life to develop a carapace or shell was the trilobite. This is an extinct form
of life that resembled the modern horseshoe crab. It had three lobes (hence its
name) -one central and two lateral lobes. In addition it had three main parts -
a head (or cephalon), a middle body (or thorax) and a tail (or pygidium). In the
rocks just above this sign are to be found thousands of pieces of trilobites.
Because the carapace was shed as the
trilobite grew larger, there can be many fragments of such carapaces left by a
single individual during its lifetime. Additionally, the carapaces are made of
material like human fingernails, so they fall apart when the animal dies,
leaving many disarticulated heads and tails. Such accumulations of fragments are
nonetheless useful for identifying and classifying trilobites.
Environments of Deposition
Most trilobites lived in
relatively shallow marine waters. This region was near the shoreline of the
extensive Cambrian seas (as noted on the Flathead beach sand discussions). On
the adjacent diagram, note the location of Red Lodge Mountain with respect to
this Cambrian sea.
Some trilobites are known to have
foraged along the shallow sea bottoms for food, taking in the muds with their
enclosed microscopic organisms. Others swam above the bottom and filter fed on
small swimming and floating organisms. Still others appeared to rise in a
"hopping motion" above the sea floor into the shallower zones. They
all needed relatively clear and shallow water. When condition changed, they had
to migrate to more agreeable environments or else they would perish. When
conditions were right, trilobites flourished in the Paleozoic seas.
Cambrian Flourishing and Extinctions
Trilobites were the dominant life forms during the Cambrian Period. Starting with a few families, trilobites diversified and multiplied for millions of years, only to undergo drastic reductions in numbers over relatively short time intervals. They flourished when conditions were right and died out suddenly when conditions changed. This change may have been either a fairly sudden deepening of the ocean waters or, conversely, an equally rapid shallowing. In either case, the trilobites were no longer living under ideal conditions and many entire families died out. This occurred at least five times during the Cambrian Period. Only one or a couple families made it through these devastating episodes of changing environments. Each of these instances of mass extinction was followed by another episode of blossoming out into many lineages of trilobite families,only to be usurped by another mass extinction.
Dinosaur Extinction at K/T Boundary
We have been inundated by tales of the great extinction of the dinosaurs at the end of the Cretaceous Period, prior to the start of the Tertiary Period (known as the K/T boundary). This certainly was a mass extinction of tremendous proportions. Had the dinosaurs not died out, there is no telling what the sequence of life development might have been. The small mammals living during the latter stages of the reign of the dinosaurs, may not have developed into the dominant life forms of the Tertiary Period. Who knows what might have been the fate of humans under such a scenario?!