Ammonites
Temporal range: 400–65.5 Ma
Devonian - Cretaceous
Artist's reconstruction of Asteroceras
Scientific classification
Kingdom:
Phylum:
Class:
Subclass:
Animalia
Mollusca
Cephalopoda
†Ammonoidea
Zittel, 1884
Ammonites are an extinct group of
marine invertebrate animals in the
subclass Ammonoidea of the
Cephalopoda class. Ammonites are the
ancestors of the nautilus today.
Ammonites are excellent index fossils.
They rock layer that they are found are
often possible to use it to link it to a
specific geological time periods.
Ammonites originated from the
bactritoidnautiloids. They first appeared
in the Devonian period (400 million
years ago) and extinct close to the
Cretaceous period (65.5 million years
ago) along with the dinosaurs.
Scientists often use ammonites to study how creatures evolve and what factors are
involved in adaptations.
Since the ammonites and their close relatives are extinct, scientists only know little
about their lives. The knowledge we know today are obtained by examining
ammonoid shells and models.
Adaptations
Structural: Shell-Chambers
The ammonite’s shells are coiled and contain chambers
that are linked to each other. The last chamber, which is
also the largest chamber, is the only chamber that contains
the body. If a predator approaches, the ammonite could
When attacked the animal would squeeze
into all the other chambers
withdraw itself into the shell and squeeze into different chambers so that the chambers
are concealed. The shell can provide protection for the ammonite in dangerous
situations such as being hunted by predators. The chambers also contain gases, which
help them regulate their buoyancy, and support the shell from water pressure
preventing it from breaking.
Environmental Pressure: I think that they had been adapted this way mainly because
in their past generations, their ancestors lack the ability to withdraw itself into the
shell which makes it unable to protect itself against predators.
Structural: Jet propulsion
Although ammonites are able to float and swim due to
their unique construction of the shell, they also use jet
propulsion to move through water. Jet propulsion is a
common way for Cephalopod to swim fast.
Ammonites use a funnel-like opening to propel itself
in the opposite direction. Rather than waiting for their food to float around, this gave
them control moving around for food and swim away from predators faster. This also
improved their living style and at the same time it
Water leaves the funnel and causes the animal to Jet
increases its survivability from predators.
backwards
Environmental Pressure: Throughout their pass
generations, they were not able to get away from predators quick enough or not being
able to move through water as freely as it is. Therefore, I believe they were adapted
this way to increase their survivability when encountered a predator and maximizing
its movement in water.
Behavior: Squirting Ink
Ammonites have the ability to squirt ink. Ammonites
use this ability to scare of predators or hide from them
while being attacked. This ability allows the ammonite
to blur the predator’s vision giving itself time to hide
or get away from the predator. However this only
works on small predators. Large predators such as
sharks will be unlikely affected by it. This ability
allows ammonites to have larger survivability and a
less chance for it to be captured by a predator.
When being attacked, the Ammonites was able to
blur the vision of the diver by squirting ink.
Environmental Pressure: In my opinion, it’s
However it’s likely to have no effect at all as seen in
ancestors lack the ability to escape from predators
the image on large predators.
once captured giving it no chance to survive,
therefore they develop the ability to squirt ink to get away from dangerous situations.
Their close relatives such as the octopus and the squid do the same thing.
Behavior: Descending to darker waters during day
During day time, Ammonites descend to darker and
deeper waters to avoid predators. Ammonites shells
were not as well developed as the Chambered
Nautilus today. They
were not able to descend to waters more than 100m
due to the lack of water pressure resistant their shell
provides. Their shell would appear darker
Deep waters like the image shown above usually have less
when seen from above which makes it hard
for other marine creatures to spot them at the predators and makes it hard for the Ammonites to be
spotted.
bottom of the sea where waters are usually
darker.
Environmental Pressure: I believe that in their past generations, they are easily
spotted by their predators and often being hunted. They realize that they are less likely
to be hunted by predators in deep waters, therefore they always descend to dark
waters during times where predators were usually around.
Physiological: Higher Metabolism
Ammonites had a higher metabolism than the Chambered Nautilus today. This was
mainly due to their feeding habit. Their body was able to consume more food and
allows the food to be digested faster.
Environmental Pressure: I believe that their past ancestors often get over fed and
results in death due to eating too much. Therefore, their metabolism increases to
prevent it from dying and allows it to digest food fast due to their feeding habits.
Habitat
Ammonites lived in the oceans of the Jurrasic
and Cretaceous periods. When Ammonites still
exists, the world was a very different place than
the world we live in today. During the Jurrasic
Period, the supercontinent Pangea was broken
up into two supercontinent Laurasia(Northern
supercontinent) and Gondwana(Southern
supercontinent).
The climate was likely to be warmer as there
was no evidence of icecaps. Ammonites live in
oceans which genrally has a higher temperature
than the environment that the Chambered
Nautilus lives in today. They would be found in larger groups as they have a larger
population than the Chambered Nautilus today. They lived on the edges of rocks and
coral reefs which lead down into deeper waters.
Extinction Pressure
The Ammonite species disappeared along with the dinosaurs 65 million years ago.
However the real reason responsible for the extinction of Ammonites are still
unknown.
There was a huge decline in the Ammonite species at that time and previous
ammonoid cephalopods barely survived several earlier major extinctions. But the
sudden disappearance of the all Ammonites along with dinosaurs cannot be due to
natural extinction.
There were several theories that were brought up relating to the extinction of
Ammonites. All of these theories are related to the meteor impact which marked the
end of the Cretaceous period.
One theory suggested that months or years of overcast skies causes by the meteor
impact disable the ability of planktons to photosynthesis which causes the Ammonites
to starve to death.
Another theory suggested that the shell of Ammonites could not withstand the acid
rain that probably following the vaporization of limestone in the atmosphere caused
by the impact.