Sharks
Although sharks belong to the class
Chondrichtyes, there are many
different types. Sharks arose about 350 million
years ago and have remained
virtually unchanged for the past 70 million years
and still comprise a dominant
group. It is thought that sharks almost
certainly evolved from placoderms, a
group of primitive jawed fishes. It took
a long series of successful and
unsuccessful mutations with fin, jaw
positions etc to give us all the different
designs of sharks around today.
When asked to draw a shark, most people would
draw a shape along the lines of
the whaler shark family, tigers or a mackeral
shark such as a porbeagle.
However many people do not realize the sheer
diversity in the shape of
sharks, or that rays are really sharks. Seldom does
such an animal inspire
such a variety of emotions reflecting a mixture of
fascination, awe and fear.
Sharks have occasionally exacted a terrible price
from humans who have
trespassed on their territory. No better understood than
the ocean that they
inhabit, these creatures should be regarded in the same way
as lions, tigers,
and bears: as dangerous, predatory but nonetheless magnificent
animals.
Different Types of Sharks Living sharks are divided into eight major
orders,
each easily recognizable by certain external characteristics. Each
order
contains one or more smaller groups, or families. In all there are 30
families
of sharks and they contain the 350 or more different kinds or
species of sharks.
The eight major orders of sharks include the
Squantiformes, Pristiophormes,
Squaliformes, Hexanchiformes,
Carcharhiniformes, Lamniformes, Orectolobiformes,
and the Heterodotiformes.
The orders have distinguishing characteristics that
fit in each. The
Squantiformes normally have flat bodies that are ray-like with
mottled dorsal
surfaces. These sharks have a short terminal mouth, which is
armed with small
impaling teeth. They also have a caudal fin, which has a lower
lobe that is
longer than the upper lobe. Their pectoral fins extend forward over
the
ventrally directed gills. The Pristiophormes have more of an elongated
snout,
which is saw-like and edged with slender, needle-sharp lateral
teeth.
They have two dorsal fins and no anal fin. They use short
transverse mouths and
small cuspidate holding teeth in both jaws.
Squaliformes have no anal fin as
well, but their snout is not elongated, but
is somewhat long. Many have powerful
cutting teeth in both jaws. In some
species these razor sharp teeth are in the
lower jaw only and the upper teeth
serve to hold the food. Hexanchiformes have
six or seven gill slits. They are
sharks with a single spineless dorsal fin, and
an anal fin. The typical
Carcharhiniforme has an elongated snout, a long mouth
that reaches behind the
eyes, an anal fin and two spineless dorsal fins. The
eyes have movable,
nictitating lower eyelids worked by unique muscles. Teeth
vary from small and
cuspidate or flattened to large and bladelike.
Carcharhiniformes have no
enlarged rear crushing teeth. Along with this they
have a spiral scroll
intestinal valve. A Lamniforme shark has an elongated
snout. Most have long
mouths that reach behind the eyes, an anal fin and two
spineless dorsal fins.
They also have a ring intestinal valve. The
Orectolobiformes have
pig-like snouts and short mouths that in most species are
connected to the
nostrils by grooves. There is an anal fin but no fin spines on
the two dorsal
fins. They have uniquely formed barbells at the inside edges of
the nostrils.
Heterodotiformes are the only living shark that combines fin
spines on their
two dorsal fins and anal fin. They only have five-gill slits. In
each order
there are specific types of sharks. Each shark belongs to a family
with
different species. The Angel shark (Squantiforme) is just one of the
many.
It has a single family of about thirteen species. They are all
ovoviviparous
livebearers and most do not exceed 1.5 meters. Saw sharks
(Pristiophoriformes)
are harmless bottom sharks. They are also a single
family but with five species.
They are also ovoviviparous livebearers.
Four sharks that belong to the order
Sqauliforme are the Bramble,
Dogfish, and Rough sharks. They have three families
with eighty-two species.
They too, are ovoviviparous livebearers. They have more
cylindrical bodies.
Frilled sharks, Six, and Seven gill sharks (Hexanchiformes)
have two families
and five species. Once again they are also ovoviviparous
livebearers.
Usually, these guys are found in deep waters. The Catsharks,
Finback
Catshark, False Catshark, Barbelled Houndshark, Weasel,
Houndshark,
Hammerhead, and Requiem sharks (Carcharhiniformes) have one
hundred and
ninety-seven known species. Most of these sharks are known to be
dangerous. They
are both oviparous and ovoviviparous livebearers. This is not
the type of shark
you would like to have grace you presence. From the order
of Landformes is the
Sand, Basking, Goblin, Crocodile, Megamouth,
Thresher, and Mackerel sharks. They
come complete with seven families and
fifteen or sixteen species. All of them
are ovoviviparous livebearers. These
sharks are found in all seas except Arctic
and Antarctic. The last group of
sharks would be the Collared Carpet sharks,
Blind, Wobbegongs, Zebra,
Longtailed Carpet Sharks, Whale, and Nurse sharks.
They all belong to the
order Orectolobiformes and have seven families and
thirty-three species.
These sharks prefer the warmer water and are both
ovoviviparous and oviparous
livebearers. Obviously these sharks come in many
different sizes and some are
more dangerous than others. At least eighteen
species in four families and
nine genera have been implicated in attacks on
humans. Obviously a small
shark such as the Pygmy is harmless, but they still
must be treated as a
predator especially the bigger ones. The smallest of all
sharks is the Pygmy
Ribbontail Catshark, which is about 0.24 meters. Next in
line from smallest
to largest would be the Port Jackson Shark, which is about
1.65 meters.
After them would be the Ornate Wobbegong (2.88m) and then the Bull
shark
(3.4m). The average sizes go drastically up from there to the Great
White
shark, which is incredibly larger, its about 6.4 meters. The two
greatest sizes
are the Basking shark (7.8m) and the Whale shark (13.7m).
These sharks listed
here are definitely not all the sharks in the world, they
were just meant to
give an average range of size for all sharks. Some of the
most dangerous sharks
range from about 2 to 8 meters. The Hammerhead, Great
White, Tiger, Blue, and
the Bull shark name a few. There are many types of
sharks lurking around in
today’s ocean. In every one is unique in its own
way. Some are different by
size, shape, eating habits, or even the way they
breed. Although with all these
differences they are all very similar and that
is why the shark is one of the
most amazing creatures of our time. Summary
Although sharks belong to the class
Chondrichtyes, there are many
different types. Sharks are divided into 8 major
orders. Each order contains
1 or more smaller group. There are 350 or more
different kinds of species of
sharks. The 8 orders are named the Squantiformes,
Pristiophormes,
Squaliformes, Hexanchiformes, Carcharhiniformes,
Lamniformes,
Orectolobiformes, and the Heterodotiformes. These orders
group sharks according
to certain distinguishing characteristics. The Angel
shark, Saw shark, Frilled
shark, Hammerhead shark, Sand shark, Wobbegongs,
and more all belong to a
specific order due to their characteristics. Each
one of these sharks come in
different shapes and sizes. Some are more
dangerous than others. The more
dangerous sharks range from about 2 to 8
meters. It is obvious that sharks are
one of the most amazing creatures of
our time.
Bibliography
Clark
J. 1975. Shark frenzy. Grosset
& Dunlap Publishers, New York NY. 106 pp.
Clark, E. 1981. Sharks,
magnificent and misunderstood. National Geographic
160:138-186 (Aug.
1991) Compagno, L. J. V. 1984. FAO species catalogue. Vol. 4. Sharks of the
world. An annotated and illustrated
catalogue of shark species known to date.
Part 2. Carcharhiniformes FAO Fish.
Synop. (125) Vol. 4, Pt. 2: 251-655.
Conniff R. 1993. From jaws to laws - now
the big bad shark needs protection
from us. Smithsonian 24: 32-43 (Number 2,
May1993). Burgess, R. F. 1970.
The sharks. Doubleday & Company, Inc., Garden
City NY. 159 pp