Sharks Essay Research Paper Although sharks belong

Sharks Essay, Research Paper

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 grac

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