Although sharks belong to the class Chondrichtyes, there are manydifferent types. Sharks arose about 350 million years ago and have remainedvirtually unchanged for the past 70 million years and still comprise a dominantgroup. It is thought that sharks almost certainly evolved from placoderms, agroup of primitive jawed fishes.
It took a long series of successful andunsuccessful mutations with fin, jaw positions etc to give us all the differentdesigns of sharks around today. When asked to draw a shark, most people woulddraw a shape along the lines of the whaler shark family, tigers or a mackeralshark such as a porbeagle. However many people do not realize the sheerdiversity in the shape of sharks, or that rays are really sharks. Seldom doessuch an animal inspire such a variety of emotions reflecting a mixture offascination, awe and fear. Sharks have occasionally exacted a terrible pricefrom humans who have trespassed on their territory. No better understood thanthe ocean that they inhabit, these creatures should be regarded in the same wayas lions, tigers, and bears: as dangerous, predatory but nonetheless magnificentanimals.
Different Types of Sharks Living sharks are divided into eight majororders, each easily recognizable by certain external characteristics. Each ordercontains one or more smaller groups, or families. In all there are 30 familiesof 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 thatfit in each.
The Squantiformes normally have flat bodies that are ray-like withmottled dorsal surfaces. These sharks have a short terminal mouth, which isarmed with small impaling teeth. They also have a caudal fin, which has a lowerlobe that is longer than the upper lobe. Their pectoral fins extend forward overthe ventrally directed gills. The Pristiophormes have more of an elongatedsnout, 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 andsmall cuspidate holding teeth in both jaws. Squaliformes have no anal fin aswell, but their snout is not elongated, but is somewhat long. Many have powerfulcutting teeth in both jaws. In some species these razor sharp teeth are in thelower jaw only and the upper teeth serve to hold the food.
Hexanchiformes havesix or seven gill slits. They are sharks with a single spineless dorsal fin, andan anal fin. The typical Carcharhiniforme has an elongated snout, a long mouththat reaches behind the eyes, an anal fin and two spineless dorsal fins. Theeyes have movable, nictitating lower eyelids worked by unique muscles. Teethvary from small and cuspidate or flattened to large and bladelike.
Carcharhiniformes have no enlarged rear crushing teeth. Along with this theyhave a spiral scroll intestinal valve. A Lamniforme shark has an elongatedsnout. Most have long mouths that reach behind the eyes, an anal fin and twospineless dorsal fins. They also have a ring intestinal valve. TheOrectolobiformes have pig-like snouts and short mouths that in most species areconnected to the nostrils by grooves.
There is an anal fin but no fin spines onthe two dorsal fins. They have uniquely formed barbells at the inside edges ofthe nostrils. Heterodotiformes are the only living shark that combines finspines on their two dorsal fins and anal fin. They only have five-gill slits.
Ineach order there are specific types of sharks. Each shark belongs to a familywith different species. The Angel shark (Squantiforme) is just one of the many. It has a single family of about thirteen species. They are all ovoviviparouslivebearers 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 orderSqauliforme are the Bramble, Dogfish, and Rough sharks. They have three familieswith eighty-two species. They too, are ovoviviparous livebearers.
They have morecylindrical bodies. Frilled sharks, Six, and Seven gill sharks (Hexanchiformes)have two families and five species. Once again they are also ovoviviparouslivebearers. 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 andninety-seven known species. Most of these sharks are known to be dangerous.
Theyare both oviparous and ovoviviparous livebearers. This is not the type of sharkyou would like to have grace you presence. From the order of Landformes is theSand, Basking, Goblin, Crocodile, Megamouth, Thresher, and Mackerel sharks. Theycome complete with seven families and fifteen or sixteen species. All of themare ovoviviparous livebearers.
These sharks are found in all seas except Arcticand 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 andthirty-three species. These sharks prefer the warmer water and are bothovoviviparous and oviparous livebearers. Obviously these sharks come in manydifferent sizes and some are more dangerous than others.
At least eighteenspecies in four families and nine genera have been implicated in attacks onhumans. Obviously a small shark such as the Pygmy is harmless, but they stillmust be treated as a predator especially the bigger ones. The smallest of allsharks is the Pygmy Ribbontail Catshark, which is about 0. 24 meters. Next inline from smallest to largest would be the Port Jackson Shark, which is about1.
65 meters. After them would be the Ornate Wobbegong (2. 88m) and then the Bullshark (3. 4m). The average sizes go drastically up from there to the Great Whiteshark, which is incredibly larger, its about 6.
4 meters. The two greatest sizesare the Basking shark (7. 8m) and the Whale shark (13. 7m). These sharks listedhere are definitely not all the sharks in the world, they were just meant togive an average range of size for all sharks. Some of the most dangerous sharksrange from about 2 to 8 meters.
The Hammerhead, Great White, Tiger, Blue, andthe Bull shark name a few. There are many types of sharks lurking around intoday’s ocean. In every one is unique in its own way. Some are different bysize, shape, eating habits, or even the way they breed.
Although with all thesedifferences they are all very similar and that is why the shark is one of themost amazing creatures of our time. Summary Although sharks belong to the classChondrichtyes, there are many different types. Sharks are divided into 8 majororders. Each order contains 1 or more smaller group. There are 350 or moredifferent 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 accordingto certain distinguishing characteristics. The Angel shark, Saw shark, Frilledshark, Hammerhead shark, Sand shark, Wobbegongs, and more all belong to aspecific order due to their characteristics. Each one of these sharks come indifferent shapes and sizes. Some are more dangerous than others. The moredangerous sharks range from about 2 to 8 meters. It is obvious that sharks areone of the most amazing creatures of our time.
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