Megalodon

Megalodon Temporal range: Miocene - Pleistocene
File:Megalodon diver.JPG
Size comparison between megalodon and diver
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Lamniformes Leo S. Berg, 1958
Family:	Lamnidae Müller and Henle, 1838
Genus:	Carcharodon (disputed)
Species:	C. megalodon
Binomial name
Carcharodon megalodon Agassiz, 1843

Template:Sharksportal The megalodon, (Template:PronEng or meg-la-don; meaning 'big tooth' or in Greek as μέγας 'οδόντος) is a giant prehistoric shark that probably lived between about 16 to 1.5 million years ago, and was the apex predator in its time. It is recognized as the biggest known carnivorous fish to have ever existed. It is often termed the "megatooth shark". The classification of this shark is currently under dispute and a new genus has been proposed for this shark. Fossil records reveal that the megalodon fed on large animals including the early whales.

Some cryptozoologists argue that this shark might still be alive in this modern age, probably living in the deep waters, and often cite the examples of coelacanth and megamouth shark to support their claims. But such beliefs are considered to be false and lack sufficient credibility. Still megalodon has left a lasting impact on the minds of the people around the world, as a highly fascinating monster, which is evident from the popular culture.

Taxonomy

The Swiss naturalist, Louis Agassiz, gave this shark its scientific name, Carcharodon megalodon in 1835, in his research work called "Recherches sur les poissons fossiles" (Research on fossil fishes). He completed his research work in 1843.

Due to the dental similarities among the teeth of the great white shark and megalodon, Louis Agassiz proposed Carcharodon as the genus for C. megalodon.

Classification dispute

There is a major disagreement among marine biologists and shark experts as to how megalodon should be classified. A growing number of researchers are refuting the statement the megalodon might be the ancestor of the great white shark, instead citing convergent evolution as the reason for the dental similarity.

• As indicated before, the older view is that megalodon should be classified in the Carcharodon genus with the great white shark. Though this has generated debate among the paleontologists that whether megalodon is a direct ancestor of the great white shark or whether the two species are distant relatives. Some biologists still favor the case of Carcharodon genus for megalodon.
• Around 1923, the genus, Carcharocles, was proposed to classify a very similar shark C. auriculatus. Many paleontologists are now favouring the Carcharocles genus for megalodon. One reason is that the teeth of megalodon are also closely related to the teeth of sharks that belong to Carcharocles genus. The Carcharocles proponents suggest that C. auriculatus evolved into Carcharocles augustidens, which evolved into Carcharocles chubutensis, which eventually evolved into C. megalodon. Hence, the immediate ancestor of C. megalodon is Carcharocles chubutensis, because it serves as the missing link between Carcharocles augustidens and C. megalodon and it bridges the loss of the "lateral cusps" that characterize C. megalodon.

Carcharocles proponents also point out that the true ancestry of the family of sharks belonging to the Carcharocles genus is strongly associated with an ancient shark, Otodus obliquus from the Eocene epoch. Also, the ancestor of the great white shark is not megalodon but Isurus hastalis, the "broad tooth mako". This suggestion is receiving acknowledgment from many scientists due to some convincing evidence.

Anatomy and appearance

Megalodon tooth with 2 great white shark teeth

C. megalodon is known principally from fossil teeth and a few fossilized vertebral centra. As with all other sharks, the megalodon skeleton was formed of cartilage and not bone, resulting in the poor skeletal fossil record. The teeth are in many ways similar to great white shark teeth but are much larger and can measure up to more than 18 cm long in slant.

Nevertheless, it is extrapolations from the shape and size of the teeth of C. megalodon to related modern sharks and studies of their physical characteristics, that provide us with our conceptions about what this ancient super-predator might have looked like in life. So far, the great white shark has always been considered as the favored model by many shark experts to be used as the basis for the reconstruction of this giant shark.

A model of the entire skeleton of megalodon has been put on display in Calvert Marine Museum at Solomon's island, Maryland.

Size estimation

Estimating the maximum size of megalodon is a highly controversial subject. However, in 1996 three shark experts, M. D. Gottfried, Leonard Compagno and S.C. Bowman, tried to solve this issue by developing a special method for measuring the size of sharks (including megalodon) with much greater accuracy, which was published in 1996. Using this new method, the maximum size of this creature was calculated to be 15.9 m (52.1 ft) long with a body mass of more than 35 tons. But this calculation was based on a 168 mm (6.61 inch) long upper anterior tooth which was the biggest tooth in the possession of these shark experts at the time. Since then, even larger megalodon teeth have been excavated which indicate that this creature could actually grow to more than 16 m (52.5 feet) long.

Megalodon tooth from the Miocene era. Dimensions: 13 cm straight, 18 cm in diagonal.

A very old jaw reconstruction of this shark, developed by Professor Bashford Dean in 1909, suggests a size of about 30 m (100 ft) long, but that jaw reconstruction is now considered to be inaccurate. One reason is that the teeth used as posteriors in this jaw reconstruction were not actually true posterior teeth.

Some other methods have also been developed by a few other shark experts including Randall to measure the size of megalodon, but the method that Gottfried and his colleagues suggested is actually considered to be the best among all.

Jaw dentition

Some scientists including Applegate and Espinosa have published an artificial dental formula for the megalodon in 1996. Many modern megalodon jaw reconstructions are based on this dental formula.

The dental formula of megalodon is:

Dentition
2.1.7.4
3.0.8.4

The jaws of megalodon contained four different kinds of teeth.

• Anterior - (A)
• Intermediate - (I)
• Lateral - (L)
• Posterior - (P)

Distribution, range and habitat

Megalodon was a pelagic fish and it thrived in all the oceans of the world in its time, indicating dominance over the marine world. The teeth of this ancient shark have been excavated from many parts of the world, including Europe, North America, South America, Australia, New Zealand, Japan, South Africa, Malta and India.

Megalodon most likely inhabited warm water regions around the world. But its dominance had not been hindered by this factor because the oceans, along with the climatic conditions, were noticeably warmer during the Miocene and early Pliocene epochs and made it possible for this species to flourish around the world, as evident from the fossil records.

Paleoecology

Megalodon is among the most highly studied prehistoric sharks in the world. A paleontologist Robert W. Purdy have used the fossil record of this shark to explore its paleoecology and his findings were published in 1996. His research reveals some interesting facts about this shark and its behavior in real life.

Diet

File:MEG1.jpg

Megalodon chasing two juvenile whales

Assuming similar metabolic-weight ratios as the great white shark, it is estimated that a C. megalodon would need to eat about one-fiftieth of its weight of food on average per day. In more clear terms, this shark would need to eat a lot of food on a daily basis to sustain its massive bulk.

During the time of C. megalodon's existence, the oceans were inhabited by a large variety of marine animals, including various species of whales. Several whale vertebrae and bones have been found with clear signs of large bite marks made by the teeth that match those of C. megalodon. The teeth of the megalodon are serrated, which would help in tearing the flesh of prey with great efficiency. And during various excavations, megalodon teeth have often been found lying close to the chewed-up remains of whales. Hence these kinds of evidence indicate a predator-prey relationship of C. megalodon and large animals including whales.

Like other sharks, C. megalodon was certainly piscivorous as well. However, because of its immense size, this shark's diet consisted mostly of whales and other large marine mammals including sirenians and pinnipeds.

Behavior

Most sharks are opportunistic predators and can rely on a broad spectrum of prey and scavenging. Megalodon was no exception to this rule as well. Some sharks (including the great white shark) employ ambush strategies against their prey during hunting. A large shark usually attacks its prey with great force in the first attempt to inflict maximum possible damage. Then it circles its prey and waits for it to weaken, and when the prey does the shark then proceeds to finish it off without facing any resistance. Megalodon also might have employed this type of attacking strategy against large potential prey like adult whales. Several fossilized flipper bones and tail vertebrae of whales have been found with bite marks that were caused by the attacks from megalodon. This evidence show that the megalodon most likely immobilized its prey by biting off its propulsive structures.

However, for medium-sized prey, megalodon might go directly for the middle of the body, crushing the ribs and lungs in a single devastating attack. Remains of a few whales have been found that were attacked in this manner by large C. megalodon individuals.

As with any skill, predation also has to be learned. Fossil records show that juvenile C. megalodon individuals would mostly prefer to attack small-to-medium sized prey, such as porpoises, other sharks, seals and juvenile whales. Hence, they would learn their trade by practising on small animals before proceeding to hunt the larger animals as they grew bigger with the passage of time.

Also, fossil records have revealed that the megalodon generally considered the warm water coastal regions as the ideal breeding grounds for its young pups around the world.

Extinction hypothesis

Megalodon and fossil shark teeth

It is not yet fully clear how a dominant species like megalodon would suddenly become extinct after millions of years of successful existence. However, the examples of extinction of pliosaurs, mosasaurs and basilosaurus are instructive.

Scientists believe that C. megalodon disappeared, due to a variety of possible reasons. The geological and climatic conditions of the world were considerably different during the age of C. Megalodon from the current era, and major changes in these conditions might not have proved to be favorable for C. Megalodon. Some notable reasons are mentioned below:

• The major changes in the climatic conditions of the world that took place during the late Pliocene and Pleistocene epochs due to the Ice Ages, allowed the oceans to cool down significantly.
• Some species of whales are highly migratory in nature. And fossil records have revealed to us that some species of whales migrated to polar regions at the end of the Pliocene, hence effectively getting out of the range of C. megalodon.
• Some experts also suggest that any prolonged disturbance of the food chain would wipe out a predator with such massive metabolic requirements. Some species of whales and dolphins did in fact became extinct during the Pliocene epoch and were most likely among such animals that were regarded as the preferred prey by C. megalodon. The Odobenocetops is also among the list of such animals.
• Glaciation occupied much of the planetary water supply during the late Pliocene and Pleistocene periods due to the Ice Ages, locking many regions away in massive sheets of opalescent ice and the closing of the Isthmus of Panama might have caused changes in the oceanic circulation and these factors might have caused the sea level to drop significantly, which allowed many shallow coastal areas to dry up that would have served as ideal breeding grounds for the megalodon pups.

Hence, from the reasons mentioned above, a hypothesis can be constructed, that at the end of the Pliocene epoch, the polar seas became too cold for the megalodon to thrive in. Several species of whales including cetotheriids became extinct during the late Pliocene epoch, while some species of whales showed a trend towards the cooler polar regions. And many shallow warm water regions dried up at that time, which served as the ideal breeding grounds for the megalodon. So, these significant disturbances in the ecosystem caused major problems for C. megalodon and they could not follow the surviving species of whales in the cold regions. Hence, these factors resulted in a lessened food supply and the megalodon most likely starved to death.

Relict

Carcharodontosaurus tooth from the Sahara Desert with a megalodon tooth, and a 25 mm diameter coin (US quarter).

While most mainstream experts contend that available evidence suggests that C. megalodon is extinct, the idea of a relict population seems to have seized the public imagination , but evidence supporting such ideas is generally seen as scant, ambiguous and lacking sufficient credibility.

C. megalodon teeth have been discovered that some argue date as recently as 10,000 to 15,000 years ago. This claim is based on the discovery of two teeth by the HMS Challenger scientific expedition (these teeth were dated by estimating the amount of time it took for manganese to accumulate on them, although it is quite possible the teeth were fossilized before being encrusted). Problems with this dating method include the simple fact that deposition of manganese oxide on the seafloor is not constant, and can only serve as a minimum age. In all likelihood, these teeth are probably much older.

Scientists now suggest that these recent estimates for these teeth are inaccurate, and being based on outdated testing and methodology. Another possible explanation is that some C. megalodon teeth might have been eroded from pre-Pleistocene deposits and re-deposited in younger strata, such as those from the late Pleistocene.

Megamouth analogy

Some proponents of modern-day C. megalodon survival suggest that the shark might be lurking in the deep waters and often cite the case of the megamouth shark as an example and state that the oceans oceans can still harbour large species unknown to man. However, the research has suggested that the megamouth shark is not a perfect analogy to support the existence of ancient large animals like C. megalodon, unless the animal is proposed to be a highly specialized mesopelagic planktivore and megalodon was not certainly like such a creature.

Research concludes that C. megalodon was a large carnivorous shark that adapted to a coastal, warm and food-rich marine habitat and was an active predator of large animals like whales. And such a creature would not be able to survive in the cold, food-poor deep-sea.

Supposed megalodon sightings

Some relatively recent reports of large shark-like creatures have been interpreted as surviving C. megalodon, but such reports are usually considered misidentification of basking sharks, whale sharks or submarines.

One well-known example was reported by writer David G. Stead in his book Sharks and Rays of Australian Seas, that was released in 1963. The brief excerpt of this account is mentioned below:

In the year 1918 I recorded the sensation that had been caused among the "outside" crayfish men at Port Stephens, when, for several days, they refused to go to sea to their regular fishing grounds in the vicinity of Broughton Island. The men had been at work on the fishing grounds---which lie in deep water---when an immense shark of almost unbelievable proportions put in an appearance, lifting pot after pot containing many crayfishes, and taking, as the men said, "pots, mooring lines and all". These crayfish pots, it should be mentioned, were about 3 feet 6 inches [1.06 m] in diameter and frequently contained from two to three dozen good-sized crayfish each weighing several pounds. The men were all unanimous that this shark was something the like of which they had never dreamed of. In company with the local Fisheries Inspector I questioned many of the men very closely and they all agreed as to the gigantic stature of the beast.

This report actually got considerable attention from the media and David G. Stead himself believed in this account. But most shark experts through careful examination of this account, pointed out some clear signs of exaggerations at several points (including the size factor) and questioned the authenticity of this account, because the sailors themselves were giving contradictory statements. Hence, those sailors were most likely exaggerating the details of that event. One expert even said that those sailors might have concocted this story, after they lost their crab pots in an accident.

Another well-known account was reported by writer Zane Grey and his son Loren in 1933. His actual comments have been narrated by Gross in 1987:

At first I thought it was a whale, but when the great brown tail rose in the ship’s wake as the fish moved ponderously away from the liner, I knew immediately that it was a monstrous shark. The huge round head appeared to be at least 10 to 12 feet across if not more ... It was my belief that this huge, yellowish, barnacled creature must have been at least 40 or 50 feet long. He was not a whale shark: the whale shark has a distinctive white purplish green appearance with large brown spots and much narrower head. So what was he---perhaps a true prehistoric monster of the deep?

After careful examination of this case as well, most shark experts concluded that Grey's description of the animal still closely matches that of the whale shark and he is wrong about the coloring of this animal. An expert, Castro, gives a good explanation of the coloring of the skin of whale sharks. He points out that many white or yellowish spots can be observed on the skin of whale sharks. And it is clear that a whale shark has a very wide, squarish, yet slightly rounded head.

In fiction and popular culture

Ever since the remains of this shark were discovered, it has immensely fascinated people. In the past, people used to think that the oceans were inhabited by dangerous monsters big enough to destroy boats and could be regarded as serious threats to fishers. C. megalodon has made its way onto the list of such monsters.

C. megalodon has been portrayed in several works of fiction, including movies and novels, and continues to hold its place among the most popular subjects for fictional works. It is, however, interesting to note that in most of these works of fiction, C. megalodon is shown to surface from the vast depths of the oceans, either through human intervention or through natural means.

Films

• Shark Hunter (2001)
• Shark Attack 3: Megalodon (2002)
• Megalodon (2004)
• Hai-Alarm auf Mallorca (2004)
• Meg (to be released)

Novels

• Extinct Charles Wilson (1997)
• Meg: A Novel of Deep Terror Steve Alten (1997)
• The Trench Steve Alten (2000)
• From the Dark Below Cari McKnight (2001)
• Meg: Primal Waters Steve Alten (2004)
• Meg: Hell's Aquarium Steve Alten (2008)
• Meg: Night Stalkers Steve Alten (to be released)

Shows

• Walking with Dinosaurs: Sea Monsters (2003)

The megalodon is featured in a marine environment, which is considered to be the third most dangerous sea of all times in this show. During the show, Nigel Marven, at first, decided to see a juvenile megalodon to get a basic idea about the nature of this shark. Later on he decided to meet an adult individual. Nigel preferred to use his circular shark cage during his encounter with the adult shark but he soon realized that he was not safe even in that big cage and headed back to his ship called Mariner. However, he was successful in attaching a waterproof video camera to the big shark from the surface of his ship. The purpose of the camera was to reveal more about the behavior and hunting strategies of the shark. And the the camera revealed that the big shark later on, proceeded to ambush a large whale.

Games

• Shark! Hunting the Great White (2001)
• Sea Monsters Adventure (2003)
• Jaws Unleashed (2006)

Misc

• The band Mastodon dedicated a song to megalodon on their album Leviathan.
• A variable volume mixed gas closed circuit rebreather developed by a company, InnerSpace Systems Corp, is called the Megalodon Rebreather.
• Small megalodon teeth are often used for developing shark tooth necklaces.

See also

• List of sharks
• Prehistoric fish
• List of apex predators

Notes

• ^ a:  The method is: "Megatooth's" Total Length in meters = ((0.96) X (Slant height of tooth in [cm]) minus (0.22))
  

• ^ b:  In the case of megalodon, this tooth appears to be upper anterior because it is fairly symmetrical and does not points mesially and is techically termed as "A3", but this tooth is still designated as an intermediate tooth. However, in the case of the great white shark, the intermediate tooth does points mesially. This point has often been raised in the Carcharodon vs Carcharocles debate regarding the megalodon and favors the case of Carcharocles proponents.
  

• ^ c:  In the Jaws Unleashed game, the megalodon itself does not appear, but a megalodon tooth can be found in the eighth level of this game. The excavation of this tooth yields 3,000 points for the player.
  

External links

• Megalodon fact file from BBC, with pictures and video
• An impressive photograph of this shark's jaw

Educational videos

• Long Ago, in the Chesapeake Bay from Discovery Channel
• Perfect Shark (2006) with Michael deGruy from British Broadcasting Corporation (BBC)