Megalodon

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Megalodon Fossil range: Miocene - Pleistocene
Megalodon tooth with great white shark's teeth.
Conservation status
Extinct (IUCN 2.3)
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Chondrichthyes Subclass: Elasmobranchii Order: Lamniformes Family: Lamnidae Genus: Carcharodon Species: C. megalodon
Binomial name
Carcharodon megalodon Agassiz, 1843
Synonyms
Procarcharodon megalodon Casier, 1960

The megalodon (pronounced /ˡmɛ.gə.ləˌdɒn/ or MEG-a-la-don; meaning "big tooth" or in Greek as μέγας 'οδόντος) was a giant shark that lived in prehistoric times, between about 18 million to 1.5 million years ago^a[›] and was the apex predator of its time. It is the largest carnivorous fish known to have existed,^[1] and quite possibly the largest shark to have ever lived. It is believed that the average size of the megalodon was between 12 metres (39 ft) and 18 metres (59 ft). This species is a member of the lamnidae family but its classification is in dispute and a new genus has been proposed. Fossil evidence has revealed that megalodon fed upon large animals, including the early whales.^[2]

Some cryptozoologists argue that this shark might still be alive today, probably living in deep waters, and often cite the examples of coelacanth and megamouth shark to support their claims.^[2] However, such beliefs have earned no credibility in the mainstream scientific community.

Contents 1 Taxonomy 1.1 Classification dispute 1.1.1 Megalodon within Carcharodon 1.1.2 Megalodon within Carcharocles 2 Anatomy and appearance 2.1 Size estimation 2.2 Jaw dentition 2.3 Skeletal reconstruction 3 Distribution, range and habitat 4 Paleoecology 4.1 Diet 4.2 Behavior 5 Extinction hypothesis 6 Relict 6.1 Megamouth analogy 6.2 Supposed C. megalodon sightings 7 In fiction and popular culture 7.1 Films 7.2 Novels 7.3 Television 7.4 Games 8 See also 9 Notes 10 References 11 External links 11.1 Educational videos

[edit] Taxonomy

The Swiss naturalist, Louis Agassiz, gave this shark its scientific name, Carcharodon megalodon in 1835,^[3] in his research work Recherches sur les poissons fossiles (Research on fish fossils), which he completed in 1843. Due to the dental similarities of the teeth of the great white shark, Carcharodon carcharias, and megalodon, Agassiz proposed Carcharodon as the genus.^[3] In-short, this shark is termed C. megalodon by shark researchers. However, it is often dubbed the "mega-tooth shark".

[edit] Classification dispute

Cladogram of the "hastalis hypothesis" highlighting the position of C. megalodon Muizon et al. 1985[3] Lamniformes  void void void I. hastalis  void  Sacaco Sp. C. carcharias void C. megalodon *Note: The hastalis hypothesis shows that C. carcharias is more closely related to I. hastalis than C. megalodon.[3]

There is a major disagreement among scientists as to how C. megalodon should be classified.^[1][2] The controversy is that whether C. megalodon is a close relative of the extant great white shark or whether the two species are distant relatives. The trend among shark researchers is to dismiss the statement that C. megalodon is a close relative of the great white shark, in favor of citing convergent evolution as the reason for the dental similarity.

[edit] Megalodon within Carcharodon

The traditional view is that C. megalodon should be classified within the genus Carcharodon along with the great white shark. The Carcharodon proponents suggest that C. megalodon and C. carcharias share a common ancestor known as Carcharodon orientalis.^[1][3][4]

[edit] Megalodon within Carcharocles

Around 1923, the genus, Carcharocles, was proposed by two shark researchers, D. S. Jordan and H. Hannibal, to classify a very similar shark C. auriculatus. Many marine biologists and paleontologists are now favoring the Carcharocles genus for C. megalodon.^{[1][2][3][5][6]} One reason for this shift is that the teeth of C. megalodon are also similar to the teeth of some sharks that belong to Carcharocles lineage. The Carcharocles proponents suggest that the direct ancestor of the sharks belonging to the Carcharocles genus, is an ancient shark called Otodus obliquus, which lived during the Paleocene and Eocene epochs.^[1][5] According to Carcharocles proponents, Otodus obliquus evolved in to Carcharocles aksuaticus,^[1][5] which evolved in to Carcharocles auriculatus,^[1][5] which evolved into Carcharocles augustidens,^[1][5] which evolved into Carcharocles chubutensis,^[1][5] which eventually evolved into megalodon.^[1][5] Hence, the immediate ancestor of C. megalodon is Carcharocles chubutensis,^[1][5] 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.^[1][5]

Carcharocles proponents also point out that the great white shark is more closely related to an ancient shark Isurus hastalis, the "broad tooth mako," than C. megalodon. This suggestion is given credence by many scientists due to some convincing evidence.^[3][6][7] One reason is that the teeth of I. hastalis and C. carcharias are remarkably similar in shape, differing only in that the former lack the characteristic serrations of the latter.^[1][3][7]

[edit] Anatomy and appearance

C. megalodon is known principally from fossil teeth and a few fossilized vertebral centra.^[8] As with all other sharks, the megalodon skeleton was formed of cartilage and not bone, resulting in a poor skeletal fossil record.^[2] 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 in slant.^[1]

Nevertheless, it is extrapolations from the shape and size of the teeth of C. megalodon when compared with 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. Thus far, the great white shark has been considered the favored model for the basis for the reconstruction of C. megalodon.^[4][8]

[edit] Size estimation

Estimating the maximum size of C. megalodon is a highly controversial subject. An early jaw reconstruction of this shark, developed by Professor Bashford Dean in 1909, indicates a length of more than 25 metres (82 ft), but that jaw reconstruction is now considered to be inaccurate.^[8] One reason is that the teeth used as posteriors in this jaw reconstruction were not true posterior teeth. However, several scientists have tried to solve this issue in later years and some examples are mentioned below.

In 1973, the ichthyiologist John E. Randall suggested a method to measure the size of the large sharks.^[9] According to Randall, the enamel height of the largest tooth in the upper jaw of the shark can be used to determine its total length. He concluded that C. megalodon could grow to 13 metres (43 ft).^[9]

However, in 1996, three shark experts, Michael D. Gottfried, Leonard J. V. Compagno and S. Curtis Bowman, questioned the reliability of Randall's method. According to them, shark's tooth enamel height does not necessarily increase in proportion with the animal's total length.^[4] Hence, Gottfried and his co-workers tried to solve this issue by means of conducting new research and analysis to create a method for measuring the size of large sharks (including C. megalodon) with much greater accuracy, which was published in 1996.^b[›] Using this new method, the maximum size of megalodon was calculated to be 15.9 metres (52 ft) with a body mass of more than 50 short tons (45 MT).^[4] But this calculation was based on a 168 mm (6⅝ inch) long upper anterior tooth, which was the biggest tooth in the possession of this team at the time. Since then, even larger C. megalodon teeth have been excavated which indicate that the shark could grow to more than 17 metres (56 ft).^[1][10][11]

Shark researcher Cliff Jeremiah also has suggested a method to determine the size of the large sharks, including C. megalodon,^[1] and his method is considered to be among the most reliable.^[1] He suggested that the jaw perimeter of a shark is directly proportional to its total length, with the width of the roots of the largest teeth being a proxy for estimating jaw perimeter. For every centimeter of root width of the largest tooth, he asserts, there was approximately 4.5 feet of the shark. He concluded that C. megalodon could grow up to 18.2 metres (60 ft).^[1] Many scientists acknowledge this conclusion.^[1][12]

Hence, from the research of several scientists, it is clear that C. megalodon is the largest macropredatory shark that has ever lived and is among the largest fishes known to have existed.^[4]

[edit] Jaw dentition

Some scientists including Applegate and Espinosa published an artificial dental formula for C. megalodon in 1996.^[8] Several modern C. megalodon jaw reconstructions are based on this dental formula.

The dental formula of C. megalodon is:

2.1.7.4

3.0.8.4

As evident from the dental formula, the jaws of C. megalodon contained four different kinds of teeth.^[8]

• Anterior - (A)
• Intermediate - (I) ^c[›]
• Lateral - (L)
• Posterior - (P)

Paleontologists suggest that C. megalodon had a total of about 250 teeth.^[1]

[edit] Skeletal reconstruction

Aside from estimating the size of C. megalodon, Gottfried and his colleagues also have tried to determine how C. megalodon might have looked like in real life.^[4] After conducting a comprehensive analysis of the available evidence, they concluded that C. megalodon was a very robust shark and it was more massively proportioned than many modern large sharks including C. carcharias due to several reasons including:

• C. megalodon had a more massive, stouter and more strongly developed chondrocranium and jaws than those of modern macropredatory sharks, in order to functionally support a massive and very robust dentition.^[4]
• The fins of C. megalodon were significantly larger and thicker because they needed to be adapted for propulsion and control of movements of such a massive shark.^[4]
• It had a higher vertebral count than that of any large shark including C. carcharias.^[4]

Gottfried and his colleagues eventually developed a model of the entire skeleton of C. megalodon with the above mentioned characteristics, which has been put on display in Calvert Marine Museum at Solomons island, Maryland in USA.^[4][5][13]

[edit] Distribution, range and habitat

C. 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.^[1][8]

C. megalodon most likely inhabited warm water regions around the world.^[2] Its range would not have been constricted by its reliance on warm waters as the oceans were noticeably warmer during the Miocene and early Pliocene. This would have made it possible for this species to flourish around the world, as evident from the fossil records.

[edit] Paleoecology

[edit] Diet

It is believed that C. megalodon would have had a huge appetite, which would be necessary for sustenance of its enormous bulk.^[13] It was contemporaneous with 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.^[1][4][8] The teeth of C. megalodon are serrated,^[1][3] which would have improved efficiency in slicing the flesh of prey items. Various excavations have revealed C. megalodon teeth lying close to the chewed remains of whales.^[4][5] This evidence suggests a predator-prey relationship between C. megalodon and large marine animals including whales ^[8] (e.g. sperm whales,^[1] Cetotherium,^[2] and Odobenocetops^[14]), sirenians,^[1] dolphins,^[1] and pinnipeds.^[2] Like other sharks, C. megalodon was certainly piscivorous as well.^[2][13]

[edit] Behavior

Most sharks are opportunistic predators and rely on a broad spectrum of prey coupled with scavenging. C. megalodon was unlikely to have been an exception to this rule.^[2] Some large sharks (including the great white shark) employ ambush strategies against their prey during hunting. A 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, before dispatching it without facing any resistance. Some paleontologists suggest that C. megalodon also may have employed a similar hunting strategy against large potential prey, like adult whales. Several fossilized flipper bones, and caudal vertebrae of whales have been found with bite marks that were caused by the attacks from C. megalodon.^[1][4] This evidence indicates that C. megalodon most likely injured and immobilized its prey by biting off its propulsive structures, before proceeding to feed on it.^[1][4]

However, remains of a large prehistoric baleen whale have been excavated from Chesapeake Bay, which provided the first opportunity to quantitatively analyse the feeding behavior of C. megalodon, and this specimen revealed that the attacking behavior of C. megalodon was more aggressive than that of the great white shark.^[11] One reason is that the shark apparently focused its attack on the bony portions of the prey, which great white sharks generally avoid.^[11]

From fossil evidence, juvenile C. megalodon individuals would mostly prefer to attack small-to-medium sized prey, such as porpoises, other sharks, pinnipeds and juvenile whales. Hence, through ontogeny C. megalodon proceeded to hunt larger animals.^[4] In addition, fossil evidence suggests that the preferred breeding grounds of C. megalodon were mostly warm coastal regions.^[4]

[edit] Extinction hypothesis

There are several hypotheses as to how an apex predator like C. megalodon suddenly became extinct after millions of years of existence. However, the extinction of large-bodied marine predators, such as pliosaurs, mosasaurs, ichthyosaurs and Basilosaurus, are instructive as to the possible mechanism involved.

Scientists believe that C. megalodon disappeared due to a variety of reasons.^[2] The geological and climatic conditions of the world when C. megalodon existed, were considerably different from those now. It is possible that these major climatic changes may have been unfavorable for C. megalodon. Some notable climatic shifts are:

• During the late Pliocene and Pleistocene epochs there were significant ice ages,^[15][16] which cooled the oceans significantly.^[8]
• From the fossil record, whale migatory patterns from the end Pliocene have been reconstructed, suggesting that some species migrated to polar regions, effectively "getting out of the range" of C. megalodon.^[2][8]
• Prolonged disturbance of food chains can wipe out predators with massive metabolic requirements. During the Pliocene, some species of whales and dolphins (e.g. Odobenocetops and Cetotherium) became extinct. As these species would most likely have been among the potential prey of C. megalodon,^[2] sustaining the dietary requirements of such a large predator would have become increasingly difficult.
• In addition, wide-scale glaciation trapped much of the oceanic salt water during the late Pliocene and Pleistocene through-out the ice ages. At its height sea levels dropped significantly, restricting many shallow coastal areas, that have been thought to serve as breeding grounds for the C. megalodon pups.^[2]

Consequently, a hypothesis can be constructed, that at the end of the Pliocene, the polar seas became too cold for C. megalodon to survive. Several species of whales, including cetotheriids, became extinct during the late Pliocene, while some whale species showed a trend towards the cooler polar regions. Many of the shallow warm water regions dried out at that time, that may have been breeding grounds for C. megalodon. As such, these significant disturbances in the ecosystem would have caused major problems for C. megalodon. Being unable to follow the surviving whale species into the polar seas the food supply of C. megalodon lessened, which over time lead to the extinction of the species.^[2]

[edit] Relict

While scientists contend that available evidence shows that C. megalodon is extinct, the idea of a relict population seems to have seized the public imagination.^[1][2] Evidence supporting such ideas is generally seen as scant, ambiguous and lacking sufficient credibility.^[1][2]

C. megalodon teeth have been discovered that some argue date to as recently as 10,000 to 15,000 years ago. This claim is based on the discovery of two teeth from the South Pacific 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 long 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.^[2]

Scientists now suggest that these recent estimates for these teeth are inaccurate, and being based on an outdated testing methodology. Another possible explanation is that some C. megalodon teeth might have been eroded from pre-Pleistocene deposits and re-deposited in the much younger strata, such as those from the late Pleistocene.^[2]

[edit] 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 can still harbor large species unknown to man.^[2] However, the research has suggested that the megamouth shark is a false analogy to the possible existence of C. megalodon, unless the proposed individual was a highly specialized mesopelagic planktivore with poorly calcified skeleton; C. megalodon was certainly not such a creature.^[2]

Research concludes that C. megalodon was a large carnivorous shark that adapted to a warm and food-rich marine habitat and was an active predator of large animals like whales. Such a creature would not be able to survive in the cold, food-poor deep-sea.^[2]

[edit] Supposed C. 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.^[1][2]

This report received considerable attention from the media, and David G. Stead himself believed in the account. Most shark experts, however, after careful examination of this account questioned its authenticity, as the sailors themselves were giving contradictory statements regarding the details of the event, including the size factor of the mystery animal. Hence, those sailors were most likely exaggerating the details of the event. One critic even said that those sailors might have concocted this story, after they lost their crab pots in an accident.^[1]

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?^[2]

After careful examination of this case, most shark experts concluded that Grey's description of the animal still closely matches that of the whale shark and he was wrong about the color of the 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. Their heads are very wide, squarish, yet slightly rounded.^[2]

Another less well known incident was narrated by Cartmell in 1978. His narration is mentioned below:

In the 1960’s along the outer edge of Australia’s Great Barrier Reef, an 85 foot [26 m] ship experienced engine trouble which forced it to weigh anchor for repairs. Although the men subsequently refused to openly report what they had seen for fear of public ridicule, the captain and his crew later told friends of sighting an immense shark as it moved slowly past their ship. Whitish in color, they were awed by its size. It was as long if not longer than their boat! Experienced men of the sea, they too were certain the creature was not a whale.^[2]

The problem in this case is that no evidence has been provided by Cartmell to support his claim. Hence his narration has also been dismissed as unreliable.^[2]

Similarly a few other cases of C. megalodon sightings have also been presented but all of them have been declared to be false due to lack of convincing evidences.^[2]

[edit] In fiction and popular culture

Ever since the remains of C. megalodon were discovered, it has been an object of fascination. It has been portrayed in several works of fiction, including films and novels, and continues to hold its place among the most popular subjects for fictional works involving sea monsters. 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 as a result of human intervention or through natural means.

[edit] Films

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

[edit] Novels

• Jaws Peter Benchley (1974) ^d[›]
• 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)

[edit] Television

• Sea Monsters: A Walking with Dinosaurs Trilogy (2003)

[edit] Games

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

[edit] See also

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

[edit] Notes

• ^ a:  The oldest C. megalodon teeth found are about 18 million years old.^[1] Though, C. megalodon became extinct in the Pliestocene epoch probably about 1.5 million years ago.^[2]
  
• ^ b:  The actual method is: "Megatooth's" Total Length in meters = [− (0.22) + (0.096) × (Slant height of tooth in [mm])].^[4] Though, this method has often been interpreted as: "Megatooth's" Total Length in meters = [(0.96) × (Slant height of tooth in [cm] − (0.22))], because it yields same results.^[10]
  
• ^ c:  In the case of C. megalodon, this tooth appears to be upper anterior and is technically termed as "A3" because it is fairly symmetrical and does not points mesially, but this tooth is still designated as an intermediate tooth.^[3] 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.
  
• ^ d:  The Jaws novel contains a lengthy discussion of C. megalodon and its possible survival. This does not appear in the film version.
  

[edit] References

[edit] External links

• Snorkeling teen finds ancient shark tooth from MSNBC
• Fossil Field Guide, Carcharodon Megalodon from San Diego Natural History Museum
• Fact File: Megalodon from BBC, with pictures and video
• An impressive photograph of Megalodon's jaw
• Megalodon jaws on display in South Carolina State Museum
• The largest modern Megalodon jaw reconstruction in the world (NOTE: Reconstructed by Vito Bertucci)

[edit] Educational videos

• A video clip of the Perfect Shark (2006) program from BBC
• Long Ago, in the Chesapeake Bay from Discovery Channel (NOTE: Flash Player required)