Megalodon

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Megalodon Fossil range: 18–1.5 Ma PreЄ Є O S D C P T J K Pg N Miocene - Pleistocene
Jaws of the Megalodon.
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Chondrichthyes Subclass: Elasmobranchii Order: Lamniformes Family: Disputed; either Lamnidae or Otodontidae Genus: Disputed; either Carcharodon or Carcharocles Species: C. megalodon
Binomial name
Disputed; either Carcharodon megalodon or Carcharocles megalodon For Carcharodon megalodon, Agassiz, 1843
Synonyms
Procarcharodon megalodon Casier, 1960

The megalodon (pronounced /ˈmɛɡələdɒn/ MEG-ə-lə-don, "big tooth" in Greek, from μέγας and ὀδούς), Carcharodon megalodon or Carcharocles megalodon (in dispute), was a giant shark that lived in prehistoric times. The oldest remains of this species found are about 18 million years old^[1] and C. megalodon became extinct in the Pleistocene epoch probably about 1.5 million years ago.^[2] It was the apex predator of its time and is the largest carnivorous fish known to have existed.^[1]

C. megalodon could grow to more than 18 metres (59 ft) long and is also quite possibly the largest shark ever to have lived. From scrutiny of its remains, scientists conclude that C. megalodon belongs to the order Lamniformes. However, scientists are still debating which genus would be most appropriate for C. megalodon from the two proposed. Fossil evidence has revealed that megalodon fed upon large marine animals.^[2]

Contents 1 Discovery 1.1 Glossopetrae 1.2 Identification 2 Fossils 2.1 Fossil teeth 2.2 Fossil vertebrae 2.3 Fossil Range 3 Anatomy and appearance 3.1 Size estimation 3.2 Jaw dentition 3.3 Skeletal Anatomy 4 Distribution and range 5 Paleoecology 5.1 Prey relationships 5.2 Hunting Behavior 5.2.1 Bite force 5.3 Nursery areas 6 Extinction 6.1 Climatic upheavals 6.2 Shortage of food 6.3 The hypothesis 7 Taxonomy 7.1 Megalodon within Carcharodon 7.2 Megalodon within Carcharocles 8 In fiction and popular culture 9 See also 10 References 11 External links 11.1 Educational videos

[edit] Discovery

[edit] Glossopetrae

According to Renaissance accounts, large, triangular fossil teeth often found embedded in rocky formations were once believed to be petrified tongues, or glossopetrae, of dragons and snakes. This interpretation was corrected in 1667 by a Danish naturalist Nicolaus Steno, who recognized them as ancient shark teeth (and famously produced a depiction of a shark's head bearing such teeth).^[3] He mentioned his findings in a book, The Head of a Shark Dissected, which also contained an illustration of a C. megalodon tooth, previously considered to be a tongue stone.^[4]

[edit] Identification

A Swiss naturalist, Louis Agassiz, gave this shark its scientific name, Carcharodon megalodon in 1835,^[5] in his research work Recherches sur les poissons fossiles^[6] (Research on fossil fish), which he completed in 1843. The teeth of the C. megalodon are morphologically similar to the teeth of the great white shark, Carcharodon carcharias. On the basis of this observation, Agassiz assigned the genus Carcharodon to the megalodon.^[5] While the scientific name is C. megalodon, it is often informally dubbed the megatooth shark or giant white shark.^[1][7]

[edit] Fossils

As with all other prehistoric sharks, the megalodon skeleton was formed of cartilage and not bone, resulting in mostly poorly preserved fossil specimens.^[2]

[edit] Fossil teeth

The most common fossils of C. megalodon are its teeth. The teeth are morphologically similar to great white shark teeth but are more robust,^[8] more regularly serrated,^[8] and are much larger, exceeding 18 cm in slant height.^[1]

[edit] Fossil vertebrae

Some partially preserved fossil vertebrae of C. megalodon have also been found.^[4] The most notable example is a partially preserved vertebral column of a single C. megalodon excavated from Belgium in 1926. This specimen comprises of 150 vertebral centra.^[8]

[edit] Fossil Range

The fossils of C. megalodon have been excavated from many parts of the world, including Europe^[1][4], North America^[1][8], South America^[4][8], Puerto Rico^[9], Australia^[4][8], New Zealand^[1], Japan^[4][8], Africa^[4][8], Malta^[1], and India.^[1][4]

[edit] Anatomy and appearance

Extrapolations of the remains of C. megalodon when compared with related modern sharks actually provide us with our conceptions about what this ancient shark might have looked like in life. The great white shark is considered to be the closest living analogue to C. megalodon and is the favored model for the basis of reconstruction and estimating the size 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.^[4] One reason is that in Dean's time the knowledge of C. megalodon's dentition was relatively poor. Furthermore, it is not clear how Dean estimated the size of the C. megalodon. Scientists have pointed out that the teeth and anatomical studies of closest living relatives of extinct sharks can offer useful clues for determining their body lengths.

In 1973, the ichthyologist John E. Randall suggested a method to measure the size of C. carcharias and C. megalodon.^[10] According to Randall, the enamel height of the largest anterior tooth in the upper jaw of the shark can be used to determine its total length. The largest tooth in his possession at that time had an enamel height of 115 mm. On the basis of the enamel height of this tooth, he concluded that C. megalodon could grow to 13 metres (43 ft).^[10]

However, 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.^[8] Gottfried and his co-workers found a correlation between the tooth slant height and total body length in C. carcharias after a thorough research and scrutiny of many specimens. Hence, they proposed a method for measuring the size of C. carcharias and C. megalodon, which has been acknowledged as more accurate, and was published in 1996. The proposed method is: "Megatooth's" Total Length in meters = [− (0.22) + (0.096) × (Slant height of tooth in [mm])].^[8] Using this new method, the maximum size of C. megalodon was calculated to be 15.9 metres (52 ft) with a body mass of about 47 metric tons (52 short tons).^[8] But this calculation was based on an upper anterior tooth with slant height of 168 mm (6.61 inch), and was the biggest tooth in the possession of this team at the time.^[8] Since then, even larger C. megalodon teeth have been excavated which indicate that the shark could grow larger.^[11]

Shark researcher, Dr. G. Hubbell, has pointed out that using the slant height of the tooth to determine the size of a shark is also an imperfect technique. He asserts that the teeth can vary in slant length within the jaws of sharks of similar sizes even from the same genus.^[1] However in 2002, shark researcher, Cliff Jeremiah, also proposed a method to determine the size of C. carcharias and C. megalodon,^[1] which is considered to be reliable.^[1] The proposed method is: "Megatooth's" Total Length in feet = [(Root width of an upper anterior tooth in [cm]) x (4.5)]. It translates as for every centimeter of root width of an upper anterior tooth, there is approximately 4.5 feet of the shark. C. Jeremiah asserts 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.^[1] The largest tooth in the possession of C. Jeremiah had a root width of nearly 12 cm, which yielded a 15.5 metres (51 ft) size.^[1] However, C. megalodon teeth with root width of more than 12 cm have appeared in the fossil records, once again indicating that the shark could grow larger.

The largest fossils indicate that C. megalodon likely approached or exceeded 18.2 metres (60 ft) and Bashford Dean's estimations may not have been far fetched, despite errors in his works. A massive upper anterior C. megalodon tooth was discovered and excavated by shark researcher, Vito Bertucci, which has a slant height of 184 mm (7.25 inch)^[1] and has a root width of over 5.5 inch (13.97 cm). According to size estimation method proposed by shark researcher, Cliff Jeremiah, it indicates a body length of more than 19.1 metres (63 ft). To date, reports of even larger C. megalodon teeth persist.

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.^[8] It is widely acknowledged that C. megalodon could have grown up to 18 metres (59 ft) or more,^[1][12] with a body mass of 70 metric tons (77 short tons) or more.

[edit] Jaw dentition

A team of Japanese scientists, T. Uyeno, O. Sakamoto, and H. Sekine, discovered and excavated the partial remains of a C. megalodon, with nearly complete associated set of its teeth, from Saitama, Japan in 1989.^[4] Based upon this discovery, two scientists, S. Applegate and L. Espinosa, published an artificial dental formula for C. megalodon in 1996.^[4] Most accurate modern C. megalodon jaw reconstructions are based on this dental formula.

The dental formula of C. megalodon is:

Dentition
2.1.7.4
3.0.8.4

As evident from the dental formula, C. megalodon contained four different kinds of teeth in its jaws.^[4]

• Anterior - A
• Intermediate - I (In the case of C. megalodon, this tooth technically appears to be an upper anterior and is termed as "A3" because it is fairly symmetrical and does not points mesially (side of the tooth toward the midline of the jaws where left and right jaws meet), but this tooth is still designated as an intermediate tooth.^[5] 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.)
• Lateral - L
• Posterior - P

Paleontologists suggest that C. megalodon had a very robust dentition,^[8] and it had a total of about 250 teeth in its jaws.^[1]

[edit] Skeletal Anatomy

Aside from estimating the size of C. megalodon, Gottfried and his colleagues also have tried to reconstruct an entire skeleton of C. megalodon^[8]. After conducting a comprehensive analysis of the fossilized remains of C. megalodon, they concluded that C. megalodon was a very robust shark and it was more massively proportioned than any other large shark including C. carcharias due to several reasons including:

• In order to functionally support a massive and very robust dentition, C. megalodon most likely had a massive, stouter and more strongly developed chondrocranium than those of modern macropredatory sharks.^[8]
• The fins of C. megalodon were most likely significantly larger and thicker because they needed to be adapted for propulsion and control of movements of such a massive shark.^[8]
• It had a higher vertebral count than that of any large shark including C. carcharias.^[8]

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.^[13][8][14]

[edit] Distribution and range

'The fossil records of C. megalodon indicate that it was a warm water pelagic fish and it thrived in all the oceans of the world in its time. 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.

[edit] Paleoecology

[edit] Prey relationships

There is evidence that C. megalodon preyed on whales^[4] (e.g. sperm whales,^[1] bowhead whales,^[14] Cetotherium,^[2] and Odobenocetops^[15]), sirenians,^[1] dolphins,^[1], porpoises,^[1] pinnipeds,^[2] and giant sea turtles. Whales were likely an important prey item for C. megalodon as many whale bones (including vertebrae and flippers) have been found with clear signs of large bite marks made by the teeth that match those of C. megalodon,^[1][8][4] and various excavations have revealed C. megalodon teeth lying close to the chewed remains of whales.^[13][8] Like other sharks, C. megalodon was almost certainly piscivorous.^[2][14]

[edit] Hunting 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. Such sharks usually attack their prey with great force in the first attempt to inflict maximum possible damage and wait for the prey to become weakened due to massive blood loss before dispatching the prey without facing any resistance. Some paleontologists suggest that C. megalodon also may have employed a similar hunting strategy against large potential prey such as whales. The teeth of C. megalodon are serrated,^[1][5] which would have improved efficiency in slicing the flesh of prey items.

In addition, 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][8] This evidence indicates that C. megalodon most likely injured and immobilized its prey by ripping apart or biting off its propulsive structures, before proceeding to kill and feed on it.^[1][8]

However, remains of a prehistoric baleen whale excavated from Chesapeake Bay suggest that the attacking behavior of C. megalodon may have been more aggressive and possibly different from that of the great white shark^[16] and other large sharks. Based on this first opportunity to quantitatively analyse the feeding behavior of C. megalodon, it appears that the shark focused its attack on the bony portions of the prey, which great white sharks generally avoid.^[16] The exceptionally robust teeth of C. megalodon were not just good cutting tools but also were well suited for grasping powerful prey and would seldom crack even when slicing through the bones.^[16] Additionally, the fossil evidence indicates that C. megalodon likely delivered a killer bite on the part of the body of the whale where rib cage was present. The victim may have died quickly due to massive internal injuries as a result.^[16] Remains of another victim (a bowhead whale) of the C. megalodon have been found which indicate that it was also attacked in a similar ferocious manner.^[14]

[edit] Bite force

A team of scientists led by Stephen Wroe conducted an experiment in 2008 to determine the bite force of the C. megalodon and concluded that very large specimens were capable of exerting a bite force of up to 40,131 pounds per square inch (276 MPa; over 5 times greater than that of T. rex), arguably making the giant shark one of the most formidable and powerful predators to have ever inhabited the oceans.^[17]

[edit] Nursery areas

Fossil evidence suggests that the preferred breeding grounds of C. megalodon were mostly warm shallow water regions.^[8] Juvenile C. megalodon most likely preyed upon porpoises, fish, giant sea turtles, other sharks, pinnipeds and juvenile whales, proceeding on to larger prey as they reached maturity.

[edit] Extinction

It is not yet absolutely clear how an apex predator like C. megalodon suddenly went extinct after millions of years of existence and dominance, however two main factors believed to be involved are: climatic upheavals and shortage of food.

[edit] Climatic upheavals

• The Isthmus of Panama closed around 5 million years ago and fundamentally changed global ocean circulation.^[4][18] It initially set the stage of glaciation in northern hemisphere,^[18] and later on also facilitated in cooling of the entire planet.^[18] Consequently, during the late Pliocene and Pleistocene epochs there were significant ice ages,^[19][20] which cooled the oceans significantly^[4] along with Earth's climate and caused wide-scale glaciation. The cooling trend in oceans may have spelled doom for the C. megalodon, as it predominantly thrived in warm waters.^[4]

• In addition, wide-scale glaciation during the late Pliocene and Pleistocene tied up huge volumes of water in continental ice sheets about 1,500–3,000 m thick, resulting in sea level drops of 100 m or more over the entire surface of the Earth. This lowered sea level may have restricted many of the shallow warm water coastal areas that are thought to have served as C. megalodon's breeding grounds. The loss of many ideal breeding grounds may have jeopardized the safety of C. megalodon pups who were likely vulnerable to attacks from larger C. megalodon and odontocetes in deep waters.

[edit] Shortage of food

• Prolonged disturbance of food chains can wipe out predators with massive metabolic requirements. Fossil records reveal that during the Pliocene, many species of whales and dolphins (e.g. Odobenocetops, Cetotheriids, and several other mostly unknown taxons) became extinct. Due to such extinctions of the main prey of C. megalodon, the food supply for this large bodied predator was drastically shortened.
• Additionally, whale migratory patterns from the end Pliocene have been reconstructed from the fossil record, suggesting that most surviving species migrated to polar regions, effectively "getting out of the range" of C. megalodon.^[2][8][4] Such migrations also contributed to the already diminishing food supply for the C. megalodon in warm waters, and thus sustaining the dietary requirements of such a predator would have become increasingly difficult.

[edit] The hypothesis

Consequently, a hypothesis can be constructed that climatic upheavals posed a severe challenge to C. megalodon's survival at the end of the Pliocene. Several species of large marine mammals became extinct during this period, while the surviving large marine mammals (i.e. mostly whales) moved toward cooler polar regions too cold for C. megalodon to successfully breed in. C. megalodon's food supply was greatly reduced, as it was unable to follow the surviving whale species into the polar seas, which over time led to the extinction of this specialized super predator.^[2][13]

[edit] Taxonomy

Even after decades of research and scrutiny, the controversy on phylogeny of C. megalodon still persists.^[1][2] Several shark researchers (e.g. J. E. Randall, A. P. Klimley, D. G. Ainley, M. D. Gottfried, L. J. V. Compagno, S. C. Bowman, and R. W. Purdy) insist that C. megalodon is a close relative of the great white shark. However, several other shark researchers (e.g. D. S. Jordan, H. Hannibal, E. Casier, C. DeMuizon, T. J. DeVries, D. J. Ward, and H. Cappetta) dismiss the proposal that C. megalodon is a close relative of the great white shark, and cite convergent evolution and heterochrony as the reasons for the dental similarity. Most paleontologists, convinced by the arguments, favor Carcharocles genus more over Carcharodon genus for C. megalodon.^[13]

Lamniformes  I. hastalis Sacaco sp. C. carcharias C. megalodon The megalodon hypothesis shows that C. carcharias is more closely related to C. megalodon than I. hastalis.[5]

Lamniformes  I. hastalis Sacaco sp. C. carcharias void C. megalodon The hastalis hypothesis shows that C. carcharias is more closely related to I. hastalis than to C. megalodon.[5]

[edit] Megalodon within Carcharodon

The traditional view is that C. megalodon should be classified within the genus Carcharodon along with the great white shark because the remains of the C. megalodon indicate close morphological ties with the great white shark. The supporters of classification as Carcharodon for C. megalodon suggest that C. megalodon and C. carcharias share a common ancestor, Palaeocarcharodon orientalis.^[1][5][8]

[edit] Megalodon within Carcharocles

Lamniformes  O. obliquus C. megalodon I. hastalis C. carcharias The Isurus-Origin hypothesis shows that C. carcharias descends from I. hastalis.[21]

Around 1923, the genus Carcharocles was proposed by two shark researchers, D. S. Jordan and H. Hannibal, to classify a shark C. auriculatus. Many marine biologists and paleontologists are now favoring the Carcharocles genus for C. megalodon.^{[1][2][5][13][22]} One reason for this shift is that the teeth of C. megalodon seem to indicate very close evolutionary ties with the teeth of sharks that belong to Carcharocles lineage.^[1][13] The supporters of classification as Carcharocles for C. megalodon suggest that the direct ancestor of the sharks belonging to the Carcharocles genus, is an ancient giant shark called Otodus obliquus, which lived during the Paleocene and Eocene epochs.^[1][13] According to supporters of classification as Carcharocles for C. megalodon; Otodus obliquus evolved in to Carcharocles aksuaticus,^[1][13] which evolved in to Carcharocles auriculatus,^[1][13] which evolved into Carcharocles angustidens,^[1][13] which evolved into Carcharocles chubutensis,^[1][13] which eventually evolved into megalodon.^[1][13] Hence, the immediate ancestor of C. megalodon is Carcharocles chubutensis,^[1][13] 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][13] Scientist, D. J. Ward have further elaborated on this evolutionary process by implying that this lineage represents a family tree, stretching from Paleocene to Pliocene, of a single giant shark which gradually changed through time, suggesting a case of chronospecies.^[1] This stunning revelation has received recognition from several shark researchers (e.g. J. Bourdon, L. Andrez, H. Capetta, V. I. Zhelezko, and V. A. Kozlov).

Carcharocles proponents also point out that the great white shark is closely related to an ancient shark Isurus hastalis, the "broad tooth mako", rather than to C. megalodon. This suggestion is given credence by many scientists due to some convincing evidence.^[5][22][23] 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][5][23]

Further evidence linking the great white shark more closely to ancient mako sharks, rather than to C. megalodon, has been provided in 2009. The fossilized remains of an ancient form of the great white shark were excavated from southwestern Peru in 1988, which are about 4 million years old. These fossilized remains demonstrate a likely shared ancestor of modern mako and great white sharks.^[24][21]

[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. Many of these works of fiction posit that at least some C. megalodon actually survived extinction and lurk in the depths of the ocean, which manage to surface from the vast depths, either as a result of human intervention or through natural means.

Some works of fiction (such as Shark Attack 3: Megalodon and Steve Alten's Meg series) incorrectly depict Megalodon as being a species over 70 million years old and to have been alive at the time of Dinosaurs.

[edit] See also

For a topical guide to this subject, see Outline of sharks.

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

[edit] References

[edit] External links

Wikimedia Commons has media related to: Megalodon

Wikispecies has information related to: Carcharocles megalodon

• Ancient Shark's Bite More Powerful Than T. Rex's from LiveScience
• Carcharocles: Extinct Megatoothed shark
• Fossil Field Guide, Carcharocles Megalodon from San Diego Natural History Museum
• Fact File: Megalodon from BBC, with pictures and video
• Prehistoric Megalodon Information
• 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)
• Paleoworld - Megalodon (NOTE: Flash Player required)