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Megalodon (Carcharocles megalodon), meaning "big tooth" from Ancient Greek: μέγας (megas) "big, mighty" and ὀδoύς (odoús) "tooth", is an extinct species of shark that lived approximately 23 to 2.6 million years ago (mya), during the Early Miocene to the end of the Pliocene. In the past, the two major interpretations were Carcharodon megalodon (under the family Lamnidae) or Carcharocles megalodon (under the family Otodontidae). However, consensus has been reached that the latter view is correct and that megalodon is of the family Otodontidae deriving from sharks of the genus Otodus, and thus should be placed under the genus Carcharocles. The shark has made appearances in several works of fiction such as the Discovery Channel's Megalodon: The Monster Shark Lives.

Megalodon
Temporal range:
Early Miocene-Late Pliocene, ~23–2.6 Ma
Large black model of shark jaws with two visible rows of teeth, suspended by wires inside a room.
Model of megalodon jaws at the American Museum of Natural History
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Lamniformes
Family: Otodontidae
Genus: Carcharocles
Species: C. megalodon
Binomial name
Carcharocles megalodon
(Agassiz, 1843)[1]
Synonyms[2][3]

Scientists suggest that megalodon looked like a stockier version of the great white shark (Carcharodon carcharias). Regarded as one of the largest and most powerful predators in vertebrate history, fossil remains of megalodon suggest that this giant shark reached a length of 18 meters (59 ft), though there are many other competing figures; for example, 24 to 25 meters (79 to 82 ft). Their large jaws could exert a bite force of up to 110,000 to 180,000 newtons (25,000 to 40,000 lbf). Their teeth were thick and robust, built for grabbing prey and breaking bone.

Megalodon probably had a profound impact on the structure of marine communities. The fossil record indicates that it had a cosmopolitan distribution. It probably targeted large prey, such as whales, seals, and giant turtles. Juveniles inhabited warm coastal waters where they would feed on fish and small whales. Unlike the great white which attacks prey from the soft underside, megalodon probably used its strong jaws to break through the chest cavity and puncture the heart and lungs of its prey.

The animal faced competition from whale-eating cetaceans, such as Livyatan and killer whales (Orcinus orca), which likely contributed to its extinction. As it preferred warmer waters, it is thought that oceanic cooling associated with the onset of the ice ages, coupled with the lowering of sea levels and resulting loss of suitable nursing areas, may have also contributed to its decline. A reduction in the diversity of baleen whales and a shift in their distribution toward polar regions may have reduced megalodon's primary food source. The extinction of the shark appeared to affect other animals; for example, the size of baleen whales increased significantly after the shark had disappeared.

Contents

Taxonomy

Etymology

 
The depiction of a shark's head by Nicolaus Steno in his work The Head of a Shark Dissected

According to Renaissance accounts, gigantic, triangular fossil teeth often found embedded in rocky formations were once believed to be the petrified tongues, or glossopetrae, of dragons and snakes. This interpretation was corrected in 1667 by Danish naturalist Nicolaus Steno, who recognized them as shark teeth, and famously produced a depiction of a shark's head bearing such teeth. He described his findings in the book The Head of a Shark Dissected, which also contained an illustration of a megalodon tooth.[4][5][6]

Swiss naturalist Louis Agassiz gave the shark its initial scientific name, Carcharodon megalodon, in 1835,[7] in his research work Recherches sur les poissons fossiles.[1] The specific name megalodon translates to "big tooth", from Ancient Greek: μέγας (megas) "big, mighty" and ὀδoύς (odoús), "tooth"[8][9] Megalodon teeth are morphologically similar to the teeth of the great white shark (Carcharodon carcharias), and on the basis of this observation, Agassiz assigned megalodon to the genus Carcharodon.[7] The shark is also often informally dubbed the "giant white shark,"[10] the "megatooth shark," the "big tooth shark," or "Meg".[11]:4

Fossils

While the earliest megalodon remains were reported from the Late Oligocene dated to around 28 million years ago (mya),[12][13] competing figures still exist as to when it evolved, such as 16 mya and 23 mya.[14] It is believed that megalodon became extinct around the end of the Pliocene, probably about 2.6 mya;[14][15] reported Pleistocene megalodon teeth are considered to be unreliable claims.[15]

 
Megalodon tooth with two great white shark teeth

The most common fossils of megalodon are its teeth. Diagnostic characteristics include a triangular shape, robust structure, large size, fine serrations, and a visible V-shaped neck (where the root meets the crown).[16]:55[17] Megalodon teeth can measure over 180 millimeters (7 in) in slant height (diagonal length) and are the largest of any known shark species.[11]:33

Some fossil vertebrae have been found. The most notable example is a partially preserved vertebral column of a single specimen, excavated in the Antwerp Basin, Belgium in 1926. It comprises 150 vertebral centra, with the centra ranging from 55 millimeters (2.2 in) to 155 millimeters (6 in) in diameter. However, the shark's vertebrae may have gotten much bigger.[16]:63–64 Another partially preserved vertebral column of a megalodon was excavated from Gram Formation in Denmark in 1983. This specimen comprises 20 vertebral centra, with the centra ranging from 100 millimeters (4 in) to 230 millimeters (9 in) in diameter.[18]

Phylogeny

Lamniformes



Otodus obliquus



Carcharocles megalodon






Isurus hastalis



Carcharodon carcharias




Relationship between megalodon and the great white shark (Carcharodon carcharias)[19]
 
The great white shark (Carcharodon carcharias) and megalodon were previously thought to be close relatives.[7][19]

The great white shark was previously considered to be a close relative to megalodon, and the two were placed in the same genus, due to dental similarity, but most authors currently believe that this is due to convergent evolution. In this model, the great white shark is more closely related to the shark Isurus hastalis than to megalodon, as evidenced by more similar dentition in those two sharks; megalodon teeth have much finer serrations than great white shark teeth. However, proponents of the former model, wherein megalodon and the great white shark are more closely related, argue that the differences between their dentition are minute and obscure.[16]:23–25 In this model, the great white shark is more closely related to the mako shark, with a common ancestor around 4 mya.[7][19] However, some great white shark fossils are about 16 million years old and predate the transitional Pliocene fossils.[13]

Megalodon was previously considered to be a member of the family Lamnidae, but it is now considered to be a member of the family Otodontidae, genus Carcharocles.[14][15][20][21] The genus Carcharocles currently contains four species: C. auriculatus, C. angustidens, C. chubutensis, and C. megalodon.[11]:30–31 The genus was proposed by D. S. Jordan and H. Hannibal in 1923 to classify the shark C. auriculatus into. Later on in the 1980s, megalodon was assigned to Carcharocles.[7][11]:30

Before this, however, in 1960, the genus Procarcharodon was erected and included those four sharks, and was considered separate from the great white shark. It is now considered a junior synonym of Carcharocles.[11]:30 The genus Palaeocarcharodon was erected alongside Procarcharodon to represent the beginning of the lineage, and, in the model wherein megalodon and the great white shark are closely related, their last common ancestor. However, it is believed to be an evolutionary dead-end and unrelated to the Carcharocles sharks by authors who reject that model.[16]:70

Another model of the evolution of this genus is that the direct ancestor of the Carcharocles is the shark Otodus obliquus, which lived during the Paleocene and Eocene epochs.[19][22] In this model, O. obliquus evolved into O. aksuaticus, which evolved into C. auriculatus, and then into C. angustidens, and then into C. chubutensis, and then finally into C. megalodon. The evolution of this lineage is characterized by the increase of serrations, the widening of the crown, the development of a more triangular shape, and the disappearance of the lateral cusps.[11]:28–31[22] The genus Otodus is ultimately derived from Cretolamna, a shark from the Cretaceous period.[20][23]

Another model of the evolution of Carcharocles is that the three other species are actually a single species of shark that gradually changed over time between the Paleocene and the Pliocene, making it a chronospecies.[11]:17[13] Some authors suggest that C. auriculatus, C. angustidens, and C. chubutensis should be classified as a single species in the genus Otodus, leaving C. megalodon the sole member of Carcharocles.[13][17]

The genus Carcharocles may be invalid, and the shark may actually belong in the genus Otodus, making it Otodus megalodon.[24] A 1974 study on Paleogene sharks erected the subgenus Megaselachus, classifying the shark as Otodus (Megaselachus) megalodon, along with O. (M.) chubutensis.[25] A 2006 review of Chondrichthyes elevated Megaselachus to genus, and classified the sharks as Megaselachus megalodon and M. chubutensis.[24] The discovery of fossils assigned to the genus Megalolamna in 2016 led to a re-evaluation of Otodus, which concluded that it is a paraphyly. The inclusion of the Carcharocles sharks in Otodus would make it monophyletic, with the sister clade being Megalolamna.[20]

Anatomy

External appearance

 
Megalodon may have had a build similar to the basking shark (Cetorhinus maximus).[11]:35–36

One idea on how megalodon appeared was that it was a robust-looking shark, and may have had a similar build to the great white shark. The jaws may have been blunter and wider than the great white, and it may have had a pig-eyed appearance, in that it had deep-set and small eyes. The fins would have also been similar in shape, though thicker due to its size.[16]:64–65

Another idea is that megalodon bore a similarity to the whale shark (Rhincodon typus) or the basking shark (Cetorhinus maximus). The tail fin would have been crescent-shaped, the anal fin and second dorsal fin would have been small, and there would have been a caudal keel present on either side of the tail fin (on the caudal peduncle). This build is common in other large aquatic animals, such as whales, tuna, and other sharks, in order to reduce drag while swimming. The head shape, however, can vary between species as most of the drag-reducing adaptations are toward the tail end of the animal.[11]:35–36

Since Carcharocles is derived from Otodus, and the two had teeth that bear a close similarity to those of the sand tiger shark (Carcharias taurus), megalodon may have had a build more similar to the sand tiger shark than to other sharks. However, since sand tiger sharks are axial swimmers that flex their body for propulsion, and use drag to displace water, they are required to move around three or four times their own weight in water on each tail stroke. A large sand tiger shark would require large fins to propel itself, however this in itself would create more drag and offset efficiency, so it is unlikely that they had similar body shapes given how large megalodon was.[11]:35–36[26]

Size

Statistics

 
Megalodon (gray and red representing the largest and smallest estimates) with the whale shark (violet), great white shark (green), and a human (black) for scale

Due to fragmentary remains, there have been many contradictory size estimates for megalodon, as they can only be drawn from fossil teeth and vertebra.[11]:87[27] Due to the lack of well-preserved fossil megalodon skeletons, the great white shark is the basis of its reconstruction and size estimation,[16]:57 as it is regarded as the best analogue to megalodon.[17] Various size estimates exist for megalodon; one possible maximum size estimate is 18 metres (59 ft), with the average size being 10.5 metres (34 ft);[14][15][21] however other estimates calculate that the maximum length attained was 24 to 25 meters (79 to 82 ft).[28][29] It is possible that different populations of megalodon around the globe had different body sizes and behaviors due to different ecological pressures.[21] If it did attain a size of over 16 metres (52 ft), it would have been the largest fish that has ever lived, surpassing the Jurassic fish Leedsicthys.[30]

Mature male megalodons may have had a body mass of 12.6 to 33.9 metric tons (13.9 to 37.4 short tons), and mature females may have been 27.4 to 59.4 metric tons (30.2 to 65.5 short tons), given that males could range in length from 10.5 to 14.3 metres (34 to 47 ft) and females 13.3 to 17 metres (44 to 56 ft).[16]:61[31] A 2015 study linking shark size and typical swimming speed estimated that megalodon would have typically swam at 18 kilometres per hour (11 mph), given that its body mass was typically 48 metric tons (53 short tons), which is consistent with other aquatic creatures of its size, such as the fin whale which typically cruises at speeds of 14.5 to 21.5 kilometres per hour (9.0 to 13.4 mph).[32]

Its large size may have been due to climactic factors and the abundance of large prey items, and it may have also been influenced by the evolution of regional endothermy (mesothermy) which would have increased its metabolism. However, since the Otodontidae sharks are considered to have been ectotherms, and megalodon was a close relative to them, megalodon may have also been ectothermic. Contrary to this, the largest contemporary ectothermic sharks, such as the whale shark, are filter feeders, implying some metabolic constraints with a predatory lifestyle.[33]

Estimations

The first attempt to reconstruct the jaw of megalodon was made by Bashford Dean in 1909, displayed at the American Museum of Natural History. From the dimensions of this jaw reconstruction, it was hypothesized that megalodon could have approached 30 meters (98 ft) in length. However, Dean had overestimated the size of the cartilage on both jaws, causing it to be too tall.[30][34]

Reconstruction by Bashford Dean in 1909
Tooth compared to hand

John E. Randall, an ichthyologist, used the enamel height (the vertical distance of the blade from the base of the enamel portion of the tooth to its tip) to measure the length of the shark, yielding a maximum length of about 13 meters (43 ft).[35] However, tooth enamel height does not necessarily increase in proportion to the animal's total length.[16]:99

Shark researchers Michael D. Gottfried, Leonard Compagno, and S. Curtis Bowman proposed a linear relationship between a shark's total length and the height of the largest upper anterior tooth. The proposed relationship is: total length in meters = − (0.096) × [UA maximum height (mm)]-(0.22).[13][16]:60 They had estimated the average height, based on the slant height of the largest tooth discovered, for large female megalodon to be 15.6 meters (51 ft), though larger teeth may exist.[16]:55–60

In 2002, shark researcher Clifford Jeremiah proposed that total length was proportional to the root width of an upper anterior tooth. He claimed that for every 1 centimeter (0.39 in) of root width, there are approximately 1.4 meters (4.6 ft) of shark length. Jeremiah pointed out 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 tool for estimating jaw perimeter. The largest tooth in Jeremiah's possession had a root width of about 12 centimeters (4.7 in), which yielded 16.5 meters (54 ft) in total length.[11]:88

In 2002, paleontologist Kenshu Shimada of DePaul University proposed a linear relationship between tooth crown height and total length after conducting anatomical analysis of several specimens, allowing any sized tooth to be used. Shimada pointed out that the previously proposed methods were based on a weaker evaluation of the dental homology between megalodon and the great white shark, and that the growth rate between the crown and root is not isometric, which he considered in his model. Using this model, the upper anterior tooth possessed by Gottfried and colleagues corresponded to a total length of 15 meters (49 ft).[36] Among the specimens found in the Gatun Formation of Panama, other shark researchers used this method and calculated a maximum height of 16.8 meters (55 ft) for a specimen,[17] and for another a total length of 17.9 meters (59 ft). However this result appears to be an error within the matrix and the average position for this individual is actually 19.6 meters (64 ft) [37]

Largest known specimens

Gordon Hubbell from Gainesville, Florida, possesses an upper anterior megalodon tooth whose maximum height is 184.1 millimeters (7.25 in).[11]:87 In addition, a 2.7-by-3.4-meter (9 by 11 ft) megalodon jaw reconstruction contains a tooth whose maximum height is reportedly 193.67 millimeters (7.625 in). This jaw reconstruction was developed by fossil hunter Vito Bertucci, who was known as "Megalodon Man".[38][39]

Teeth and bite force

 
Reconstruction showing the position of the replacement teeth

In 1989, a nearly complete set of megalodon teeth was discovered in Saitama, Japan. Another nearly complete associated megalodon dentition was excavated from the Yorktown Formations in the United States, and served as the basis of a jaw reconstruction of megalodon at the National Museum of Natural History (USNM), which is part of the Smithsonian Institution. Based on these discoveries, an artificial dental formula was put together for megalodon in 1996.[16]:55[40]

 
Reconstructed jaws on display at the National Aquarium in Baltimore

The dental formula of megalodon is: 2.1.7.43.0.8.4. As evident from the formula, megalodon had four kinds of teeth in its jaws: anterior, intermediate, lateral, and posterior. Megalodon's intermediate tooth technically appears to be an upper anterior and is termed as "A3" because it is fairly symmetrical and does not point mesially (side of the tooth toward the midline of the jaws where the left and right jaws meet), but this tooth is still designated as intermediate. Megalodon had a very robust dentition,[16]:20–21 and had over 250 teeth in its jaws, spanning 5 rows.[11]:iv It is possible that large megalodon individuals had jaws spanning roughly 3.0 meters (10 ft) across.[11]:129 The teeth were also serrated, which would have improved efficiency in cutting through flesh or bone.[7][11]:1 The shark may have been able to open its mouth to a 75° angle, though a reconstruction at USNM approximates a 100° angle.[16]:63

In 2008, a team of scientists led by S. Wroe conducted an experiment to determine the bite force of the great white shark, using a 2.5-meter (8 ft) long specimen, and then isometrically scaling the results for its maximum confirmed size and the conservative minimum and maximum body mass of megalodon. They placed the bite force of the latter between 108,514 and 182,201 N (24,390 and 40,960 lbf) in a posterior bite, compared to the 18,216 N (4,095 lbf) bite force for the largest confirmed great white shark, and 5,400 N (1,210 lbf) for the placoderm fish Dunkleosteus. In addition, Wroe and colleagues pointed out that sharks shake sideways while feeding, amplifying the force generated, which would probably have caused the total force experienced by prey to be higher than the estimate.[31]

Skeletal anatomy

 
Reconstructed megalodon skeleton on display at the Calvert Marine Museum

Megalodon is represented in the fossil record by teeth and vertebral centra.[16]:57 As with all sharks, the skeleton of megalodon was formed of cartilage rather than bone; this means that most fossil specimens are poorly preserved.[41][42] To support its large dentition, the jaws of megalodon would have been more massive, stouter, and more strongly developed than those of the great white, which possesses a comparatively gracile dentition. The jaws would have given it a "pig-eyed" profile. Its chondrocranium would have had a blockier and more robust appearance than that of the great white. Its fins were proportional to its larger size. Scrutiny of the partially preserved vertebral megalodon specimen from Belgium revealed that it had a higher vertebral count than specimens of any known shark, possibly over 200 centra. Only the great white approached it.[16]:64–65

Gottfried and colleagues reconstructed the entire skeleton of megalodon, which was later put on display at the Calvert Marine Museum in the United States and the Iziko South African Museum.[16]:56[22] This reconstruction is 11.3 meters (37 ft) long and represents a mature male, though relative and proportional changes in the skeletal features of megalodon are ontogenetic in nature, in comparison to those of the great white, as they also occur in great white sharks while growing.[16]:61

Paleobiology

Range and habitat

 
Coprolite attributed to megalodon

Megalodon had a cosmopolitan distribution;[14][37] its fossils have been excavated from many parts of the world, including Europe, Africa, the Americas, and Australia.[16]:67[43] It most commonly occurred in subtropical to temperate latitudes.[14][16]:78 It has been found at latitudes up to 55° N; its inferred tolerated temperature range is 1–24 °C (34–75 °F). It arguably had the capacity to endure such low temperatures due to mesothermy, the physiological capability of large sharks to conserve metabolic heat by maintaining a higher body temperature than the surrounding water.[14]

Megalodon inhabited a wide range of marine environments (i.e., shallow coastal waters, areas of coastal upwelling, swampy coastal lagoons, sandy littorals, and offshore deep water environments), and exhibited a transient lifestyle. Adult megalodon were not abundant in shallow water environments, and mostly inhabited offshore areas. Megalodon may have moved between coastal and oceanic waters, particularly in different stages of its life cycle.[11]:33[44] However, megalodon teeth have been excavated from regions far away from continental lands, such as the Marianas Trench in the Pacific Ocean.[11]:iv

Fossil remains show a trend for specimens to be larger on average in the southern hemisphere than in the northern, with mean lengths of 11.6 and 9.6 meters (38 and 31 ft), respectively; and in the Pacific more so than the Atlantic, with mean lengths of 10.9 and 9.5 meters (36 and 31 ft) respectively. They do not, however, suggest any trend of changing body size with absolute latitude, or of change in size over time (although the megatooth lineage in general is thought to display a trend of increasing size over time). The overall modal length has been estimated at 10.5 meters (34 ft), with the length distribution skewed towards larger individuals, suggesting an ecological or competitive advantage for larger body size.[21]

Locations of fossils

Megalodon had a global distribution and fossils of the shark have been found in many places around the world, bordering all oceans of the Neogene.[2]

Age Formation State Continent
Pliocene Luanda Formation   Angola Africa
  Libya Africa
  South Africa Africa
Castell'Arquato Formation   Italy Europe
Arenas de Huelva Formation   Spain Europe
Esbarrondadoiro Formation   Portugal Europe
Touril Complex Formation   Portugal Europe
Red Crag Formation   United Kingdom Europe
San Mateo Formation   California North America
Towsley Formation   California North America
Bone Valley Formation   Florida North America
Tamiami Formation   Florida North America
Yorktown Formation   North Carolina North America
Highlands Formation   Antigua and Barbuda North America
Refugio Formation   Mexico North America
San Diego Formation   Mexico North America
Tirabuzon Formation   Mexico North America
Onzole Formation   Ecuador South America
Paraguaná Formation   Venezuela South America
Black Rock Sandstone   Australia Oceania
Cameron Inlet Formation   Australia Oceania
Grange Burn Formation   Australia Oceania
Loxton Sand Formation   Australia Oceania
Whaler's Bluff Formation   Australia Oceania
Tangahoe Formation   New Zealand Oceania
Miocene
  Egypt Africa
Madagascar Basin   Madagascar Africa
  Nigeria Africa
Varswater Formation   South Africa Africa
Baripada Limestone   India Asia
Arakida Formation   Japan Asia
Bihoku Group   Japan Asia
Fujina Formation   Japan Asia
Hannoura Formation   Japan Asia
Hongo Formation   Japan Asia
Horimatsu Formation   Japan Asia
Ichishi Formation   Japan Asia
Kurahara Formation   Japan Asia
Maenami Formation   Japan Asia
Matsuyama Group   Japan Asia
Sekinobana Formation   Japan Asia
Suso Formation   Japan Asia
Takakubo Formation   Japan Asia
Tonokita Formation   Japan Asia
Tsurushi Formation   Japan Asia
Wajimazaki Formation   Japan Asia
Yoshii Formation   Japan Asia
  Myanmar Asia
Burgeschleinitz Formation   Austria Europe
Melker Sand Formation   Austria Europe
Rzehakia Formation   Austria Europe
Weissenegg Formation   Austria Europe
Antwerpen Sands Member   Belgium Europe
  Cyprus Europe
Hrušky Formation   Czech Republic Europe
Gram Formation   Denmark Europe
Aquitaine Basin   France Europe
  Germany Europe
Libano Sandstone   Italy Europe
Blue Clay Formation   Malta Europe
Globigerina Limestone   Malta Europe
Aalten Member   Netherlands Europe
Breda Formation   Netherlands Europe
Korytnica Clays   Poland Europe
Leitha Limestone   Poland Europe
Esbarrondadoiro Formation   Portugal Europe
Filakovo Formation   Slovakia Europe
Arjona Formation   Spain Europe
Calcarenites of Sant Elm   Spain Europe
  Turkey Europe
Monterey Formation   California North America
Puente Formation   California North America
Purisima Formation   California North America
San Mateo Formation   California North America
Santa Margarita Formation   California North America
Temblor Formation   California North America
Topanga Formation   California North America
Bone Valley Formation   Florida North America
Calvert Formation   Maryland
  Virginia
North America
Kirkwood Formation   New Jersey North America
  Barbados North America
Cojímar Formation   Cuba North America
Kendance Formation   Grenada North America
  Jamaica North America
Aymamón Limestone   Puerto Rico North America
Almejas Formation   Mexico North America
Carrillo Puerto Formation   Mexico North America
Chagres Formation   Panama North America
Chucunaque Formation   Panama North America
Gatun Formation   Panama North America
Paraná Formation   Argentina South America
Bahía Inglesa Formation   Chile South America
Castilletes Formation   Colombia South America
Miramar Formation   Peru South America
Pisco Formation   Peru South America
Camacho Formation   Uruguay South America
Cantaure Formation   Venezuela South America
Caujarao Formation   Venezuela South America
Socorro Formation   Venezuela South America
Urumaco Formation   Venezuela South America
Batesford Limestone   Australia Oceania
Black Rock Sandstone   Australia Oceania
Gippsland Limestone   Australia Oceania
Mannum Formation   Australia Oceania
Morgan Limestone   Australia Oceania
Port Campbell Limestone   Australia Oceania
  Fiji Oceania
  French Polynesia Oceania
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Locations of megalodon fossil discoveries, yellow from the Pliocene and blue from the Miocene[2][14]

Prey relationships

 
Vertebra of a whale bitten in half by a megalodon with visible gashes from teeth

Sharks generally are opportunistic feeders, but scientists propose that megalodon was largely a formidable predator. Its great size, high-speed swimming capability, and powerful jaws, coupled with a formidable feeding apparatus, made it an apex predator capable of consuming a broad spectrum of animals.[16]:71–75[31] A study focusing on calcium isotopes of extinct and extant elasmobranch sharks and rays revealed that megalodon fed at a higher trophic level than the contemporaneous great white shark.[45]

Fossil evidence indicates that megalodon preyed upon many cetacean species, such as dolphins, small whales, cetotheres, squalodontids, sperm whales, bowhead whales, and rorquals.[30][46][47] In addition to this, they also targeted seals, sirenians, and large sea turtles.[44] Being an opportunist, it would have also gone after smaller fish and other sharks given the opportunity.[30] Like other sharks, megalodon also would have been piscivorous.[42] Many whale bones have been found with deep gashes most likely made by their teeth.[16]:75 Various excavations have revealed megalodon teeth lying close to the chewed remains of whales,[16]:75[22] and sometimes in direct association with them.[10]

The feeding ecology of megalodon appears to have varied with age and between sites, like the modern great white. It is plausible that the adult megalodon population off the coast of Peru targeted primarily cetothere whales 2.5 to 7 meters (8.2 to 23 ft) in length and other prey smaller than itself, rather than large whales in the same size class as themselves.[46] Meanwhile, juveniles likely had a diet that consisted more of fish.[17][48]

Competition

 
Megalodon may have faced competition from large sperm whales, such as Livyatan melvillei.[49]

Megalodon faced a highly competitive environment.[49] However, its position at the top of the food chain[50] probably had a profound impact on the structuring of marine communities.[49][51] Fossil evidence indicates a correlation between megalodon and the emergence and diversification of cetaceans and other marine mammals.[16]:78[49] Juvenile megalodon preferred habitats where small cetaceans were abundant, and adult megalodon preferred habitats where large cetaceans were abundant. Such preferences may have developed shortly after they appeared in the Oligocene.[16]:74–75

Megalodon were contemporaneous with whale-eating odontocetes (particularly killer sperm whales and squalodontids), which were also probably among the era's apex predators, and provided competition.[49] In response to competition from megalodon, whale-eating odontocetes may have evolved defensive adaptations; some species became pack predators,[22][52] and some attained gigantic sizes, such as Livyatan melvillei, which grew from 13.5 to 17.5 meters (44 to 57 ft). By the Late Miocene, killer sperm whales experienced a significant decline in abundance and diversity. However, other hyper-predatory cetaceans began to emerge during the Pliocene to fill this ecological void, such as the killer whale (Orcinus orca).[49][53]

Fossil evidence indicates that other notable species of sharks, such as the great white shark, responded to competitive pressure from megalodon by avoiding regions it inhabited by mainly inhabiting the cooler waters of the time. In areas where their ranges seems to overlap, such as in Pliocene Baja California, it is possible that megalodon and the great white shark occupied the area at different times of the year while following different migratory prey.[16]:77[54] The shark probably also had a tendency for cannibalism, much like contemporary sharks.[55]

Feeding strategies

 
Artistic impression of a megalodon pursuing two Eobalaenoptera whales

Sharks often employ complex hunting strategies to engage large prey animals. Great white shark hunting strategies may be similar to how megalodon hunted its large prey.[56] However, megalodon bite marks on whale fossils suggests that it employed different hunting strategies against large prey than the great white shark.[30]

One particular specimen – the remains of a 9 meters (30 ft) long prehistoric baleen whale (of an unknown Miocene taxon) – provided the first opportunity to quantitatively analyze its attack behavior. Unlike great whites which target the underbelly of their prey, megalodon probably targeted the heart and lungs, with their thick teeth adapted for biting through tough bone, as indicated by bite marks inflicted to the rib cage and other tough bony areas on whale remains. They probably also targeted the flipper in order to immobilize the whale before killing it.[30] Furthermore, attack patterns could differ for prey of different sizes. Fossil remains of some small cetaceans, for example cetotheres, suggest that they were rammed with great force from below before being killed and eaten.[56]

During the Pliocene, larger and more advanced cetaceans appeared.[57] Megalodon apparently further refined its hunting strategies to cope with these large whales. Numerous fossilized flipper bones (i.e., segments of the pectoral fins) and caudal vertebrae of large whales from the Pliocene have been found with megalodon bite marks. This suggests that megalodon would immobilize a large whale by ripping apart or biting off its locomotive structures before killing and feeding on it.[31]

Nursery areas

 
Collection of teeth of juvenile megalodon and C. chubutensis from a probable nursery area in the Gatun Formation of Panama

Fossil evidence suggests that the preferred nursery sites of megalodon were warm-water coastal environments, where threats were minor and food plentiful.[17] Nursery sites were identified in the Gatun Formation of Panama, the Calvert Formation of Maryland, Banco de Concepción in the Canary Islands,,[58] and the Bone Valley Formation of Florida. Given that all extant lamniform sharks give birth to live young, this is believed to have been true of megalodon also.[59] Neonate megalodons were around 3.5 meters (11 ft) at their smallest,[16]:61 and the pups were vulnerable to predation by other shark species, such as the great hammerhead shark (Sphyrna mokarran) and the snaggletooth shark (Hemipristis serra).[17] Their dietary preferences display an ontogenetic shift:[16]:65 Young megalodon commonly preyed on fish,[17] giant sea turtles,[44] dugongs,[11]:129 and small cetaceans; mature megalodon moved to off-shore areas and consumed large cetaceans.[16]:74–75

However, an exceptional case in the fossil record suggests that juvenile megalodon may have occasionally attacked much larger balaenopterid whales. Three tooth marks apparently from a 4-to-7-meter (13 to 23 ft) long Pliocene shark were found on a rib from an ancestral blue or humpback whale that showed evidence of subsequent healing, which is suspected to have been inflicted by a juvenile megalodon.[60][61]

Extinction

Climate change

The Earth experienced a number of changes during the time period megalodon existed which affected marine life. A cooling trend starting in the Oligocene 35 mya ultimately led to glaciation at the poles. Geological events changed currents and precipitation; among these were the closure of the Circumtropical Seaway between the Americas and through the Tethys Sea, contributing to the cooling of the oceans. The stalling of the Gulf Stream prevented nutrient-rich water from reaching major marine ecosystems, which may have negatively affected its food sources. As its range did not apparently extend into colder waters, megalodon may not have been able to retain a significant amount of metabolic heat, so its range was restricted to shrinking tropical waters.[62][47][63] Fossil evidence confirms the absence of megalodon in regions around the world where water temperatures had significantly declined during the Pliocene.[16]:77 The largest fluctuation of sea levels in the Cenozoic era occurred in the Plio-Pleistocene due to the expansion of glaciers at the pole, which negatively impacted coastal environments, and may have contributed to its extinction along with those of several other marine megafaunal species.[64] These oceanographic changes, in particular the sea level drops, may have restricted many of the suitable shallow warm-water nursery sites for megalodon, hindering reproduction.[62] Nursery areas are pivotal for the survival of many shark species, in part because they protect juveniles from predation.[65]

However, an analysis of the distribution of megalodon over time suggests that climate change did not play a major role in its extinction. Its distribution during the Miocene and Pliocene did not correlate with warming and cooling trends; while abundance and distribution declined during the Pliocene, megalodon did show a capacity to inhabit anti-tropical latitudes. It was found in locations with a mean temperature ranging from 12 to 27 °C (54 to 81 °F), with a total range of 1 to 33 °C (34 to 91 °F), indicating that the global extent of suitable habitat should not have been greatly affected by the temperature changes that occurred.[14]

Changing ecosystem

 
Competition from cetaceans such as the killer whale (Orcinus orca) may have contributed to the decline of megalodon.[53]

Marine mammals attained their greatest diversity during the Miocene,[16]:71 such as with baleen whales with over 20 recognized genera in comparison to only six extant genera.[66] Such diversity presented an ideal setting to support a super-predator such as megalodon.[16]:75 However, by the end of the Miocene, many species of mysticetes had gone extinct;[49] surviving species may have been faster swimmers and thus more elusive prey.[11]:46 Furthermore, after the closure of the Central American Seaway, tropical whales decreased in diversity and abundance.[63] The extinction of megalodon correlates with the decline of many small mysticete lineages, and it is possible that it was quite dependent on them as a food source.[46] Additionally, a marine megafauna extinction during the Pliocene was discovered to have eliminated 36% of all large marine species including 55% of marine mammals, 35% of seabirds, 9% of sharks, and 43% of sea turtles, likely aiding in its extinction;[64] megalodon may have been too large to sustain itself on the declining tropical food supply.[62] The cooling of the oceans during the Pliocene might have restricted the access of megalodon to the polar regions, depriving it of its food source of large whales which had migrated there.[42][63]

Competition from new superpredators, such as killer sperm whales which appeared in the Miocene, and killer whales and great white sharks in the Pliocene,[49][53][67] may have also contributed to the decline and extinction of megalodon.[14][11]:46–47[62] Fossil records indicate that the new whale-eating cetaceans commonly occurred at high latitudes during the Pliocene, indicating that they could cope with the increasingly prevalent cold water temperatures; but they also occurred in the tropics (e.g., Orcinus sp. in South Africa).[53]

The extinction of megalodon set the stage for further changes in marine communities. The average body size of baleen whales increased significantly after its disappearance, although possibly due to other, climate-related, causes.[68] Conversely however, the increase in baleen whale size may have contributed to the extinction of megalodon, as they may have preferred to go after smaller whales; bite marks on large whale species may have come from scavenging sharks. Megalodon may have simply become coextinct with smaller whale species, such as Piscobalaena nana.[69] The extinction of megalodon had a positive impact on other apex predators of the time, such as the great white shark, in some cases spreading to regions where megalodon became absent.[14][67][70]

In fiction

 
The HMS Challenger discovered megalodon teeth which were erroneously dated to be around 11,000 to 24,000 years old.[42]

Megalodon has been portrayed in several works of fiction, including films and novels, and continues to be a popular subject for fiction involving sea monsters.[71][72] Three individual megalodon, two adults and one juvenile, were portrayed in BBC's 2003 TV series Sea Monsters, where it is defined as a "hazard" to the era.[73] The History Channel's Jurassic Fight Club portrays a megalodon attacking a Brygmophyseter sperm whale in Japan.[74] Several films depict megalodon, such as Shark Attack 3: Megalodon and the Mega Shark series (for instance Mega Shark Versus Giant Octopus and Mega Shark Versus Crocosaurus).[71] In Justice League: Throne of Atlantis, Aquaman summons one to defeat Black Manta.[75] Some stories, such as Jim Shepard's Tedford and the Megalodon, portray a rediscovery of the shark.[76] Steve Alten's Meg: A Novel of Deep Terror has portrayed the inaccuracy that it lived with dinosaurs with its prologue and cover artwork depicting megalodon killing a Tyrannosaurus in the sea.[77] The sequels to the book also star megalodon: The Trench, Meg: Primal Waters, Meg: Hell's Aquarium, and Meg: Origins.[71]

Animal Planet's pseudo-documentary Mermaids: The Body Found included an encounter 1.6 mya between a pod of mermaids and a megalodon.[78] Later, in August 2013, the Discovery Channel opened its annual Shark Week series with another film for television, Megalodon: The Monster Shark Lives,[79] a controversial docufiction about the creature that presented alleged evidence in order to suggest that megalodon was still alive. This program received criticism for being completely fictional; for example, all of the supposed scientists depicted were paid actors. In 2014, Discovery re-aired The Monster Shark Lives, along with a new one-hour program, Megalodon: The New Evidence, and an additional fictionalized program entitled Shark of Darkness: Wrath of Submarine, resulting in further backlash from media sources and the scientific community.[30][80][81]

There have been a few alleged sightings of large sharks, purportedly megalodon, measuring anywhere from 10 to 90 meters (40 to 300 ft) throughout the 1900s, however they all lack supporting evidence. More likely they were misidentified whale sharks. One Polynesian myth regards a 30-meter (100 ft) shark called Lord of the Deep, but this is probably an exaggeration of a whale shark. Reports of supposed fresh megalodon teeth, such those made by HMS Challenger in 1873 which were erroneously dated to be around 11,000 to 24,000 years old, are probably teeth that were well-preserved by a thick mineral-crust precipitate of manganese dioxide, and so had a lower decomposition rate and retained a white color during fossilization. Fossil megalodon teeth can vary in color from off-white to dark browns and greys and may have been redeposited into a younger stratum. The claims that megalodon could remain elusive in the depths, similar to the megamouth shark which was discovered in 1976, are unlikely as the shark evolved around warm coastal waters and probably could not survive in the cold and nutrient-poor deep sea environment.[42][72][82]

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Further reading

External links

Paleontological videos

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