Megalodon Fossil range: Late Oligocene-Early Pleistocene 25–1.5 Ma PreЄ Є O S D C P T J K Pg N
Reconstructed jaws on display at the American Museum of Natural History
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Lamniformes
Family:	Disputed; Lamnidae or Otodontidae
Genus:	Disputed; Carcharodon or Carcharocles
Species:	†C. megalodon
Binomial name
Disputed; Carcharodon megalodon or Carcharocles megalodon For Carcharodon megalodon, Agassiz, 1843
Synonyms
Procarcharodon megalodon Casier, 1960 Megaselachus megalodon Glikman, 1964

The megalodon (pronounced /ˈmɛɡələdɒn/ MEG-ə-lə-don, "big tooth" in Greek, from μέγας and ὀδούς) was a giant shark that lived in prehistoric times during the late Oligocene epoch and Neogene period,^[1] and was a super-predator.

It was by far the largest and most powerful fish of its time, and its maximum size is theorized to be around 20 metres (66 ft). From scrutiny of its remains, scientists conclude that C. megalodon belongs to the order Lamniformes but its genus is disputed. Fossil evidence has revealed that C. megalodon fed upon large marine animals.

Contents 1 Discovery 1.1 Glossopetrae 1.2 Identification 2 Fossils 2.1 Fossil teeth 2.2 Fossil vertebrae 2.3 Fossil distribution and range 3 Physical anatomy 3.1 Size estimation 3.1.1 Method proposed by John E. Randall 3.1.2 Method proposed by Gottfried et al 3.1.2.1 Body mass estimation 3.1.3 Method proposed by Clifford Jeremiah 3.1.4 Maximum size 3.2 Dentition 3.3 Skeletal anatomy 3.3.1 Chrondocranium 3.3.2 Jaw structure 3.3.3 Fins 3.3.4 Axial skeleton 3.3.5 The complete skeleton 4 Paleoecological and Paleobiological considerations 4.1 Prey relationships 4.2 Role of teeth 4.3 Hunting behavior 4.4 Bite force 4.5 Interspecific competition 4.6 Range and habitat 4.6.1 Nursery areas 5 Extinction 5.1 Climatic upheavals 5.2 Changes in the food chain 5.3 Cannibalism 5.4 Competition 6 Taxonomy 6.1 Megalodon within Carcharodon 6.2 Megalodon within Carcharocles 6.2.1 Evolutionary origins of the great white shark 6.3 Additional controversy 7 In fiction 8 See also 9 References 10 External links 10.1 Paleontological 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 the 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).^[2] 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.^[3]

[edit] Identification

A Swiss naturalist, Louis Agassiz, gave this shark its scientific name, Carcharodon megalodon, in 1835,^[4] in his research work Recherches sur les poissons fossiles^[5] (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.^[4] While the scientific name is C. megalodon, it is often informally dubbed the megatooth shark^[6] or giant white shark^[7] or even monster shark.^[8]

[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.^[9]

[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,^[6] more regularly serrated,^[6] and much larger, exceeding 18 cm (7.1 in) in slant height (diagonal length).^[1]

[edit] Fossil vertebrae

Some partially preserved fossil vertebrae of C. megalodon have also been found.^[3] The most notable example is a partially preserved but associated vertebral column of a single C. megalodon specimen excavated from Belgium in 1926. This specimen comprises 150 vertebral centra.^[6]

[edit] Fossil distribution and range

The fossils of C. megalodon have been excavated from many parts of the world, including Europe,^[3] North America,^[6] South America,^[3][6] Puerto Rico,^[10] Jamaica,^[11] Australia,^[3][6] New Zealand,^[1] Japan,^[3][6] Africa,^[3][6] Malta,^[1] Grenadines,^[12] and India.^[3] C. megalodon teeth have also been excavated from regions far away from continental lands (i.e. Mariana Trench in the Pacific).^[1]

The earliest remains of C. megalodon have been reported from late Oligocene strata.^[1][13] It is believed that C. megalodon became extinct in the Pleistocene epoch probably about 1.5 million years ago.^[9] Some scientists argue that reports of Pleistocene records of C. megalodon are unsubstantiated and suggest that youngest C. megalodon remains are from late Pliocene strata at most.^[6] However, the possibility of occurrence of C. megalodon fossils from strata extending beyond the Tertiary boundary has not been completely ruled out.^[14]

[edit] Physical anatomy

The great white shark is considered to be the closest extant analogue to C. megalodon.^[3][6] The lack of exceptionally preserved fossil skeletons of C. megalodon have forced the scientists to rely on the morphology of the great white shark for the basis of its reconstruction and size estimation.^[6]

[edit] Size estimation

Estimating the maximum size of C. megalodon is a highly controversial subject. The first attempt on reconstructing the jaw of this shark was made by Professor Bashford Dean in 1909. From the dimensions of this jaw reconstruction, the size of C. megalodon was hypothesized to be more than 25 metres (82 ft), but in the light of new fossil discoveries and advances in vertebrate sciences, this jaw reconstruction is now considered to be inaccurate.^[15] The major reason cited for this inaccuracy was that in Dean's time, the knowledge of C. megalodon's dentition was relatively poor.^[15] To rectify such errors, scientists, aided by new fossil discoveries of C. megalodon and improved knowledge of its closest living analogue's anatomy, introduced more quantitative methods for estimating its size based on the statistical relationships between the tooth sizes and body lengths in the great white shark.^[6][15]

[edit] Method proposed by John E. Randall

In 1973, the ichthyologist John E. Randall introduced a method to determine the size of the great white shark and extrapolated it to estimate the size of C. megalodon.^[16] The proposed method is: "Megatooth's" Total Length in meters = [(0.096) × (enamel height of tooth in [mm])].^[15][16] The logic behind this method is that the enamel height (the vertical distance of the blade from the base of the enamel portion of the tooth to its tip) of the largest upper anterior tooth in the jaw of the shark can be used to determine its total length.^[15] The largest C. megalodon tooth in his possession at that time had an enamel height of 115 mm,^[15] which yielded 13 metres (43 ft) length.^[15][16] However, two shark experts, Richard Ellis, and John E. McCroker, pointed out a flaw in Randall's method in 1991.^[6] According to them, shark's tooth enamel height does not necessarily increase in proportion to the animal's total length. This observation led to proposal for new, more accurate methods to determine the size of the great white shark and similar sharks.^[6]

[edit] Method proposed by Gottfried et al

Three shark experts, Michael D. Gottfried, Leonard J. V. Compagno and S. Curtis Bowman, after thorough research and scrutiny of many great white shark specimens, proposed a conservative but more accurate method for measuring the size of C. carcharias and C. megalodon that was published in 1996. The proposed method is: "Megatooth's" Total Length in meters = − (0.22) + (0.096) × [(Tooth maximum height in [mm])].^[6] The biggest C. megalodon tooth in the possession of this team was an upper anterior specimen, which had a maximum height of 168 mm (6.61 inch). This tooth was discovered by L. J. V. Compagno in 1993, and it yielded a length of 15.9 metres (52 ft).^[6] However, rumors of larger C. megalodon teeth persisted at that time.^[6] The maximum tooth height for this method is measured as a vertical line from the tip of the crown to the bottom of the lobes of the root, parallel to the long axis of the tooth.^[6] In short words, the maximum height of the tooth is its slant height.^[17]

[edit] Body mass estimation

Gottfried et al, also introduced a method to determine the body mass of the great white shark after studying the length – mass relationship data of 175 specimens at various growth stages and extrapolated it to estimate the body mass of C. megalodon. The proposed method is: Weight in kilogram = 3.29E⁻⁰⁶[TL in (meters)^3.174].^[6] And according to this method, a 15.9 metres (52 ft) long specimen would have a body mass of about 47 metric tons (52 short tons).^[6]

[edit] Method proposed by Clifford Jeremiah

Shark researcher Gordon Hubbell asserts that no formula based on statistical relationships between tooth height and body length in sharks is accurate. He pointed out that the shark teeth can vary in height within the jaws of sharks of similar sizes even within a single genus.^[1] However in 2002, shark researcher Clifford Jeremiah also proposed a method to determine the size of great white shark and similar sharks (i.e., 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 Dr. C. Jeremiah had a root width of nearly 12 cm, which yielded a 15.5 metres (51 ft) size.^[1]

[edit] Maximum size

In light of new fossil discoveries, experts now believe that C. megalodon exceeded 17 metres (56 ft) in length.^[1][7] According to a hypothesis presented by Gottfried et. al, in 1996, C. megalodon could likely approach a maximum length of 20.3 metres (67 ft),^[6] and would have a body mass of 103 metric tons (114 short tons) on the basis of shark weight measuring technique suggested by the same team.^[6] In later years, some C. megalodon teeth have been discovered that yield comparable estimates on the basis of the shark tooth size to body length statistical relationships proposed by experts. An example often cited is a massive upper anterior C. megalodon tooth, which is now under possession of Gordon Hubell but was discovered and excavated by a deceased fossil hunter, Vito Bertucci. This tooth has a slant height of 7.37 inch (187 mm) and a root width of 5.5 inch (140 mm). To date, reports of even larger C. megalodon teeth persist. (See "external links" below)

These new findings suggest that older estimations of the size of C. megalodon were perhaps not far fetched despite errors in the works of Bashford Dean. 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.^[6] C. megalodon is also one of the largest predators to have ever roamed the oceans.^[8]

[edit] 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.^[3] Another nearly complete associated C. megalodon dentition was excavated from Yorktown formations of Lee Creek, North Carolina in USA and served as the basis of a jaw reconstruction of C. megalodon in American Museum of Natural history in NYC.^[6] These associated tooth sets solved the mystery of determining the exact number of teeth, which would be present in the jaws of the C. megalodon in each row in real life. Hence, highly accurate jaw reconstructions were now possible. More associated dentitions of C. megalodon have also been found in later years. Based upon these discoveries, two scientists, S. Applegate and L. Espinosa, published an artificial dental formula (representation of dentition of an animal with respect to types of teeth and their arrangement within the animal's jaw) for C. megalodon in 1996.^[3][6] 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.^[3]

• 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.^[4] However, in the case of the great white shark, the intermediate tooth does point 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

Scientists suggest that C. megalodon had a very robust dentition,^[6] and it had a total of about 276 teeth in its jaws. (See "external links" below)

[edit] Skeletal anatomy

Aside from estimating the size of C. megalodon, Gottfried et al, also have tried to determine the schematics of the entire skeleton of C. megalodon^[6].

[edit] Chrondocranium

The chrondocranium of C. megalodon would have a blockier and more robust appearance than that of the great white shark, in order to functionally reflect its more massive jaws and dentition in comparison.^[6]

[edit] Jaw structure

To functionally support the very large and robust dentition, the jaws of the C. megalodon would have been massive, stouter, and more strongly developed than that of the great white shark, which possesses a somewhat gracile dentition in comparison.^[6] The strongly developed jaws would have somewhat of a pig-eyed appearance.^[6]

[edit] Fins

The fins of C. megalodon would have been most likely proportionally larger and thicker in comparison to fins of great white shark because relatively larger fins were a necessity for propulsion and control of movements of such a massive shark.^[6]

[edit] Axial skeleton

Through thorough scrutiny of the partially preserved vertebral C. megalodon specimen from Belgium, it became apparent that C. megalodon had a higher vertebral count than found in large specimens of any known shark.^[6] Only the vertebral count in great white shark came close in quantity, symbolizing close anatomical ties between the two species.^[6]

[edit] The complete skeleton

On the basis of the characteristics mentioned above, Gottfried and his colleagues eventually developed a model of the entire skeleton of C. megalodon, which has been put on display in Calvert Marine Museum at Solomons island, Maryland in USA.^[6][18][19] This C. megalodon skeletal model is 11.5 metres (38 ft) long and represents a young individual.^[6] The team stresses that relative and proportional changes in the skeletal features of C. megalodon are ontogenetic in nature in comparison to that of great white shark, as they occur in great white sharks while growing larger.^[6]

[edit] Paleoecological and Paleobiological considerations

[edit] Prey relationships

Sharks are generally opportunistic in nature. However, a combination of factors such as large size, efficient metabolism, high-speed swimming capability, and powerful jaws can make a shark versatile enough to become an apex predator and hunt a broad spectrum of fauna. C. megalodon was one of the most formidable carnivores ever to have existed.^[8][20] There is evidence that C. megalodon was an aggressive hunter and could predate upon a variety of marine animals including cetaceans (i.e., whales,^[3] {some examples are: sperm whales,^[1] bowhead whales,^[7] cetotherrids,^[9] squalodonts,^[8] rorquals,^[8] and Odobenocetops.^[21]} dolphins,^[1] and porpoises^[1]), sirenians,^[1] pinnipeds,^[9] and giant sea turtles.^[22] Due to its size, C. megalodon would have fed primarily on large animals, and whales were likely important prey — many whale bones have been found with clear signs of large bite marks made by the teeth that match those of C. megalodon,^[1][3][6] and various excavations have revealed C. megalodon teeth lying close to the chewed remains of whales,^[6][18] and sometimes even embedded in them.^[23] Like other sharks, C. megalodon also would have been piscivorous.^[9][19]

[edit] Role of teeth

The exceptionally robust teeth of C. megalodon are serrated,^[1][4] which would have improved efficiency in slicing the flesh of prey items. Paleontologist Dr. Bretton Kent suggests that these teeth are comparatively thicker for their size with much lower slenderness and bending strength ratios. They also have roots that are substantially larger relative to total tooth heights, and so have a greater mechanical advantage. Teeth with these traits are not just good cutting tools but also are well suited for grasping powerful prey and would seldom crack even when slicing through the bones.^[24]

[edit] Hunting behavior

Sharks often employ complex hunting strategies to tackle challenging prey. Some paleontologists suggest that the hunting strategies of the great white shark may offer clues as to how C. megalodon might have hunted its leviathan prey (i.e., whales).^[8] However, fossil evidence suggests that attacking strategies of these two sharks could differ with respect to the prey items involved.

Paleontologists have conducted a survey of fossils to determine attacking patterns of C. megalodon on prey.^[24] One particular specimen — remains of a 9 metres (30 ft) long prehistoric baleen whale (unknown taxon from Miocene) provided the first opportunity to quantitatively analyze the attacking behavior of C. megalodon. The findings indicate that the attacking behavior of C. megalodon on cetaceans was different but more effective from that of the great white shark.^[24] C. megalodon primarily focused its attack on the tough bony portions (i.e. bony shoulders, flippers, rib cage, and upper spine) of the prey,^[24] which great white sharks generally avoid.^[24] Dr. Bretton Kent elaborated that C. megalodon attempted to crush the bones and damage delicate organs (i.e. heart, and lungs) harbored within the rib cage of the prey.^[24] An attack on these essential body parts would have ensured swift immobilization of the prey and the victim would also have died quickly due to massive internal injuries as a result.^[24] These findings also clarify why the ancient shark needed more robust dentition than the great white shark's.^[24]

During the Pliocene epoch, larger and more advanced cetaceans appeared.^[8] C. megalodon apparently further refined its attacking strategies to tackle these behemoths. Numerous fossilized flipper bones (i.e., segments of the pectoral fins), and caudal vertebrae of large whales from Pliocene have been found with bite marks that were caused by attacks of C. megalodon.^[6][8][20] This paleontological evidence suggests that C. megalodon would attempt first to immobilize a large prey item by ripping apart or biting off its propulsive structures before killing and feeding on it.^[6][8][20]

[edit] Bite force

A team of scientists led by Stephen Wroe have conducted an experiment in 2008 to determine the bite force of the C. megalodon and results indicate that very large specimens were capable of exerting a bite force of around 182,000 newtons (N)^[20] or 41,000 pound-force; over 28 times greater than that of Dunkleosteus at 6.3 kN (6,300 lbf), over 10 times greater than that of great white shark at 18 kN (4,100 lbf), over 5 times greater than that of T. rex at 31 kN (7,000 lbf), and also greater than that of Predator X at 150 kN (33,000 lbf).

[edit] Interspecific competition

The enormous jaw power, great size, and paleontological evidence suggesting C. megalodon was the active predator of large cetaceans, indicate that C. megalodon was one of the most formidable predators ever to have inhabited the oceans,^[8][20] and secured a firm position at the top of the food chain. However, other apex predators of the time could have offered competition. Paleontologist Robert Purdy revealed through a survey of fossils that other notable species of predatory sharks (e.g. great white sharks) responded to competitive pressure from C. megalodon by avoiding regions it inhabited.^[6] The evolution of pack predator cetaceans, culminating with the appearance of the orca, would have presented a greater challenge. These predators had several potential competitive advantages, in particular coordinated hunting behavior and greater intelligence.

[edit] Range and habitat

C. megalodon was a pelagic fish that predominantly inhabited temperate and warm water environments. The fossil records of C. megalodon confirm that it was a cosmopolitan species.^[1] Prior to the formation of Isthmus of Panama, the oceans were relatively warmer.^[25] This would have made it possible for the species to thrive in all the oceans of the world.

C. megalodon had enough behavioral flexibility to inhabit wide range of marine environments (i.e. coastal shallow waters,^[22] coastal upwelling,^[22] swampy coastal lagoons,^[22] sandy littorals,^[22] and offshore deep water environments^[1]), and exhibited a transient life-style.^[22] However, adult C. megalodon were not abundant in shallow water environments^[22] and mostly lurked offshore.

[edit] Nursery areas

Fossil evidence suggests that the preferred nursery sites of C. megalodon were likely warm water coastal environments, where potential threats were minor and food sources were plentiful.^[1] Juvenile C. megalodon most likely preyed upon pinnipeds, fish, giant sea turtles, dugongs, and small cetaceans. Upon approaching maturity, C. megalodon predominantly preferred off-shore cetacean high-use areas and preyed upon large cetaceans.^[6]

[edit] Extinction

It is not yet clear why C. megalodon became extinct after millions of years of dominance; however, several factors may have been involved.

[edit] Climatic upheavals

The Isthmus of Panama closed around 5 million years ago and fundamentally changed global ocean circulation.^[3][26] It initially set the stage for glaciation in the northern hemisphere,^[26] and later also facilitated cooling of the entire planet.^[26] Consequently, during the late Pliocene and Pleistocene epochs there were ice ages,^[27][28] which cooled the oceans significantly.^[3] The cooling trend adversely impacted C. megalodon, as it preferred warmer waters.^[3][6][8]

In addition, wide-scale glaciation during the Pliocene and Pleistocene tied up huge volumes of water in continental ice sheets, resulting in significant sea level drops.^[25] Lower sea levels may have restricted many of the suitable warm water nursery sites for C. megalodon, hindering population maintenance.

[edit] Changes in the food chain

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.^[1] Additionally, whale migratory patterns from the Mid Pliocene have been reconstructed from the fossil record, suggesting that most surviving species migrated towards polar regions, effectively "getting out of the range" of C. megalodon.^{[3][6][9][25]} This may have diminished the food supply for C. megalodon in warm waters and the adult individuals were too large to thrive on other smaller animals.^[1]

[edit] Cannibalism

C. megalodon likely had a tendency for cannibalism.^[29] The shortage of food sources in warm waters during Pliocene and Pliestocene epochs might have fueled cannibalism within C. megalodon.^[8] The juvenile individuals were at increased risk from attacks by adult individuals during times of starvation.^[8]

[edit] Competition

The orca evolved around the time of C. megalodon's disappearance, and there is speculation that it may have contributed to the extinction, since it would have been a direct competitor.^[30] Although the orca is smaller, it would have had the advantages of numbers (being a pack predator), a higher metabolic rate, echolocation, and higher intelligence. The ability of orca to live in cooler waters may have given them a significant edge during glacial periods.

[edit] Taxonomy

Even after decades of research and scrutiny, the controversy on phylogeny of C. megalodon still persists.^[1][9] 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. Many paleontologists, convinced by the arguments, favor Carcharocles genus more over Carcharodon genus for C. megalodon.^[18]

Lamniformes  I. hastalis Sacaco sp. C. carcharias C. megalodon The megalodon hypothesis claims that C. carcharias is more closely related to C. megalodon than I. hastalis.[4]

Lamniformes  I. hastalis Sacaco sp. C. carcharias void C. megalodon The hastalis hypothesis claims that C. carcharias is more closely related to I. hastalis than to C. megalodon.[4]

[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][4][6]

[edit] Megalodon within Carcharocles

Lamniformes  O. obliquus C. megalodon I. hastalis C. carcharias The Isurus-Origin hypothesis claims that C. carcharias descends from I. hastalis.[31]

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][4][9][18][32]} 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][18] 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][18] According to supporters of classification as Carcharocles for C. megalodon; Otodus obliquus evolved in to Carcharocles aksuaticus,^[1][18] which evolved in to Carcharocles auriculatus,^[1][18] which evolved into Carcharocles angustidens,^[1][18] which evolved into Carcharocles chubutensis,^[1][18] which eventually evolved into megalodon.^[1][18] Hence, the immediate ancestor of C. megalodon is Carcharocles chubutensis,^[1][18] 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][18] Scientist, D. J. Ward have further elaborated on this evolutionary process by implying that this lineage, stretching from Paleocene to Pliocene, is of a single giant shark which gradually changed through time, suggesting a case of chronospecies.^[1] This hypothesis has received recognition from several shark researchers (e.g. J. Bourdon, L. Andrez, H. Capetta, V. I. Zhelezko, and V. A. Kozlov). However the latter two argue that the Otodus genus should be used for sharks within the Carcharocles lineage and the Carcharocles genus should be discarded. (See "external links" below)

[edit] Evolutionary origins of the great white shark

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 several scientists.^[4][32][33] One reason cited is that the dental morphometrics (variations and changes in the physical form of objects) of I. hastalis and C. carcharias are remarkably similar.^[4][8]

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.^[31][34]

[edit] Additional controversy

Paleontologist Dr. Chuck Ciampaglio asserts that similarities between the teeth of C. megalodon and the great white shark are superficial and there are noticeable morphometric differences between them. These findings are sufficient to warrant a separate genus for C. megalodon.^[8] However, some proponents of the Carcharodon genus for C. megalodon (i.e. M. D. Gottfried, and R. E. Fordyce) have provided more reasons to ascertain close relationship between the extinct megatooth sharks and the great white shark.^[13] With respect to the recent controversy regarding fossil lamnid shark relationships, the overall morphology – particularly the internal calcification patterns – of the great white shark vertebral centra have been compared to well-preserved fossil centra from the megatooth sharks, including C. megalodon and C. angustidens. The close morphological similarity apparent from these comparisons provides supporting evidence for the idea that the giant fossil megatooth species are closely related to living white sharks.^[13][35]

With respect to the case of the origins of the great white shark, M. D. Gottfried, and R. E. Fordyce have pointed out that some great white shark fossils are about 16 million years old and predate the transitional fossils of Pliocene.^[13]

The Oligocene records of C. megalodon,^[1][13] contradict with the suggestion that Carcharocles chubutensis is the immediate ancestor of the C. megalodon. These records also indicate that C. megalodon actually co-existed with Carcharocles angustidens.^[13]

Hence, proponents for the Carcharodon genus for C. megalodon argue that extinct megatoothed sharks should be placed within the genus Carcharodon.^[13]

[edit] In fiction

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. Jim Shepard's story "Tedford and the Megalodon" is a good example of this.

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. The writers of the movie Shark Attack 3: Megalodon depicted this assumption by referring to and using an altered copy of a book by shark researcher, Richard Ellis, called "Great White Shark". The altered copy had several pages that don't exist in the real book. The author of the original book sued the film's distributor Lions Gate Entertainment, asking for a halt to the film's distribution along with $150,000 in damages.^[36] Steve Alten's Meg: A Novel of Deep Terror is probably best known for portraying this inaccuracy with its prologue and cover artworks depicting a Megalodon killing a Tyrannosaurus rex in the sea.

[edit] See also

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

• List of sharks
• Prehistoric fish
• List of apex predators
• Largest prehistoric organisms

[edit] References

[edit] External links

Wikimedia Commons has media related to: Megalodon

Wikispecies has information related to: 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
• Quick Facts about Megalodon: Largest Shark That Ever Lived!
• The largest modern Megalodon jaw reconstruction in the world
• Shark Tales featuring Megalodon with demonstration of the chewing action of the giant shark by Dr. Chuck Ciampaglio
• Prehistoric megalodon shark makes legendary great white look tiny
• Prehistoric Shark Nursery Spawned Giants from Discovery Channel News

[edit] Paleontological videos

• A video clip of the Perfect Shark (2006) program from BBC (NOTE: Flash Player required)
• Video Gallery containing video clips featuring Megalodon from Discovery Channel (NOTE: Flash Player required)
• A paleontologist, Mark Renz, shows a huge Megalodon tooth (one of the largest ever discovered) (NOTE: Flash Player required)
• A video clip depicting the struggle of Megalodon against pack predator (Brygmophyseter) for dominance from History Channel. (NOTE: Flash Player required)