MEGALADON

   

 

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The megalodon ("big tooth" in Greek) is an extinct megatoothed shark that existed in prehistoric times, from the Oligocene to Pleistocene epochs, approximately 25 to 1.5 million years ago.

Paleontological research indicates that C. megalodon is among the largest and most powerful macro-predatory fishes in vertebrate history. C. megalodon is principally known from partially preserved skeletal remains, which indicate a shark of gigantic proportions  approaching a length of around 20.3 metres (67 ft). C. megalodon is widely regarded as the largest shark to have ever lived. After scrutiny of its remains, scientists have assigned C. megalodon to the order Lamniformes but its phylogeny is disputed. Scientists suggest that C. megalodon looked like a stockier version of the great white shark, Carcharodon carcharias, in life. Fossil evidence confirms that C. megalodon had a cosmopolitan distribution. C. megalodon was a super-predator, and bite marks on fossil bones of its victims indicate that it preyed upon large marine animals.

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

The earliest remains of C. megalodon have been reported from late Oligocene strata. Although fossils of C. megalodon are predominantely absent in strata extending beyond the Tertiary boundary, they have been reported from Pleistocene strata. It is believed that C. megalodon became extinct in the Pleistocene probably about 1.5 million years ago

The great white shark is considered to be the closest extant analogue to C. megalodon. 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

Size estimation

Estimating the maximum size of C. megalodon is a highly controversial and difficult subject. However, scientific community acknowledges that C. megalodon was larger than the whale shark, Rhincodon typus. 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 theorized to be around 30 metres (98 ft), but in the light of new fossil discoveries and advances in vertebrate sciences, this jaw reconstruction is now considered to be inaccurate. The major reason cited for this inaccuracy was that in Dean's time, the knowledge of C. megalodon's dentition was relatively poor. Experts suggest that a rectified version of C. megalodon's jaw model by Bashford Dean would be about 70 percent of its original size and would depict a shark size consistent with modern findings. Hence, to resolve 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.

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. The proposed method is: "Megatooth's" Total Length in meters = [(0.096) (enamel height of tooth in mm)]. 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. The largest C. megalodon tooth in his possession at that time had an enamel height of 115 mm, which yielded 13 metres (43 ft) length. However, two shark experts, Richard Ellis, and John E. McCroker, pointed out a flaw in Randall's method in 1991. According to them, shark's tooth enamel height does not necessarily increase in proportion to the animal's total length. This observation led to proposals for new, more accurate methods to determine the size of the great white shark and similar sharks.

Method proposed by Gottfried et al

Three scientists, 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)]. 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). However, rumors of larger C. megalodon teeth persisted at that time. 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. In short words, the maximum height of the tooth is its slant height.

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]. 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).

Method proposed by Clifford Jeremiah

In 2002, shark researcher Dr. Clifford Jeremiah also proposed a method to determine the size of great white shark and similar sharks (i.e., C. megalodon). which is believed to be based on a sound principle that works well with most large sharks. The proposed method is: "Shark'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. Dr. 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. The largest tooth in the possession of Dr. C. Jeremiah had a root width of nearly 12 cm, which yielded 15.5 metres (51 ft) length.

Maximum size and verdict

At present, scientists commonly suggest that C. megalodon likely approached a maxima of 18.220.3 metres (6067 ft) in length.[10][22][23] In 1994, a marine biologist Patrick J. Schembri claimed that C. megalodon may have approached a maximum length of 25 metres (82 ft). The early size estimation of C. megalodon was perhaps not far fetched. However, Gottfried et al., in 1996, proposed that C. megalodon could likely approach a maximum length of 20.3 metres (67 ft).The shark weight measuring technique suggested by the same team indicates that C. megalodon at this length would have a body mass of 103 metric tons (114 short tons).

Hence, scientific research makes it clear that C. megalodon is the largest shark that has ever lived and is among the largest fish known to have existed.

Dentition and Jaw Mechanics

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. 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. 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 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. Most accurate modern C. megalodon jaw reconstructions are based on this dental formula.

Paleontologists suggest that a very large C. megalodon had jaws over 2 metres (7 ft) across.

Bite force

In 2008, a team of scientists led by Stephen Wroe have conducted an experiment to determine the bite force of the C. megalodon and results indicate that it was capable of exerting a bite force of around 182,000 newtons (N) or 41,000 pound-force; over 28 times greater than that of Dunkleosteus at 6.3 kN (1,400 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).

Role of teeth

The exceptionally robust teeth of C. megalodon are serrated, 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.

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.

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.

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. The strongly developed jaws would have somewhat of a pig-eyed appearance.

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.

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.

 

Prey relationships

Sharks are generally opportunistic predators. However, scientists propose that C. megalodon was "arguably the most formidable carnivore ever to have existed." The factors  great size, efficient metabolism, high-speed swimming capability, and powerful jaws combined with formidable killing apparatus, ensured a super-predator with the capability to take on a broad spectrum of fauna. Fossil evidence indicates that C. megalodon preyed upon cetaceans (i.e., whales, including sperm whales, bowhead whales, cetotherrids, squalodontids, rorquals, and Odobenocetops, dolphins, and porpoises), sirenians, pinnipeds, and giant sea turtles. 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 (deep gashes) made by the teeth that match those of C. megalodon, and various excavations have revealed C. megalodon teeth lying close to the chewed remains of whales, and sometimes even embedded in them. Like other sharks, C. megalodon also would have been piscivorous.

Hunting behavior

Sharks often employ complex hunting strategies to engage large prey animals. Some paleontologists suggest that the hunting strategies of the great white shark may offer clues as to how C. megalodon might have hunted its unusually large prey (i.e., whales). However, fossil evidence suggests that C. megalodon employed more effective hunting strategies against large prey compared to the strategies employed by the great white shark.

Paleontologists have conducted a survey of fossils to determine attacking patterns of C. megalodon on prey. The findings suggest that the attack patterns could differ against prey with respect to its size. Fossil remains of some small cetaceans suggest that they were likely rammed with great force from below before being killed and eaten. 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 predator primarily focused its attack on the tough bony portions (i.e. bony shoulders, flippers, rib cage, and upper spine) of the prey, which great white sharks generally avoid 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. An attack on these essential body parts would have immobilized the prey, which would have died quickly due to massive internal injuries as a result. These findings also clarify why the ancient shark needed more robust dentition than the great white shark's.

During the Pliocene, larger and more advanced cetaceans appeared. C. megalodon apparently further refined its attack strategies to cope with these larger animals. Numerous fossilized flipper bones (i.e., segments of the pectoral fins), and caudal vertebrae of large whales from the Pliocene have been found with bite marks that were caused by attacks of C. megalodon. 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.

Interspecific competition

C. megalodon faced a highly competitive environment during its time of existence. Paleontologist Robert Purdy found 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. However, the predatory toothed whales (odontocetes) had some potential competitive advantages, in particular, coordinated hunting behavior, echolocation, and higher intelligence. The ancient physeterids (e.g. Brygmophyseter) and squalodontids are among the earliest notable examples. Odontocetes usually exhibit a social lifestyle, and pod members may have defended each other against potential threats. However, paleontological research suggests that C. megalodon was likely one of the most powerful and dominant predators in vertebrate history, and it would have been an energetic costly and risky act to tackle it, and such an encounter could result in loss of pod members for odontocetes. In addition, paleontological evidence suggests that C. megalodon possessed the capability to compete with odontocetes  bite marks on the fossil remains of odontocetes (e.g. squalodontids) indicate a predator-prey relationship between very large sharks and these cetaceans.

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. Prior to the formation of the Isthmus of Panama, the oceans were relatively warmer. 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, coastal upwelling, swampy coastal lagoons, sandy littorals, and offshore deep water environments), and exhibited a transient life-style. The adult C. megalodon were not abundant in shallow water environments, and mostly lurked offshore.

Fossil evidence suggests that the preferred nursery sites of C. megalodon were likely to have been warm water coastal environments, where potential threats were minor and food sources were plentiful.As is the case with most sharks, C. megalodon also likely gave birth to live young. The size of the neonate C. megalodon teeth indicate that C. megalodon pups were around 23 metres (710 ft) in length at birth.The young 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

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

Climatic cooling and ice ages

A major reason cited behind the extinction of C. megalodon is the decline in ocean temperatures at global scale. The Isthmus of Panama closed around 5 million years ago and fundamentally changed global ocean circulation. This geological event initially set the stage for glaciation in the northern hemisphere, and later on, also facilitated cooling of the entire planet. Consequently, during the late Pliocene and Pleistocene, there were ice ages, which cooled the oceans significantly. The cooling trend adversely impacted C. megalodon, as it preferred warmer waters. Fossil evidence confirms the absence of C. megalodon in regions where water temperatures had significantly declined during the Pliocene.

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. Lower sea levels may have restricted many of the suitable warm water nursery sites for C. megalodon, hindering population maintenance. Nursery areas are pivotal for the survival of a species.

Decline in food supply

Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera in comparison to only six living genera. Such diversity presented an ideal setting to support a giant predator like C. megalodon. However, the dependency of C. megalodon on large prey made it over-specialized. In addition, during the Pliocene, many species of cetaceans became extinct, and most surviving species disappeared from the tropics. Whale migratory patterns during the Pliocene have been reconstructed from the fossil record, suggesting that most surviving species showed a trend towards polar regions. The cooler water temperatures during the Pliocene cut C. megalodon off from polar regions, and large prey was effectively "no longer within the range" of C. megalodon after the migrations.These developments diminished the food supply for C. megalodon in warm waters. Paleontologist Albert Sanders suggests that C. megalodon had become too large to sustain itself on the available food supply in the tropics.

Cannibalism

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

Evolution of the orca

The ancient relatives of the orca evolved during the Pliocene, and some paleontologists have speculated that these odontocetes may also have contributed to the extinction of C. megalodon. However, paleontologist Robert Purdy pointed out that there is not much fossil evidence for the history of marine vertebrates for the last three million years. In addition, by the early Pliocene, C. megalodon was already absent in high latitudes due to cooling trend in oceans, where ancient relatives of the orca commonly occurred. Although competition may have occurred in other regions  bite marks on the fossil remains of dolphins have been observed, which indicate that these odontocetes were prey for C. megalodon. Consequently, this observation suggests that C. megalodon effectively competed with dolphins of its time. However, the relatively common occurrence of the ancient relatives of the orca in high latitudes during the Pliocene indicates the potential of these animals to cope with cold water temperatures. This capability likely favored their survival while C. megalodon was ill-fated.

 

 

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