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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
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.
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.
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).
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.
At present, scientists commonly suggest that C. megalodon likely
approached a maxima of 18.2–20.3 metres (60–67 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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 2–3 metres (7–10 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.
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.
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.
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.
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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