______________________________________________
A Critical Evaluation of the Supposed
Contemporary
Existence of Carcharodon megalodon
by Ben S. Roesch
______________________________________________
Roesch, Ben S. 1998. A Critical Evaluation of the Supposed Contemporary
Existence
of Carcharodon megalodon. The Cryptozoology Review 3 (2):
14-24.
Copyright 1999 Ben S. Roesch (bspeersr@uoguelph.ca)
Many consider the white shark (Carcharodon carcharias) to be
among the most incredible creatures to roam the oceans today. Growing to
lengths upwards of 6 m (20 ft) and weights of more than 2 000 kg (4 400 lb),
this large lamnid shark is responsible for occasional attacks on humans. It
has become the quintessential shark to many, especially after the success of
the movie Jaws, which made the white shark’s name and toothy
visage infamous.
About 16 million years ago during the Miocene (1), however, an even larger shark, possibly
similar to the C. carcharias, appeared in the world’s oceans.
Carcharodon (or Carcharocles) megalodon may have
attained an astonishing maximum length of 15 m (50 ft), and weighed as much
as 50 tonnes (49 tons) (Gottfried et al. 1996). Such estimates are gleaned
from teeth and very rare skeletal components of the animal (sharks have a
cartilaginous skeleton that does not readily fossilize; most species of
fossil sharks are known from their teeth only, which are very durable
structures). Traditional research holds that C. megalodon was
ancestral to the white shark, but recent research suggests that it was
actually a close relative (2). Authors
such as Gottfried et al. (1996) envision C. megalodon as a much
larger and bulkier version of this white shark. With a mouth large enough to
swallow a cow whole and broad, triangular teeth much like those of the white
shark (but up to 17 cm [7 inches] high, as opposed to a maximum of 6 cm [2
inches] in white sharks [Fig. 1]), C. megalodon apparently fed on
primitive whales and other large marine mammals (Fig. 2) (3). It is possible that C. megalodon
hunted in the same stealthy manner that white sharks often employ to prey on
pinnipeds---stalking prey from below and then rising up at a high speed to
deliver a massive, often fatal first bite (4). About 1.5 million years ago at the end of
the Pliocene, C. megalodon disappeared, due to a variety of possible
reasons (Applegate and Espinosa-Arrubarrena 1996), some of which will be
discussed below.
Fig. 1. Tooth of Carcharodon megalodon, actual size.
Illustration by Richard Ellis (1975).
Despite the general consensus among zoologists and paleontologists that
C. megalodon is extinct, it has been suggested by several
cryptozoologists and other researchers (e.g. Stead 1963; Clark 1968;
Clostermann 1969; Perry 1972; Cartmell 1978; Goss 1987; Bright 1989; Corliss
1991; Shuker 1991, 1995, 1997) that this enormous shark may continue to
exist in the deep-sea or another remote part of the ocean. These proponents
of C. megalodon survival cite a small body of ‘evidence’ to
support their claim, including eyewitness accounts, unfossilized and
recently fossilized C. megalodon teeth, and the discovery of the
megamouth shark (Megachasma pelagios) in 1976. (Other researchers,
such as Ellis [1975, 1994], Ellis and McCosker [1991], and, to a lesser
extent, Steel [1985], provide a level-headed, yet open-minded, review of the
question of C. megalodon survival). It will be argued below, however,
that all of this proposed evidence is weak, and that the suggestion of
present-day survival of C. megalodon does not conform with accepted
paleontological and ecological knowledge.
Fig. 2. In a Miocene sea, Carcharodon
megalodon chases down an early pinniped called Allodesmus. From a
forthcoming book written and illustrated by Richard Martin. Artwork
Copyright Richard Martin, 1998.
Eyewitness Accounts
A few reports of alleged encounters with large, unidentified sharks have
been proposed as evidence for C. megalodon survival. One of the most
widely cited is an extraordinary tale recounted by Australian naturalist
David Stead (1963: 45-46):
In the year 1918 I recorded the sensation that
had been caused among the "outside" crayfish men at Port Stephens,
when, for several days, they refused to go to sea to their regular fishing
grounds in the vicinity of Broughton Island. The men had been at work on the
fishing grounds---which lie in deep water---when an immense shark of almost
unbelievable proportions put in an appearance, lifting pot after pot
containing many crayfishes, and taking, as the men said, "pots, mooring
lines and all". These crayfish pots, it should be mentioned, were about
3 feet 6 inches [1.06 m] in diameter and frequently contained from two to
three dozen good-sized crayfish each weighing several pounds. The men were
all unanimous that this shark was something the like of which they had never
dreamed of. In company with the local Fisheries Inspector I questioned many
of the men very closely and they all agreed as to the gigantic stature of
the beast. But the lengths they gave were, on the whole, absurd. I mention
them, however, as a indication of the state of mind which this unusual giant
had thrown them into. And bear in mind that these were men who were used to
the sea and all sorts of weather, and all sorts of sharks as well. One of
the crew said the shark was "three hundred feet [90 m] long at
least"! Others said it was as long as the wharf on which we
stood---about 115 feet [35 m]! They affirmed that the water
"boiled" over a large space when the fish swam past. They were all
familiar with whales, which they had often seen passing at sea, but this was
a vast shark. They had seen its terrible head which was "at least as
long as the roof on the wharf shed at Nelson's Bay." Impossible, of
course! But these were prosaic and rather stolid men, not given to 'fish
stories' nor even to talking about their catches. Further, they knew that
the person they were talking to (myself) had heard all the fish stories
years before! One of the things that impressed me was that they all agreed
as to the ghostly whitish color of the vast fish. The local Fisheries
Inspector of the time, Mr Paton, agreed with me that it must have been
something really gigantic to put these experienced men into such a state of
fear and panic.
This report initially sounds promising, especially considering Stead’s
proclamation of the witnesses’ integrity. But how can we actually
believe a report that speaks of a 150-300 ft (35-90 m) creature---longer
than any other animal ever recorded? Shuker (1991, 1995, 1997) contends
that, if the account is true---as he seems to believe---fear and surprise
could have resulted in these unbelievable figures. Shuker expresses
confidence that the actual size of the creature responsible must still have
been gigantic to instil such a shock in the fishermen. Stead and Shuker
propose that a living C. megalodon would be a near-perfect
match.
I remain unconvinced. Admittedly, I cannot disprove this story because of
its anecdotal nature, but that trait alone would be grounds enough for most
scientists to dismiss it as an unverified “fish-story”. Even if
one is asked to ignore the inadmissibility of anecdotal evidence, the
enormity of the alleged shark sighted is absurd, even if exaggerated by
shock. The “ghostly whitish color” of the alleged animal is also
bizarre. Very few marine animals maintain such a colouring; certainly not
the white shark, which despite its name is only white on its underside,
whereas its back is a distinct dark charcoal grey or bronze-grey. This
demarcation is termed dorsal-ventral countershading. In many sharks and
pelagic fishes, the darker back reduces contrast with the background and
renders the animal less conspicuous. This allows a certain degree of stealth
when stalking prey or avoiding predators. Traditional thought holds that the
lighter underside works in much the same way when the animal is viewed from
below, by matching the down-welling light and eliminating some of the
silhouette effect. There is actually an insignificant reduction in
silhouette under ambient light conditions. C. megalodon is believed
to have occupied a neritic lifestyle much like the white shark (see below),
and it is likely that it was similarly countershaded. Thus, the ghostly
white shark seen in 1918 appears to be at odds with a well-known
environmental adaptation.
Also worth noting in reference to the colour of the 1918 alleged shark is
that while some researchers have suggested that the resurrected C.
megalodon might live in the deep-sea (see below), deep-sea sharks
certainly are not white---in fact most are uniformly dark, both on the
dorsal and ventral surfaces of their bodies. (I mention this because I can
imagine that some supporters of C. megalodon survival might suggest
that the whitish colour of the 1918 alleged shark could be an adaptation to
the virtually lightless deep-sea. It seems instilled in the minds of many
that a dark environment results in white animals. While this is the case in
many cave animals and a few deep-sea creatures, lack of pigmentation is
certainly not a general feature of deep-sea animals).
Shuker (1995) and Goss (1987) include two more reported sightings of very
large sharks that they interpret as possible evidence for C. megalodon
survival. One involved Zane Grey, the famous author of western novels
and an avid deep-sea angler, and the other his son Loren. (Not having access
to the Grey’s original works in which their sightings are recounted, I
rely on Goss [1987] for details). The first sighting occurred when Zane Grey
was deep-sea fishing off Rangiroa in the South Pacific in 1927 or 1928.
Glancing over the boat’s railing, he spotted an enormous “yellow
and green” shark with a “square head, immense pectoral fins and a
few white spots.” Grey claimed it was “considerably longer than my
boat---conservatively between 35 and 40 feet [10.5 and 12 m].” Some New
Zealand fishermen aboard who also saw the great shark agreed with
Grey’s estimate. Initially, Grey thought the shark was a whale shark
(Rhincodon typus) (Fig. 3), which grows to a length of at least 12 m
(40 ft), but according to Goss (1987) Grey thought “only the size of
this ... shark was the same; otherwise it was in no way similar.” Here
I beg to differ with Grey. Not only does the size correspond well, but whale
sharks also have very wide, squarish heads, enormous pectoral fins and are
covered with white spots (admittedly, Grey mentions only “a few”
white spots, but the degree of spotting in whale sharks is highly variable
among individuals and by body region [Richard Martin pers. comm.]).
Nonetheless, Grey stated: “I figured out that the fish ... was not a
harmless whale-shark but one of the man-eating monsters of the South
Pacific. Then I was more frightened than I remember for a long time.”
Despite his dramatic style, I would identify Grey’s shark as a whale
shark long before suggesting that what he saw was a living C. megalodon
or, say, an enormous tiger shark (Galeocerdo cuvier). (This
latter species may exceed 5 m [16 ft] in length and has a characteristically
squarish snout. Grey caught a great number of tiger sharks in his day and
was probably thinking of them when he wrote the above quoted phrase.)
Fig. 3. Whale shark (Rhincodon typus).
Illustration by Richard Martin (1995).
The second sighting took place in 1933, again off the coast of Rangiroa.
Aboard the S.S. Manganui, Grey and his son Loren were returning to
San Francisco after a fishing trip to Tahiti. One evening at about 5:00
p.m., Loren was at the rail when he saw a small flock of spiralling sea
gulls and, near by, an area of yellow water (5):
At first I thought it was a whale, but when the
great brown tail rose in the ship’s wake as the fish moved ponderously
away from the liner, I knew immediately that it was a monstrous shark. The
huge round head appeared to be at least 10 to 12 feet across if not more ...
It was my belief that this huge, yellowish, barnacled creature must have
been at least 40 or 50 feet long. He was not a whale shark: the whale shark
has a distinctive white purplish green appearance with large brown spots and
much narrower head. So what was he---perhaps a true prehistoric monster of
the deep?
What we had seen was something [that] no ichthyologist had ever dreamed
existed. The largest known specimen of this type of shark, generally known
as a sand shark or black-tipped shark, had hardly been known to exceed a
length of about 15 feet.
Despite Loren Grey’s assertions that what he saw was not a whale shark
(mirroring his father’s reaction to his own sighting), it is most
likely that that is exactly what is was. Grey’s description of a whale
shark is completely erroneous: whale sharks are a dark grey, greenish grey
or reddish colour above, with many white or yellowish spots and transverse
stripes, and are yellowish or white on the underside (Castro 1983). As
mentioned previously, they also have a very wide, squarish, yet slightly
rounded head. All of these traits fit well with Grey’s description.
Both of the sharks seen by the Greys were at the surface, which mirrors
whale shark behaviour. In deep waters, many pelagic and neritic sharks,
including the white shark, stay deep much of the day, near the thermocline
(where the warm surface water layers sit on and mix with the colder deeper
layers). In shallower waters, sharks like the white shark stay near the
bottom most of the time, usually only visiting the surface during feeding.
The planktivorous whale shark, on the other hand, is often seen browsing the
surface layers of the water column, where its food often reaches the highest
concentrations.
(Shuker [1995] suggested that the creature that the Greys spotted may be the
same responsible for a traditional belief among Polynesian (6) fishermen in New South Wales, Australia. They
speak of an enormous 100 ft [30 m] long sea monster, not unlike a white
shark, which they call the Lord of the Deep. Such a parallel, however, is
completely speculative without further evidence showing an identifiable
similarity between this mythical animal and the Grey’s sightings.)
The last eyewitness accounts interpreted as being of C. megalodon
are put forward by Cartmell (1978). His first piece of evidence is sonar
trackings by “one of the new breed of underwater exploratory
vehicles” of an unidentifiable object about 100 ft (30 m) long that was
travelling faster than any submarine. The absurdity of this account---which
supposedly serves as evidence for C. megalodon survival---will not
be commented upon. Cartmell also mentions another eyewitness account of a
giant shark:
In the 1960’s along the outer edge of
Australia’s Great Barrier Reef, an 85 foot [26 m] ship experienced
engine trouble which forced it to weigh anchor for repairs. Although the men
subsequently refused to openly report what they had seen for fear of public
ridicule, the captain and his crew later told friends of sighting an immense
shark as it moved slowly past their ship. Whitish in color, they were awed
by its size. It was as long if not longer than their boat! Experienced men
of the sea, they too were certain the creature was not a whale.
Cartmell provides no references for his claims, so without verifiable
sources, the above stories (the latter of which drips with tabloid style and
reads much like a rewritten account of the 1918 giant shark) are useless as
evidence.
What is one to make of these alleged sightings? A whale shark identity does
not fit perfectly with the Grey’s sightings, but does, however, provide
the most sensible and believable explanation. As for the 1918 giant shark, I
remain unconvinced that the story is true. Cartmell’s stories are, as
mentioned above, even more unbelievable. In any case, the usage of these
five unconfirmed and dubious anecdotes as evidence for the resurrection of a
giant, extinct shark is ridiculous. As is the case with a large percentage
of cryptozoological sightings, the above reports simply are not worthwhile
evidence: they are lacking in details, corresponding eyewitness accounts,
and overall reliability. If, for example, there were 50 similar sightings of
an enormous shark in the South Pacific or elsewhere that did not fit a whale
shark identity, attention might be warranted. As it stands, however, there
are only five sightings (two of which can be reasonably attributed to whale
sharks) and they are highly questionable ones at that. Eyewitness accounts
provide no good evidence for the proposed modern-day survival of C.
megalodon .
Evidence from Teeth
One of the most persistent and erroneous myths in the case of alleged C.
megalodon survival is the claim that unfossilized C. megalodon
teeth have been dredged from the ocean floor. The claim, cited as evidence
by Cartmell (1978), Goss (1987), and Shuker (1991, 1997), ignores the
ironclad fact that no unfossilized C. megalodon tooth has ever been
found. This point has been expounded repeatedly by Ellis (1975, 1994) and
Ellis and McCosker (1991), yet no cryptozoologist who has written about
C. megalodon has bothered to acknowledge it. The myth of
unfossilized C. megalodon teeth appears to have originated from at
least three different publications, as discussed by Ellis (1975, 1994) and
Ellis and McCosker (1991). The first is Whitley (1940) who wrote:
Fresh-looking [my italics] teeth [of
C. megalodon ] measuring 4 by 3 1/4 inches [10 by 8 cm] have been
dredged from the sea floor, which indicates that if not actually still
living, this gigantic species must have become extinct within a recent
period.
The next source is Smith (1953: 49), who wrote in his discussion of the
white shark:
Teeth 5 ins. [13 cm] long have been dredged
from the depths, indicating Sharks of 100 ft. [30 m] with jaws
at least 6 ft. [2 m] across. These monsters may still live in deep water but
it is better to believe them extinct.
The third source is Stead (1963: 46). In reference to the 1918 Port Stephens
giant shark (see above), he writes:
Personally I have little doubt that in this
occurrence we had one of those very rare occasions when humans have been
vouchsafed a glimpse of one of these enormous sharks of the White Death
[white shark] type which we know to exist, or to have existed in the recent
past, in the depths of the sea. While they are probably not abundant they
may yet be so. Lest the reader may still think me to be credulous I would
like to say that I have seen actual teeth of a shark of this type which were
no less than five inches (individually) across the base. They had been
dredged up from the bottom of the Pacific Ocean. These, I believe [my
italics], were not fossil teeth, such as are found in various Tertiary
deposits---from which large quantities of great teeth of the White Shark
type have been obtained. In my opinion they were so recent as to justify the
belief that they had come from Great Sharks of a type which might still
exist in the deep seas!
A reading of each of these quotations gives some idea as to how the myth of
unfossilized C. megalodon teeth has crept into the literature. It is
important to note that none of the authors---except Stead---are outright in
their proclamation of the teeth as unfossilized. The teeth that Whitley and
Stead examined are undoubtedly fossilized specimens dredged up by
oceanographic surveys such as the Challenger expedition (1873-1876).
When found, these teeth are encrusted in layers of manganese dioxide, a
mineral that precipitates from sea water over thousands of years. As Ellis
(1975) points out, these teeth are often discussed and illustrated in the
literature after they have been cleaned of this coating. Such preparation
often results in teeth that look like they have been plucked directly from
the mouth of a live shark, except for the fact that they are not white but
rather a brownish or blackish colour. Many of these teeth are very well
preserved, and some have even been found that are a whitish colour (Richard
Martin, pers. comm.), possibly a result of geographical and/or
biogeochemical variability of the concentration of certain precipitating
elements. Such features could conceivably trick an untrained observer
(neither Whitley nor Stead were paleontologists) into thinking the teeth
were unfossilized.
Surely, the teeth noted by Smith are also fossilized specimens dredged up by
oceanographic expeditions. However, because he does not specify that they
were fossilized, his comments have been taken as suggestive of the discovery
of unfossilized, fresh C. megalodon teeth from the abyss. Despite
the persisting rumours of such fresh C. megalodon teeth---rumours
which appear to have originated from the above three inconclusive
sources---the fact remains that all those discovered to date are
unequivocally fossilized.
Supporters of C. megalodon survival have also looked to fossilized
C. megalodon teeth for evidence that the species is still alive
today. The basis for this argument involves two 12.5 cm- (5 inch-) high
C. megalodon teeth dredged up from 4 300 m (14 300 ft) in the South
Pacific by the Challenger expedition. Both of the teeth were
encrusted in manganese dioxide; one had a 1.7 mm (0.067 inch) layer of the
mineral and the other a layer of 3.64 mm (0.14 inches). In 1959, Dr. W.
Tschernezky of London’s Queen Mary College dated the teeth by comparing
the layer of manganese dioxide on them to an accepted rate of deposition of
the mineral in the deep-sea, 0.15 - 1.4 mm per 1000 years. Using the lower
value of deposition (see below), Tschernezky (1959) found the teeth to be
only about 11 000 and 24 000 years old, respectively. Such a period is a
mere blink in the scale of geological time, and Tschernezky’s findings
made many ponder the idea that C. megalodon did not go extinct near
the close of the Pliocene about 1.5 million years ago, but survived until
the end of the Ice Age. It is thus unsurprising that the proponents of C.
megalodon survival used this evidence as another reason to believe that
C. megalodon could still exist.
These proponents, however, are relying on a paper published nearly 40 years
ago. Researchers now believe that this and all other claims of post-Pliocene
C. megalodon teeth (some of which are more convincing than
Tschernezky’s work) are erroneous, representing reworked material from
older deposits (Applegate and Espinosa-Arrubarrena 1996; John Bruner pers.
comm.; Henry Mollet pers. comm.; David Ward unpubl. data). This means that
C. megalodon teeth have been eroded from pre-Pleistocene deposits and
redeposited in younger strata, such as those from the Pleistocene. Whereas
reworked fossil bones often show wear from the process, shark teeth (and
vertebrate teeth in general) are very durable structures that can withstand
high pressures, erosive forces and long-distance transport. Their durability
makes it difficult to determine if they have been reworked from older
deposits. For example, teeth of fossil sharks reworked into present day
beach deposits in southern England are microscopically identical in
sharpness to teeth of present-day sharks (Darren Naish, pers. comm.).
Besides probably representing reworked material, a fundamental flaw in
Tschernezky’s findings lies in his use of manganese dioxide as an
indication of geological age. Manganese dioxide deposition is far from
constant, varying due to fluctuations in the concentrations of ions of iron
(especially Fe2+) and other elements in sea water. The presence
of phytoplankton also plays a factor in the rate of manganese dioxide
deposition, partly because Fe2+ is a key ingredient in
photosynthesis. Therefore, when a plankton bloom occurs---often caused by an
increased concentration of Fe2+---more Fe2+ is removed
from the sea water (often remaining removed for many years) and less is
available to help form manganese nodules (Valiela 1995; Waller 1996; Richard
Martin pers. comm.). Furthermore, Tschernezky only used the lower value of
the manganese dioxide deposition rates to obtain his oft-cited age
estimates. Some readers may have noticed that by using the higher values for
manganese deposition, one obtains dates for the teeth at 1214 years old and
2600 years old, respectively. It is a mystery that the proponents of C.
megalodon survival have never jumped on this fact to help support their
claim. They would be in error to do so, however, as the large discrepancy in
dates caused by the rather wide range of possible depositions of manganese
is indicative of the unreliability of this method of dating. For example, if
one found a hypothetical C. megalodon tooth that had a layer of
manganese 50 mm (2 inches) thick, the approximate datings for that tooth
would be 333 000 years old for the lower value (which Tschernezky used) and
36 000 years old for the high value. The difference between those two dates
is 297 000 years. Utilizing the higher value consistently gives a date
representing only 10% of that of the lower value. Such a large range of
error is hard to accept and thus dating by rates of manganese deposition is
inaccurate and unreliable.
One final piece of tooth “evidence” put forward by some C.
megalodon survival supporters regards a story involving the Australian
cutter Rachel Cohen (Clostermann 1969; Barloy 1985). While in an
Adelaide dry dock in March 1954, workers found 17 teeth embedded in the
ship’s wooden hull that reportedly resembled those of the white shark.
Unlike the white shark, however, the teeth were said to have been 8 cm (3
inches) wide and 10 cm (4 inches) high; the largest white shark teeth on
record measure about 6 cm (2.5 inches) in height. The teeth were arranged in
a semi-circle (typical of a shark bite) about 2 m (6 ft) in diameter, and
the “bite” was near the propeller. The propeller shaft itself was
bent. The Rachel Cohen’s captain recalled a shudder the boat
experienced one night during a storm near Timor, Indonesia. At the time, he
thought it had been caused by a collision with a floating tree trunk, which
are apparently common in the area. While this report makes entertaining
reading, it is useless for a critical examination of supposed evidence for
the present-day survival of C. megalodon . Even if the story is true,
the sizes of the teeth may be exaggerated (Richard Ellis, pers. comm.), and
it is even reasonable to suggest that the ‘teeth’ were
misidentified (Richard Martin, pers. comm.) (7). The sources of the story are unreliable and
give no references, which if provided could be used to verify or disprove
the claim.
The Megamouth Analogy
Ever since the megamouth shark (Fig. 4) was accidentally discovered
tangled up in a U.S. Navy deep-sea anchor in 1976, cryptozoologists have
been keen on using it to point out that the oceans can still harbour large
species unknown to man. Some proponents of modern-day C. megalodon
survival have also used the megamouth to support their claim (e.g., Shuker
1995). However, the comparison of the megamouth with C. megalodon ,
or almost any other marine cryptid, is illogical.
Fig. 4. Megamouth (Megachasma pelagios).
Illustration by D. Bryan Stone III, from Castro (1983).
As a very general analogy, the megamouth does show that the oceans have a
lot of secrets left to reveal, but one has to realize that the megamouth is
by nature a very elusive, highly specialized and unique creature. Inhabiting
mesopelagic waters (200-1000 m [660-3300 ft] in depth), it is a vertical
migrator, following the diel (night/day) movements of its prey, euphausiid
shrimps and other small marine animals. A megamouth tracked off California
by Nelson et al. (1997) was found to stay deep in the water column during
the day, at about 100-200 m (330-660 ft) or more; at night it moved
shallower, to within 12-25 m (39-82 ft) of the surface. Because of its
deep-water habits it is thus unlikely to be encountered by humans. Much of
our knowledge of deep-sea creatures comes from long-lines and trawls set at
depth, but these methods would not help in finding a megamouth. Being a
planktivore, it would not be interested in a baited hook, and because of its
large size it probably would not be swept up in a trawl (admittedly, this
latter point applies equally to other hypothetical large marine cryptids).
Also, many trawls have doors that close when the net is raised to the
surface, and as far as we know, the megamouth does not cruise close to the
sea floor. These factors, among others, highlight why the megamouth may have
remained undiscovered for so long.
It is also important to note that the megamouth shark is highly adapted to
its nutrient-poor deep-sea environment, with a poorly calcified skeleton,
flabby muscles and a low activity level (Taylor et al. 1983). These and
other specializations represent millions of years of evolution, and cannot
be achieved “over-night” by species with different adaptations and
ecologies, including C. megalodon (see below).
The megamouth is not a useful analogy to support the existence of marine
cryptids, including C. megalodon, unless the marine cryptid is
proposed to be a highly-specialized mesopelagic planktivore. In our case, it
is safe to say that C. megalodon was certainly not such a
creature.
Ecological Counter-Evidence
The ultimate point that debunks the suggestion of modern-day survival of
C. megalodon is the current paleoecological view of the shark.
Simply put, all available evidence suggests that C. megalodon
inhabited tropical waters and, like the extant white shark, was a coastal
species (Purdy 1996). It was not a deep-sea inhabitant that fed on
giant squids (Architeuthis sp.), as envisioned by many proponents of
C. megalodon survival (e.g. Clark 1968; Shuker 1995). A creature as
large and adapted to a coastal, warm and food-rich marine habitat as C.
megalodon could not survive in the cold, food-poor deep-sea. Millions
of years of evolution moulded C. megalodon to be an active,
shallow-water predator of primitive whales, not a sluggish, deep-sea,
squid-eating leviathan. In fact, C. megalodon may have died out due
partially to the Pliocene extinction of a major food source, early baleen
whales known as cetotheriids. (Other possible factors in the extinction of
C. megalodon include changes in oceanic circulation, the closing of
the Isthmus of Panama [which might have cut off access to mating and pupping
areas] and even competition from other large predators such as orcas
[Orcinus orca] [Richard Martin in prep.].) The whales that survived
and evolved into the species we know today may have simply been too fast for
C. megalodon to catch (Richard Martin in prep.). These new whales
also showed a trend towards colder waters, to which C. megalodon was
not suited. These factors resulted in a lessened food supply, and in a
sense, C. megalodon may have starved to death.
Some proponents of C. megalodon survival might still say that C.
megalodon could have adapted to a deep-sea environment after its
accepted extinction date of about 1.5 millions years ago. This argument
lacks all reason. Deep-sea fishes and other animals are extremely well
adapted to the harsh conditions of their environment, with reduced skeletons
and tissues, pressure- and temperature-insensitive enzymes, low activity and
metabolic rates, and specialized foraging methods, among other adaptations
(Ellis 1996; Helfman et al. 1997). Likewise, C. megalodon was
probably well adapted to its very different shallow-water environment. The
idea that C. megalodon could simply change all of its anatomical,
physiological and behavioural specializations to adapt itself to a totally
different environment, such as the deep-sea, is fatuous.
If C. megalodon were still alive today, than it would have to exist
in the shallow, food-rich continental shelf waters to which it was so well
adapted. I doubt that any serious proponent of C. megalodon survival
would suggest that the great shark could remain undetected in this region.
Like the extant white shark, C. megalodon surely fed near the sea
surface at times, and if it were still alive today we would have ample
evidence of its existence. Certainly, popular activities such as surfing,
swimming and boating would become that much more hazardous with a 15 m,
super-predatory shark swimming around.
Conclusion
The suggestion by some researchers and cryptozoologists that C.
megalodon has survived to the present-day lacks any acceptable
supporting evidence. Furthermore, the idea conflicts with current
paleontological and ecological knowledge. The case of C. megalodon
survival can thus be safely classified as a popular myth without any basis
in fact. Pending further, substantial and tenable evidence, the question of
C. megalodon’s continued existence should provisionally be
considered answered: the shark is dead. In the opinion of this researcher,
the question of C. megalodon survival warrants no further serious
attention.
Acknowledgements
I would like to express my deepest thanks to Richard Martin, John Moore,
and Darren Naish for providing references, encouragement, comments, and
criticism. Thanks also to John Bruner, Richard Ellis, Ian Fergusson, Henry
Mollet, and David Ward for various comments.
Endnotes
(1) Some evidence exists that suggests
that C. megalodon
appeared as early as the Eocene, about 50 million years ago, but these
finds are largely discounted by most researchers as results of
misidentification or poor documentation (Ellis and McCosker 1991; Applegate
and Espinosa-Arrubarrena 1996; Purdy 1996).
(2) There is a fair amount of controversy
over the phylogeny of
C. megalodon . Some researchers think it is related to the white
shark and therefore deserves to be placed in the genus Carcharodon.
Others subscribe to the theory that C. megalodon is only a distant
relative of the white shark, and that it should be given its own genus,
Carcharocles, and placed in a separate lineage that gave way to the
modern day odontaspidid sand tiger sharks (Cappetta 1987). (If the latter
theory is true, than C. megalodon may not have looked much like the
white shark, but possibly more like an oversized sand tiger shark with much
larger and broader teeth [Richard Martin in prep.].) For the sake of
stability, the more popularly used genus, Carcharodon, is used in
this discussion. It should be noted, however, that in the paleontological
literature, Carcharocles is presently the favoured genus for C.
megalodon (Richard Martin pers. comm.). For more details on the
Carcharodon vs. Carcharocles debate, see various papers in
Klimley and Ainley (1996) and paleoichthyologist Jim Bourdon’s web site
at http://www.elasmo.com/
(3)A significant part of the white
shark’s diet at all
growth phases consists of fishes, and C. megalodon was certainly
piscivorous as well. Because of its large size, however, C. megalodon
was probably more reliant on marine mammals as a food item than is the white
shark. Like extant tiger sharks, C. megalodon may have also
scavenged to a greater extent than does the white shark, augmenting its diet
in its nutrient-poor tropical environment (Richard Martin pers. comm.).
(4) This is a rather simplistic view of
white shark predatory
behaviour, and recent research hints at more complicated and dynamic
interactions between it and its prey.
(5) The yellow water mentioned by Loren
Grey could have been the
result of a plankton bloom or coral spawn---an occurrence that often attract
whale sharks (Richard Martin pers. comm.).
(6) It is probable that Shuker meant
Melanesian.
(7) A one-time loss of 17 teeth from a
white shark or other shark
represents a considerable reduction of dentition. Sharks continuously shed
and lose teeth throughout their life, but they almost never lose more than a
few teeth at a time. Typically, lost teeth are from the functional
(outermost and oldest) series, with the lower teeth shed or lost more
frequently than the upper teeth. If a shark really did chomp down on the
Rachel Cohen’s hull, it would have been essentially toothless
for sometime: a white shark that lost 17 teeth would be missing some 65% of
its upper functional series and about 70% of its lower functional series. It
is unlikely that a white shark or other shark would lose that many teeth
with one bite (Richard Martin pers. comm.).
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