Excerpted from new book, "MEGALODON: Hunting the Hunter", by Mark Renz
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Otodus obliquus 25 foot model in progress by Cliff Jeremiah. Some researchers think the shark would have looked like a modified great white shark (above), basking shark, or even a sand tiger. Photo by Pat Jeremiah.
Chapter 4: The Rise...
If visiting scientists from another galaxy were to study humans around our planet, they might conclude that we were made up of a variety of species, rather than a single species divided by cultures and geographical regions. Not only are there variations in the color of our skin, shape of our eyes and size of our bodies from one continent to another, but there can be great variations within individuals of the same neighborhood.
Within the course of a city block almost any place in America, you can encounter people of the same race with markedly different weights, heights, hair color and feet size. Some of us wear permanent frowns and some of us smiles. Some of us have flat noses and big ears, while others have big noses and small ears. When I talk, I have a slight Southern drawl. My biological grandfather has an Irish last name, was born of a U.S. military family in Panama, and spent a lot of his life in Louisiana. My mom is from Georgia. My wife speaks with a trace of her mother's Puerto Rican accent, although her father is also from Georgia. If we had children, the mix would even be more stirred up.
Identifying species – or in our case – race or ethnic background -- becomes even more difficult when all we have for comparison are the teeth. Mine are slightly crooked, while my wife's are perfectly straight (as are my sister's).
Even though shark vertebrae and denticles (hard parts of the skin) can be found in the fossil record, it's mostly teeth that sharks leave behind. Again, there can be so many variations within a species, it is a real challenge to accurately trace a shark's family tree. Consider that a shark's jaws may have as many as 250 teeth, each one slightly different in size and shape. Some juvenile Megs had cusplets on their lateral teeth that were lost when the shark became an adult. But those same cusplets can be found on adult ancestors of Meg.
Add to the puzzle, teeth changes based on the sex, as well as pathology. A study undertaken by members of the North Carolina Fossil Club estimated that at least 10 percent of the teeth they collected from one of Meg's ancestors, were mildly pathological (abnormal).
So for the purpose of identifying Meg, her ancestors and cousins, we have some good fossil records that are traceable, and some poor records that are not so easy to follow. There can be disagreement too, among experts pouring over the same information. Paleontology, as with other sciences, is a search for information. Information is interpreted, and then re-interpreted as new information becomes available. The complete story can never be written, but as our working knowledge of these sharks expands and is tested, we can begin to speak reliably about them. We can know at least part of the shark story.
Artist Todd Marshall's interpretation of Meg and a great white shark.
Will the real Meg please swim forward?
It would be great if all scientists agreed on Meg's origins, but they don't. There is a major rift between researchers, some of whom think Meg should be classified as Carcharodon megalodon (which it was called from the early 1800s to 1960), and some who argue that it should be called Carcharocles megalodon, which it was changed to in 1960. Both genus names are in use today.
Meg's closest ancestors, as well as the ancestors of today's great white shark, first appear in the fossil record about 60 million years ago, when seas were warm--even at high latitudes. Based on the fossil record, these sharks inhabited the Paleocene seas of southern Russia, Morocco, Angola and the United States. For the professional paleontologist, or even the serious amateur, the phylogenetic map from that point on is riddled with dead-ends and backroads that go anywhere but in a straight line.
Take the final stage of C. megalodon as it was going through the largest stage of tooth development in the early to mid-Miocene. When its teeth were compared with teeth from the great white, scientists assumed the two sharks must be closely related. They saw similarities between the teeth of extremely large great whites and some of Meg's ancestors, such as finer serrations, crown proportions, shape of the root and a broader neck – and classified it as Carchardon megalodon.
Even though mako and great white shark teeth looked a lot alike (with the exception of serrations), researchers passed the similarity off as resulting from the two sharks having similar diets (convergent evolution).
Fossil shark specialist Gordon Hubbell says researchers also previously assumed that the third upper anterior tooth in Meg was positioned in the same manner as great whites, in that the tooth is smaller and has a sharp curve toward the shark's gape. But in studying modern great white shark jaws, as well as associated and partially-associated teeth of Meg and her ancestors, Hubbell reached a different conclusion.
First three upper anterior teeth in the great white shark (Carcharodon carcharias). Notice in the top photo, which shows the left quadrant, that the 3rd tooth on (far left) is significantly smaller than the first two, although the angle of slant does not appear to lean sharply toward the shark's gape. Jaw from private collection of Gordon Hubbell. Photo by author.
First three and first four upper anterior teeth in Meg (left quadrant). Notice in the top photo that the 3rd tooth is only slightly smaller than the first two, and the angle of slant changes very little. Assocated teeth from private collection of Gordon Hubbell. Photo by author.
"The third and fourth teeth in megalodons are almost identical in size," he said. "The only difference is that as you go out from the first tooth, it gets slightly smaller and the angle of slant increases very, very slightly. That tells us that because there is no 3rd tooth in there that slants in, or 4th tooth that slants out, there is no space in there where the jaw is constricted."
"The reason why it does that in the white shark is that there is a stricture in the jaw there" added Hubbell. "There is no space for a big tooth to develop. It has to be a little slanted tooth there that angles inward, because the jaw is constricted and there is no pouch in there for it to develop."
According to Hubbell and other researchers, Meg was a dead-end and great whites evolved from makos.
Proposed evolution of the mako into the great white. The 10 million year-old tooth on the left is smooth-edged, the 7 million year-old old middle tooth is beginning to develop serrations, and the 5 million year-old third tooth is completely serrated. From the private collection of Steve Alter. Size: 1-3/4 to 2-1/2 inches. Photo by author.
"You can see plainly in the Peruvian depsosits where in a 10 million year deposit you have the makos with no serrations, then in a 7 million year deposit you get makos with wavy edges, and by 5 million years makos have serrations," says Hubbell. "You can see from associated sets of Isurus hastalis that the teeth are exactly the same as the modern white shark, they're just not serrated."
Smithsonian fossil shark specialist Robert Purdy is one researcher who steadfastly believes Meg should continue to be identified as the genus Carcharodon. He says that the dentition in some great white sharks mirror the dentition of Megs, in that the third upper anterior tooth is also only slightly smaller than the first and second upper anterior teeth.
"The absence of a gap between the intermediate and first lateral teeth cannot be inferred from the associated dentitions on the basis of tooth width, and we have in the museum fish collections two dentitions where these two teeth almost abut." says Purdy.
He also believes there is no evidence that great whites evolved from makos, even if some of the mako teeth are partially or fully serrated.
Purdy and other pro-Carcharodon researchers who want to keep Meg's genus Carcharodon, offer these additional reasons:
(1) Meg and the great white both have a symmetrical first upper anterior tooth, whereas the mako's first anterior tooth is asymmetrical,
(2) This tooth is the largest in the dentition, whereas the lower second anterior is the largest in makos and other lamndid sharks,
(3) The intermediate teeth point mesially (side of the tooth toward the midline of the jaws where left and right jaws meet) rather than distally (side of the tooth away from the midline of the jaws) as in makos,
(4) The third lower anterior tooth points mesially rather than distally as in makos and other lamndid sharks,
(5) Vertebrae in Megs and great whites more closely resemble each other than with makos.
Meg's lineage: one shark, more than one school of thought
Meg had to start somewhere. Many of those within the Carcharodon camp believe Cretalamna may have been that start, followed by Palaeocarcharodon orientalis, also known as Carcharodon orientalis. Those members of the Carcharocles persuasion believe that Otodus obliquus was an early direct ancestor of Meg. They also suggest that the species orientalis was an evolutionary dead-end and as such, was not a direct ancestor to great whites or Megs.
In some popular books, this line is referred to as extinct mackerel sharks. But U.K. fossil shark specialist David J. Ward warns against it:
"I appreciate that some amateurs prefer vernacular names rather than latinised scientific names, but I feel, in some cases they add to confusion by implying relationships that are just plain wrong," he says. "Thus Otodus is not a giant mackerel shark - because it has long been known that it bears no relationship to the extant mackerel shark Lamna. It is nearer the sand sharks. Ditto pigmy white shark, extinct mako shark and false mako shark."
That is not to say common names should never be used. Bretton Kent, faculty member in the College of Life Sciences at the University of Maryland, says common names actually serve a useful purpose in acknowledging similarities in form between organisms.
"For example, 'sabertooth cat' is a very useful term describing a characteristic body form that is found among separate lineages in the felids, nimravids and thylacosmilids," says Kent. "Common names such as this are useful for describing similar grades of organization, where unrelated animals have converged on a similar body form. This is different than the clades of common descent that are the basis of scientific names. Both common and scientific names convey information, but different types of information."
In addition to lively debates over the official genus for Meg, there is disagreement over the exact order in which individual species evolved within the particular genus. This section will focus on two possible routes by which Meg's post-Cretaceous ancestors evolved, starting approximately 60 million years ago. There is plenty of room for error here, even within the generally accepted versions of Meg's phylogeny, so do not cling to this information as if it is carved in stone (no pun intended). The section is divided into seven parts, begining (arguably) with Meg's oldest ancestor, then moving forward to the final stage of Meg itself.
1. Cretalamna, 50-60 mya. (The genus was first erected by Leonid Glyckman in 1958 -- and spelled Cretalamna. In all subsequent spellings he spelled it Cretolamna. However, the first spelling is the proper one to use.)
Extinct shark Cretalamna appendiculata from the Middle Cretaceous of western Kazakhstan. This is a common species in the Middle and Late Cretaceous of the USA, Europe and Asia. Both the Carcharodon and Carcharocles camp believe this shark is one of the ancestors of C. megalodon. It is often referred to as a mackerel shark, but according to David J. Ward bears no relationship to the extant Mackerel shark Lamna. Rather, it is nearer the sand sharks. Size: 3/4 and 7/8 inches. Specimen and image David J. Ward.
2. Palaeocarcharodon orientalis , 45-50 mya.
Palaeocarchardon sp. (top two photos). Unserrated form. Age: Early Danian. Location: Morocco. Palaeocarcharodon orientalis (bottom two photos). Location: Morocco. Age: Late Danian. Size: 1-1/8 inches and 1-3/8 inches. Photo and specimen David J. Ward.
Palaeocarchardon orientalis is also known as Carcharodon orientalis. Carcharodon believers list this shark as Cretalamna's direct descendant, while Carcharocles followers say it was an evolutionary dead end, unrelated to Cretalamna. Instead they place Otodus between C. appendiculata and Carcharocles in the Meg line. Palaeocarcharodon is found worldwide. The earliest known teeth are unserrated, then irregular, then more regular serrations evolved. "It is easily distinguished from the megalodon lineage," says shark expert David Ward, "by its flatter crown and root, and a narrow, evenly wide burlette." "It was an early attempt to be a white shark that sadly failed." This shark lived from the early to middle Paleocene.
Some Palaeocarcharodon teeth are comparable in size to a modern 17-foot great white shark.
3. Otodus obliquus
(approximately 60-50 mya)
Otodus obliquus. Moroccan land find. Unserrated. Age: Early Eocene. Size: 2-3/4 to 4 inches. Photo by author. Teeth from private collection of Gordon Hubbell.
Otodus obliquus probably reached at least 30 feet in length and -- if you follow the Carcharocles hypothesis -- would eventually lead to Meg. The teeth look a lot like a porbeagle or sand shark which have fairly small teeth. Yet Otodus teeth measure up to four inches long and the vertebrae are over five inches across. It would have been a huge shark and probably fed mostly on large fish. Otodus had large, thick teeth with cusplets and no serrations.
Those researchers who believe Carcharodon should remain the official genus name, do not include Otodus in Meg's phylogeny. Smithsonian fossil shark specialist Robert Purdy, a defender of Carcharodon, believes that the geological time frame for Otodus to make the transformation into Carcharocles auriculatus is just too short to be credible.
"...In instances where we can see evolutionary change through intermediate species such as in the reptile to mammal transition, these changes take place over a period of several million years," says Purdy. "From geochemical evidence, we know that gene mutation in sharks is the slowest of all vertebrates. The Eocene associated dentition of "Carcharodon" auriculatus from Belgium has a lamnid (resembling a great white) dental formula rather than an odontaspid (resembling a sand tiger) formula as in Otodus.
"In geological terms, this is an abrupt change," says Purdy. "The same is true if you consider Isurus as the ancestor of Carcharodon carcharias. If that were true, the teeth of juvenile Carcharodon should be identical in form to those of adults; this would be true also for which tooth was largest in the dentition, the orientation of the tip of the intermediate tooth and third lower anterior tooth, and the form of the first upper anterior tooth. In both cases, there is no good evidence to support transitions between the putative (supposed) ancestors and descendants."
On the other hand, David Ward does find the Otodus to Carcharocles transition credible: "By arranging loose teeth, you can reconstruct a passable white shark (Carcharodon) dentition by slipping in a lower lateral tooth into the third upper anterior position," he says. "If you have an associated dentition (most of the teeth from one shark) as Gordon Hubbell does, this mistake shows up - as a gap in the lower jaw. This only fools those who cannot tell a lower tooth from an upper!"
"One thing you must understand is that we are talking about a lineage - a single undivided branch of the family tree stretching from the Paleocene to the Pliocene- not a series of separate species. There was only one Carcharocles present at any one time, so a tooth, or for that matter the whole shark, from the USA will be virtually indistinguishable from one, say, from Europe. How many species you divide this lineage into, is not really important. Names are artificial. What is important is to understand that we are talking about the family tree of a single giant shark, that changed gradually through time.
"I have collected Otodus, Carcharocles and all intermediate forms bed by bed, from an outcrop in Kazakstan," says Ward. "The transition has been recognized in the literature for almost 40 years and has been well documented by Russian scientist Victor Zhelesko.
Ward says that approximately 51 million years ago, Otodus teeth developed very fine folds in their cutting edges. Serrations appeared, at first low, on either side of the crown by the cusplets, spreading up to close to the tip. This form, the first Carcharocles, is called Carcharocles aksuaticus, named after a locality on the Emba river in northwest Kazakhstan. The tooth has relatively simple lateral cusps and a rather irregular serration. This process took in the region of half a million years.
"The reason we have to resort to collecting as far away as Kazakhstan is because rocks of this age are uncommon," says Ward. "It was a time of low sea levels over most of Europe and the USA. Not entirely by coincidence, evolution in sharks takes place much faster at these times - when the major ocean basins are separated and shark populations may have been isolated from each other - and had to rapidly adapt to a different diet.
"A similar effect is seen in mammals on small islands. In the UK, where I collect, there is a gap in the sedimentary record (rocks) at this point, so we go straight from clays with Otodus obliquus to sands with C. auriculatus. On the Potomac, southeast of Washington DC, it is possible to collect Otodus teeth just showing the first stages of serrations before there is a gap in the record. In Kazakhstan, I can chose a bed and predict how serrated the Otodus/Carcharocles in it will be before I find them. It is just like seeing evolution happen right in front of you. "
"Of course, you have to respect other people's opinions about relationships and evolution, but you could not witness a better example of a transition if you tried."
The next species - or recognizable shape - is Carcharocles auriculatus. As its name implies, it has large, rather ragged lateral cusps, and even serrations that almost, but not quite, reach the tip of the crown. Fairly recently, the name C. poseidoni has been used for the first of the Carcharocles lineage that has an almost fully serrated crown. This is a Late Eocene species, and occurs fairly commonly in Egypt and Northwest Kazakhstan.
The Late Eocene - Early Oligocene species C. sokolovi differs little other than having slightly less ragged lateral cusps and more even serrations. The name C. angustidens is used for a range of shapes as the crown widens and becomes more triangular. The form where the lateral cusps are disappearing into the sides of the crown-proper - seen in the late Oligocene and through the middle Miocene is called C. chubutensis by some and C. subauriculatus by others.
Ward says these are just names and are not too important. They are just ways of expressing stages of evolution in the teeth of a giant shark.
"The final stage, the star of the show," he says, "occurs when, in adults, the lateral cusps are lost, imperceptible in the base of the wide crown. This is C. megalodon."
A slightly serrated Otodus obliquus. Size: 1-3/4 inches. Location: Potomac River, Virginia. Photo and specimen David J. Ward. Photo is also his.
A tooth, intermediate in shape between Carcharocles aksuaticus and C. auriculatus, Bed 5, Aktulagay, Northwest Kazakhstan, Middle to Early Eocene. The serrations are a little too irregular and the lateral cusps ragged enough for a classical Middle Eocene C. auriculatus. Size: 1-1/2 inches. Location: Potomac River, Virginia. Photo and specimen Rick Johnson.
Three teeth - see scale = 1 inch. From left to right: Otodus obliquus, Bed 1, Aktulagay, Northwest Kazakhstan, earliest Early Eocene. Carcharocles aksuaticus, Bed 3, Aktulagay, Northwest Kazakhstan, Mid-Early Eocene. Carcharocles auriculatus, Bed 5, Aktulagay, Northwest Kazakhstan, Mid-Early Eocene. Photo and specimens: David J. Ward.
Tooth on left: Otodus obliquus. Morocco, earliest Eocene. Tooth on right: Carcharocles aksuaticus from Bed 3, Aktulagay, NW Kazakhstan, Mid-Early Eocene. Size: 1-3/4 inches. Photo and specimens: David J. Ward.
A tooth, intermediate in shape between Carcharocles aksuaticus and C. auriculatus, Mid-Early Eocene, Egem, Belgium. Size: 1-3/4 inches. Note; this is not typical of those currently being collected, which tend to be rather less serrated. Photo and specimen Rick Johnson.
Carcharocles auriculatus, Bracklesham Bay, UK. Middle Eocene. Size: 1-1/4 inches. Note gradational serra which are not continuous over the tip of crown. Photo and specimen by David J. Ward.
A note from a poster David J. Ward wrote some years ago::
Carcharocles: This genus was originally erected by Jordan & Hanibal (1923) for those teeth of the (presumed) Carcharodon lineage possessing lateral cups. He chose for his type, Squalus auriculatus (Blainville 1818). This usage was not universally adopted and virtually forgotten. Casier (1960) realised the morphological differences between the teeth of recent Carcharodon and those of what is now known as the Carcharocles lineage, and erected the genus Procarcharodon. He included the species auriculatus, angustidens and megalodon, with "C". angustidens as the type. This usage was taken up by most workers until it became evident in the 1980's that it was a junior synonym of Carcharocles.
4. Meg ancestor Carcharodon auriculatus, also known as Carcharocles auriculatus (approximately 50 to 42 mya,). This shark is only found in the Middle Eocene.
Early megatooth shark, Carcharodon auriculatus, (also known as Carcharocles auriculatus). Main characters of this tooth is a gradation of serrations to an unserrated tip and large ragged lateral cusps. These two teeth have rather puffy roots and are typical of the late Middle Eocene of the eastern USA. Although best called C. auriculatus, they are distinctive and perhaps merit a name of their own. Age: Middle Eocene. Location: Santee Limestone South Carolina. Size: 2 inches and 1-5/8 inches. Photo and specimens: David J. Ward.
5. Meg ancestor Carcharodon angustidens, also known as Carcharocles angustidens (approximately 35 to 22 mya)
C. angustidens tooth. South Carolina river find. Note the wide crown base and partial loss of the lateral cusplets. Only a little way to go to be a meg! Size: 4 inches. Age: Oligocene. From the private collection of Jeff McManus. Photo by author.
6. Meg's most recent ancestor Carcharodon subauriculatus, also known as Carcharocles chubutensis (approximately 28 to 22 mya as a species, and 28 to 5 mya as a morpho species.
Meg's most recent ancestor, Carcharodon subauriculatus, also known as Carcharocles chubutensis. Size: 4-1/8 inches. Found in Cooper River, SC. Age: Mid Miocene. From private collection of Jeff McManus. Photo by author.
7. Carcharodon megalodon, also known as Carcharocles megalodon (30 to 2 or 3 mya). (Most of the oldest Meg teeth date back to about 18 mya, but David J. Ward has an Oligocene Meg tooth from the Chandler Bridge Formation of Summerville, South Carolina.)
End of the line. Carcharodon megalodon, also known as Carcharocles megalodon. Found in a South Carolina land site. Size: 6-1/2 inches. Age: Miocene to Pliocene. Photo by author; tooth from his private collection.
When trying to determine precisely which of Meg's ancestors you have found, Ward emphasizes that you have to first sort out exactly what constitutes a Meg.
"There are two conflicting classifications," he says. "The first - morphospecies - is just shape based. Thus, if it is big, with no lateral cusps, it is a Meg. The other, a more scientific approach, attempts to get closer to a zoological species. The name used is based only on the adult shape. In the Miocene, and possibly in the latest Oligocene, all adults have lost their cusps, and are all, by definition, Megs. The problem with using the former, is that, for instance, a Carcharocles, living in the Middle Miocene starts life as an angustidens, passes its "teens" as chubutensis, and is a Meg as an adult."
The zoological species classification will be used in this book.
Where were Meg's birthing suites?
We do not know of every birthing location used by pregant female Megs, but according to Purdy who wrote a chapter for the Peter Klimley and David Ainley book, Great White Sharks, one of them includes the late Oligocene Chandler Bridge Formation of Summerville, South Carolina. Purdy says this site has produced a bone bed with a dozen primitive odonticete (toothed whales) and small mysticete (non-toothed whales) skulls and about 100 teeth of juvenile Megs.
However, Purdy is not without his critics:
"The Summerville site does not have neonate (newborn up to about a month old) Megs - as implied, it has small, young Megs," says Ward. "I have never found a neonate tooth there, although I have no doubt that they occur. Nor does it have many big adult teeth. This was not a birthing area, it was a feeding area. It makes no sense to give birth where there are lots of predators - and in the Chandler Bridge there were lots - including whales. On the contrary, they gave birth somewhere else, probably in deeper water, but the young came in to feed in the rich warm coastal waters."
The Bone Valley Region of Florida has multiple Miocene nursery sites in which neonate and young Meg teeth are abundant, as well as food sources. Young Megs probably consumed a lot of large fish but because fish vertebrae don't hold up well in the fossil record, it's difficult to get an accurate reading. Bones from dugongs, dolphins and small whales have been found with possible Meg shark bite marks on them, but are not common.
Tooth of newly born Meg. Bone Valley, Florida. These teeth are sometimes referred to as Hubbell teeth, after researcher Gordon Hubbell, whose specimens were used to illustrate an arcticle on megatooth sharks. Size: 1-1/2 inches. Photo and specimen: David J. Ward.
In various stretches of the Peace River (Hardee County), small Meg teeth with 3/4" wide roots and a perpendicular enamel height of 1/4" can be found on a regular basis. The largest Meg teeth in these stretches are 2-3 inches in slant height and are common. Teeth over 3 inches are extremely rare. Dugong ribs and vertebrae are abundant at this site. Dolphin teeth and ear bones are common, although not plentiful. With regard to young Meg's predators, signs of them are few and far between. Large whale teeth are rare while large earbones (possibly belonging to non-toothed whales) are more common, although not plentiful. Occasional mako shark teeth up to 2 inches are found, but are not nearly as common as the young Meg teeth. Great white shark teeth are extremely rare.
It makes sense that a practical place for mom to give birth would be an area where predators are smaller and food sources more plentiful so the young Megs could grow in relative safety. The Peace River sites (which were once a shallow saltwater bay) seem to fit that scenario well.
Even in sediments that produce--say a 2 inch mako shark tooth and a 2 inch Meg tooth at the same level, it is possible that the two teeth were deposited in different seasons, if not different years. A 15-foot mako, for instance, may have lost its tooth in March while feeding--perhaps on a newborn Meg. Then again, it may have lost its tooth in March and the young Meg may lose its tooth in May, or even several years later. The inclusion of different animals in the same deposit does not always indicate they were there at the exact same time.
Teeth get redeposited on a regular basis too, which makes it even more difficult to obtain exact time lines for reconstructing what happened and when. Broken sharks teeth found imbedded in bone make it obvious that the shark was feeding on the animal, but even in that situation, who is to say whether the animal was killed by the shark or simply was feeding on a dead animal's carcass--killed perhaps by some other cause? There are constant variables to consider in the fossil record.
NOTE: For the remainder of this book, Carcharodon megalodon and Carcharocles megalodon will be referred to as C. megalodon or just Meg.
Where do Makos and Great Whites fit in?
Extinct mako shark (Cosmopolotodus hastalis) teeth. Some in the Carcharodon camp assign the genus name "Isurus" for the species hastalis, but David J. Ward says hastalis looks nothing like a mako and everything like an unserrated great white. Then why not call it "Carcharodon", one might ask? "Beats me," says Ward. "Perhaps when the Carcharodon/Carcharocles debate is over, we will." Size: 1-3/4 to 2 inches. Lived from Oligocene to Pliocene epochs. Bakersfield, CA land find. Photo by Steve Alter; teeth from his private collection.
Great white (Carcharodon carcharias) shark. Illustration by Kyle Kirby.
Left: Fossilized great white (Carcharodon carcharias) tooth found in South Florida. Size 2-3/4 inches. Lived Miocene to Present. Photo by author; tooth from his private collection. Right: Cast of modern tooth belonging to a great white shark that was over 19 feet long. Size: 2-1/2 inches. Photo by author.
Mako/great white ancestor Isurus praecursor (also known as Cosmopolitodus praecursor by many in the Carcharocles camp), had no lateral cusplets on the teeth, and no serrations. It began in the mid-Paleocene, then branched out in two directions. One became "Isurus" hastalis (or Cosmopolitodus hastalis), then Isurus xiphodon (or Cosmopolitodus xiphodon) and then Isurus escheri (or Cosmopolitodus escheri). Officially, the Carcharodon carcharias, or modern day great white is not classified with makos, but some in the Carcharocles camp are convinced it followed Isurus escheri. The other mako branch became Isurus desori, then Isurus oxyrinchus, or the modern mako.
Some Carcharodon followers also call today's great white shark "small-toothed white shark" and have it evolving as a separate line extending from Carcharodon orientalis to Carcharodon auriculatus and Carcharodon carcharias.
Parotodus benedeni (often "erroneously" referred to as "False Mako")
(Parotodus benedeni). Ridgeville, SC land find. Size: 2 5/8 inches. Late Pliocene (appx 2 million). Photo and specimen: Steve Alter.
Parotodus benedeni. The teeth were also large, but generally had no side cusplets or serrations. Shark researcher Mikael Siverson believes that Parotodus could be derived from a Mid Cretaceous shark called Cardabiodon, while others point to the similarity with Otodus. In the Oligocene, some are figured with cusps and in the Pliocene some very large specimens were serrated.
What did Meg really look like?
Skeletal reconstruction of C. megalodon. There are differing views among shark researchers regarding the shape of Meg. This is just one possibility. Illustration by Marisa Renz, modified from Klimley and Ainley book "Great White Sharks" (Academic Press).
How can anyone really know what Meg looked like?
Bretton Kent thinks he has a pretty good idea. Some fossil shark researchers believe Meg may have been closely related to great whites and therefore should look like a modified version of the great white. Others suggest Meg was more closely related to sand tiger sharks and should have a design like a sand tiger. Kent believes that if Meg is more closely related to sand tiger sharks, the relationship is largely irrelevant for determining body shape.
"I'm a functional morphologist by training and argue that the
constraints on shape are so severe for an axial swimmer (i.e., that
flexes the body to provide propulsion) of this size that a sand tiger
style of body is phyically impossible," says Kent. "Sand tigers have an
acceleration body form and use drag to displace water when
swimming. Displacement swimmers need to move a water mass
equivalent to 3-4 times their body mass with each stroke of the tail
to swim by this mechanism."
Kent says that the problem arises at really big sizes
like that of Meg.
"This problem is based on classic biological
scaling," he says. For objects of similar shape, doubling the length causes
surface area (e.g., fins) to increase four times and volume (i.e.,
mass) to increase eight times. Consequently, a really large sand
tiger would need enormous fins to offset the tremendous increase
in mass. Unfortunately, these fins would also generate an
enormous amount of nonproductive drag that would impede
"The only way large axial swimmers have evolved is to switch over
to a cruising body form that generates propulsion by lift rather than
drag," says Kent. "Cruising fish need only displace a fraction of their body
weight when swimming, relying instead on increasing the speed,
rather than the mass, of the water over the tail. All of the large
marine, axial swimmers (tunas, porpoises, whales, white, mako,
basking and whale sharks) use a cruising body form. As far as we
know, no really large marine animal with an acceleration body
shape has ever evolved. They all appear to be cruisers."
Kent suggests that a more reasonable shape would be that of a basking or whale shark.
"The front ends of these sharks are rather different, but the back ends
(where drag is a real problem) are remarkably similar," he says. "The caudal
fin is nearly lunate, the second dorsal and anal fins are tiny, and
there is a caudal keel on each side of the caudal peduncle. The
same pattern occurs in other large axial swimmers (e.g., bluefin
tuna, billfish, whales, great whites & makos), not because they are
related to each other, but because they're simply big. Again the
front ends may be different, but the back ends have the same low
"I personally use basking sharks as the basis for my reconstruction
of the Meg body shape," adds Kent. "Robustness of the body would be due to the interaction
between limits on muscle-based underwater swimming speeds and
the proportion of white muscle for burst swimming in the body."
How do you grow a 40-60 foot shark?
C. megalodon vertebra. Size: 4 inches wide x 2 inches thick. South Carolina river find. From the private collection of Jeff McManus. Photo by author.
C. megalodon vertebrae. Size: 4 inches wide x 2 inches thick. South Carolina river find. From the private collection of Jeff McManus. Photo by author.
Dr. Bruce J. MacFadden, associate director of the Florida Museum of Natural History in Gainesville, FL, along with University of Florida geology student Joann Labs, want to know how Meg managed to grow so large.
"I'm interested in asking the question, "How do you grow a very large shark like a megalodon from a small, sort of average size ancestor?" says MacFadden. "What were the mechanisms in terms of evolution? How do you grow a large shark over time? And that relates to a field in paleontology called heterochrony, which is the study of how growth rates change from ancestors to descendants."
MacFadden says his questions were prompted by an elementary student who visited the museum, pointed to the Meg jaw on display and asked, "How old was that shark?"
"That stuck in my mind and I've been looking for a way to answer that question," says MacFadden. "We know how to predict the size of a megalodon. What we don't know is the individual age of the animal. If you have a megalodon that you estimate to be 20 feet long or 40 feet long, did the shark grow really fast or did it grow slowly like a Galapagos tortoise over 100 or 200 years? That's the crux of the whole problem. If you could get a handle on the individual age, how old it was when it became 40 feet long, then you'll know about the heterochrony. You'll know about how that animal developed into a larger animal.
MacFadden is hoping that Meg's vertebrae will provide the answers he's looking for. "The vertebrae centra are like tree rings," he says. "But you don't know if they're annual. We're looking at the chemistry of the centra and will be able to tell the seasonal cycles. From those cycles we can tell that a particular series of bands represents an annual couplet, meaning two that were formed in the summer and winter."
"We did a pilot study with Otodus obliquus," says MacFadden. "My Ph.D. student, Joann Labs, is making her geology thesis on the rates of growth and development in megalodon using centra. Her doctoral dissertation in the geology department here is to focus on three things: One is to understand how shark centra are fossilized, and how the chemistry is preserved from the original animal. The second is to look at modern shark growth and the chemistry of modern shark centra that have grown for a known number of years to see if that animal has growth rings that correspond with its age.
"And finally, she's going to look at megalodons world-wide and ask if within megalodon there were different rates of growth. Perhaps some populations in the North Atlantic got large but not humongous, and other populations were much larger on average. She'll be able to tell that from the shark centra."
"What we do with the vertebrae is drill out about two dozen little grooves. Some of them are in the middle of the growth rings and some of them are right on the growth rings. Then we analyze the chemistry of those patterns and it can tell us the season of growth. And what we're finding is that those growth rings are annual. So you count the growth rings in this particular animal and you can tell how old it was when it died."
MacFadden admits there are potential complications. "The conflicts are that the growth rings could have really slowed down at the end of the animal's life. It's the oxygen content of the vertebae that are the indicator. Oxygen is incorporated into the vertebrae at different amounts based on the temperature at which it forms. So in cold times the oxygen forms in one quantity and in warm times the oxygen forms in another quantity. This animal might grow really fast initially and then slow down its rate of growth near the end of its life. In that case, the rings at the rim of the centra may have been deposited in a much slower fashion.
Another potential complication says MacFadden is that the fossilized mineral content of the vertebrae could have been completely obliterated after the animal died by background waters perculating through the fossil.
"But what we discovered going back into the Eocene for our pilot Otodus obliquus is that this wasn't the case."
Dr. Bruce MacFadden with Otodus obliqus vertebrae from Morocco. Size: Approximately 5 inches wide x 1-3/4 inches thick. Florida Museum of Natural History collection. Photo by author.
For 62 million years, this leviathan and its predecessors ruled with iron teeth. Then suddenly, about two to three million years ago, the fossil record comes screeching to a halt. Again, why? How could such a powerful beast disappear while the great white and mako sharks lived on? Did Meg really die off? Or is it possible the toothy fish still exists somewhere in the depths of our vast blue oceans?
To understand where meg fits into the grand scheme of things, scientists have her classified as follows:
Family: Carcharodontidae (for Carcharodon believers) or Otodontidae (Carcharocles followers)
Genus: Carcharodon or Carcharocles