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.

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.

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.

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.

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.

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.

(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.

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 swimming.

"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 drag shape.

"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."