ABOUT WHITE SHARKS

The great white shark has many names around the world. Among these names are white shark, white pointer, blue pointer (South Africa), tommy shark. Where the term ‘Great White’ came from is unknown, and tends to imply there is a ‘lesser white shark’ – which there is not.

Universally, the scientific name for the white shark is ‘Carcharodon carcharias’. Carcharias comes from the Greek karcharos which, loosely translated means ‘sharp or jagged’ (presumably referring to the serrations along the teeth). The species were given the scientific name Squalus carcharias by the classifier Carolus Linnaeus in his 1785 catalogue, Systema Naturae. Linnaeus’s system provided all species with two names, the generic and specific. This was so that closely related species could be recognized in a named grouping, the genus. The tenth edition of Linnaeus ‘book was chosen as the earliest publication available for scientific names, so his Squalus carcharias is the oldest acceptable name for the great white shark. A different generic name has to hold the ‘great white’ because scientists after Linnaeus realized that this his Squalus included many very different kinds of sharks. Squalus therefore needed to be restricted, so several new names had to be created to sort out the other species placed there. In 1833 Sir Andrew Smith proposed the generic name Carcharodon, but it wasn’t until 40 years later that Sir Andrew’s generic name was identified with Linnaeus’ specific name.

Recognition

The term ‘white shark’ stems from the belly of the animal, the ventral surface being a pure white colour. The upper surface of the shark varies dependent on geographical location, and there is evidence to support that as the animal migrates from one location to another, the upper surface colour alters to maintain the animal’s camouflage. Upper surface colours range from dark sea grey (almost black) to bronze. Generally it’s accepted that the colour fades to a dull grey when the animal is dead. Flanks of the white shark vary too, fading from the upper surface colour to a grey or silver/gray with a definite demarcation line along to flank where the white ventral colour starts. Dorsal, upper pectoral and caudal fins are generally darker grey. The lower lobe of the caudal fin is almost as large as the upper lobe (typical of all mackerel fish) and the white of the ventral surface spills on to the lower lobe in varying amounts. In all except white sharks found in Mediterranean waters, there is a black auxiliary marking behind the pectoral fin – this is usually covered by the aft pectoral fin area. The lower pectoral fins tip has a black marking and often this continues along the forward and aft edges of the fin toward the body (blending into the upper grey colour). The tail of the animal, to the caudal fin has a very pronounced flattened broad caudal keel. A lateral line can be followed from almost the gill area back to the caudal keel. There are five large gill slits forward of the pectoral fin.

Great White Shark (Carcharodon carcharias)

As with all sharks, the white shark is a spindle or torpedo shape, however, it tends to be somewhat stockier and thicker in appearance than any other lamniform. The snout is short and conical with nostril openings on the lower outer edges of the snout. The lower snout is peppered with sensory pits called the Ampullae of Lorrenzini (more on these later) which gives the snout a ‘5 o’clock shadow’ appearance.

Eyes are often described as black. In actual fact, although the pupil is black and large, there is a defined blue boarder (iris) to it.

Ampullae of Lorrenzini. Juvenile male white shark (1.47m TL) Copyright WSCT 2017

Juvenile male white shark (1.47m TL) Copyright WSCT 2017

Unlike any other shark the teeth are triangular and deeply serrated. There are usually 26 upper teeth and 24 lower teeth in use with replacement teeth developing behind and attached to the jaw cartilage. As a tooth is lost a new tooth moves forward to replace it like a ‘conveyor belt’. The process takes less than 48 hours. Upper teeth triangular shape is generally broad and flat for slicing though soft tissue. The point is sharp for piercing and separating bone. Tooth size reduces from the center of the mouth round to the outer jaw area. Lower teeth tend to be finer and less broad.

There is often a pronounced curve to the middle teeth as these are used for holding prey. The teeth shape subtly changes as the shark grows, becoming broader with age. Some scientists believe this to be due to the animal changing diet from fast swimming pelagic fish such as tuna to seals (the sharper pointed teeth being better suited to holding fish, whilst the broader blade type shape being better suited to slicing through thick energy rich blubber). Researchers attributed this to the larger animals not being able to keep up with the fast swimming pelagic fish as their bulk increased, and switching to a diet of pinnipeds that are slower swimmers.

Photo copyright and credit to Andrew Fox 2002

ANCESTRAL HISTORY OF WHITE SHARKS

From fossil records, the white shark, Carcharodon carcharias, first appeared around 11 million years ago, and whilst the evolution of sharks is well documented from fossilized teeth found worldwide, the white shark’s exact ancestry and evolution (as with the living animal) remains clouded. Some scientists believe the white shark is descended from the megatooth shark (Carcharocles megalodon, formerly known as Carcharodon megalodon) whilst other scientists believe the true line originates from Isurus (modern mako sharks). Originally the megatooth shark was grossly exaggerated as the first mock-up jaws were constructed from similarly sized teeth making the whole jaw and resulting estimated shark size truly enormous.

Reconstructed jaws of Carcharocles megalodon by the American Museum of Natural History, New York. This 1927 reconstruction is now thought to be about 30% too big, based on what is known about the teeth. Photo Credit: Wikimedia

It is unusual to find a cluster of fossil teeth from one shark. Normally, fossil shark teeth are found isolated. The way in which teeth grow into place in living sharks explains the abundance of single fossil teeth. In living sharks, old teeth are shed regularly as new teeth move into position in the jaws. The shed teeth fall to the sea floor where, because they are formed of resistant minerals, they fossilize readily. As more studies of the modern white shark (and other sharks) were made, scientists realized that as with the modern white shark, the megatooth shark teeth would not have all been the same size and, with more fossilized teeth being uncovered, and the rare discovery of a complete fossilized tooth set, a far more accurate jaw (and later, vertebrae) was mocked up. Carcharocles megalodon was still a huge animal (see comparison below), thought to prey on whales (fossil whale bone has been found on numerous occasions with the tail-tail lacerations from the megatooth teeth.)

Illustration showing size comparison between C. Megalodon and C.carcharias.

When you examine a megatooth shark tooth you can instantly see the resemblance to the modern great white shark and it is easy to see why so many scientists are convinced that Carcharocles megalodon is the evolutionary grandfather to the modern white shark. It is when entire tooth sets are compared that disparity occurs however.

 

Carcharocles megalodon teeth display the serrations synonymous with modern white sharks. Early mako shark ancestors such as Isurus hastalis lacked these serrations however the overall dentition shape of early Isurus sp. is close to that of juvenile modern white shark.

Carcharocles megalodon (left) and Isurus sp. upper jaw teeth

The third tooth from centre of the upper jaw of the white shark is prominently curved forward, as is C. megalodon, in stark difference to Isurus sp. which curves backward. Additionally, teeth grouping and numbers of Isurus are a far closer match to the modern white shark.