MANEATERS — And Their Teeth

Auckland Star, Volume LXX, Issue 303, 23 December 1939, Page 5 (Supplement)

MANEATERS — And Their Teeth

A RARE species of shark recently caught by Mrs. W. J. Brambley, of Wattle Bay, Manukau Harbour, has been presented to the Auckland Museum. The species is remarkable on account of its curiously shaped teeth which show that it belongs to a primitive group of sharks, the remains of which have occurred in the rocks for millions of years past; back to the distant cretaceous period. The usual shark's tooth is narrowly triangular, flattened, with fine saw-teeth-like serrations, ivory white, and extremely hard and durable. So indestructible in fact that fossil examples of these teeth invariably retain polished surfaces.

ByA. W. B. Powell

This Manukau shark is "Notorhyncliua pcctorosus, or the seven-gilled shark, better known by its former scientific name of Kotidanus. This shark is not common in New Zealand waters, but it is a widely distributed species, occurring in Australia, Tasmania, South Africa, India and Jaoan. It is considered the most primitive of all living species of sharks, for its spinal column is entirely cartilaginous, without trace of lime, its teeth are like sections of a hack saw, and it has only one small dorsal fin set well back near the tail. The gill slits number six or seven, whereas most sharks have but five. The length cf the Wattle Bay specimen was six feet, but the species has been known to grow up to twenty-six feet. The size of a shark, how-

ever, is no indication of its ferocity, for one of the largest living species, the basking shark, grows up to thirty feet, yet it is sluggish in its habits and quite harmless. The teeth of the basking shark are represented by a dense mass of rod-like structures no more than a quarter of an inch in height. Unlike the carnivorous kinds, the basking shark is content with a mass diet of tiny shrimp-like organisms, which it collects, as do many of the whales, by sifting the sea water through comb-like structures, which in the case ef this shark are associated with the gill slits. Another

species, the Port Jackson shark, has its teeth represented by smooth, hard pads and rounded plates which it uses to crush shellfish. It will be seen, then, that from a glance at a shark's teeth one may learn if that particular species is a likely man-eater or not. However, the anxious bather is not likely to seek first-hand" assurance if lie finds himself at close quarters witJi any member of the shark fraternity. ' To the large man-eating sharks belong the large triangular serrated-edged teeth. The great white shark, one of the most formidable, has this style of teeth. This is the shark responsible for most of the bathing fatalities in Australia and the racific islands. It also occurs at times in New Zealand waters, but, as the species favoui s oceanic waters, there is little or no danger at our bathing resorts, most of which are in fairly enclosed situations. AnoMier notorious Australian shark is the grey nurse, a species which definitely does not occur in New Zealand waters, although its

supposed presence here has often been reported by casual observers. The New Zealand species which is confused with the grey nurse is the common sharp-finned whaler, a harmless species, unless it is cornered or accidentally encountered, when it has been known to inflict wounds in self* defence. Our mako has not the reputation of a man-eater, but by its formidable teeth it could quite easily be one. Apparently only its deep water habits keeps it free from the temptation afforded by bathers. In Sydney the popular bathing beaches, often thronged with thousands of bathers, are situated on the open coast adjacent to deep water, and this is why attacks there by sharks are not infrequent. On the Queensland coast, where the same species of sharks, occur, but the water is shallower, affording richer and more extensive feeding grounds, attacks upon bathers are very rare indeed. Fortunately the world's largest and presumably most ferocious shark has been extinct for some millions of years. It was the giant Carcharodon, allied to the great white shark, but with individual teeth were sometimes six inches long and five inches broad, the shark itself being round about ninety feet in length. The singular mode of growth of the teeth in sharks deserves mention. We have to be content with two sets, but goodness knows how many sets a shark has, nor how long each set lasts. Usually, behind the erect functional teeth, there are five or more rows of accessory teeth, all lying (lot but ready to be moved up to the front line as those in service become worn or damaged, and are shed. When the flrst row is shed, the next moves into position, and away at the back of the jaw a new series gradually forms to keep up the stock. &&ss&&&*££sss&