The Shedding of Teeth by Carcharias littoralis (Mitchill)

Abstract

A FTER having seen sharks shed their teeth for some twenty years it came somewhat as a surprise to learn that the process was still being questioned. Cawston (1938a, 1938b, 1939, 1940a, 1940b, and 1941) denies that there is a succession in sharks' teeth and in arguing his case states in his first two papers, Sharks' teeth are not found in aquariums, where they would occur if constantly shed under natural conditions, but many, which have resisted disintegration after the rest of the fish has been devoured, are found on the ocean bed. In his 1940a paper he writes Although one or two teeth have been collected and sent me from the aquarium at Tangora Park, Sydney, I do not consider there is proof that the shark which has been kept in captivity there for four years has shed any of its teeth. The shark tanks of the New York Aquarium have their floors littered with the cast teeth of sharks, literally by the thousands, numbering many more than the total number of teeth in all the sharks contained therein since the establishment of the individual tanks. These teeth are for the most part perfect and rest there mingled with the sand until removed. Thinking this an item of public interest we established a display plaque over the chief shark tank explaining the process in 1939. On this board, among other things was a large glass tube filled with several hundred teeth recovered from the aquarium. A photograph of this exhibit is shown in the Annual Report for that year, (Breder, 1940). These remarks refer to Carcharias littoralis (Mitchill), close to or identical with Carcharias taurus Rafinesque which Cawston discusses most fully. In addition to the accumulation of the teeth of Carcharias in aquaria, which could have no other source than shedding, direct evidence on the shedding process was repeatedly obtained. It usually took from two days to a week for the directly observable loosening tooth to become detached. Such loss of teeth generally took place a single tooth at a time. It would first be noted that one of the teeth in the front row was protruding further forward than the others. Later it would be noted that it stood straight out in an approximately horizontal position. Usually it would next be found missing but on a few occasions could be seen dangling from one of its points of attachment, that is, from either end of the broad basal portion. These occurrences were noted generally when for one reason or another the fishes were feeding lightly, for apparently the process of feeding customarily dislodged the teeth at an early time before their advanced movement could be easily noted. This manner of losing teeth suggests that the rows advance to some extent independently of each other for never was anything noted to suggest the simultaneous loss of an entire row. Further examination of the rows in a number of jaws showed no regularity between teeth in adjacent rows, even where there was considerable overlapping of the bases. It should be noted that in the aquarium referred to there were seldom more than three sharks and consequently it was a simple matter to keep track of individual fish. Also