Although the Pinnipedia (seals) and Cetacea (whales) are not related to each other, they are grouped for convenience in the same chapter because they are both aquatic.

Order PINNIPEDIA

The pinnipedes (sealions, walruses and seals) bear many features indicative of a relationship to the Carnivora they first appeared in the Miocene as an offshoot of the Oligocene carnivores, fully adapted to an aquatic life. They used to be placed in a sub-order of the Carnivora but the trend today is to give them the status of a separate order.

In general, their dentitions consist of singlerooted teeth with crowns of simple morphology adapted to a sea-food diet prehended and consumed within water. There is little distinction between molars and premolars and the dental formulae quoted here are based partly on the fossil evidence.

The deciduous dentition is non-functional and tends to be shed soon after birth in some seals it does not erupt at all and is resorbed in utero. The first two upper incisors of the Otaridae (sealions and fur seals) differ from those of all the other pinnipedes in having a mesio-distal groove across the occlusal surface (Harrison and King, 1965). The grooved incisors can be seen in Fig. 5.1.

Pinnipedes show considerable individual variation in the number of teeth and, to quote Bateson (1894), ‘illustrate nearly all the principles observed in the numerical variation of the teeth. In both premolars and molars there are examples of the replacement of one tooth by two, and in some of these the resulting teeth stand in series while in others they do not. Besides these there are numerous instances of extra premolars and molars belonging to various categories’.