AQUATIC MAMMALS 



To attempt to interpret the reason for this lack of uniformity would be 

 idle because we can have no conception of the precise manual needs of 

 a particular sort of whale, nor what form would constitute an ideal 

 equilibrator for its precise body form. I think one should work on the 

 theory not that the cetacean pectoral limb has evolved from a single flip- 

 per form, but that diverse kinds of whales split off from one or more 

 stocks long before the manus had assumed a paddle shape, so that sub- 

 sequently that of each has developed independently, with many some- 

 what different lines of specialization according to individual needs. 



The width of the cetacean manus depends upon the disposal of the 

 phalanges. In a broad flipper the digits are spread somewhat fanwise 

 and are relatively short. The breadth of flipper is marked, according 

 to Flower (1876) in Physeter, Hyperoodon, Monodon, Delphinapterus, 

 Inia, Platanista, Orca, and Orcella. In the latter genus (fig. 41) this 

 broadness in relation to moderate length is especially marked. A very 

 narrow flipper is usually long, just as in the case of the wing of a bird. 

 The limb of Globiocephala is especially noteworthy for this feature, 

 and accompanying, and contributing to, the condition is the fact that 

 the border digits are much reduced in length, while the second and 

 third are remarkably elongated. The second may have about eleven 

 elements in the adult and as many as nineteen in the late fetal stages, 

 and a comparable situation obtains in at least some of the other por- 

 poises (as Phocaena) . Leboucq, I believe, was the first to make this 

 claim, later (1888) denied by Weber, but reaffirmed by Kiikenthal. 

 This is, of course, evidence that the flipper of such porpoises is under- 

 going reduction in length, but it must not be inferred that this is neces- 

 sarily the case in all cetaceans. That great length of flipper is not in- 

 variably associated with extreme hyperphalangy is shown by the case 

 of the humpback {Megaptera) . This genus has the longest flipper of 

 any living whale, the exposed part of the arm reaching a length ex- 

 ceeding twelve feet, although in the mounted specimen in the National 

 Museum there are in the second digit but 6 phalangeal elements in ad- 

 dition to the metacarpal, while there are 5 such plalanges in the 

 mounted Sibbaldus. These facts have aroused much speculation. It 

 is commonly reported that the flippers of Megaptera are used for giving 

 gargantuan and resounding love pats to the opposite sex, and it has 

 been claimed that they are also employed for clasping during mating, 

 as well as to help "herd" schools of fish into the cavity of the capacious 

 mouth. This is all that we have to go on, unless we fall back on the 

 theory that the great arm length has been purely in the nature of an 

 overspecialization. 



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