AQUATIC MAMMALS 



Potomogale is an inhabitant of the streams of equitorial Africa. Ex- 

 ternal ears are present. The muzzle is flattened and the body is cy- 

 hndrical, continuing uninterruptedly into the thick, powerful tail, which 

 is excessively compressed laterally. The legs are short, rather weak, 

 and the toes are not webbed, but the lateral border of the hind foot is 

 broadened to a thin edge so that it may be folded back more smoothly 

 against the tail. The latter is evidently the exclusive means of aquatic 

 propulsion, the feet being then pressed against the body and base of 

 the tail. 



The aquatic members of the Talpidae and Soricidae may be consid- 

 ered as a unit. The insectivores are among the most primitive of 

 placental mammals and reasonably close to the original prototype. They 

 are notoriously conservative, some of them, we know, having remained 

 virtually unchanged since Cretaceous times. Remains of desmans which 



Figure 4. The African insectivore otter Potomogale, from a mounted specimen 

 in the National Museum. 



are considered to be congeneric with the living animal are known from 

 the Middle and Lower Miocene of Europe. So we can rest assured 

 that the aquatic insectivores are no very recent development but that 

 their modifications have been brought about throughout very long 

 geologic periods. That such specialization is not now more marked 

 than merely in the form of the hind feet and at times, slight changes 

 in the tail and ear, may be attributed to the conservativeness of the 

 insectivore phylum and the fact that they are so largely dependent upon 

 the land. 



Potoj)iogale is a paradox, for it is extremely unlikely that any land 

 mammal would take to the water and from the very start use its tail 

 as the sole means of propulsion. In other cases a flattening of the tail 

 follows acquisition of webbing by, and at times an increase in the size 

 of, the hind feet. Yet the feet of this genus are unwebbed and re- 

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