CHAPTER V 



THE INSECTIVORES 



The order to which a Mammal belongs is no real indication of 

 its diet — Central position of the order Insectivora among 

 placental Mammals — Dilambdodonts and Zalambdodonts — 

 Relationship of the Tree Shrews to ancestral Primates — 

 Parallel evolution in modern Tree Shrews and Lemurs — 

 Convergences displayed by the Marsupial Mole and 

 Zalambdodonts — Derivation of the Zalambdodont denti- 

 tion. 



In describing the dentition of the Marsupialia a fact of very 

 great importance emerged namely that within a single order 

 variations in dietary habit are found to be associated with dif- 

 ferences in dentition. This should be borne definitely in mind 

 in studying the various mammalian groups for it is easy at 

 first to confuse the ordinal position of a Mammal with the type 

 of its feeding habits. Among the so-called Carnivora for ex- 

 ample the Cats are pure flesh feeders but the Dogs are omniv- 

 orous and even the most purely carnivorous Bear, the Polar 

 Bear, varies its diet of seal with berries and grass during the 

 short Arctic summer. One must realize therefore that the name 

 of the order to which an animal belongs is no real guide to its 

 customary diet. One must not infer from the foregoing de- 

 scription of the Marsupialia however that a complete sequence 

 can be traced in every order commencing always with a central 

 insectivorous or insectivorous-omnivorous form. Recent Mam- 

 mals usually represent specialized and often isolated modifica- 

 tions from the ancestral type and it is only in the Marsupialia 

 that a fairly complete and comprehensive sequence can be 

 traced in existing forms. In some orders every species is now 



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