494 VERTEBRATE LIFE AND ORGANIZATION 



South American anteater, order Edentata (Fig. 24.15 C), is representative 

 ol tliis mode ol lile. Its large claws enable it to open ant hills, and then 

 it laps up the insects with its long, sticky tongue. In contrast to a primi- 

 tive insectivore, which crushes its insect food with its teeth, an anteater 

 swallows whole the insects that it eats. Its teeth were not needed for 

 survival and have been lost. 



The tree sloth and armadillo belong to this same order, though 

 they retain vestiges of teeth. The pangolins of Africa and Asia (order 

 Pholidota) and the aardvark of South Africa (order Tubulidentata) are 

 superficially similar, but this is a result of adaptation to a similar mode 

 of life. The acquisition by distantly related or unrelated groups of 

 similar features as a result of adaptation to a common environment is 

 known as convergent evolution. When closely related groups evolve 

 similarly the phenomenon is known as parallel evolution. 



Primates. Members of the order Primates, the group to which 

 monkeys and man belong, are also closely related to the primitive in- 

 sectivorous stock. Indeed, one member of the order, the Oriental tree 

 shrew (Tupnia, Fig. 24.16 A), has at times been considered to be an 

 insectivore. Primates evolved from primitive, semiarboreal insectivores, 

 and underwent further specializations for life in the trees. Even those 

 that have secondarily reverted to a terrestrial life bear the stamp of this 

 prior arboreal adaptation. Our flexible limbs and grasping hands are 

 fundamentally adaptations for life in the trees. Claws were transformed 

 into finger- and toenails when grasping hands and feet evolved. The 

 reduction of the olfactory organ and olfactory portion of the brain, and 

 the development of stereoscopic, or binocular, vision, represent other 

 adaptations of our ancestors to arboreal life. Keen vision and the 

 ability to appreciate depth are very important for animals moving 

 through trees, whereas smell is less important for organisms living some 

 distance from the ground than it is for terrestrial species. Muscular 

 coordination is also very important, and the cerebellum of primates is 

 unusually well developed. The evolution of stereoscopic vision, increased 

 agility, and particularly the influx of a new sort of sensory information 

 gained by the handling of objects with a grasping hand, was accom- 

 panied by an extraordinary development of the cerebral hemispheres. 

 The cerebrum is the chief center for the integration of sensory informa- 

 tion and the initiation of appropriate motor responses in all mammals, 

 but it is particularly prominent in primates. It is believed that higher 

 mental functions such as conceptual thought could only have evolved 

 in organisms with a grasping hand. In a very real sense, we are a product 

 of the trees. 



Three levels of primate organization are commonly recognized by 

 dividing the order Primates into three suborders. The first, suborder 

 Lemuroidea, includes the tree shrew, lemurs, lorises, and the peculiar 

 aye-aye. Although fossils of lemurs are found in North America, lemur- 

 like primates are now confined to the Old World tropics; Madagascar 

 has a particularly rich fauna of lemurs. All are rather primitive creatures, 

 in which such primate specializations as grasping feet and toenails have 

 begun to appear. However, most lemurs retain a rather long snout, for 



