specialized forms that existed millions of years ago. 

 This evolution, or development, has proceeded slowly 

 and is the result of a combination of Biological and 

 Physical factors. Certainly, Natural Selection, physi- 

 ological and physical adaptations to food and tempera- 

 ture, moisture, and topographical variations, have 

 played an obvious part. 



The mammals are the most recently developed 

 group in the animal world. Moreover, their develop- 

 ment has been remarkably rapid when it is contrasted 

 with the development of many other forms. After the 

 other Vertebrates (Fishes, Amphibians and Reptiles) 

 had failed, in succession, to maintain the supremacy of 

 the world, the mammals with a keener intelligence, 

 which brought with it parental care, have advanced to 

 a position which is more or less dominant. 



Although there is still some difference of opinion 

 regarding the origin of mammals, the evidence seems 

 to point to reptilian ancestors. Fossil remains of ex- 

 tinct, dog-toothed reptiles in the Triassic rocks of 

 South Africa, appear to possess, structures which sug- 

 gest that present day mammals and those that preceded 

 them were, more or less, directly descended from rep- 

 tilian forms. 



As has been shown in every animal group that has 

 attained a high degree of specialization, the mammals 

 have undergone a prog^ressive development from sim- 

 pler ancestral forms. The earliest known mammals 

 appear to have been of a very small size, arboreal and 

 insectivorous in their habits. A small Tree Shrew, 

 living in Africa, is thought to more closely represent 

 the earliest placental mammals than any other living 

 creature. 



