696 COLLEGE ZOOLOGY 



THEROMORPHA, which are known only from fossil remains. 

 Above the monotremes are placed the MARSUPIALIA, and finally 

 the PLACENTALIA, which are the highest of all animals. The 

 PRIMATES, the group that includes man, seem to have descended 

 from the primitive INSECTIVORA. The line of descent within 

 the group is probably somewhat as follows: 



1. MONOTREMATA. Egg-laying Mammals. 



2. MARSUPIALIA. Marsupials. 



3. INSECTIVORA. Insectivores. 



4. LEMURID.E. Lemurs. 



5. CERCOPITHECID^:. Old World Monkeys with Tails. 

 ' 6. SIMIID^E. Anthropoid Apes. 



7. PITHECANTHROPUS. An Extinct " Ape-Man." 



8. HOMO NEANDERTHALENSIS. The Extinct Neanderthal 



Man. 



9. HOMO SAPIENS. Modern Man. 



3. THE FOSSIL REMAINS or VERTEBRATES 



a. Succession of Life in General 



The fossil remains of animals that lived millions of years ago 

 give us authentic records of the fauna present upon the earth's 

 surface at that time. These records, unfortunately, are frag- 

 mentary, since only the hard parts of the animals were preserved, 

 and these, when discovered, are almost always broken and in- 

 complete, making the reconstruction of many parts necessary. 

 From the evidence obtained from fossils, paleozoologists have 

 constructed a table (Table XVII) showing the geological periods, 

 arranged in the order of their succession, and the time of origin 

 of the different groups of animals. 



Such a table shows that the invertebrates appeared first, since 

 their remains occur in the oldest strata, unaccompanied by the 

 remains of vertebrates; that the invertebrates became more 

 complex in the succeeding periods; that the fishes (low in the 

 scale of vertebrate life) were the first vertebrates to appear; 



