EXTINCT ANIMALS 



teeth of mastodon, rhinoceros and tapir. It 

 seems to be a correct conclusion that this huge 

 shark {Carcharodon megalodon) was nearly one 

 hundred feet in length, since its teeth were 

 fully three times the length of an almost identi- 

 cal recent shark {Carcharias rondeletii), which 

 measures thirty feet in length. 



" Extinct animals " include, as must be 

 obvious at once, a vast number of smaller 

 creatures besides the vertebrate Fishes, Am- 

 phibians, Reptiles, Birds and Mammals. Rocks 

 occur containing thousands, even millions, of 

 shells of Molluscs (whelks, bivalves, etc.) 

 crowded together in a space of a few feet. 

 Remains of minute shrimps are equally abundant, 

 and whole mountains are built up of rock formed 

 by the coral or calcareous skeleton of minute 

 polyps resembling our sea-anemone. Many of 

 these are very peculiar forms, unlike those now 

 living. Others, again, are remarkable for the 

 fact that though found in the most ancient rocks 

 they yet closely resemble creatures still living 

 to-day. 



We will now glance at a few of the more 

 remarkable " fossils " of these lower or simpler 

 kinds. (See the table of classes on p. 56.) 



266 



