GANOIDS 113 



In the first alcove to the left, by the window, is a "fossil aquarium" 

 Fossil in which a number of models of these earliest fishes 



Aquarium are arranged in a group, as though alive in the sea. 



In the next alcove are the early fossil sharks which superseded the 

 tribe of plated fishes just mentioned. These sharks had soft skeletons, 

 Sh . simple fins and a number of other primitive features which 

 lead to the belief that all the higher fishes, and the higher 

 back-boned animals therefore as well, were descended from them, their 

 simpler structures becoming more complicated in many directions. In 

 one of the early sharks here exhibited, impressions of soft parts such as 

 muscles and gill filaments have been preserved. 



In the third alcove appear rare fossils of silver sharks or Chimaeroids, 

 which appear to have been developed from a primitive race of sharks. 

 _,,. .. Curiously enough fossil egg capsules of these forms are 



sometimes preserved, and examples are here present. 

 In the neighboring cases are shown ancient lungfishes and ganoids — 

 groups from which all land-living quadrupeds are believed to be 

 descended. 



In the fourth alcove are shown the ganoid fishes which dominated the 

 waters during the Age of Reptiles. They were of many kinds and 

 G ., sizes, most of them with lozenge-shaped scales of bone, 

 with enamelled surface. 



In the fifth alcove are the petrified fishes of the Age of Mammals. By 



this time nearly all of the primitive fishes, like sharks, lungfishes and 



Teleosts ganoids, had become extinct; and the common forms were 



bony-fishes, or teleosts, closely related to our herrings, 



perches, mackerels and daces. 



Return to the South Pavilion or Hall of Mastodons and Mammoths. 



South Central Wing 



GEOLOGY AND INVERTEBRATE PALEONTOLOGY 



Turning northward at the center of the Quaternary Hall containing 

 the mastodons and mammoths, the visitor enters the South Central Wing 

 of the building and is in the Hall of Geology and Invertebrate Palaeon- 

 tology. Palaeontology is the science of the ancient life of the earth; its 

 field is the study the of fossilized shells and other hard parts and the 

 various kinds of imprints left by the animals formerly inhabiting the 

 seas and lands, and preserved in deposits which now form our stratified 

 rocks. As normally the upper layers of a series of strata are more recent 

 than the lower, the fossils reveal hee succession of life forms in the earth's 



