GANOIDS 111 
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 sizes, most of them with lozenge-shaped scales 
of bone, with enamelled surface. One of the few survivors “Amia’’ of 
this ancient group is here shown living ‘‘in a window aquarium,” to give 
the visitor a clearer idea of the fishes of the ‘‘ Middle Ages”’ of the world. 
In the fifth alcove are the petrified fishes of the Age of Mammals. By 
this time nearly all of the primitive fishes, like sharks, lung- 
fishes and ganoids, had become extinct; and the common 
forms were bony-fishes, or teleosts, closely related to our herrings, 
perches, mackerels and daces. 
Ganoids 
Teleosts 
[Return to the South Pavilion or Hall of Mastodons and Mammoths.| 
SoutH CENTRAL WING 
GEOLOGY AND INVERTEBRATE PALZONTOLOGY 
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 Palseon- 
tology. Palwontology is the science of the ancient life of the earth; its 
field is the study of the 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 the succession of life forms in the earth’s 
crust and thus are of the highest value and interest to the student of 
historical geology. Since, however, the remains of only a small propor- 
tion of the animals living at a given period are permanently preserved 
in the marine, river, lake and subaerial deposits of that period, the 
geological record of animal and plant forms is far from complete. Inas- 
much as invertebrate animals are far less free in their movements than 
the vertebrate forms, they are accepted as the best determinants of the 
geological age of a bed of rock, even when remains of both kinds are 
found together. Invertebrate life, too, appeared on the globe far earlier 
than vertebrate, and remains of certain species are abundant in the 
lowest “oldest” of our stratified rocks. 
