THE AMERICAN MUSEUM OF NATURAL HISTORY 



fossil fishes illustrating the rise and differentiation of the 

 lowest vertebrates from the earliest (Upper Silurian) time 

 (ending 20,000,000 years ago) to recent (Quaternary) time 

 (ending 3,000,000 years ago). Most of the forms repre- 

 sented are North American and belong to five great divi- 

 sions. 



The first three cases confronting the visitor contain 

 specimens of the armored fish-like forms, some of which 

 were of huge size and armed with powerful teeth, or sharp- 

 ened jaw blades. This form is best represented by the 

 fish-like animal Dinichthys, displayed in the center of the 

 room. Dinichthys lived about 20,000,000 years ago in the 

 sea that existed on the site of the present State of Ohio, 

 and was one of the most destructive and ferocious animals 

 that ever lived in the sea. Although fish-like in appearance, 

 it is regarded as belonging to a more primitive class of ver- 

 tebrate animals. The head and front half of the body were 

 protected by heavy plates of bone, and it had powerful jaws 

 with "fangs" in front of and behind them, knife-like cutters 

 which chopped against each other. 



In the first alcove to the left is a "fossil aquarium," de- 

 signed as an aid in interpreting the fossils in the adjoining 

 cases, and it undoubtedly gives an accurate picture, since 

 all the fishes shown were found in a single locality and in a 

 single layer of Old Red Sandstone. 



Proceeding to the right the visitor finds the sharks, rays 

 and chimaeroids, which are the earliest true vertebrates with 

 cartilaginous skeletons and jaws, followed by the lung- 



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