XU FOREWORD 



which appeared in the fossil record 450,000,000 years 

 ago. Here he postulates that the first fishes appeared in 

 fresh water because the kidney of primitive types of 

 fishes living today is adapted to life in fresh water. It 

 has a large glomerulus, and therefore it is able to filter 

 and excrete the large quantities of water which con- 

 tinuously dilute body tissue. When the book was first 

 published in 1953, paleontologists agreed that the first 

 fishes probably appeared in a fresh-water habitat, that 

 Dr. Smith's evidence was critical, and that it strength- 

 ened the paleontological findings: the fauna, flora, and 

 chemical composition of certain geological beds sug- 

 gested that they were laid dov/n in fresh water. But now 

 the fresh-water habitat theory is no longer completely 

 acceptable. Newly discovered facts about other geologi- 

 cal beds, their faima, flora, and chemical make-up, and 

 the time in which they were laid down, suggest that the 

 first fishes appeared in a marine habitat. Recently at 

 Harvard, where A. S. Romer leads the exponents of the 

 fresh-water habitat theory. Dr. Smith was asked about 

 the evidence presented by the Chicagoan, R. H. Deni- 

 son, in support of the salt-water theory. Dr. Smith re- 

 phed that he had read Denison's work carefully, admired 

 it, and felt it merited serious consideration. However, he 

 maintained that his loyalties remain with his Cambridge 

 colleague, Dr. Romer. These two views are in strong op- 

 position, and they will force important revisions when 

 more facts are gathered and analyzed. The problem is 

 intriguing and one that needs solution. Students of pa- 

 leontology are now working on the problem; this volume 

 should be of considerable importance to their studies. 



EVELYN SHAW 



Research Associate in 

 Animal Behavior 



March 1961 



The American Museum of 



Natural History 



