342 



SCIENCE 



[N. S. Vol. XXVII. No. 687 



Pollowing the introductory section is an 

 admirable classification of the Mammalia and 

 a diagram showing the chronological and 

 stratigraphic succession of the formations in 

 which fossil mammals have been found in 

 the western states. 



Chapter I. is a reprinted essay on the teeth 

 of the Mesozoie mammals; Chapter II. sets 

 forth the first outline (1888) of tritubercular 

 evolution in mammals; Chapter lU., tri- 

 tubereuly in relation to the human molar 

 teeth and the Primates; Chapter IV., tri- 

 tuberculy in its application to the molar teeth 

 ■of the ungulates or hoofed mammals and the 

 completion of the nomenclature; Chapter V., 

 the second outline (1897) of tritubercular evo- 

 lution in Mammalia with discussions of 

 criticisms; Chapter VI. is a brief review of 

 the dental types observed in the successive 

 geological periods; their chronological and 

 geological succession ; while Chapter VII. will 

 prove of extreme value to the student of 

 paleontology as it discusses and illustrates all 

 of the ordinal types of molar teeth and often 

 t;he entire dentition. Bibliographical refer- 

 •ences are found at the close of each section of 

 this chapter and serve to show how far afield 

 one must go to fitnd the wealth of informa- 

 tion which it contains. In the eighth 

 chapter the evolution of the premolar teeth is 

 discussed. Those of primitive mammals; 

 and the adaptation of premolars in which 

 ■" they either (a) enter upon an especial 

 adaptive evolution of their own, as for example 

 in the upper sectorials of the cats (Felidse), 

 or the elaborate fourth premolars of the 

 PlagiolacidfE, or (b) by a serial analogous de- 

 velopment they more or less closely mimic 

 fhe structure and supplement the exact func- 

 tions arid uses of the molar teeth; this 

 mimicry reaches its highest extreme among the 

 Perissodactyl or odd-toed Ungulates, where the 

 premolars gradually metamorphose into the 

 ■molar pattern and even become superior to 

 the molars in size and complication." 



Osborn speaks further of this premolar 

 metamorphosis as being " from the biological 

 standpoint most interesting as illustration of 

 convergence, because form exactly similar to 

 that of the molars is finally attained from 



somewhat dissimilar beginnings." This of 

 course depends upon whether one holds to the 

 Cope-Osborn theory or that of premolar 

 analogy. If the latter be true this premolar 

 adaptation is merely a case of parallelism. 



Chapter IX. is a very frank review of the 

 objections and difficulties which have arisen 

 with reference to the Cope-Osborn theory and 

 of the rival theories that have been set forth. 

 Professor Osborn finds that two classes of 

 criticism have arisen: (I.) That the trituber- 

 cular tjrpe is not primitive. (II.) That the 

 Cope-Osborn theory of the origin of the su- 

 perior molars is incorrect. (I.) The opposing 

 theories to that of trituberculy each presup- 

 pose a more complex tooth as the primitive 

 one, arguing that the tritubercular, tricono- 

 dont and protodont stages are secondary sim- 

 plifications. The weight of evidence, however, 

 seems to be largely in favor of trituberculy. 

 (H.) The three powerful arguments arrayed 

 against the Cope-Osborn idea of the origin of 

 the upper molars, that of embryogony, pre- 

 molar analogy, and finally a different interpre- 

 tation of the paleontological record, seem dif- 

 ficult to combat. Osborn believes the ques- 

 tion to be still suh judice, in spite of the fact 

 that he and Gregory have brought forth all 

 of the evidence which ripe learning and ex- 

 haustive study have produced. 



Writers agree that the Osborn nomencla- 

 ture should in any case be retained because of 

 its wide use in paleontological literature and 

 its great convenience. One is somewhat dis- 

 mayed, however, by the fact that the fourth 

 upper premolar and first molar of the horse, 

 for instance, teeth almost indistinguishable 

 in structure, must needs be described by 

 totally different nomenclatures. 



The final chapter discusses the idea of recti- 

 gradations in the evolution of tooth cusps. 



The whole book gives evidence of the most 

 painstaking work, not only on the part of 

 the author but of his able editor as well. 

 Perhaps its most delightful feature is the 

 judicial fairness and frankness with which the 

 whole evidence is reviewed and discussed. 



EiCHAED S. Lull 



Yale Univeksitt 



