660 



SCIENCE. 



[N. S. Vol. I. No. 24. 



Fosdl Mammah of the Puereo Beds. Bj- Henry 

 Fairfield Osborn and Charles Earle. 

 Bull. American Museum of ISTatural 

 History. Vol. viii., Art. I. Pp. 1-70. 

 The Puereo Eocene (or Post-Cretaceous) 

 was discovered and named by Cope in ISSO, 

 and up to the present time our knowledge of 

 its very remarkable and interesting fauna 

 has been due almost entu'ely to his labors. 

 It is a fauna which in many ways is veiy 

 puzzling and raises many exceedinglj^ diffi- 

 cult problems. To the solution of these 

 problems the admirable work of Osborn and 

 Earle is an important contribution. While 

 adding but few new names to the long list 

 of genera and species already established 

 by Cope, the authors have accomplished 

 what is of far greater value, namely, materi- 

 ally increased our knowledge concerning 

 the structure and systematic relationships 

 of many mammals which had previously 

 been known only from fragmentary remains. 

 In this way the character of the fauna as a 

 whole is set in much clearer light than ever 

 before. 



Of the more significant results of this in- 

 vestigation, the following deserve particu- 

 lar mention : (1) The determination of the 

 complete dentition of Polymastodon, a repre- 

 sentative of the Multituberculata, which 

 was one of the dominant tj^pes of Mesozoic 

 mammals. (2) The description of parts of 

 the skeleton of Indrodon, showing that it 

 was a true lemuroid, as had been doubtfuUj^ 

 surmised before, and the reference of the 

 Chriaddce to the same group. Cope had re- 

 ferred the genera of this family to the creo- 

 donts, an example which I had followed, 

 though expressing the opinion that Chria- 

 cus and its allies might eventually prove 

 to be lemuroids. (3) A very welcome con- 

 tribution to our knowledge of the Puereo 

 creodonts is the description of an excellent 

 skeleton of Dissacus, the ancestral form of the 

 Mesonychidie. What renders this particular- 

 \j valuable is the fact that the Bridger genus 



Mesonyx is already very completely known, 

 and the comparison of the two forms is very 

 instructive for discerning some of the modes, 

 of mammalian development. (4) A nearly 

 complete skull of the primitive tillodout 

 Onychodectes is described and has an im- 

 portant bearing upon the early morphology 

 of the mammalian skull. (5) The skull of 

 Pantolambda, the forerunner of the corj-pho- 

 donts, which became so abundant and vai-ied 

 in the succeeding Wasatch time, is for the 

 first time made kn-o'mi. This is one of the 

 most valuable results of the whole investiga- 

 tion. (6) The suggestion originally made 

 by Schlosser, that iliochemis and its allies 

 are ungulates rather than creodonts, is con- 

 firmed, and a new familj^ of Condylarthra is 

 established for their reception. (7) The 

 upper teeth of Protogonodon are determined 

 and the likeness of its dentition to that of 

 the primitiA^e artiodactyls pointed out. 



Of the greatest general interest to both 

 geologists and biologists are the conclusions 

 reached regarding the character of the 

 Puereo fauna as a whole, which is shown 

 to be of a prevailingly Mesozoic type. Only 

 a small fraction of this fauna is ancestral 

 to Wasatch and Bridger types, and of these 

 most do not persist beyond the Eocene, 

 while bj' far the greater number of Puereo 

 genera die out without leaving anj- succes- 

 sors behind them. This generalization is 

 of much importance in clearing away cer- 

 tain stratigraphical diflBculties. It is hardly 

 an exaggeration to say that the Puereo 

 mammalian fauna differs more from that 

 of the Wasatch than does the latter from 

 the recent fauna. If the Wasatch mammals, 

 as a whole, were derived from those of the 

 Puereo, then we must assume the existence 

 of a long, unrecorded gap between the two 

 formations, an assumption which geological 

 data do not support. When, however, M'e 

 examine the Wasatch genera which clearly 

 were derived fi-om Puereo ancestors, such 

 as CorypJwdon, Pachycma, Didymidis, Ana- 



