

SCIENCE PROGRESS 



probable that mammals originated during the Triassic period 

 from the cynodont reptiles of South Africa, and that from this 

 original stock there diverged at an early period a branch which 

 gave rise to the Multituberculata, and later, after considerable 

 specialisation and degeneration, to the Monotremata. In the 

 general form of their skulls, and to some degree in their 

 dentition, the multituberculates show an approximation to the 

 rodents, but this is probably a case of parallelism in develop- 

 ment. Very noteworthy is the fact that the Tertiary American 

 genus Polymastodon makes a nearer approximation to mono- 

 tremes than does the Triassic African Tritylodon. The former 

 genus was described by the late Prof. E. D. Cope so long ago as 



Fig. 3. — Upper view of skull of Polymastodon taoensis. 



Fr, frontal ; Ju, jugal ; Mx, maxilla ; Pa, parietal ; Pmx, premaxilla ; Sq, squamosal. 



(From Broom, Bull. Amer. Afus. Nai. Hist.) 



1870, on the evidence of a fragmentary skull and teeth from the 

 Puerco, or Lowest, Eocene of New Mexico, and has hitherto been 

 very imperfectly known. An expedition despatched by the 

 American Museum to the Puerco beds of New Mexico was, 

 however, fortunate enough to discover a number of remains ol 

 the genus, among them being a skull which, although much 

 crushed and broken, was found to be capable of restoration. In 

 the general characters of its dentition and its relative shortness and 

 breadth, the skull (figs. 3, 4), which measures about 6 in. in length, 

 distantly recalls that of a rodent, the dental formula being— 



1. -, c. -, p. + m. •£. 



