MORRISON MAMMALS: PANTOTHERIA 



87 



other difference, however slight. These jaws and teeth are the most complicated known 

 from the Jurassic and it seems inconceivable that two such well-known and complex 

 forms could really belong to two different genera differing in no slightest detail save in 

 the possession of seven or of eight molars. The slight variations in measurements are 



Fig. 37. Docodon. Diagrammatic internal view of right lower jaw. 

 Three times natural size. 



within the probable limits of error in taking such minute dimensions. The teeth agree 

 not only cusp for cusp but even, on the molars, in the fine details of the furrows and 

 rugosities on the enamel. In view of the known facts of dental embryology and varia- 

 tion it is quite impossible to maintain the two genera as distinct. The apparent absence 

 of Ms in Docodon striatus might be interpreted in three ways : ( i ) as due solely to the 

 youth of the type, (2) as an individual anomaly, such as is not infrequent in other 

 mammalian groups, or (3) as a taxonomic distinction of not more than specific value. 

 The t)^e is young, but careful dissection of the posterior portion failed to reveal the 

 germ of an additional tooth. It seems more probable that the variation in molar num- 

 ber is an anomaly, perhaps the more likely in these mammals with seven or eight simi- 

 lar molars, but for the present it seems best to retain Marsh's species provisionally. 

 Docodon striatus rests on a single specimen which had not quite reached maturity. An 

 analogous case is seen in Amblo titer turn, in which the molar number is usually eight, 

 also, but is seven in one individual specimen and nine in another. 



"Enneodan" {Ennacodon) was defined as having a comparatively short, robust 

 jaw with nine post-canine teeth, all of the same tjpe, and with Po larger than Pi 

 rather than smaller as in Docodon and Dicrocynodon. Two species were defined, each 

 based on a single, immature specimen. Measurements show that the jaws in these spe- 

 cies are shorter than in the others referred to the family but that they are more slender, 

 both absolutely and relatively to the size of the teeth. Both differences in proportion 

 could be due to immaturity. The post-canine teeth do appear to number nine, although 

 this is in part based on the number of alveoli and is a little doubtful. The statement 

 that the premolars and molars are of the same general form was based on study of the 

 teeth when half concealed by matrix. Upon being cleaned somewhat the premolars and 



