FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



Family LEPTICTIDAE Gill, 1872 



111 



Unlike many of the Paleocene and Lower Eocene groups referred 

 to the Insectivora, the Leptictidae are Insectivora sensu strido. That 

 is, they are not merely primitive forms that are presumed to have 

 been derived from an undifferentiated insectivore stock and that do 

 not enter well into an}^ other order, but are definitely insectivores in 

 a special sense, clearly related to recent insectivores. Their affinities 

 seem to be with the erinaceoids, although here they constitute an 

 extinct side line, not ancestral to the true Erinaceidae. More exact 

 elucidation of their affinities depends on full analysis of the characters 

 of the Oligocene forms, which are known from nearly complete 

 skeletons but have never been adequately studied. 



Matthew (1918) has pointed out that there is a group of genera 

 undoubtedly leptictid (now about nine genera) and that in addition 

 to these there are several diverse genera placed here without much 

 positive evidence but in default of other indications. Didelphodus, 

 Phenacops, and Acmeodon, then placed here by Matthew, are now 



