FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 105 



characters developed within the order as on characters also basic 

 for other orders but generally lost or more profoundly modified in 

 those orders. Indeed the outstanding ordinal character of the 

 Insectivora, paradoxically, is the absence of ordinal characters, in 

 the sense that these are developed in other groups. 



Although the order is thus necessarily more loosely knit than is 

 usual, it does not follow that it is altogether artificial. The retention 

 of so many primitive characters is in itself some indication that this 

 conservative group may have still been somewhat unified after the 

 more progressive orders had acquired their distinctive characters. 

 Furthermore, there are a few characters, such as those noted by 

 Matthew in the astragalus, not of wholly generalized placental 

 pattern and distinctive of the Insectivora as against many or most 

 other mammals. There are also some characters, like the peculiar 

 specializations of the incisors, that do not occur in all insectivores 

 and are occasionally paralleled in other orders but that nevertheless 

 appear so frequently among insectivores that they seem to reflect a 

 certain genetic tendency and to help to bind the group together. 



Every individual living insectivore is a speciahzed animal, each 

 species in its own way, and none can be considered, even structurally, 

 as really representing the general placental ancestry in any very 

 exact sense of the words. Yet the abstract conception Insectivora 

 based on all known forms is such that it would, almost perforce, 

 include the most primitive placental mammals. Probably the most 

 remote ancestors (in the Cretaceous) of most, perhaps of all, the 

 placental orders would be referable to the Insectivora by definition. 

 In this sense the order Insectivora is prototjrpal and ancestral to all 

 others among the Placentalia. 



Because the ordinal characters of the Insectivora are mainly primi- 

 tive and because most of the Paleocene mammals are primitive, 

 almost all known Paleocene forms resemble the Insectivora in many 

 respects. If we knew the archaic mammals of the Paleocene but had 

 no knowledge of any of the forms that lived between that time and 

 the Recent, it would be a much more logical and practical system to 

 refer almost all Paleocene mammals to the Insectivora," rather than 

 to distribute them in numerous different orders as is now the usual 

 practice. This distribution, in accordance with a "vertical" or so- 

 called evolutionary conception of classification, is accomplished by 

 the recognition of fossils intermediate between the Paleocene groups 

 and the more distinctly separated later orders and of incipient speciali- 

 zations within the Paleocene groups themselves that point toward 

 groups later to become so distinct that they are granted ordinal rank. 



51 This is approximately the sense of Cope's Bunotheria, a broad group including the Insectivora and 

 various other primitive mammals. Cope did, however, separate and distribute among other orders some 

 Paleocene mammals, such as the Condylarthra, that were on the whole as primitive as those included in 

 the Bunotheria. 



