68 BULIjETIN 169, UNITED STATES NATIONAL MUSEUM 



EXTENT OF KNOWLEDGE OF MIDDLE AND UPPER PALEOCENE FAUNAS 



Aside from details concerning only special students, the impor- 

 tance of such collections as those here described lies, from a more 

 general point of view, in the knowledge they give of the broader out- 

 lines of mammalian life in their time and area. To permit the proper 

 drawing of inferences in this broader field, it is essential to consider 

 the adequacy of the collections and their probable relationship to the 

 faunas as a wdiole represented by them. The adequacy of a paleon- 

 tological sample depends principally on three quite distinct factors: 



1. The adequacy of the collection studied as a sample of the fos- 

 sils actually preserved in the rocks. 



2. The adequacy of the preserved fossils (collected or uncollected) 

 as a sample of the whole fauna that actually lived in the area. 



3. The adequacy of the real local fauna as a sample of the regional 

 fauna of the whole land mass on which it lived. 



Probably the best criterion of the adequacy of a collection as a 

 sample of the preserved fossils is that of repetition. "When collecting 

 begins to pile up mainly or only duplicates, it probably has achieved 

 sampling adequacy for the local deposit, but as long as many species 

 remain very rare in collections, it probably has not. 



Of the 51 surely separate species known from the Gidley and 

 Silberling Quarries, 15 are here represented by only one specimen each, 

 but of these four are known by other specimens from elsewhere in the 

 field. Seven here have only two specimens each, but one is fairly 

 common elsewhere. Six are here known from three specmiens each, 

 but two are also represented elsewhere. The other 23 species are 

 represented by five or more specimens each from these quarries. In 

 the field as a whole, of the 79 species, 19 are represented only by one 

 specimen. Four of these represent genera still unknown elsewhere, 

 and hence loiown from but one specimen each: Stilpnodon simplicidens, 

 Unuchinia asaphes, Elphidotarsius Jlorencae, and Spanoxyodon 

 latrunculus. Of the other 15 species here represented by only one 

 specimen each, three (Leptacodon cf. tener, Psittacotherium multi- 

 fragum, and Thryptacodon laustralis) are inseparable from species 

 well known in other fields, and the others all belong to genera well 

 known from other species, some of them abundant. For broader 

 studies of morphology and faunal succession, local species are not 

 very important, and of the 51 genera known to occur in this field, 

 not more than five can be considered as very poorly represented in 

 Middle Pal eocene faunas generally.^* 



From these data, as well as the general make-up of the collections 

 and other considerations, the collections appear to represent the real 



i» At least one of these, Elphidotarsius, and possibly one or two others are closely allied to well-known 

 genera. 



