1912] Miller: Pacific Coast Avian Palaeontology 63 



assistance extended by him to the author, our knowledge of the 

 Hawver Cave deposits has been greatly advanced. To each of 

 these persons the author's sincere thanks are extended. 



SIGNIFICANCE OF OSTEOLOGICAL CHARACTERS IN ORNITHOLOGY 



In a zoological group of such narrow delineation and of such 

 great homogeneity as the class Aves, where separation into the 

 various systematic divisions is based upon relatively small varia- 

 tions and where these variations affect structures not preserved 

 for study, a considerable degree of care must be exercised when 

 interpreting discoveries of the palaeontologist in terms of modern 

 systematic zoology. The difference noticeable to. a worker in the 

 former field should in many cases be multiplied by a very large 

 factor upon their transposal to the latter. Degrees of diver- 

 gence which to the palaeontologist seem of no more than specific 

 rank might, by the worker in systematic ornithology, having 

 also various intricate details of color-pattern or feather struc- 

 ture at his disposal, be found correlated with differences of 

 more than generic importance. The distinction upon osteological 

 characters of many well-defined species of Recent birds is a 

 matter requiring complete skeletons of individuals of known sex ; 

 even then conclusions are often in question. It is here con- 

 ceded as possible under these conditions, and considering the 

 fact that most of the fossil specimens are not capable of articula- 

 tion, that many of the fossil specimens ascribed to living species 

 might, if all characters were determinable, be separated as dis- 

 tinct forms. It must be remembered also that within certain 

 groups the osteological differences between species is greater than 

 in others. The feather of the bird is an epidermal structure 

 which reflects with sensitiveness the activities of the animal and 

 is plastic as a specific character under the influences of environ- 

 mental changes. It is a proper basis of specific distinction, yet 

 it is almost never preserved in the fossil state. The tooth of 

 the mammal, likewise an epidermal structure and highly repre- 

 sentative of the animal's activities, is a character used in com- 

 mon by the palaeontologist and the modern systematist. Zoology 

 and palaeontology are then much more nearly upon the same 



