THE 
AMERICAN NATURALIST 
Vor. XXXV. April, rgor. No. 412. 
A THEORY OF THE ORIGIN AND EVOLUTION OF 
THE AUSTRALIAN MARSUPIALIA. 
B. ARTHUR BENSLEY. 
INTRODUCTION. 
ALTHOUGH considerable attention has been given to the 
discussion of the family and generic affinities of the Aus- 
tralian marsupials from a systematic standpoint, until very 
recently the phylogenetic aspects of the question have been 
generally neglected. On this account, and also from the 
fact that little information has been forthcoming either from 
paleontology or geographical distribution, it has not been 
possible, up to the present time, to form an adequate con- 
ception of the origin of the fauna and its phylogenetic 
relationships. 
The present paper is the result of an attempt to outline a 
plan of evolution for the group by comparing the adaptive 
modifications of the teeth and feet with those of placental mam- 
mals, in which the course of evolution is fairly well known. 
On account of the difficulties with which the writer has had to 
contend in having only a small number of marsupial types at 
his disposal, the present plan is advanced simply as a working 
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