26 
The Queensland Naturalist. 
July, 1925 
cal occurrences of fossil aiui living repreKcntatives. 
Knowledge of the earliest occurrence, as revealed, say, by 
fossil forms, leads us to assume that the locality in ques- 
tion represents the centre of origin, and from this centre' 
we follow the radiations in subsequent times and inter- 
pret the geography of tliose times accordingly. Pro- 
vided we limit our conclusions to identical foi'ms we 
may be right, hut when we attempt to interpret the dis- 
tribution of representatives of a group on these lines we 
may be quite wrong. We know far too little about the 
proces'^es of organic evoliTtion to make such assumptions 
— ^an opinion may be helpful inasmuch as it stimulates 
research, but a final conclusion is not attainable. 
Yon are all familiar with the theory which woulir 
explain the ])resent distribution of Marsupials by assum- 
ing a connection between Australia and South America, 
via the Antartie Continent. The Marsupials are limited 
at tlie present day to the Australian region and America 
(mainly Soutli Amei'ica). Fossil records indicate a one- 
time widt'r distribution, including Europe, but the 
forms represented in this wider area of occurrence are 
limited to tliose carnivorous types which we designate 
as Polyprotodronts. The living forms include the lierbi- 
voroiis Eiprotodont. as well as Polyprotodonts^ and the 
])eeuliar South American form, Cenolestes. This occur- 
rence of the Diprotodonts has generated the idea that 
they must have evolved in one area and migrated to the 
othei’, thus suggesting an Antarctic land bridge; move- 
ment of the forms along any other route such as via the 
Pacific coasts of America and Asia being apparently piv- 
cliuled by The absence of any remains of these forms.. 
The theory is attractive, because it u^onld serve to ex- 
plain the distribution of other forms, but the same sup- 
port can be afforded to other counter-theories, Tltere is 
no reason beyond that of orthodox prejudice why the 
Diprotodonts could not have been evolved indejiendentiy 
in the two areas where they now exist. Without calling 
on an Atlantic land liridge. we might explain the present 
areas of occurrence of the Marsupials as representing 
each an asylum wliere the relics of a one-tirne universal 
Marsupial stock have been jire.served. The limitation of 
their area of distribution might have taken place at a 
time Avhen the existence of herbivorous fauna was at first 
impossible, but with the evolution and differentiation of 
the Angiosperms or flowering plants the po.ssibilities of' 
pasturage were opened up. 
