20 
Psyche 
[March 
and from Australia to Tasmania. Mammals show, by occurrence of 
many identical or closely related species on opposite sides of the exist- 
ing water gaps, that both bridges did exist recently and that some 
forest-living animals crossed both of them. Carabidae show additional, 
different things about the two bridges. In the case of the Australian- 
Tasmanian bridge, the Carabidae agree with the mammals. Many 
wet forest Carabidae including many flightless ones evidently crossed 
this bridge without meeting important ecological barriers, although 
cold climate stopped some other animals, especially some reptiles 
(Darlington i960, p. 659). In the case of the New Guinea-Austral- 
ian bridge, however, the flightless rain forest Carabidae show that 
there was an ecological barrier upon the land, and that the barrier 
existed for a long time. New Guinea and Australia cannot have 
been connected by a continuously rain-forested ridge within the time 
of existing carabid faunas. The recent connection was evidently low 
and rain forest was probably not continuous across it, although it was 
nearly enough continuous to allow certain forest trees, mammals, 
birds, and winged insects to get across. These organisms probably 
crossed the bridge by way of more or less separate forest “stepping- 
stones” and strips of gallery forest that did not allow continuous 
passage of flightless rain forest Carabidae, which do not disperse 
easily across even narrow gaps of unsuitable land. Rain forest is 
discontinuous on Cape York now. The Carabidae suggest that it has 
been so for a long time in the past, and that conditions on Cape York 
now are like the conditions that existed on the land bridge when New 
Guinea and Australia were connected. 
Historical Implications : Climatic Fluctuations 
The present distribution of wet forest Carabidae shows that many 
of them have been able to move up or down the eastern edge of 
Australia between North and South Queensland, across what are now 
wide gaps of comparatively dry country. The degree of relationships 
of different Carabidae in the tropical and subtropical rain forest 
systems varies. In some cases ( e . g. Pamborus of the tropicus group) 
the North and South Queensland representatives of single original 
stocks are only slightly differentiated, but in other cases ( e . g. Leira- 
dira and its allies) they have diverged as subgenera or genera. This 
suggests either several periods of dispersal and isolation, accompanying 
fluctuations of rainfall and rain forest, or occasional trickling of 
dominant wet forest Carabidae across the drier gaps of central Queens- 
land. In either case wet forest Carabidae seem to have followed a 
rather narrow path along the continental divide, and have usually 
