60 THE NOTOG^IC REALM. [CHAP. 



that the giant flightless species such as Phororhachis and Bron- 

 tornis of the Patagonian Tertiaries have been recently shown to 

 form a totally distinct group the Stereornithes, and it is quite 

 probable that the same may prove to be the case with Gastornis, 

 Dasornis, and Diatryma of the lower Eocene of the northern 

 hemisphere. Apart from these, the earliest known ratites are 

 Hypselornis of the Pliocene of India which appears to be allied 

 to the emeus and cassowaries and the Australian Dromornis, 

 one species of which is likewise of Pliocene age; all the other 

 forms being Plisiocene. Moreover, it is now tolerably certain 

 that the true ratites have originated from flying birds, and it is 

 therefore highly probable that the group is an essentially modern 

 one 1 . Accordingly, there is a strong presumption that the ances- 

 tors of these birds did not enter Notogsea till comparatively late 

 in the Tertiary period ; and that, in fact, their southern migration 

 was not far removed in time from that of the giant land-tortoises, 

 noticed in the next chapter. Possibly they may have entered 

 Australia by way of New Guinea during the connection which 

 Mr Hedley believes to have existed between those two countries 

 late in the Tertiary epoch ; while the New Zealand forms may 

 have made their way by means of the presumed land-connection 

 between these islands and the Solomons, New Hebrides, etc. 



Of course there is the difficulty as to why mammals did not 

 enter the Polynesian region at the same time; but it is conceivable 

 that even at this date the mammalian fauna of South-eastern Asia 

 may have been very poor in Eutherians, while it is quite possible 

 that the ancestral forms of these birds may not have required the 

 complete land-connection necessary for the passage of the higher 

 mammals. Such connection as served for these birds, however, 

 may have well sufficed for the transit of the ancestors of the 

 Australian murine rodents, which almost certainly entered the 

 country at a later date than the original marsupials and mono- 

 tremes. 



Assuming, then, that the marsupials and monotremes of the 

 Australian region did not reach their present home till the early 

 part of the Tertiary epoch, we must make the further assumption 



1 Captain Hutton is of opinion that the moas originated directly from flying 

 birds in New Zealand, but the evidence in favour of this view appears insufficient. 



