ANCIENT BIRDS 229 
back, the geological record informs us that, in the Pliocene 
period, they inhabited what is now Northern India. In Australia 
we have the Cassowary (Casuarius) and the Emeu (Dromaius) ; 
in New Zealand, the Apteryx (or Kiwi). Now, as none of these 
birds can either fly or swim, it is impossible that they could 
have reached these regions separated as they now are; and it 
is hardly likely that they arose spontaneously in each district 
from totally different ancestors. But the doctrine of evolution 
affords a key to the problem, and tells us that they all sprang 
from a common ancestor, of the struthious type (probably 
inhabiting the great northern continental area), and gradually 
migrated south along land areas now submerged. In this way 
we get some idea of the vast changes that have taken place in 
the geography of the world during later geological periods. 
Perhaps they were compelled to move south, until they reached 
abodes free from carnivorous enemies. Having done so, they 
evidently flourished abundantly, especially in New Zealand, where 
there are so few mammals, only those recently introduced by 
man. 
In North America Professor Cope has reported a large wingless 
fossil bird from the Eocene strata of New Mexico. In England 
we have two such—namely, the Dasornis, from the London Clay 
of Sheppey (Eocene period), and the Gastornis, from the Wool- 
wich beds near Croydon, and from Paris (also Eocene). 
Lake Callabonna in Australia (see p. 310) has yielded the bones 
of some huge ratite birds, e.g. Genyornis, with very slender toes. 
It lived with the Diprotodon. In South America the living 
Rheas were preceded by such large birds as Brontornis, of 
which casts of limb-bones are to be seen in the Natural History 
Museum. The famous Sivalik strata of India have yielded 
remains of an ostrich, Struthio asiaticus, and these may be seen in 
