PDF - Wallace Online

CHAP. XVIII.] BIRDS. 371
not come into existence, and preserved only in those areas
which were long free from the incursions of such dangerous
enemies. The discovery of Struthious remains in Europe in the
Lower Eocene only, supports this view ; for at this time carnivora
were few and of generalized type, and had probably not acquired
sufficient speed and activity to enable them to exterminate
powerful and quick-running terrestrial birds. It is, however, at
a much more remote epoch that we may expect to find the
remains of the earlier forms of this group ; while these Eocene
birds may perhaps represent that ancestral wide-spread type
which, when isolated in remoter continents and islands, became
modified into the American and African ostriches, the Emeus
and Cassowaries of Australia, the Dinornis and u^'pyornis of
New Zealand.