CHAP. XXI.] 
NEW ZEALAND. 
451 
to all sound principles of reasoning in questions of geographical 
distribution. For it depends upon two assumptions, both of 
which are at least doubtful, if not certainly false — the first, 
that their distribution over the globe has never in past ages 
been very different from what it is now ; and the second, that 
the ancestral forms of these birds never had the power of flight. 
As to the first assumption, we have found in almost every case 
that groups now scattered over two or more continents formerly 
lived in intervening areas of existing land. Thus the marsupials 
of South America and Australia are connected by forms which 
lived in North America and Europe ; the camels of Asia and 
the llamas of the Andes had many extinct common ancestors 
in North America ; the lemurs of Africa and Asia had their 
ancestors in Europe, as did the trogons of South America, 
Africa, and tropical Asia. But besides this general evidence we 
have direct proof that the struthious birds had a wider range 
in past times than now. Remains of extinct rheas have been 
found in Central Brazil, and those of ostriches in North India; 
while remains, believed to be of struthious birds, are found in 
the Eocene deposits of England ; and the Cretaceous rocks of 
North America have yielded the extraordinary toothed bird, 
Hesperornis, which Professor O. Marsh declares to have been 
“ a carnivorous swimming ostrich.” 
As to the second point, we have the remarkable fact that all 
known birds of this group have not only the rudiments of wing- 
bones, but also the rudiments of wings, that^is, an external 
limb bearing rigid quills or largely-developed plumes. In the 
cassowary these wing-feathers are reduced to long spines like 
porcupine-quills, while even in the Apteryx, the minute 
external wing bears a series of nearly twenty stiff quill-like 
feathers . 1 These facts render it probable that the struthious 
birds do not ow T e their imperfect wings to a direct evolution 
from a reptilian type, but to a retrograde development from 
some low form of winged birds, analogous to that which has pro- 
duced the dodo and the solitaire from the more highly-developed 
pigeon-type. Professor Marsh has proved, that so far back as 
1 See fig. in Tran?, of N. Z. Institute, Vol. III., plate 126, fig. 2. 
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