CHAP. XXI.] 



NEW ZEALAND. 



451 



to all sound j)rinciples 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 0. 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.^ These facts render it probable that the struthious 

 birds do not ow^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 Trans, of N. Z. Instituie, Vol. III., plate 12b, fig. 2. 



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