INTRODUCTION. 
li 
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 f . These facts render it probable that the Struthious birds do not owe 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 produced the Dodo and the Solitaire 
from the more highly developed Pigeon type. Professor Marsh has proved that, so far back as the 
Cretaceous period, the two great forms of birds — those with a keeled sternum and fairly developed 
wings and those with a convex keel-less sternum and rudimentary wings — already existed side by side ; 
while in the still earlier Archaeopteryx of the Jurassic period we have a bird with well-developed 
wings, and therefore probably with a keeled sternum. We are evidently, therefore, very far from a 
knowledge of the earlier stages of bird-life, and our acquaintance with the various forms that have 
existed is scanty in the extreme ; but we may he sure that birds acquired wings, and feathers, and 
some power of flight before they developed a keeled sternum, since we see that bats (with no such 
keel) fly very well. Since, therefore, the Struthious birds all have perfect feathers, and all have 
rudimentary wings, which are anatomically those of true birds, not the rudimentary fore legs of 
reptiles, and since we know that in many higher groups of birds— as the Pigeons and the Rails— the 
wings have become more or less aborted, and the keel and the sternum greatly reduced in size by 
disuse, it seems probable that the very remote ancestors of the Rhea, the Cassowary, and the Apteryx 
were true flying birds, although not perhaps provided with a keeled sternum or possessing very great 
powers of flight J. But in addition to the possible ancestral power of flight, we have the undoubted 
fact that the Rhea and the Emu both swim freely, the former having been seen swimming from island 
to island off the coast of Patagonia. This, taken in connection with the wonderful aquatic Ostrich of 
the Cretaceous period discovered by Professor Marsh, opens up fresh possibilities of migration; while 
* Reinhardt is of opinion that “the ancient and the modern lihea are of one and the same species.” — Ibis, 1882, p. 332. 
t “ See Buller’s illustration in Trans. N.-Z. Instit. vol. iii. plate 12 b. fig-. 2.” 
t “ Professor Marsh has shewn that there is good reason for believing that the power of flight was gradually acquired by Birds, 
and with that power would bo associated the development of a keel to the sternum, on which the volant faculty so much depends, 
and with which it is so intimately correlated that, in certain forms which have to a greater or less extent given up the uBe of their 
fore-limbs, the keel, though present, has become proportionally aborted. Thus the Carinate type would, from all we can see at 
present, appear to have been evolved from the Ratite. This view receives further support from a consideration of the results of 
such embryological research as has already been made — the unquestionable ossification of the Ratite sternum from a smaller 
number of paired centres than the Carinate sternum, in which (with the doubtful exception of the Anatidm) an additional, 
unpaired centre makes its appearance. Again, the geographical distribution of existing, or comparatively recent, Ratite forms 
points to the same conclusion. That these forms — Moa, Kiwi, Emeu and Cassowary, Rhea, and finally Ostrich— must have 
had a common ancestor nearer to them than is the ancestor of any Carinate form seems to need no proof. If we add to these 
the JEgyornis of Madagascar, the fossil Ratitoc of the Siwalik rocks, and the as yet but partially recognized Stndhiolithus of 
Southern Russia, to say nothing of Gmtornis , the evidence is stronger still. Scattered as these Birds have been or are through- 
out the world, it seems justifiable to consider them the survivals of a very ancient type, which has hardly undergone any 
essential modification since the appearance of Bird-life upon the earth— even though one at least of them has become very 
highly specialized.”— Prof. Neivton in Enc. Brit. vol. xviii. pp. 43, 44. 
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