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1882.] PROF. OWEN ON THE STERNUM OF NOTORNIS. 693 likewise included in the subclass "Ratita" of a binary ornithological system ? O n a conjectural ancestral relation of the keelless external character to the present advanced volant faculty of the Avian class, the Dodo had made some progress thereto from its assumed " ratite " progenitor : it had risen to the rudiment of a keel. To this conclusion, however, another conjecture opposes itself. Dodos (Didida), having gained in bulk and weight upon other geographically associated birds of their own family or genus, and finding sufficient sustenance on the ground, with convenience for nidification, had no call to exert the strenuous act of flight. The stimulus thereto, which we daily witness in birds about us, was wanting. There were no enemies, quadrupedal or bipedal, in the tract of land now reduced to the islands of Mauritius and Rodriguez, to disturb their wellbeing and threaten their existence. I have elsewhere remarked, as bearing upon the interesting question of the relation of the simplified sternum to the genesis of Birds, that Pezophaps, the largest land-bird seen by the early settlers in the island of Rodriguez, " differed in no other respect from the class-rule in other birds, save in the inability to fly by the action of the fore limbs. There were no enemies, native to the island, able to take advantage of that disablement-' II ne s'y trouve aucun animal a quatre pieds, que des rats, des lezards, et des tortues de terre,' writes Leguat in his interesting little book1. The ' Solitaires' had no call to practise or to endeavour to practise that hardest mode of locomotion to obtain sustenance or fulfil any of the conditions of preservation of the individual or of the species ; they were never scared into the violent volant exercise"*1. The exiled Huguenots derived the best, if not largest, proportion of their animal food from the wingless birds of Rodriguez. The advent of M a n , with or without a subservient carnivorous quadruped, is an intelligible cause of the extinction of species, especially of birds attracting his hunger by their size and unable to escape by flight. Thus the huge wingless Dromomis3, like Diprotodon, has become known to us only by the osseous remains in Australia. The smaller E m u and Cassowary are there restricted in range and numbers, and seem to be gradually passing away. The fact of a range of variety in size has been determined in the individuals of many species. Such variety affecting a Cereopsis Goose to the degree shown by Cnemiornis1 would, in a corresponding degree, render the act of flight more difficult and laborious. Consequently, if that act were not needed for the acquisition of food, it might seldom or never be exercised in the absence of any enemy from which it would offer a way of escape. By long disuse of the wings, continued through successive generations, those organs, agreeably 1 Voyage et Avantures de Francois Leguat, &c. 12mo, a Londres, 1708. 2 Memoirs on the Extinct Birds of New Zealand, and on those of Mauritius, Australia, &c. 4to, 1878. Appendix III. p. 5. 3 Ib. Appendix I. p. 1. 4 Trans. Zool. Soc. vol. v. 1865, p. 395. |
