Avifauna of Central America. 773 



obviously to be sought for in the Old World, and appar- 

 ently in Africa. This much is indicated, in the first place, 

 by the occurrence in western Africa of Heliornis, which 

 turns up again in Assam and Sumatra. But there are two 

 other families in this assemblage which have to be taken into 

 account. One of these is the Rhinochetidae, represented 

 by the Kagu of New Caledonia, the other the Mesitidse of 

 Madagascar. 



In Mesites we probably have the nearest living repre- 

 sentative of the ancestral stock from which the Gruiformes, 

 on the one hand, and the Galliformes, on the other, were 

 derived. A discussion of the relative degrees of affinity 

 between these several types would be inadmissible here. 

 Suffice it to say that the relationship is universally admitted. 

 The inferences to be drawn therefrom are hardly less open 

 to dispute. The fact that the giant flightless bird Phoro- 

 rhacos of the Miocene of Patagonia is nearly related to the 

 Cariamidse, indicates the date of entry of these several types 

 into South America, and this accords well with what has 

 been adduced in regard to the Galliformes and Coracii- 

 formes. The presence of members of the Heliornithidae and 

 Aramidse in Central America is extremely interesting, for 

 they must be regarded as comparatively late immigrants, 

 forcibly demonstrating the mode of distribution along 

 narrow tracts linking large land-masses. 



The Struthious types — Rheidse and Tinamidae — are the 

 only others which can now be discussed with profit, and in 

 the matter of their distribution they present some puzzling 

 features. Only one of these families — the Tiuamidae — 

 occurs in Central America, but they are doubtless com- 

 paratively late immigrants thereto. What has to be 

 accounted for is the presence of Struthious birds at all in 

 the New World, for it seems clear that these are Old World 

 types, of which the most primitive living members are the 

 Emus of the Australian Region. After these comes the 

 African Ostrich. The American Struthiones, it is signi- 

 ficant to note, present characters in common, on the one 



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