362 ORIGIN OF LIFE IN AMERICA 



its nearest relations are all marine forms, its ancestors, as 

 Professor Eigenmann * remarks, could only have entered the 

 area when it was still a gulf of the sea. 



In the Eocene Period " Archiguiana," as Dr. von Ihering 

 named the ancient highland of Guiana and eastern Venezuela, 

 was supposed by this writer to have been isolated from the 

 highland of Brazil. And, indeed, the mountain plateau of 

 Guiana contains a very large number of archaic and most 

 peculiar types, some of which seem to spread westward into 

 Venezuela and Colombia rather than into Brazil. Yet the 

 great majority of these ancient forms of Guiana also occur 

 southward in eastern Brazil. One of the most noteworthy 

 birds, the hoatzin (Opisthocomus hoatzin), whose young 

 climb about among the branches of the trees by means of 

 well -developed claws on their wings, and which have been 

 placed into a distinct order by themselves, range southward 

 as far as Bolivia. The chatterers (Cotingidae) comprising 

 some of the most ornate and peculiar birds of South America, 

 are almost equally divided between Brazil and Guiana. The 

 familiar umbrella bird (Cephalopterus ornatus), the bell bird 

 (Casmorhynchus niveus), the bald-headed crow (Gymnoce- 

 phalus calvus), and the cock-of -the-rock (Rupicola crocea), all 

 belong to genera which have spread westward from Guiana 

 rather 'than into Brazil. In all these cases we have to deter- 

 mine what was the original centre of dispersal. The singular 

 genus of snails Ampullaria probably spread across South 

 America from a Brazilian centre, and so did the fresh -water 

 crab (Pseudothelphusa) and the whole family of fishes called 

 Cichlidae. The snail Strophocheilus, the fresh-water mussel 

 Unio, the archaic arthropod Peripatus, the family of tortoises 

 Cinosternidae and others, have apparently entered Brazil from 

 the north and west. As I shall endeavour to show in the next 

 chapter, many of the forms that have spread from the Brazi- 

 lian highlands have near relations in Africa, while among the 

 northern and western immigrants into Brazil scarcely any 

 have succeeded in crossing the Atlantic area to Africa. 



* Eigenmann, C. H., " Freshwater Fishes of South America," p. 521. 



