104 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



An example of similar faunal relations is presented by the marine 

 faunae on the two coasts of Central America. Though the isthmus of 

 Panama now forms an impassable barrier, the West Indian seas con- 

 tain a number of Pacific genera of sea anemones, otherwise absent 

 from the Atlantic. 13 The genus of corals Fungia, mainly confined to 

 the tropical Pacific and Indian oceans, has a single representative, 

 F. elegans, in the Caribbean Sea. 14 The sea urchins, according to Alex- 

 ander Agassiz, show a high degree of relationship or are identical on 

 the two sides of Central America. Although there are no identical 

 species of mollusks, there are pairs of related forms on the two sides of 

 the barrier. 15 Hippa eremita occurs on both coasts, and a number of 

 other genera of decapods have pairs of related species in the Pacific 

 and Atlantic. The Pacific sharks of the genus Urolophus, which are 

 confined to tropical and shallow waters, is represented in the West 

 Indies, 16 and of 374 species of bony fishes of the Gulf of Panama, 

 almost 15% occur in the Caribbean side of the isthmus. 17 All this 

 evidence indicates a former water connection at this point, and this is 

 further supported by the deep-seated differences between the early 

 Tertiary mammalian faunae of North and South America, which would 

 also be explained by the existence of a separating sea. In the later 

 Tertiary there was an extensive exchange of mammalian types be- 

 tween the two continents. The conclusion is thus plain that an early 

 Tertiary connection of the Atlantic and Pacific was followed by an 

 Upper Miocene north-south land connection. 18 The geological evidence 

 supports the zoogeographic indications. 



These examples show how both periods of union and the appear- 

 ance of separating barriers may be dated by the comparison of the 

 geologically older elements of the faunae of given areas. Similarity 

 (i.e., homology) of faunae speaks for union at the period of origin or 

 active dispersal of the forms in question, differences may be supposed 

 to have arisen since the date of separation. 



The Sarasins 19 have analyzed the fauna of Celebes, especially the 

 mollusks, the amphibians and reptiles, and the birds, with reference to 

 the relations with the inhabitants of the surrounding islands. On the 

 basis of their evidence it appears very probable that the present fauna 

 has reached Celebes by four distinct routes, since the emergence of this 

 island in the Eocene. The groups investigated, which are taxonomically 

 widely distinct, and which also have decidedly different ecological rela- 

 tions, exhibit a surprisingly uniform result, which increases the reli- 

 ability of the conclusion. The groups examined are distributed as 

 follows: 



