vi] DISTRIBUTION OF SELECTED GROUPS 105 



extend northwards with the cold Humboldt current, 

 which may account for their existence on the Gala- 

 pagos, right under the equator. Fossil penguins are 

 known from the Oligoceue of New Zealand and 

 Miocene of Patagonia. 



Divers and Grebes. Divers (Colymbus) and 

 Grebes (Podicipes) seem to be connected by the 

 Oligocene French genus Colyniboides. The four kinds 

 of recent divers are restricted to the northern hemi- 

 sphere. Grebes.are cosmopolitan, with one interest- 

 ing flightless kind on Lake Titicaca in Bolivia. 



Petrels and Albatrosses are cosmopolitan groups; 

 albatrosses are, however, more common in the southern 

 hemisphere. 



Gamuts and Cormorants are cosmopolitan, 

 Pelicans are restricted to the warmer zones. The 

 largest cormorant happens to be a flightless species 

 of the Galapagos Islands. Fossil Steganopodes (i.e. 

 rudder-feet, so called because all these birds have 

 all the four toes webbed together) are known from 

 the Oligocene onwards. 



Herons are cosmopolitan. The tall Balaeniceps, 

 whale-headed heron or shoebill of the Upper Nile, 

 and the small Cancroma or boatbill in tropical 



America, are remarkable illustrations of isotelv or 



t/ 



so-called parallel development or convergence. 



Storks proper are essentially an Old World family, 

 namely Indo-African, whence some species migrate 



