456 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



yet very few collections have been made. Collections now under 

 study, made by the U.S. Antarctic Program, the Navy "Deep-Freeze" 

 Program, and others, will ultimately yield some of this needed informa- 

 tion, but the distribution of collecting stations is still very sparse. 



From examination of the shallow-water corals of the Argentine 

 Shelf, the Chilean Region, the Antarctic Shelf, and the New Zealand 

 Shelf, it is apparent that a plexus of very closely related species exists. 

 Highly specialized species, living in special environments, differing 

 from one another only in minor features which make them difficult to 

 identify, and having counterparts in each of the areas given above, 

 apparently signify recent evolution. In other words, the stock is not 

 an old one which has had opportunity to diversify greatly and to be- 

 come quite specialized morphologically, but is a recent one, probing 

 into new areas. For example, there is a plexus of species, not all 

 members of which have been as yet distinguished, within the genus 

 Flahellum. On the Argentine shelf are the species F. curvatum^ F. 

 thoursii^ and F. patagonicum. The first lives free upon the bottom, 

 while the second lives only where there are pebbles to which it may 

 become attached. In the Antarctic are F. impensum and F. antarc- 

 tixmm and a third unnamed species. In New Zealand there are F. 

 gracile and F. rubrum. This closely knit group of species is not found 

 elsewhere in the world and has, as yet, been only partly studied. It 

 appears to be a recently evolved plexus. 



Recent evolution should not be unexpected, however, for during the 

 Pleistocene glaciation it would be presumed that mass mortality oc- 

 curred among the animals living on the Antarctic Shelf. As the glacial 

 ice moved out across the shelf, many were physically exterminated, 

 the remainder of the species found their lebensraum severely curtailed. 

 "With the retreat of the glacial ice, whole new areas were opened to 

 colonization and it would be only from the areas to the north that the 

 new immigrants could come. But from where did they come ? 



To logically answer this question one inquires into the historical 

 aspects of the observed distribution of the animal. How much of the 

 distribution noted today is the result of past factors? Were past 

 migration routes, current patterns, or land connections the same as, 

 or in some degree similar to, present-day situations? There are two 

 possible approaches to problems of this nature: One, to understand 

 the geological history of the region and to deduce from this knowledge, 

 what the patterns of seas, currents, and physical environments were 

 during any given episode of geological time. A second approach 

 would be to observe the distribution of animals in the past by means 

 of the fossil record and to obtain from this a series of working hypoth- 

 eses about the arrangements of the physical and chemical environ- 

 ments which would have fostered the observed distribution. 



