GULF OF MEXICO 



505 



gentle sag or flat platelike basin . . . With the 

 Middle Cretaceous, the area commenced to sub- 

 side . . . and this downward tendency persisted 

 until the Gulf reached its present great depth and 

 extent." [See also Lynch's article, pp. 67-86.] 



It is therefore safe to assume that shallow- 

 water or shore fishes were the first to become 

 established in the Gulf of Mexico and that they 

 constitute the oldest element of its ichthyological 

 fauna. 



As already indicated, the shore fish fauna of 

 the Atlantic coast continued into the Gulf of 

 Mexico before peninsular Florida was established 

 as a barrier to many of the species during the 

 Pleistocene. nA connection with the Caribbean 

 Sea through the Yucatan Channel was established 

 during the Pliocene. It would seem, therefore, 

 that the North Atlantic element became estab- 

 lished in the Gulf before Caribbean fishes were 

 able to disperse through the Yucatdn Channel. 



PELAGIC FISHES 



As might be expected from the foregoing dis- 

 cussions, the pelagic fishes of the Gulf of Mexico 

 are. the same as those of the Caribbean Sea and 

 adjacent parts of the Atlantic Ocean. They are 

 mostly associated with the Gulf Stream, and the 

 paleogeographic evidence would seem to indicate 

 that their presence in the Gulf dates from relatively 

 recent times. 



DEEP-SEA FISHES 



As already pointed out above, the Gulf of 

 Mexico originated as a shallow basin. Bathic 

 and other associated ecological conditions suitable 



to deep-sea fishes were not established until 

 comparatively recent times. This would seem 

 to indicate that the deep-sea fish fauna of the 

 Gulf did not evolve in situ but was recently 

 derived from the older, adjacent oceanic areas, 

 such as the Caribbean Sea and the Atlantic Ocean. 

 In fact, most of the deep-sea fishes of the Gulf 

 of Mexico also occur in the Caribbean Sea and 

 the Atlantic Ocean, and many of the species are 

 cosmopolitan in distribution. 



Owing to obvious collecting difficulties, deep- 

 sea fish faunas are poorly known taxonomically 

 as well as geographically, and further exploration 

 may extend the range of a few species so far 

 reported only from the Gulf of Mexico. 



As already indicated in the introduction, the 

 present depth of the Yucatan Channel and the 

 Straits of Florida cannot be construed as barriers 

 preventing the dispersal of deep-sea fishes to and 

 from the Gulf. 



LITERATURE CITED 



GiNSBURG, I. 



1952. Eight new fishes from the Gulf coast of the 

 United States, with two new genera and notes on 

 geographic distribution. Jour. Washington Acad. 

 Sci., 42 (3): 84-101, figs. 1-9. 



RivAS, L. R. 



1949. Check list of the Florida game and commercial 

 marine fishes including those of the Gulf of Mexico 

 and the West Indies, with approved common names. 

 State of Florida Board of Conservation (Marine Lab. 

 Univ. Miami), Ed. Ser. 4, 39 pp. 



SCHUCHERT, C. 



1935. Historical geology of the Antillean-Caribbean 

 region. John Wiley and Sons, New York, xxvi-811 

 pp., 17 figs., maps. 



