 The rail was once more widespread , with fossil bones found at Havana , Pinar del Río and the Isla de la Juventud . Barbour did not believe that the rail , Zapata sparrow and Zapata wren were relics in the sense that they once ranged widely over Cuba ( as did , for example , the dwarf hutia and the Cuban crocodile ) , since the birds are so highly modified for swamp conditions . He considered that conditions similar to those found today may once have extended over the large submerged area now represented by the shallow banks , with scattered mangrove keys , which stretch towards the Isla de la Juventud and perhaps eastward along the southern Cuban coast . The birds fossilized at Isla de la Juventud are smaller than the single extant specimen , but the paucity of available material makes it impossible to establish whether the populations were genuinely different . 
