| OCR Text |
Show 2 4 4 ON MEXICAN AMPHIBIANS AND REPTILES. [June G, Unless this conclusion be accepted, we have to resort to violent interpretations. Either complete extinction all o\ er Is orth America, a measure which receives no support from actual distribution; or we must be prepared to assign to the Opisthoglypha a Cretaceous age, as a family not descended from North-American Colubrinse; or, lastly, if we should insist upon the Opisthoglypha as a natural group, the only explanation would be a land-connection across the Equatorial Atlantic, which with shifting modifications is supposed to have existed from Lower or Mid-Cretaceous into at least the Oligocene epoch. This bridging of the Atlantic is somewhat problematic. For our purposes we can discard the Cretaceous Brazil-Africa connection. Of more concern to periarctic distribution is the Europe- Greenland-North America continuity, which is supposed to have persisted well into the Tertiary period. But there was a third, more direct bridge, although one of a curious and mysterious structure, which by its several advocates is dimly described as composed of a shallow sea interspersed with many islands; or as a solid land-belt; or, lastly, as a long archipelago with a continuous coast. This mysterious structure is supposed to account for the unmistakable similarity between the now extinct Antillean and Mediterranean coral-fauna, Old-World and Antillean land-mollusca, &c. Obviously the corals require sea, the mollusca land. The apparent contradiction may be solved by the suggestion that there existed between Central America and the Mediterranean a sea (part of the Tethys of Suess and Ortmann, later their " Great Mediterranean"), shallow during the Oligocene epoch, studded with islands, bordered by continuous land in the South (Brazilia to West Africa, or later between N. South America and West Africa, part of the Mesozonia of Ortmann) and in the North (Western Europe to Appalachia). Subsequently the Tethys increased to a big " bay " in Mid-Atlantic, this bay extending, spreading south and north, drowning first the southern land-belt, driving the northern land farther and farther north, with the ultimate result of a junction of the South with the North Atlantic; in other words, establishment of the whole Atlantic. Now these land-bridges, provided they existed long enough and at the light time and place, the Southern until at least the beginning of the Eocene, the Northern at least through the Oligocene epoch, would explain many a puzzle in geographical distribution ; for instance, that of the Aglossa, Boas, Poclocnemis, Amphis-baenidse, Solenodon. The Northern bridge would throw light upon the Anguidte and upon Sp>elerp>es, a large American genus with a solitary species in Sardinia and Italy. But this is at present a land of dreams. With more claim to reality, we can conclude that Central America, although genetically part of the North-American continent, has received its dominant, most characteristic fauna from South America, and this southern fauna has surged northwards chiefly to the east and west of the Mexican plateau. |
